M20 stroker questions?

[Kotty30]

So I'll tell you my plan at the moment and I'd appreciate it if you corrected me since I have done to much research on stroker builds.. I'm currently rebuilding my m20 I was thinking about putting the eta crank in keeping the I rods and getting a set of customs Pistons. I'm also going to hone cylinders and new rings and bearings of course. Is their anything wrong with that? I see a lot of people recommend eta crank with eta rods but will the I rods work with eta crank? What size engine will it be considered if I do this? A 2.7? 2.8? Just looking for some advice and direction thanks!


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[SkiFree]

What are your intentions with the car? Is this a fun street car, a dual purpose car, a race car? Do you plan on owning it for a long time? Do you have smog limitations? Are you prepared for tuning? Do you have a strict budget?

What you propose now would be considered a 2.8L build (w/ an 85mm bore), given the low cost of an M52 crank there is little reason to not go with it instead.

[Kotty30]

What are your intentions with the car? Is this a fun street car, a dual purpose car, a race car? Do you plan on owning it for a long time? Do you have smog limitations? Are you prepared for tuning? Do you have a strict budget?



What you propose now would be considered a 2.8L build (w/ an 85mm bore), given the low cost of an M52 crank there is little reason to not go with it instead.

My intentions are to go turbo but before I do that I want to rebuild/stroke bottom end so I feel confident in a turbo build. Everyone always tells me to just slap a turbo on it and don't touch it but I would have a feeling in my gut every time I get on it and I don't want that. It will be a street car. Maybe down the road get on the track a little but not in my plans. I do plan on owning for a long time already have a lot of money into the car and I love it and probably couldn't make a profit if I tried to sell it. No smog limits!! I'm not prepared exactly on tuning yet I have some stuff in mind but planning on doing that after the build! Thinking a standalone! And I would like to keep it as cheap as I can but not without it being crap I'm willing to put money into it just don't wanna spend 15 grand to make a 300hp engine. I also was trying to stay away from boreing it! Thanks!


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[jeffnhiscars]

My only thought is that if you intend to do a complete tear down and buy new Pistons...custom or not...then you should rebore the cylinders to guarantee proper tolerances. Honing alone won't get you there.

[SkiFree]

Gotcha, initially understand then that if your stroker build will be speced for a future turbo setup that you will not see a dramatic increase in power while it's being driven NA.

As Jeff said, if you are planning on custom pistons and turboing it then you need to plan on boring it. I cannot emphasize enough the importance of good machine work, (from boring the block, rebushing the rods, balancing, etc.). If you sit down with your machinist and tell him your intentions, chances are they already have a preconceived idea of what needs to be done (without doing too much or too little).

On the rods, the 135mm "i" rods are doable but if you want, use the M52 or S52 rods. Perhaps you could find someone selling an M52 bottom end and harvest the crank and rods. I do not recommend a 3.0L or a 3.1L setup for a turbo engine being built to last.

[Kotty30]

Thanks for your guys input! I do have a question tho.. If I get custom Pistons but have them be stock bore size. Why would I need to bore it?


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[digger]

The bore would likely be worn and not round anymore unless it's a new block or very low mileage

[mr2peak]

Here's some great info on building a 2.8

http://www.e30zone.net/e30zonewiki/index.php/Building_a_2.8

[Kotty30]

Thanks for the info!


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[jeffnhiscars]

The bore would likely be worn and not round anymore unless it's a new block or very low mileage

+1

Def don't out new Pistons in an old block. The cost of a rebore relative to the Pistons is small but the advantages are significant.

This is the "best practice".

[Kotty30]

Thanks but will the I rods work with the work with eta crank custom pistons 885 head and a bore for sure (obviously if put together properly?


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[digger]

yeah, it makes sense to look for a set of 24V rods that are 135mm long though as they are lighter, stronger and more compact

[mr2peak]

This is what I discovered in my research, YMMV.

If you use an ETA crank, you need to use 130mm (eta) rods. Moving up to a 2.8 with the M52 crank, stock 2.5i pistons are used with 130mm rods, bumping the pistons spec up proximately 1 point. If you use 135mm rods, pistons must be custom which adds a lot to the cost. If you're going custom pistons, you might as well go for an S50 crank. At this point, 135mm rods start taking away space for the ring lands, leading to excess oil consumption. Moving to a 3.2L crank, the piston starts to come very very far down into the block, and the sleeves move past the ends of the bores. This leads to excess piston skirt wear, which leads to bore wear, which leads right back to oil consumption. You also have to clearance a few places in the block when using a crank larger than the M52.

Many people end up parting out pieced-together stroker kits and going with an off-the-shelf kit for these reasons; those kits have been engineered to overcome some of those obstacles.

An M52 2.8L is hard to beat. It skips a lot of these issues, goes together with stock parts, bumps up the compression ratio and maintains an ok rod/stroke ratio. New stock pistons are a good idea, and maybe a hone, but every M20 I've looked inside of still had the factory crosshatching without any visible signs of bore wear.

In summary: If you want to BUILD a stroker, 2.8l is the best bang per buck option. Still not cheap.

[digger]

it should be possible to use a 86mm crank without an oil ring rail with custom pistons and 135mm rod. without a good cylinder head you wont make anymore power just more bottom end and midrange

[Hooffenstein HD]

What is the 86mm crank from? I thought 2.8 was 84mm then it went up to 89.6mm for the 3.0?