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MG MGB GT V8 Factory Originals Technical - Why 215?

This is intended to be a philosophical sort of thread, as it's an old topic, but with the increasing popularity of Ford 302 and V6 conversions I'd like to bring it up again just to see what's new out there.

In my case the die was cast some 20 years ago and I now have enough invesment in the 215 to make change impractical, but let me start things off by explaining my reasons for beginning with that engine and then for staying with it.

Having heard rumors that the 215 ala Rover 3500 had been used in the Costello conversions and the factory MGB-GT I scouted around and found a source for rebuildable 215 engines. At $40 each. Now other engines were also available at this price as well, but the SBC was just a bit too big and the SBF had the now familiar sump problem which I did not want to deal with, plus my target horsepower requirement I estimated at 200 initial requirement with the potential to increase to 300. V6's were still either a bit low on the horsepower potential and/or had reliability problems yet to be solved and the rotary was a similar case with 300 hp outputs often causing case warpage. The 215 seemed to slot into these requirements rather ideally and though tight in a '71, it *would* fit with a minimum of work that wasn't already needed anyway. (I had some front end damage to repair as well.) So I dragged a Buick 215 down off the hill, took it home and began disassembly. It turned out to have some water damage to the coolant passages, so I took it back and dragged down another one, this time an Olds. When it turned out to have a crack in the outside of the block I sold it to a buddy and went back and got another Buick, later also getting another core and a spare set of heads. This Buick turned out to have infitessimal wear and no ridge, and all I could determine was that it must have been one of those engines that got the rings put in upside down. I rebuilt it using the stock pistons, but upgraded the cam and fitted it with a 600 Holley and the headers that are on my car today. With those changes my best estimate is that horsepower output was in the neighborhood of 240 and it would readily rev to 7000 rpm. Needless to say it exceeded my expectations. But all good things must come to an end and eventually I broke the skirt of a piston and spun a bearing. Having re-acquired through trade the Olds with the now heli-arced crack it was pressed into service and fitted with a Jetfire turbo to make up for lack of compression from inadvisably installed Buick low compression pistons and did quite well but it was never the engine the Buick was, and when the turbo bearing gave up the ghost an excuse was born.

All my adolescent and adult life I have lusted after a car with a blower on it. Hard to explain why, there's just something about it. So actually having a newly professionally rebuilt Jetfire engine with low compression pistons in my garage the plot was hatched to fit it with a blower and fuel injection, as well as an experimental intercooler. Mind you this entire progression had been and continued to be a low budget process and that meant I had to keep expenses down and make most of the parts myself, but indeed, I did have the technology. To make a long story short, The end result is what you see here:

In the final analysis, the horsepower output is on par with what would be had with a well sorted 302 (5.0L) conversion, and to my mind that's all that is wanted. Since only my opinion matters in this specific case, that explains everything. A blower on a 302 in an MGB would clearly be an excess and one that would not make sense in this car considering the necessary modifications and discarding of existing work, and I am not likely to start over with another car and do all the same modifications to it, as the production of this car has been something of an artwork. And as a side note, a V6 just would not have the panache.

Would I consider a Rover or a larger displacement 215? Certainly. In fact, I do have a set of 300 heads and a crank, so that path is clearly an option. But hopefully for many more years one that will remain untrodden by yours truely.

Jim Blackwood

Yes, why the 215? They're old, they're breaking, they never were really "great" to begin with, and there are better alternatives. Why use a 40 year old block and heads, when you can pick up a rover 3.9L V8, or 4.0 V8 for a good price these days. It's common knowledge that the 3.9L's perform much better because the valves are unshrouded, and one can easily hop them up to even bigger values. (300 crank, etc) 302's are VERY nice! SUPER FAST, easy to build, and plentiful, but those darn aluminum heads get pricey. From a cost standpoint, I don't see much of a difference doing a well sorted 3.9 vs a well sorted 302. You just spend the money on different things. If you want to push the envelope, Glenn Towery, and others will say 4.2L is the optimal displacement from the rover block. My local machine/racing shop took a look in my engine bay, and figured a vortech s-trim centrifugal blower would mate up to the front of the engine quite easily. Might have to cut some inner fender area on the drivers side (assuming alternator is on the passenger side) but it'd fit without serious hacking. Once again, no cheaper then a 302, just a different place to spend the money. Someone could add that blower to their existing rover motor and make some SERIOUS power. I'm just guestimating, but if I took a nicely flowed and ported 4.2L and gave it around 9:1 compression, and 5-7 psi on the blower, I bet I could make around 375hp. Especially if I grafted the ford injection system into the car, and installed a tweecer into the computer. Total control!

Crap, I think I got off topic there, but dang! ;)


I went with the 215 because it was inexpensive, in my particular case, and offered a certain appeal in its vintage engineering. Having grown up with british cars, and working in a british only garage since I was 15, the project seemed doable. No major trails to blaze and reasonably more power for minimal investment. As I was talking it over with an engine builder friend, he mentioned that he had a load of the 215 stuff that some guy had dropped off at his shop to be worked, and never showed up again, and he wanted it outta there. I got the whole lot for $200 which included the 215 skylark block (with 6th head bolt hole), steel crank, bearings, rebuilt 4 bbl olds heads, NOS shiefer aluminum flywheel, etc. Some of that sold to finance the project, but the rest went into the car. Ive personally never even ridden in a V8 mgb, but I love the idea of american engineering and british styling. Hopefully it will fire up here next week, and I can't wait to take it on the road. Why the 215? Vintage class. Same reason I keep and collect vintage tools. Same reason I put the HIF6's on there instead of a Holley. Who knows, maybe a 302 in the future, it sounds great, or a strokes Rover, but for now I enjoy the 215.

My car came with the 215 in it already, so I didn't exactly go looking for that engine (I'm re-doing a conversion that was done in all the wrong ways), but I think it's the rarity of the engine that appeals to me, plus it's just a good looking powerplant when you get it all cleaned up properly. If it came to practicallity, I think the course would have been a bit different, more to the tune of a later model with a v6, but I like the engine, and I like the chrome bumpers(Of course if the entire project was centered around practicallity, would it even include a 'B'?...).

But as I mentioned above, there's something the aluminium offers in terms of asthetics, that the cast iron of other blocks doesn't. But then, what does that really matter once the hood's closed?
Anthony Morgan

I did my first MGBV8 conversion in 1980, lomg before most of you had even heard of the idea, much less started a project. Remember, this was before Al Gore invented the internet & there was little to no information in the US about V8 MGB's.

The project started at Mountjoy's Auto Shop as a discussion of what to replace my 1963 side curtain midget with that would be a better beltway driver (70 MPH back then). A MGB was the obvious choice, but I wanted A/C because of the hot D.C. summers. The owner, & my MG guru, racer & mechanic Tim Mountjoy had read about the British MGV8 & though we could duplicate it, & that it would have enough power to run the dealer installed A/C units.

It soon became obvious that Tim had been doing a bit more than thinking about this for as while, as he had collected several Buick/Olds & Rover V8 engines. Someone had given him a Xerox pamphlet about converting A MG to a V8 engine. We had both read a bit about the factory V8 in Porter's book, an it turned out that another of Tim's customers was Glenn Towery who had done one or 2 V8 conversions in his own Delaware shop.
Also, about that time, one of our local MG Club members imported a real MGBGTV8 (another long story) & I was able to visit, crawl around & take pictures.

So, the project started. The engine choice was a 215 Olds that had been rebuilt to go into an airplane, a failed project, that had landed in Mountjoy's back room. An article in Hot Rod Magazine introduced us to Phil Baker & Dan LaGrou, then & now, the 215 experts. A call to one of the local salvage yards yielded a previously unheard of T-5 transmission that would fit the GM bell housing that Tim got with one of the engines. From then it was a slam dunk that only took 9 months to complete. D & D supplied a few bits like the alternator bracket from their Vega swap kit & a friendship with Dan. Glenn Towery offered a visit & examination of a covversion in his shop. Headers came from England, & so on.

The weak, pourous block that others complain about lasted 270,000 miles before a rocker shaft broke, I got an average of 70,000 miles out of the crappy(?) T-5 trannies- used- over 100,000 miles from both of the factory fuel pumps, but did wear out 2 MGC rear ends.

Choices today & information are greater, primarily due to the internet & faster/broader comunication. V8 conversions are widely accepted in the MG world, with many shows having V8 classes. We have a V8 Newsletter, & almost an international V8 conversion club. I was almost thrown out of the D.C. MG club for owning a conversion in the early '80's.

This was followed with a 4.2 Rover in the early 90's, another 215 in the mnid 90's, & now a 300 Buick GT. I guess I just like the 215 & its derivities, maybe for sentimental reasons, maybe because they are so easy to do, maybe because they are dependable & just a whole hell of a lot of fun.

Just one old fart's opinion, not a knock against Fords, V6's, etc.

Jim Stuart

Jim Stuart

Jim it seems you and I are contemporaries in this regard, as I began the original conversion mid '81 IIRC. Things sure were different then weren't they? Dan had the needed parts but his quality has improved noticeably since then, and I don't guess Phil is quite as active as he used to be. Unlike you, I'd only gotten a short look at the one MGB-GT V8 I'd ever seen while in Florida, so all I really had to go on was the sure knowledge that it could be done. And if you nearly got kicked out of the MG club, I'd have been certain to have been run out of town on a rail! Good times for sure.

But one thing I neglected to mention about the 215's positive features that I doubt anyone else will bring up, and which only apply to the Olds version, are the 6 bolts per cylinder. Why is this important? Well it's not for a normal engine, but for one with forced induction such as I've been doing for the last ten or twelve years it's a big factor. If not for that I could not run the kind of boost I'm running and get away with it for so long. Now I don't know if a 302 could run 15 lbs from a roots blower and live without special treatment and I really don't care because that's in a different spectrum in terms of power output, but a Buick won't do it, and a Rover won't either, simply because they don't have the balanced clamping force of those 6 bolts around each cylinder. So certainly in some ways newer isn't necessarily better.

Incidentally, Justin- how outrageous! I hope you're not serious ;-) I mean, if I can go out to the strip and get the same performance that Larry's getting then what's so wrong about 40 year old iron- er, I mean *aluminum!* ? I've got an EEC-IV SEFI and EDIS ignition, and there's the aforementioned head bolt advantage, and running that godawful high level of boost, so I really think yer pretty much all wet, son!


Jim Blackwood


I'm not going to disagree with you completely, but I know I've heard the buick blocks were really poor quality, with all the shifting liners, and what not. If you stroked out your block with the 300 crank, would you still run 15psi on your blower? In the mid 80's the brits stiffened up the block to help strength, and c.'94 brought us cross bolted mains.

I'm also talking about probabilities. What's the probability that a 40 year old motor will be more susceptible to wear and abuse than a 6 year old motor. Obviously, not every engine fits this case, but if you double, or quadruple the number of potential owners, the chances for damage could go up.

That's all I'm really getting at here. Gotta love debating. =)


I guess that depends on what you mean by really poor. It is true there were rumors of core shift. If I had one with the liners really thin on one side I'd sure not be all that thrilled with the idea of boosting it, at least not if I had to overbore very much, but if the bores are well centered or close to stock bore, why not? Any 215 that is still in rebuildable condition though is likely to be one of the good ones as there've been a lot of years and miles to thin the ranks, and I think I've really only seen one bad block. The porosity you mention was I believe really more a result of owners using straight water in the radiator (common back then) which caused corrosion and leaks. Again, not too many of those around anymore. Also I certainly would have no more problem with boosting a stroker motor than stock. With the longer stroke it should work out even better and cylinder pressures would be no higher so there would be no reason not to. Though a cross-bolted block is not available, the Jetfire block that I'm using is pretty stout and there's some debate about how necessary crossbolted mains are anyway in a skirted block design, especially if it redlines below 6 grand and with the blower there's really no need to go higher. As far as the number of owners is concerned I don't see that as an issue where the engine is going to be rebuilt anyway. Any concern there is probably more than balanced out by having a well seasoned block to start with. In other words, I really don't see the difference. Yes, you can get bigger valves and fancier combustion chambers and a little better ports in some of the later Rovers. For the money you can do that to a 215 too, or build a stroker to increase the displacement, or bore and sleeve the block for bigger pistons, or all the above. But I'd rather just pick up a good motor for cheap and stick a blower on it. Makes the basic unit *so* much easier to replace if something goes awry.

Jim Blackwood

My reasons for using a 215 are a bit different from those that most quote. The extremely short stroke gives the kind of torque/HP curve that more closely matches what a "sporting" engine should feel like (IMHO) and the peak torque is low enough not to tear things apart. I have 300 heads for my Olds, bought it over 20 years ago to do a BGT, got sidetracked (ran a VW store, so the MG stuff was off-limits) lost it in a fire, replaced it yet again, finally got a '75 roadster in Texas with NO rust last year to do the swap. About the only thing better than a 215 with 300 heads would be a single plane crank to REALLY make it sound right.

Pat Dolan

Are Buick 300 heads compatable with a 215 block?

They are.

Yes, but....

The 300 heads will bolt on a 215 Buick or Olds, & a Rover as well, but they have a larger combustion chamber to go along with larger valves, thus lowering compression, for perhaps a performance loss unless the compression issue is addressed. They also have a larger diameter than the cylinder bore, creating a shelf, which is not good for chamber design.

For most applications, they are not desireable. If you have re-sleeved your engine to a bore close to a match for the 300 heads, & use the correct pistons, then they will be a good idea. If you are adding a blower like Jim B. & need to lower compression anyway, again, a good idea.
Jim Stuart

Jim, here's a cross post from the V6 thread in case you haven't been following that one. It has as much to do with the 215 as the V6, but we were discussing the effective compression ratio while running and I needed this example which points out that sometimes less is more:

A lot of people do not realize how large a part intake efficiency plays in C/R. A fairly extreme example is my blown 215 Olds. Here the static C/R is 8.5:1 but max boost is over 15 psi and I don't have detonation problems. How is this possible with a roots type blower? Fuel injection, intercooling and electronic ignition of course play a part, but for the real answer we have to go back to the basic engine itself. Recall that of the BOP/Rover family the Olds design has the poorest performance in terms of port flow. When you consider the effect this has at maximum output it's not too hard to see that a substantial part of the blower's output is being used simply to overcome the shortcomings of the head itself. If the blower wasn't there at all, at some point the bottom would drop out of the dynamic C/R but with the boost power output is quite dramatic. However, take the same blower and put it on a Buick or 3.5L Rover and it would be unlikely to live real long simply because those heads flow better and the dynamic C/R would go up with the likely result being the onset of detonation. Power output might be no more than with the Olds and could be considerably less. The other factor is that boost increases as engine speed goes up, meaning that it isn't possible to dump 15 psi into the intake at 2000rpm, so again mechanical factors come into play and protect the engine. So the point is, that you can have an engine with a high static C/R, which improves efficiency and economy but at the same time have a lower dynamic C/R which prevents the auto-destruct-sequence. Knowing this, it should be possible for me to build an Olds short block that will run 10:1 C/R with the Jetfire heads, drop the blower output back to about 8 psi and get largely the same results only with better fuel economy. This might increase the risk of detonation at low RPM but otherwise I don't see a downside to it.

On second thought, I expect 8 psi would not get me to the same level of performance with 10:1 compression, but that I would be closer to 10 psi due to the intake restriction. But I don't intend to try it anytime soon. Anyway this once again demonstrates the versatility of the 215. Here we have a supposedly antiquated design, and it turns in a surprising performance. Not to say a newer engine would not do as well, it was just one of those fortuitous combinations that you run across every now and then.

Jim Blackwood

This thread was discussed between 29/10/2003 and 04/11/2003

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