Should I use my s52 or m52 for my setup?

[Boostedhoopty]

I am building a z3 that I plan to almost exclusively drag race/street race. I have an m52 bottom end that I planned on putting in the car, but I also have an old mercedes that I swapped an s52 into. I have no problem with robbing the engine out of it and putting the m52 in it as the merc is just a cruiser. Would this be beneficial to the z3?
My goal is 700whp but obviously I am wanting to make as much as possible.

The rest of the setup is a nv head with 264/256 schricks, nv rods, .82 t3 6266 cea with 3.5" fender exit, Vems v3, bosch 2000's, twin disk with a zf. It will be on e85. The car is going to be gutted on the interior and has zero hvac components, wipers, etc. so it should be very light

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[JPE36M3]

Honestly, I’m already regretting using my stock s52 in my car. I have an m52 and the extra bore tolerances would be a nice peace of mind in constant high boost situations with the extra seal space between cylinders. I’d take your s52 crank out of the other car and swap into the m52 block

[rajicase]

I would definitely run the s52. Without a doubt. The extra torque and spool will be huge. I wouldn't worry about wall thickness till you are pushing 1000whp. Even then, I would stick with my s52. You could easily see an extra 100ft/lbs of tq from the s52 over the m52. I hope you are planning to build the motor for your power goal, at that power from a fast spooling 6266 your motor wont last 1k miles on factory rods.

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Ohhh I see NV rods. Missed that. Those should be good, disregard my statement on the rods.

[pbonsalb]

When I built a motor using an M52 block, I went to the S52 bore for the displacement. I agree with not worrying unless you are trying for 1000 rwhp. I am at about 700 rwhp and have no concerns about the bore.

[Boostedhoopty]

Thank you guys, I appreciate your input. My other concern is that the 6266 could be a little small for my goals if I used the s52 due to the extra displacement. Is my thinking out of line on that? A different turbo is not out of the question but I do already own it and have my complete hotside built around it, so I would prefer to use it if possible.

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[rajicase]

Thank you guys, I appreciate your input. My other concern is that the 6266 could be a little small for my goals if I used the s52 due to the extra displacement. Is my thinking out of line on that? A different turbo is not out of the question but I do already own it and have my complete hotside built around it, so I would prefer to use it if possible.

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I would get a bigger turbo period; but if youre going to run the 6266, might as well put it on the s52. 700whp will really be pushing it. For your goals I would go with a Borg S366sxe or S369sxe.

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I have been running a s366sxe at ~24psi for almost a year now. Should be 650-700whp on my s52. Perfect set up IMO.

[pbonsalb]

6266 should do 700 rwhp while offering great response, but that is probably about it (one member ran a 6266 to 800 rwhp but I think it broke soon after that). 6466 has done 800+ rwhp. And of course there are even bigger turbos that can make more. Usually the bigger you go the more the trade off in bottom end response. If you can use E85 fuel and tune for it, you can use higher compression and run more timing to spool a big turbo sooner. A twinscroll manifold also makes a big difference in spool.

[Boostedhoopty]

It is setup for e85 and I had a .070" gasket for the m52 and would probably do a stock compression s52 also

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[Boostedhoopty]

I am familiar with the relationship between compression and turbo sizing as well as displacement and camshafts etc. vs powerband. I have put together quite a few quick forced induction cars, just not quite sure how far a given setup will go on this platform.

My thinking was the smaller displacement engine may be able to make more power on the same small tubine, granted it will take more boost and/or rpm to accomplish that and could sacrifice torque. I just don't know if the trade off is worth it.

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[Boostedhoopty]

So I am gonna go ahead and use the s52. What headgasket would you recommend for this application? From my searching it seems that a cutring of some sort is pretty common.

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[pbonsalb]

Run the cutring gasket. CES sells it.

Are you using stock pistons?

[Boostedhoopty]

Run the cutring gasket. CES sells it.

Are you using stock pistons?

Yeah, I plan to. I figure with e85 and my power level I should be alright

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[rajicase]

I would suggest getting some forged pistons. At the least, at your power level you will need re-ring and gap your rings if sticking with stock pistons. Ask SCapelo how stock pistons worked at 600whp..

[pbonsalb]

That was my concern — the stock pistons won’t be reliable past 600 rwhp. E85 does not make them stronger. Just reduces the likelihood of detonation. And if you are going to stay at 600 or less, a big turbo like the 366 isn’t needed.

[Boostedhoopty]

I definitely plan on opening up the ring gap a little. I feel like I've seen a few guys push stock pistons into the 800whp range? I'm definitely not scared to try it and buy forged pistons if I do have an issue. e85 does seem to be an advantage when pushing the limits of sbe stuff. I agree that it won't make them any "stronger"

My turbo is just a 6266

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