Hi I am needing to replace my neglected 3.0ltr engine (head from e3 3.0si with L jet, but cracked head). I have a M30B35 with good compression but I now realise it is later castings with engine mounts in different position. I also have a M30B34 (same mountings as e9) however I believe it has head issues. So Question is can I put B35 head on the B34, are there any issues ? Note I will use an aftermarket ems ecu.
M30B34 vs M30B35
- Thread starter jeme9
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i am not an expert on this subject ... but i remember reading from SFDon that you will drop compression with that approach. (Please search as i could be very wrong). the first thing you should do is run a compression check on the b34 ... not sure if OZ has the high compression b34 (10:0) or the anemic US version (8:1) ... the compression numbers would be radically different - normal readings of 210 compared to 160 or below. now we are at the end of my limited range of knowledge on this subject.
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You can put the B35 pistons into the B34 block, and essentially build something that is functionally 100% B35 but with the right holes on the outside of the block. Or they sell engine mount adapters for that purpose, but probably only from the US.
Layne, might significantly lower your compression if its a euro b34. the euro b34 pistons were big piano tops
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I'm talking about using it with the B35 head. The only usable head he seems to have. So yeah, it's 9:1 instead of 10: 1, but if he doesn't have a good B34 head, he doesn't have the option of 10:1.
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Probably cheaper and easier to find another head though than swap pistons. I don't advise doing that without honing the block and using new rings, but other people seem to do it all the time with no problems.
Assuming the B34 bottom end is good and has the 10:1 pistons.
Assuming the B34 bottom end is good and has the 10:1 pistons.
You can buy adapters for the motor mount issue easily.
And inexpensive. Go with the B35. If you don't want to deal with that, sell the B35 and buy a B34 head. Cores are a dime a dozen. There are tens of thousands out there...
If I go with std mounting I can avoid engineering certificate in Australia, however if I use the adapters (and yes they are expensive landed in Aus) I will need engineering certificate for change. Thanks for your suggestion
Those officials can actually know the mount has been modified? Amazing.
You can make your own adapters with some angle iron.
They would seriously ding you on non OEM brackets? Thought MOT in England was anal.
They would seriously ding you on non OEM brackets? Thought MOT in England was anal.
For those adventuresome OZ folk that want to build the "Locost" version of Chapman's Lotus 7 from the book Build Your Own Sports Car for as Little as £250,
the powers that be ran finite analysis on the plans for the frame and despite there being many made elsewhere in the world, they require additional structural bracing to pass their license requirement.
the powers that be ran finite analysis on the plans for the frame and despite there being many made elsewhere in the world, they require additional structural bracing to pass their license requirement.
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Actually I can't see why you can't just put the B35 head onto the B34 high comp engine. Should lower the compression lower than the 10:1 B34, but probably not even as low as the 9:1 B35, and definitely not as low as the 8:1 B34. So it might even work better than the B35 head with B35 pistons. The B35 pistons are designed for "better" combustion characteristics, but who even knows if they achieved that. The head shape is roughly the same, with some additional space in the B35 head. You lose some of the squish pad compared to the B34 head, so maybe a little torque is lost. The piano top pistons should have no chance of striking anything since the combustion chamber is overall bigger (always check anyway). The engines are 208 and 210 hp, so a mix of the parts should land you in the 209 range. 
The piano top pistons should have no chance of striking anything since the combustion chamber is overall bigger (always check anyway). The engines are 208 and 210 hp, so a mix of the parts should land you in the 209 range.
I think your logic is flawed.
A 210 hp B34 @10:1 isn't going to make 209hp @ 9:1. If you are going to use averages, average the ho between the 8:1 NA spec motor and the euro 10:1. That is 197 hp plus a few more for lack of emissions controls. So you have two 200+ HP motors that when combined make sub 200HP.Fix the head or run the B35! Before discounting the B34, perhaps see if any members would be willing to send a good B34 head to OZ.
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It isn't going to be 9:1 most likely (I don't have time to look up dome cc's, head cc's etc and calculate it, but it can be done). It should be 9 point something.
The HP differences are not solely compression related, the B35 has bigger intake valves, bigger ports, better manifold, and most importantly, better fuel injection. My assumption is that he would use all of those better parts since he has them. Also the smiley face indicates I was being sarcastic about the 209hp figure. But there's no reason the engine wouldn't 'butt dyno' just as well as the other two.
The HP differences are not solely compression related, the B35 has bigger intake valves, bigger ports, better manifold, and most importantly, better fuel injection. My assumption is that he would use all of those better parts since he has them. Also the smiley face indicates I was being sarcastic about the 209hp figure. But there's no reason the engine wouldn't 'butt dyno' just as well as the other two.
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The total result should actually be a B35 engine with slightly raised compression, and potentially slightly worse swirl and squish characteristics of the combustion chamber. The low power of the 8:1 engine doesn't factor in at all.
Personally, I would probably spend some big bucks on 10:1 or greater pistons designed for a B35 engine, and build that using the B34 block (just to get the right mounting holes), so you have an engine likely in the 240hp range.
Personally, I would probably spend some big bucks on 10:1 or greater pistons designed for a B35 engine, and build that using the B34 block (just to get the right mounting holes), so you have an engine likely in the 240hp range.
the stock euro b34 produces 218 hp - the compression should be around 210 psi. the stock b35 is 208 hp and the compression should be around 185 to 190 (9:1) ... if i remember correctly.
Koala Motor Sports makes a beautiful bracket for the motor mounts when going to a B35 engine. There is a lot of discussion in the E24 forums regarding a B35 head on a B34 block. A definite compression loss due to the larger combustion chambers. Most of the guys doing this swap are going turbo and want to drop compression. As far as a rebuild goes, pistons to work in conjunction with the B35 can be ordered from JE in Orange County , or any other reliable piston manufacturer
Thanks everyone for your input,
sounds like B35 has lower compression than 10:1 B34, sounds like this may be a combination of larger head combustion chamber and piston shape ?
Maybe I should be building engine with B34 block with B35 head and B35 pistons ? Am I understanding correctly?
PS my B35 engine had compression 190 - 200 psi.
sounds like B35 has lower compression than 10:1 B34, sounds like this may be a combination of larger head combustion chamber and piston shape ?
Maybe I should be building engine with B34 block with B35 head and B35 pistons ? Am I understanding correctly?
PS my B35 engine had compression 190 - 200 psi.