Classic Cars

[bunnspecial]

So, little update on the MG...

I'm not sure if I mentioned it here, but I'd had a small oil weep from the differential for a while that I decided, while I was doing the rear suspension work, to tackle. I ordered two gaskets(two just to be safe), spent entirely too much time cleaning up the faces of the differential and cover, stuck a gasket to the cover with Permatex and let it set up overnight, and bolted in place.

I filled the differential full of 85W-90 GL-4 spec gear oil. That is worth a mention as essentially all gear oil available at auto parts stores now is GL-5 rated. The GL-5 spec calls for a much higher concentration of sulfur-based EP(extreme pressure) additives, but like all API oil ratings it supersedes the prior spec.

That's all good and well except that the sulfur EP additives are very corrosive toward yellow metals. GL-5 spec oil is absolutely off limits(or should be) in manual transmissions with brass synchros. It's also not a good idea to use in MGB differentials(and I'm sure some other older ones) because the thrust washers are bronze and a few other important parts are brass.

Amazon came to the rescue and turned up 85W-90 GL-4 oil.

I filled the differential up to the fill plug, put the plug back in it, and called it a day.

After the first trip out, I noticed oil on the ground. I didn't think too much of it since I'd initially been a bit messy filling and thought maybe I was seeing some drip off still.

It kept leaking, though. I snugged up all the bolts and put a wash tub under the differential that had several ounces in it the next day.

So, this week, another quart of GL-4 made its way here. I just finished tackling the cover again. I pulled it off, cleaned it up, and this time went a different route. I've been told that a lot of current gaskets are junk, so instead I just slathered the cover with Permatex Form-a-Gasket, and specifically the kind meant for rear differentials. The instructions said to put it in place, loosely attach the cover for an hour, then torque to spec(good luck getting a torque wrench back there-I went mechanic tight on them) and let it set up for 24 hours before adding oil. Hopefully this will fix it. I'll know tomorrow.

Also, the rear brakes have been my nemesis. These are manually adjusted, and especially after they're first put together it can take some driving for them to "seat" and actually adjust right. You can tell they're out of adjustment from two things-really long travel on the E-brake handle, and a mushy brake pedal(feels like air in the line) that improves when you pump or when the hand brake is on.

I readjusted the brakes today, and also fixed another embarrassing bodge. Somehow or another in all the disassembly, I'd lost the clevis pin for the hand brake cable on one side. This was bad, but I found a screw about the right size and zip tied it in place just to have something. I visited the hardware store today and fortunately they had clevis pins, although they're "universal" ones with a half dozen holes drilled in them and a couple inches long. I really should cut it off to the right length, but it works for now.

 

[bunnspecial]

So, an MG tinkering update...

Since the rebuild, my one persistent issue has been an oil leak. It's nothing like it was before(when I was losing a ton out the crankcase breather from blow-by) but still it's a quart every few hundred miles. I knew it was leaking and not burning as I'd get some under the car when I parked it.

Given where it seemed to be under the car, I had ASSUMED it was probably from the timing cover not getting sealed correctly. Like a lot of things, the gaskets are crap and there's also the potential for a few things to go together wrong there and allow an oil leak. I was REALLY afraid the shop had missed a groove in the front of the crank, and would end up having to sleeve it and replace the front crank seal, but whatever the case I wanted to make sure that's actually where it was coming form.

The last time I topped up the oil, I also dropped in a bottle of UV dye. I've been chasing a pesky tiny coolant leak on my wife's car, so went that route on both (think I found it on her car).

In any case, though, I started looking today for the oil leak and I found it. It's actually totally dry up around the timing cover. Instead, it's coming from the front tappet galley cover.

I should have known. I've fixed leaks there more times than I care to count. The front tappet cover is also where the crankcase breather and oil/air separator is located. There's a lot of oil there, and see once again my point about how the gaskets are crap holds.

Fortunately, someone has just started making cork gaskets in the correct thickness and size. I have a spare here. Still, though, I'll probably slather it with gasket crap and call it a day.

Access is the fun one on this, though. The stock MGB head is often called a "5 port head" and also is of a design referred to as a "Siamesed head." Cylinders 1 and 2 share the same intake runner, as do cylinders 3 and 4. Cylinders 2 and 3 also share an exhaust port. What all of that means is that the intake and exhaust manifolds are on the same side of the engine, and it's the same side as the tappet cover.

So, access requires removing the carburetors, heat shield and all the other accoutrements. As best as I remember, it CAN be accessed with the exhaust manifold in place, but honestly at that point I generally just remove it anyway. 4 of the studs that hold the exhaust manifold also hold the intake manifold, so from there removing the exhaust is only 2 bolts away. It doesn't need to come off the exhaust-it will move out of the way far enough that even the head can be removed from there(obviously with coolant drained, rockers and pushrods out, and probably a few other things I'm forgetting at the moment. I've pulled the head twice but there's no reason to do it here).

That invites more project creep, though. For one thing, last summer I started working on porting an exhaust manifold. It's not really finished, but is hanging on the wall in the garage, so I could finish and install that.

The bigger project, though, is the exhaust manifold. I'd wanted to have this one Jet-Hot coated prior to rebuild, but didn't. I'd talked to a friend a few weeks back and he's going to dig a spare for me out of his attic. It will probably need helicoils for bottom studs, but that's not the end of the world(the one I have now needed that done since 5/6 snapped when I removed it the first time). I can take that one, port match it to the head(although IIRC it's close already) and then send it off for jet coating. Looks like I just have some motivation to speed that along...

 

[bunnspecial]

A little fun on the MG the past few days:

The rebuilt engine has been a real pain to tune. Basically what I'd find is that I'd set the mixture at idle and get nice tan plugs, but then go for a drive and it would start falling apart. I could feel it misfiring even in 1st rolling down my street at 15mph, and it would just fall over and not run over 30 or so. When I did a "clean cut" under those conditions and pulled the plugs, they were chalk white, confirming what I thought-it was going really, really lean at speed.

So, I'd start richening it up a little at a time. I'd get smooth running at higher and higher speeds, but I'd also lose low end power and my plugs would get darker and darker. By the time I had it running well at speed, it would be dead below ~2K rpms and the plugs would be caked in soot at idle. The whole dead below 2K is sort of a consequence of the cam I'm using(and I spent some time wondering if I should have gone with a milder cam, even though this cam from Delta and its virtually identical counterpart from APT are the go-to street performance cams) but I did experiment with advancing the base timing to get some low end power back. That worked, but would put me way too advanced(~40º BTDC or better) at speed and my misfiring and poor running would return.

I talked to a few folks, and one of them-John Twist(who's one of the most respected MG guys at least in the US)-told me that he was embarrased because he was having the same issue with the same cam on his car and he couldn't straighten it out. He told me what he thought the issue was, but didn't have a solution.

His solution had to do with fuel metering in the carburetors. Typically, fuel metering in a carburetor is loosely controlled by something called a jet-a "calibrated leak" that allows vacuum in the carburetor throat to draw gasoline out. In a typical American carburetor(Holley, Edelbrock, Rochester, etc), the throat is a fixed size(called a fixed venturi, or variable velocity carburetor) and as more air flows through the carburetor, the air velocity increases, reducing the pressure in the throat and sucking more gas in. Typically the carburetor will have at least two jets-one for idle/cruising and one for acceleration.

SU carburetors work on a totally different principle. They are what are called a constant velocity, or variable venturi carburetor. As airflow through the carburetor increases, a piston in the throat rises to increase the diameter of the throat, keeping the velocity constant and consequently the vacuum.

A simple fixed size jet wouldn't work in this design, as a constant amount of gasoline would be draw out regardless of throttle position. Consequently, attached to the bottom of the piston is the "heart" of the SU carb, the metering needle. This is a long tapered needle that fits down in the jet. As the piston rises, more and more of the jet is "uncovered" as smaller diameters of the tapered needle are "plugging" the jet. This is actually a rather elegant design. Jet sizes in fixed-venturi carburetors are at best a compromise, while in an SU carburetor the jet diameter is infinitely variable within the confines of the needle profile.

The trick, though, is finding the correct needle for your application. SU catalogs quite literally hundreds of needles.

The issue I was having was that I was still using a stock needle in an engine that was now flowing SIGNIFICANTLY more air than it was stock, and of course this really comes into play at higher RPMs. Because of this, if the idle mixture was correct, the needle wouldn't allow enough gas at higher airflow and make it go lean. If adjusted to give the correct mixture at speed, the idle would be way too rich.

The solution is to change to a richer needle(one with a smaller diameter), but there again, there are hundreds of options. With that in mind, I called the stateside SU carb expert, Joe Curto. With classic NYC efficiency, he described my problem as soon as I told him what my engine set-up was, then said "I usually use an AAA needle for something like that." About 7 minutes total and the problem is diagnosed, the fix offered and paid for.

$37 and a couple of days later, I drop my new AAA needles in to replace the old AEB needles(I have no idea if there's any significance ot the letters-I can't make heads or tails without looking up a specific one). I made some quick mixture adjustments, and it was amazing. The car idled beautifully, pulled smoothly from 1K on up, and runs great now at every throttle position. I still need to dial it in a little better, but now at least I have "toast colored" plugs and the engine feels so alive now.

Our favorite big worded half-wit over at MR likes to crap on me for this kind of stuff since, you know, you really should just pay a shop to bolt on performance parts and if you have to work to get this stuff right the car is a piece of junk. Still, though, I get a tremendous amount of satisfaction from all of this. Being able to directly adjust variables like ignition timing and mixture, and then see how they interplay with each other, teaches you SO much about how this stuff actually works. Modern cars are better in pretty much every way, but I personally enjoy not just learning about this stuff but putting it into practice. Maybe that's just me though.

 

[bunnspecial]

So, a fun little project this afternoon.

I think most new MG owners get starry eyed and excited about the fact that you can basically build a car out of catalog. Most all of the parts are available, and they're also not that expensive.

Fairly quickly, though, you get jaded at the fact that just because you can buy them doesn't mean they're good. I've fought the crusade for a while on this. There are a lot of cottage industries of people making one particular part(like the guy who had a sewing machine in his dorm room at college turning out nylon axle rebound straps) but sometimes it can take some hunting to even find out about those. There are also people who refurbish old parts, but again you have to know about them. Moss Motors, who is the 800lb Gorilla in the British car business in the US, has a line of parts called "Classic Gold" that are equal if not better than OEM quality, but are also pricey. I buy parts from that line whenever I can, although I also hear people complaining about how expensive they are.

One seemingly never ending issue, though, with no off the shelf solution is the heater valve. Most of the originals lasted 40+ years, but considering that the newest MGB is now 41 years old, they're reaching EOL. The available replacement works fine, except they'll reliably start leaking in a few years. It's also not the easiest part in the world to replace thanks to bottom bolt access. When I pull the head, I always replace it just because it's easy to remove with the head off the car(plus I tend to use it as a handle to help lift it off) but 2018 was the last time I personally took mine off, and the shop that rebuilt my engine reused the old one.

Leaking is also not great because it sits right over the distributor, a part that doesn't particularly like being wet.

A few weeks ago, mine sprung a leak, although fortunately only when open. At the time, we were still in 70+ weather, so I didn't worry too much about it.

Finally, though, I decided to tackle it with a permanent, if not particularly elegant, fix brought to you from the plumbing aisle(or McMaster-Carr in my case). Basically you swap out the valve for a ball valve. The upsides are it's an off the shelf part that's much more reliable and also flows more coolant than the stock valve. The downside is attaching the dash control isn't the easiest, but then I tend to open/close it seasonally anyway so it's not a big deal to have to pop the hood.

Here's the basic plan-the old valve is chopped off at the base to give a mounting pedestal, and then drilled and tapped. The parts bill is a pipe nipple, a 90º joint, the valve, and a hose barb. That's about $20 in parts.

I ordered the parts a while ago, but realized I didn't have a 1/4" NPT tap, so had been dragging my feet. With a heater a lot more necessary now, I bit the bullet and did it.

First step, of course, is to drain the coolant. Normally on a job like this, I only drain it down to below the level of where I'm working as it's just easier. Typically I'll do that by loosening the bottom radiator hose clamp, and then I can work a screwdriver in and only hold it open to drain as long as I want. My new(er) radiator, though, has a drain plug and I thought I'd get adventurous and use it. Needless to say it fell into the drain pan, plus because it had been wrapped in teflon tape it wasn't the easiest to hand thread back in. That meant most of the coolant was gone by the time I got it back in. Oh well-you should change your coolant occasionally anyway, and somehow or another I end up doing it about every 6 months on this car .

I realized that rather than pulling the heater valve and modifying it on the bench, I could probably do it in-situ.

So, first step, hacksaw the valve apart

I cleaned it up a bit with a file, then drilled a 7/16 hole

Then on to the tap

Tapered pipe taps are not always the most pleasant to use. I can remember tapping an aluminum bar with a 3/8". I broke a tap wrench, then went over to our machine shop and talked to the machinist there-he gave me a small bottle of proper tap lube(not the 3-in-1 oil I'd been using) and said just use the biggest crescent wrench I could find, then a quarter turn at a time and back off. I spent the day on and off, increasingly veins popping out of my forehead and putting my whole weight on the crescent wrench to get it.

By contrast, this one tapped fairly easily using just some hydraulic oil(what happened to be in the oil can I had handy) and a small crescent wrench.

In any case, from there it was just pull out the Teflon tape, wrap everything up, and put it together.

Unfortunately, though, I could be president of the "Measure once, cut twice" club, and trimmed the hose to the heater too short. Not photographed, but Autozone came to the rescue and I was able to get it installed and the coolant refilled.

 

[Scepticalscribe]

In a time of electric cars, and various sorts of driver assisted motoring, and a growing disdain for what may be thought of as earth-destroying & environmentally questionable carbon-fuelled vehicles, I have to admit that I love classic cars, and will own to an unfashionable fascination for them, and take pleasure in the very idea that they exist.

Yes, in my mind, I can hear my mother muttering something about "impractical", "uncomfortable", "expensive to maintain", (and I will even concede that she is not entirely wrong).

Perhaps one can put it down to seeing (and falling mady in love with) the movie Chitty Chitty Bang Bang as a child, which left me with an enduring (if private) passion for classic cars.

Actually, not only did my brother and I see - in fact, were taken to see, at our repeated request - the movie on several occasions in the cinema (something that happened with no other movie in our childhood), we also had the album (LP) of the musical, - a thoughtful parental purchase - and we knew all the songs.

For that matter, we even had the gorgeous Chitty Chitty Bang Bang toy model cars with working wings (one each - even at the time, they cost an absolute fortune, we were awestruck with gratitude, a situation where my lovely godmother, my mother's best friend from school, bless her, did the needful), while my wonderful father, bless him, tracked down the book (by Ian Fleming) complete with illustrations, that the movie derived its inspiration from.

Anyway, ever since that, I have had a love of, fascination for, and sneaking regard for, classic cars, and will read about, and watch YouTube videos of reviews of, and drives on vintage, veteran, or classic cars.

And this thread is intended to be a place where (anything to do with) classic cars can be discussed.

And classic cars are those considered classics (or even thought to be) in any era, up to and including, the millennium.

 

[Apple fanboy]

In a time of electric cars, and various sorts of driver assisted motoring, and a growing disdain for what may be thought of as earth-destroying & environmentally questionable carbon-fuelled vehicles, I have to admit that I love classic cars, and will own to an unfashionable fascination for them, and take pleasure in the very idea that they exist.

Yes, in my mind, I can hear my mother muttering something about "impractical", "uncomfortable", "expensive to maintain", (and I will even concede that she is not entirely wrong).

Perhaps one can put it down to seeing (and falling mady in love with) the movie Chitty Chitty Bang Bang as a child, which left me with an enduring (if private) passion for classic cars.

Actually, not only did my brother and I see - in fact, were taken to see, at our repeated request - the movie on several occasions in the cinema (something that happened with no other movie in our childhood), we also had the album (LP) of the musical, - a thoughtful parental purchase - and we knew all the songs.

For that matter, we even had the gorgeous Chitty Chitty Bang Bang toy model cars with working wings (one each - even at the time, they cost an absolute fortune, we were awestruck with gratitude, a situation where my lovely godmother, my mother's best friend from school, bless her, did the needful), while my wonderful father, bless him, tracked down the book (by Ian Fleming) complete with illustrations, that the movie derived its inspiration from.

Anyway, ever since that, I have had a love of, fascination for, and sneaking regard for, classic cars, and will read about, and watch YouTube videos of reviews of, and drives on vintage, veteran, or classic cars.

And this thread is intended to be a place where (anything to do with) classic cars can be discussed.

And classic cars are those considered classics (or even thought to be) in any era, up to and including, the millennium.

I too had a Chitty Chitty Bang Bang toy car with the wings. Also a number of James Bond toy cars which would probably all be worth a fortune about now.
And as you say real classic cars do cost a fair bit to maintain (@bunnspecial is probably a better point of reference), but unlike conventional modern cars they go up in value.
I’d love a classic car but really don’t have the time or the money for one. But then as my VW Golf approached its 7th birthday, many youngsters would call that a classic these days!
Jaguar E type would be one of my personal favourites. But I’ve always had a soft spot for MG’s and triumphs.

 

[DT]

Since @bunnspecial is our resident classic car aficionado, I asked him if I could move his MG posts into this thread, I figured, 1) it would be a more meaningful thread topic, and 2) it would be nice to see them together, since it's a fun sort of journal of his efforts on his classic car

 

[chengengaun]

I am not a car person but I enjoyed watching Harry’s Garage, especially his road trips, Mille Miglia and the various concours d’elegance he participated in. I like seeing classic cars being used instead of stored in a garage.

 

[Apple fanboy]

So, a fun little project this afternoon.

I think most new MG owners get starry eyed and excited about the fact that you can basically build a car out of catalog. Most all of the parts are available, and they're also not that expensive.

Fairly quickly, though, you get jaded at the fact that just because you can buy them doesn't mean they're good. I've fought the crusade for a while on this. There are a lot of cottage industries of people making one particular part(like the guy who had a sewing machine in his dorm room at college turning out nylon axle rebound straps) but sometimes it can take some hunting to even find out about those. There are also people who refurbish old parts, but again you have to know about them. Moss Motors, who is the 800lb Gorilla in the British car business in the US, has a line of parts called "Classic Gold" that are equal if not better than OEM quality, but are also pricey. I buy parts from that line whenever I can, although I also hear people complaining about how expensive they are.

One seemingly never ending issue, though, with no off the shelf solution is the heater valve. Most of the originals lasted 40+ years, but considering that the newest MGB is now 41 years old, they're reaching EOL. The available replacement works fine, except they'll reliably start leaking in a few years. It's also not the easiest part in the world to replace thanks to bottom bolt access. When I pull the head, I always replace it just because it's easy to remove with the head off the car(plus I tend to use it as a handle to help lift it off) but 2018 was the last time I personally took mine off, and the shop that rebuilt my engine reused the old one.

Leaking is also not great because it sits right over the distributor, a part that doesn't particularly like being wet.

A few weeks ago, mine sprung a leak, although fortunately only when open. At the time, we were still in 70+ weather, so I didn't worry too much about it.

Finally, though, I decided to tackle it with a permanent, if not particularly elegant, fix brought to you from the plumbing aisle(or McMaster-Carr in my case). Basically you swap out the valve for a ball valve. The upsides are it's an off the shelf part that's much more reliable and also flows more coolant than the stock valve. The downside is attaching the dash control isn't the easiest, but then I tend to open/close it seasonally anyway so it's not a big deal to have to pop the hood.

Here's the basic plan-the old valve is chopped off at the base to give a mounting pedestal, and then drilled and tapped. The parts bill is a pipe nipple, a 90º joint, the valve, and a hose barb. That's about $20 in parts.

I ordered the parts a while ago, but realized I didn't have a 1/4" NPT tap, so had been dragging my feet. With a heater a lot more necessary now, I bit the bullet and did it.

First step, of course, is to drain the coolant. Normally on a job like this, I only drain it down to below the level of where I'm working as it's just easier. Typically I'll do that by loosening the bottom radiator hose clamp, and then I can work a screwdriver in and only hold it open to drain as long as I want. My new(er) radiator, though, has a drain plug and I thought I'd get adventurous and use it. Needless to say it fell into the drain pan, plus because it had been wrapped in teflon tape it wasn't the easiest to hand thread back in. That meant most of the coolant was gone by the time I got it back in. Oh well-you should change your coolant occasionally anyway, and somehow or another I end up doing it about every 6 months on this car .

I realized that rather than pulling the heater valve and modifying it on the bench, I could probably do it in-situ.

So, first step, hacksaw the valve apart

View attachment 9571View attachment 9572

I cleaned it up a bit with a file, then drilled a 7/16 hole

View attachment 9573

Then on to the tap
View attachment 9574

Tapered pipe taps are not always the most pleasant to use. I can remember tapping an aluminum bar with a 3/8". I broke a tap wrench, then went over to our machine shop and talked to the machinist there-he gave me a small bottle of proper tap lube(not the 3-in-1 oil I'd been using) and said just use the biggest crescent wrench I could find, then a quarter turn at a time and back off. I spent the day on and off, increasingly veins popping out of my forehead and putting my whole weight on the crescent wrench to get it.

By contrast, this one tapped fairly easily using just some hydraulic oil(what happened to be in the oil can I had handy) and a small crescent wrench.

In any case, from there it was just pull out the Teflon tape, wrap everything up, and put it together.

View attachment 9575

Unfortunately, though, I could be president of the "Measure once, cut twice" club, and trimmed the hose to the heater too short. Not photographed, but Autozone came to the rescue and I was able to get it installed and the coolant refilled.

Cutting fluid is what you want for tapping thread. I miss that smell from my engineering days. And the ability to jump on a Colchester lathe and turn something.

 

[bunnspecial]

Thanks @D.T. for spinning this off.

So, I'm floating another project, part relatively straight forward that hopefully I can work on after Christmas assuming the early pre-smog head covered in cobwebs in the corner of my parents garage is crack free.

I spent a while talking to a friend in Colorado who's a retired engineer from GM's Power train division and had a major hand in developing a lot of the current gen GM engines. He knows his crap, and in his retirement he builds a lot of race-prepped engines as well as does some high end street work on MGs.

Alloy heads can support higher C/Rs than cast iron because they can dissipate heat better. I knew that, but he basically told me that while yes, it was true, higher compression in an aluminum head was actually less efficient than the same C/R in a cast iron head.

So, talking to him, I'm going to send him a head to go balls-to-the-wall C/R and still be streetable on pump gas(although he did warn me I'd need to hunt out 93 octane specifically, have a distributor curved specifically for it, and still might need to toss a bit of octane booster). He said if I wanted to push the limits he could do 11:1, and I'm debating if I want to go that far or go for 10.5-10.7. I'm at 9.6:1 now, which is high but is common on MGs for hot street builds. I think part of his work on that would be reshaping the combustion chamber to REALLY eliminate potential hot-spots, something the B heads are notorious for and my current had has them rounded/polished but not to the extent I think this guy would do. Of course that also gets dicey since removing those means that he'd have to deck the head even more(and lead to more potential valve clash issues as well as a great need to modify the block to be sure the intakes could flow freely) as removing more metal from inside the combustion chamber increases volume rather than reducing it as desired.

He actually suggested a different head casting than the one I had. What I have on hand is a 12H906, which was the earliest MGB head casting used from 1962-1965 or so. He like the 12H12396, which I think was 66-67 only and is less common-the lack of any smog ports makes it less crack prone, and the redesigned water jackets both help reduce the chances of cracking and also help keep pinging under control.

That's all straight forward. I just need to send him a head and numbers and he'll make it happen.

Now comes the fun part that I've been playing with in my head for a few days and I want to make happen, but I'm also afraid to open ask a lot of the MG guys since they'll tell me I'm stupid. The ones who think it has some potential would tell me my effort is better directed toward installing EFI and calling it a day.

My basic idea-a triple carb set-up for the MGB.

Here's why I think it would work:

In a 4 cylinder engine, discounting valve overlap, only one intake valve is open at a time.

On a standard MGB head, cylinders 1 and 2(valves 2 and 3) share a single intake runner, and cylinders 3 and 4(valves 6 and 7) share one. These are called "siamesed" ports and they're not favored now, but they are what they are.

B series engines, and MGBs in particular, came with either two 1 1/2" carburetors or a single 1 3/4" carburetor. With dual carbs, each carb is "inline" with its respective intake runner and a crossover pipe connects the two. The single carb sits right in the middle of a manifold.

At low to moderate speeds, the dual smaller carbs are more responsive than a single larger carb. At higher speeds, though, a 1 1/2" carb doesn't flow enough for this engine(especially a hotter engine with a freer flowing head) so it draws some from the other carb. In doing so, it has to follow a convoluted path.

By contrast, the single 1 3/4" flows better at higher engine speeds. It offers plenty of airflow for all but a full race engine, and the air has a shorter and less restricted path at maximum flow. Larger carbs are less responsive at lower speeds, however. With that said, a single carb idles MUCH nicer than dual carbs ever will.

Big American engines with huge airflow demands recognize this and a "four barrel" carb is common. Basically your typical 4 barrel carb is mated to a V engine, and the "barrels" refer to what are effectively separate carburetors all in the same housing and operating in sync with each other. At idle/cruise each side of the V is fed by one barrel, and under higher airflow conditions the second barrel opens.

What I'd like to do is recreate that same concept using SU carbs.

Here's my idea-and I'd have to do some math to make sure these carb sizes match up correctly-

Basically design an intake manifold that has a single 1 1/4" carburetor(SU HIF2-I think it would have to be HIF carbs for size reasons) in line with the intake ports just like the standard twin carb manifold. Right in the center, though, would be an HIF4(1 1/2"). I'd then come up with some sort of progressive linkage to tie them all together-more on this in a second.

Going with this, the two outboard HIF2s would have their throttles completely closed at idle/cruise. The car would run only off the center 1 1/2" carb. This would give the low end responsiveness, nice idle, easy tuning, and efficiency of a single carb set up, but the responsiveness would be even better than a typical single set-up since it would be a smaller carb.

As air/fuel demand increased, the two outer carbs would start to open. This would have the benefit of giving a more direct "shot" than a single big center carb, and the excess air would have a shorter and more direct path than drawing entirely from the other carb.

The sizes may need playing with. It could be that the 1 1/4" would be better suited in the center and the 1 1/2" outside, or maybe all three should be 1 1/2".

Where I'm pondering now, though, is how to link the secondary carbs to the primary. Holly 4-barrels used two different systems-mechanical and vacuum. Basically in a mechanical progressive carb, the secondary starts to open at a certain throttle position and(properly adjusted) is fully open at WOT. This is relatively simple, and just requires a correctly sized cam to open the secondary later and faster than the primary. Manifold vacuum is related to engine load-under low load vacuum is high, and under high load vacuum is low. Using this, the secondaries will only open when engine load dictates them being necessary.

On something like a Holly 650, vacuum secondaries are usually considered preferable for a street driven car both for overall driveability and also fuel economy. There's some appeal to that approach.

Of course it needs a bit of thought to design that from scratch for discreet carbs. For one thing, you would need to rely on engine vacuum to pull the secondaries closed, and lack of vacuum to allow them to open. This makes me naturally a bit uneasy, as they would be fully open during starting(could be overcome with choke linkage design) and for another a failure in the vacuum unit could leave them fully open(and lead to a runaway condition). Consequently, I think the easy solution would be a mechanical stop to not allow them to open any further than the primary carb. The other side of doing it this way is it would take a LOT of experimenting to figure out exactly how to balance the vacuum level/springs to have them operate correctly.

Still, though, all of this is a fun project to think through.

 

[Apple fanboy]

Thanks @D.T. for spinning this off.

So, I'm floating another project, part relatively straight forward that hopefully I can work on after Christmas assuming the early pre-smog head covered in cobwebs in the corner of my parents garage is crack free.

I spent a while talking to a friend in Colorado who's a retired engineer from GM's Power train division and had a major hand in developing a lot of the current gen GM engines. He knows his crap, and in his retirement he builds a lot of race-prepped engines as well as does some high end street work on MGs.

Alloy heads can support higher C/Rs than cast iron because they can dissipate heat better. I knew that, but he basically told me that while yes, it was true, higher compression in an aluminum head was actually less efficient than the same C/R in a cast iron head.

So, talking to him, I'm going to send him a head to go balls-to-the-wall C/R and still be streetable on pump gas(although he did warn me I'd need to hunt out 93 octane specifically, have a distributor curved specifically for it, and still might need to toss a bit of octane booster). He said if I wanted to push the limits he could do 11:1, and I'm debating if I want to go that far or go for 10.5-10.7. I'm at 9.6:1 now, which is high but is common on MGs for hot street builds. I think part of his work on that would be reshaping the combustion chamber to REALLY eliminate potential hot-spots, something the B heads are notorious for and my current had has them rounded/polished but not to the extent I think this guy would do. Of course that also gets dicey since removing those means that he'd have to deck the head even more(and lead to more potential valve clash issues as well as a great need to modify the block to be sure the intakes could flow freely) as removing more metal from inside the combustion chamber increases volume rather than reducing it as desired.

He actually suggested a different head casting than the one I had. What I have on hand is a 12H906, which was the earliest MGB head casting used from 1962-1965 or so. He like the 12H12396, which I think was 66-67 only and is less common-the lack of any smog ports makes it less crack prone, and the redesigned water jackets both help reduce the chances of cracking and also help keep pinging under control.

That's all straight forward. I just need to send him a head and numbers and he'll make it happen.

Now comes the fun part that I've been playing with in my head for a few days and I want to make happen, but I'm also afraid to open ask a lot of the MG guys since they'll tell me I'm stupid. The ones who think it has some potential would tell me my effort is better directed toward installing EFI and calling it a day.

My basic idea-a triple carb set-up for the MGB.

Here's why I think it would work:

In a 4 cylinder engine, discounting valve overlap, only one intake valve is open at a time.

On a standard MGB head, cylinders 1 and 2(valves 2 and 3) share a single intake runner, and cylinders 3 and 4(valves 6 and 7) share one. These are called "siamesed" ports and they're not favored now, but they are what they are.

B series engines, and MGBs in particular, came with either two 1 1/2" carburetors or a single 1 3/4" carburetor. With dual carbs, each carb is "inline" with its respective intake runner and a crossover pipe connects the two. The single carb sits right in the middle of a manifold.

At low to moderate speeds, the dual smaller carbs are more responsive than a single larger carb. At higher speeds, though, a 1 1/2" carb doesn't flow enough for this engine(especially a hotter engine with a freer flowing head) so it draws some from the other carb. In doing so, it has to follow a convoluted path.

By contrast, the single 1 3/4" flows better at higher engine speeds. It offers plenty of airflow for all but a full race engine, and the air has a shorter and less restricted path at maximum flow. Larger carbs are less responsive at lower speeds, however. With that said, a single carb idles MUCH nicer than dual carbs ever will.

Big American engines with huge airflow demands recognize this and a "four barrel" carb is common. Basically your typical 4 barrel carb is mated to a V engine, and the "barrels" refer to what are effectively separate carburetors all in the same housing and operating in sync with each other. At idle/cruise each side of the V is fed by one barrel, and under higher airflow conditions the second barrel opens.

What I'd like to do is recreate that same concept using SU carbs.

Here's my idea-and I'd have to do some math to make sure these carb sizes match up correctly-

Basically design an intake manifold that has a single 1 1/4" carburetor(SU HIF2-I think it would have to be HIF carbs for size reasons) in line with the intake ports just like the standard twin carb manifold. Right in the center, though, would be an HIF4(1 1/2"). I'd then come up with some sort of progressive linkage to tie them all together-more on this in a second.

Going with this, the two outboard HIF2s would have their throttles completely closed at idle/cruise. The car would run only off the center 1 1/2" carb. This would give the low end responsiveness, nice idle, easy tuning, and efficiency of a single carb set up, but the responsiveness would be even better than a typical single set-up since it would be a smaller carb.

As air/fuel demand increased, the two outer carbs would start to open. This would have the benefit of giving a more direct "shot" than a single big center carb, and the excess air would have a shorter and more direct path than drawing entirely from the other carb.

The sizes may need playing with. It could be that the 1 1/4" would be better suited in the center and the 1 1/2" outside, or maybe all three should be 1 1/2".

Where I'm pondering now, though, is how to link the secondary carbs to the primary. Holly 4-barrels used two different systems-mechanical and vacuum. Basically in a mechanical progressive carb, the secondary starts to open at a certain throttle position and(properly adjusted) is fully open at WOT. This is relatively simple, and just requires a correctly sized cam to open the secondary later and faster than the primary. Manifold vacuum is related to engine load-under low load vacuum is high, and under high load vacuum is low. Using this, the secondaries will only open when engine load dictates them being necessary.

On something like a Holly 650, vacuum secondaries are usually considered preferable for a street driven car both for overall driveability and also fuel economy. There's some appeal to that approach.

Of course it needs a bit of thought to design that from scratch for discreet carbs. For one thing, you would need to rely on engine vacuum to pull the secondaries closed, and lack of vacuum to allow them to open. This makes me naturally a bit uneasy, as they would be fully open during starting(could be overcome with choke linkage design) and for another a failure in the vacuum unit could leave them fully open(and lead to a runaway condition). Consequently, I think the easy solution would be a mechanical stop to not allow them to open any further than the primary carb. The other side of doing it this way is it would take a LOT of experimenting to figure out exactly how to balance the vacuum level/springs to have them operate correctly.

Still, though, all of this is a fun project to think through.

That sounds like quite the project! You’ll have to post some pictures if you decide to go ahead with it.

 

[Scepticalscribe]

Steph (of the YouTube channel idriveaclassic) posted a list of her ten favourite classic cars yesterday (I caught it on Twitter); fascinating list, and they are not all impossibly out of reach, although some classic classics (that sublime Citroen DS, the E-Type Jaguar) do make an appearance.

@bunnspecial: I second @Apple fanboy: That does indeed sound quite a project; do let us know how it goes.

 

[bunnspecial]

Will update if it all comes to fruition.

It's kind of sad that I'm still chasing power like this on a puny little 4 cylinder engine, but at the same time the last rebuild really transformed the car and it's a blank slate for more work. Still, though, I always have to keep in mind that often times going for ultimate power sacrifices street manners.

The increase in CR should make a big difference. The triple carb project, if I go through with it, may end up being a futile exercise in frustration but in my head it makes sense and it would be something that, as best as I can tell, no one else has done. If I can work out the kinks, I could even see doing a small run of them if there is any other interest, but that's getting WAY ahead. I'm only considering it now because I have access to top notch CNC equipment through my work that's intended to be used for whatever(even members of the general public can use it) as long as I provide the material. I just need to get it drawn up...