High compression pistons, need forged rods?

[MIKe30]

In the middle of a bottom end rebuild on my s52. Had bad enough scoring on some cylinders that it didn't come out with a hone. I now have two options, 1 - keep the same block, bore it out, get high comp pistons to fit... or 2 - swap my internals over to another block machined to fit my current stock s52 internals.


My question is do I need forged rods if I bump the compression to a mere 11:1? How bout 11.5:1? Motor will see rebuilt head with sunbelt cams.

Reason I ask is Wiesco pistons don't seem too expensive, but if I have to buy new rods too I'm going to go with option 2 and keep it stock. Truthfully, as anal as it is, I'd rather have my original block stay with my motor. But buying new pistons and new rods is out of the question. I hear m54 rods are forged, is that a viable option?

Thanks.

[Beej '86 325es]

I don't think so. Although I haven't run mine outside of the garage yet, I'm running 11:1 CP pistons with stock rebuilt/rebalanced rods, and a stage 3 cylinder head.

I'm no expert, but I don't think it'd be necessary unless you're running a high boost engine.

[etxxz]

how much power and rpm you're aiming for?? software? you're really looking to spend some money on this build..

..also, what happened to the engine?

[MIKe30]

I don't think so. Although I haven't run mine outside of the garage yet, I'm running 11:1 CP pistons with stock rebuilt/rebalanced rods, and a stage 3 cylinder head.

I'm no expert, but I don't think it'd be necessary unless you're running a high boost engine.

Well thats good news. Hope I get some confirmation from an expert! :) What pistons did you go with? stage 3 head from vac?

how much power and rpm you're aiming for?? software? you're really looking to spend some money on this build..

..also, what happened to the engine?

I'm hoping for at least 270 to the wheels. Obviously I'd love more N/A, and am curious as to how likely it is with a little upped compression. I think more while maintaining reliability is possible.

Stock rpm is fine with me. I'm not really interested in pushing it past 7k. Most dyno's I've seen dont have much power after 7k anyway. In addition to all that, I would love to have RELIABILITY!

Maybe I'm a dreamer, but I think I'm being realistic. NO, i'm not looking to spend money on this stupid build... but it sure is turning out that way. It's just one thing after another that is happening. It's making me sick.



Software - right now it's looking like AA, or possibly even TRM if they get they're obd2 tune out by the time this is in the car.

What happened to the engine? You referring to the scoring?

[nando]

your rods are already forged - almost all rods are. Even eta and M10 rods are forged.

if you want to bump up the CR to 11.5:1, get an agressive cam to go with it, it will help avoid detonation at lower RPMs.

[z31maniac]

Software - right now it's looking like AA, or possibly even TRM if they get they're obd2 tune out by the time this is in the car.

At least an OBD-I manifold though right? I think 270 to the wheels with an OBD-II S52 is a bit lofty.

[MIKe30]

your rods are already forged - almost all rods are. Even eta and M10 rods are forged.

if you want to bump up the CR to 11.5:1, get an agressive cam to go with it, it will help avoid detonation at lower RPMs.

Interesting, didn't know that about the rods. Then what is the benefit of aftermarket rods - weight? I assumed aftermarket rods were forged and ours were not.

If this is the case, the question now becomes "High compression pistons, need upgraded rods?"

You don't think sunbelt sport cams are aggressive enough, or you just skimmed the OP?

At least an OBD-I manifold though right? I think 270 to the wheels with an OBD-II S52 is a bit lofty.

Yes, obd2 with obd1 manifold, vac stage 2 head with sunbelt cams, and rebuilt bottom end. That should put out 260's, with stock compression.


Second question becomes, cost vs. benefit of 11:1 vs 11.5:1. Can I run 93 on either? Does reliability become a factor with 11.5? How about longevity? So many questions, I would love to read a 10 page article right now on this stuff. :crazy:

[mentaleeill]

your stock rods are fine, just have them grinded and shot peened. i just bought cp pistons for my fi build, i thought about wisecos, but after you add rings, youre only like 200 cheaper then the cps. after reading all the drama about wiseco over on bfc, id rather pay the extra and be safe. vac has most of the cps in stock already too.

[z31maniac]

Yes, obd2 with obd1 manifold, vac stage 2 head with sunbelt cams, and rebuilt bottom end. That should put out 260's, with stock compression.


Second question becomes, cost vs. benefit of 11:1 vs 11.5:1. Can I run 93 on either? Does reliability become a factor with 11.5? How about longevity? So many questions, I would love to read a 10 page article right now on this stuff. :crazy:

Any dyno's to back that up? Not calling you out, I just thought I remembered reading threads with less than 250 on that setup.

How do the Sunbelt's affect the TQ curve? Is dead down low and a screamer up top? That may suck for something you drive on a regular basis.

[MIKe30]

your stock rods are fine, just have them grinded and shot peened. i just bought cp pistons for my fi build, i thought about wisecos, but after you add rings, youre only like 200 cheaper then the cps. after reading all the drama about wiseco over on bfc, id rather pay the extra and be safe. vac has most of the cps in stock already too.

Interesting, have a link to the bf.c wiseco thread? I'm gonna search it now. Also, why grinded? Shot peened is weighed/balanced? Pardon my ignorance, you can tell I have plenty of reading to do...

Any dyno's to back that up? Not calling you out, I just thought I remembered reading threads with less than 250 on that setup.

How do the Sunbelt's affect the TQ curve? Is dead down low and a screamer up top? That may suck for something you drive on a regular basis.

I'll look for some now. As far as TQ curve, it's less than schricks down low but it's definately a screamer up top :)

It's not a daily, so I think it'll be fine. Not to mention, the s52 low down low will still probably be more than the m20 down low... if that makes sense.

[HiTheNameIsBJ]

Im using weisco's for my e36 turbo build. Ipp sells them cheap, but they have a 5 week waiting period for custom cuts. They have rods for cheap also. As a matter of fact I'm sourcing almost 100% of my motor parts from them. P.S, lemme get that pic of the door.

[mazur]

Your rods will bend somewhere north of 600rwhp with proper tune. I wouldn't sweat it.:pimp:

[nando]

the advantages to aftermarket rods is usually strength, S50 rods are already pretty light.

[Beej '86 325es]

Well thats good news. Hope I get some confirmation from an expert! :) What pistons did you go with? stage 3 head from vac?

The pistons are CP - got them through VAC.
The head I bought mostly completed and pieced the rest together. It's got Schricks, +1mm stainless valves, ti retainers, port/polish.

Software - right now it's looking like AA, or possibly even TRM if they get they're obd2 tune out by the time this is in the car.

It sounds like you're doing a pretty similar build to mine. I plan on talking to Matt (Racer's Market) from this board when the time comes, as he does custom chips.

[mentaleeill]

[QUOTE=MIKe30;1366366]Interesting, have a link to the bf.c wiseco thread? I'm gonna search it now. Also, why grinded? Shot peened is weighed/balanced? Pardon my ignorance, you can tell I have plenty of reading to do...


a machine shop will smooth out the ridges and then shot peen them for added strength, not a have to, but why not. of course balance them. the thread on bfc was in the fi section, sigma and someone else were having problems with there specs and a few others chimed in as well. plus the fact that vac stocks the cps is alot better then waiting 3-4 weeks and possibly having a wrong part.