Forged M20B25 Build

[eThirtyAaron]

I know some are going to say this has been beaten into the ground, but I cannot find definite answers on forged internals for the M20B25. I'm doing a turbo build, and plan to be around 400, TO START. I'm a big fan of over building, and doing it right the first time.

That being said, what is a good forged setup for a stock M20B25? I've seen people use wiseco pistons, which I'm very open to, I just don't see anything vehicle specific. I've also heard of using S50 rods, but like I said, I like to overbuild the first time. Forgive me for being naive with these older BMWs, not used to the big puzzle piece of an engine these cars seem to have.

Thanks in advance for any insight, and any help given! Can't wait to be boosted!

[Best_name_available]

What have you done in the past

[digger]

paul burke imagineering pistons, for rods molnar are economical 600 ish but reportedly very good machining tolerances compared to other brands using china forgings . pauter, carillo, arrow also make some good rods but youre looking at 1k+

[eThirtyAaron]

What have you done in the past

What?

[eThirtyAaron]

paul burke imagineering pistons, for rods molnar are economical 600 ish but reportedly very good machining tolerances compared to other brands using china forgings . pauter, carillo, arrow also make some good rods but youre looking at 1k+

Thanks man. Have you personally seen a setup with the Molnar rods?

[digger]

Thanks man. Have you personally seen a setup with the Molnar rods?

im using molnar rods on a NA engine this year. there are 24V guys on BFc using molnar in turbo m52/s52 etc. The company is run by Tom Molnar and ex guy from Oliver rods. send them an email and discuss and he'll be the one who replies....

[boogle2]

I was literally just about to make a thread like this for myself. Don't mean to thread jack, but I saw that ireland engineering has the complete setup that one might need, including upgraded valve train parts.

Would it be bad idea to go IE forged pistons, rods, as well as upgraded rockers and oversize stainless valves from them? Any thoughts?

[nomansland92]

IE uses Ross racing pistons and Chinese rods.
I'm using there pistons and rods for now. I have no complaints about the pistons but the rods were the wrong size and didn't fit probably. I had to machine the sides of them so they had a little side to side play on the journals or else the motor would have locked up soon as It warmed up.
I don't know anything about there cranks though

Hope this helps

[ThatOneEuroE30]

IE uses Ross racing pistons and Chinese rods.
I'm using there pistons and rods for now. I have no complaints about the pistons but the rods were the wrong size and didn't fit probably. I had to machine the sides of them so they had a little side to side play on the journals or else the motor would have locked up soon as It warmed up.
I don't know anything about there cranks though

Hope this helps

Yes i just got some ross racing pistons from ireland and they are great quality.

[digger]

what does Ross call up for piston bore clearances on an m20 piston?

you dont need forged rods in a NA engine unless there are special circumstances. rods from a 24V engine will be fine

[SkiFree]

Ireland Engineering (Ross) pistons use 2618 which does need additional bore clearances (it will make noise on start up, but once it expands it'll be fine [pending your machinist doesn't screw up, or you don't screw up break in.....but that's with any option]).

However if you plan on big boosting then I'd much rather run 2618 than 4032 (CP, Wiseco) (which doesn't need as much clearance but sacrifices strength needed on an aggressively boosted engine).

I could do M142 MahleMotorsports alloy but custom pistons that go that route have got 2-3 month lead time and cost well over 2k. Those Paul Burke pistons would be an awesome choice as well, however he can be a bit tricky to get through to now that his health isn't the greatest.
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As digger mentioned 24v rods are a great route to go (the M52 and S52 rods are the same), but if you are going big turbo. Some stronger H-beams would be nice.
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Given this route you're taking and the machining that will be done there is no reason not to go 2.8L (81mm stroke, 135mm rods, 85mm bore) or 2.9L (84mm stroke, 135mm rods, 85mm bore).
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Lastly ... I saw your wanted add. No piston maker advices making forged pistons to fit into a pre-exhisting bore, ESPECIALLY if you want boost. You always bore to the piston, NOT vice versa.

[boogle2]

Ireland Engineering (Ross) pistons use 2618 which does need additional bore clearances (it will make noise on start up, but once it expands it'll be fine [pending your machinist doesn't screw up, or you don't screw up break in.....but that's with any option]).

However if you plan on big boosting then I'd much rather run 2618 than 4032 (CP, Wiseco) (which doesn't need as much clearance but sacrifices strength needed on an aggressively boosted engine).

I could do M142 MahleMotorsports alloy but custom pistons that go that route have got 2-3 month lead time and cost well over 2k. Those Paul Burke pistons would be an awesome choice as well, however he can be a bit tricky to get through to now that his health isn't the greatest.
-----------------------

As digger mentioned 24v rods are a great route to go (the M52 and S52 rods are the same), but if you are going big turbo. Some stronger H-beams would be nice.
-----------------------

Given this route you're taking and the machining that will be done there is no reason not to go 2.8L (81mm stroke, 135mm rods, 85mm bore) or 2.9L (84mm stroke, 135mm rods, 85mm bore).
-----------------------

Lastly ... I saw your wanted add. No piston maker advices making forged pistons to fit into a pre-exhisting bore, ESPECIALLY if you want boost. You always bore to the piston, NOT vice versa.

So in summary, if a guy was going for a big boosted M20, the ross racing (IE) pistons and a carillo rod would be a great set to have?