S50 Stroker - Pistons for 91 Octane?

[andyman2487]

Hello all,

Going to preface this with the fact that I've searched.

I'm currently rebuilding an S50 and I'm thinking of doing a stroker while I'm in there (S52 crank & S52 pistons). The car will be streeted with an occasional hard run/track day in there.

I plan to run these Schrick 276/270 cams, as the S50 ones had scored journals and can't be reused:

http://store.vacmotorsports.com/schrick---m52--s50us--s52us-sport--camshaft-set-276270-p2705.aspx

I need new S52 pistons, and I'm wondering which you guys would recommend:

New Stock Mahle (~$130/cylinder, 10.5:1 CR)
Mahle Motorsports (~$170/cylinder, 11.3:1 CR)

http://www.ctsturbo.com/cart/products/Mahle_PowerPack_S52_B32_86_6MM_Bore_11_3_1_CR_89_6mm_Stroke-3371-516.html

I like that the Mahle Motorsports pistons are much more high tech (forged 4032 alloy (low expansion/tight clearance), phosphate treated, graphite coated skirts, etc.) but I'm concerned with the higher compression ratio. Will it be overkill/hard to tune 11.3:1 with the OBD1 of the S50 on 91 octane? That's all we can dependably get in CA. Do you think I'll have issues with clearance using S52 pistons with these cams? I'll be using the Vanos limiting shim as the cams require it. I haven't heard too many stories about doing S50 strokers with aftermarket cams/pistons. I'm planning on having the thing tuned with a WAR chip after it's all built up.

Thanks!

-Andrew

[cmeptb13]

That's so cool that you get to build your motor like that. Since you're doing the pistons anyway just go for higher compression. But consider using stiffer valve springs. Also since you're going bore out the block vacmotorsports has the 87mm piston (something like that) but that will bring you a little closer to the actual 3.2L displacement.
However, the bottom line is if you were to do that to an M engine you'd be getting really nice hp. S52 you'd be pretty close to stock engine with just bolt-on mods. Don't expect any super high hp numbers.
In the end high comp, built head, cams, 3.5 maf, headers, 24lbs injectors, is going to be seriously badass, regardless.

[andyman2487]

That's so cool that you get to build your motor like that. Since you're doing the pistons anyway just go for higher compression. But consider using stiffer valve springs. Also since you're going bore out the block vacmotorsports has the 87mm piston (something like that) but that will bring you a little closer to the actual 3.2L displacement.
However, the bottom line is if you were to do that to an M engine you'd be getting really nice hp. S52 you'd be pretty close to stock engine with just bolt-on mods. Don't expect any super high hp numbers.
In the end high comp, built head, cams, 3.5 maf, headers, 24lbs injectors, is going to be seriously badass, regardless.

I have already bought VAC's dual valve spring kit, a 3.5" MAF, and 24 lb injectors so I have that part covered. I can't run headers legally (CA smog) so I'm going to try to go with stock exhaust manifolds.

What I'm wondering is with these mods and the cams mentioned above, will I have a hard time tuning with the 11.3:1 compression pistons on 91 octane? I am not sure if OBD1 makes this any more difficult. If so, I'll just go with the stock pistons. I realize that higher compression makes better power, but I want the engine to last if I'm gonna drop this kind of money on it. I plan to tune with a WBO2 and the WAR chip, I just don't want to run into pinging/detonation that a tune can't get rid of due to the high CR.

[nando]

the higher CR will be negated somewhat by the Schrick cams. But you might want to talk to some engine builders down there to see what they think, CA gas is kinda weak.

[FredK]

Rebello Racing in CA really knows their stuff. Prior to Sunbelt and Evosport having extremely hot cams available to the market, Rebello had a 300whp S5x build under their belt. This was a really long time ago, so forgive me for not remembering whether or not it was a 3.0 or 3.2.

Strangely there isn't much information online about Rebello. They still are in the BMW game; IIRC they have a 3.4L S54 crank that they machine using a stock 3.2 core.

Whether or not they'd share this information is anyone's guess, but it doesn't hurt to ask! Those new Schricks look great, and look to be a perfect compromise between the 264/256 and the more wild ~290 duration race cams out there.

[andyman2487]

Thanks guys!

CA gas is kinda weak.

Haha, agreed. There's a place a couple miles from me that sells 100 octane at the pump but I want to not worry about filling up with 91 if I'm out of the area.

I'll have to give Rebello a call, I didn't think about that. Thanks again!