It looks like I'll be running Manley's 29cc dish pistons with my built 402. Can anyone tell me what my compression is going to be around with a stock deck LS2 block, 29cc pistons, 72cc 317 heads and the new ZR1 7 layer gaskets. I'm hoping to be as close as possible to 8.5:1.

 

i would say 8.5

 

That's what I'm hoping on but with the LS9 7 layer gaskets I don't know.

 

That is too much head gasket.

Don't you think you would calculate your compression ratio BEFORE you bought pistons?

You are going to be below 8.5 with those gaskets.
Buy the proper gaskets for your application.

I would also recommend you go with a higher compression ratio than 8.5:1... closer to 9.5:1

 

hes building a high boost motor

 

The only reason I want to go with the LS9 gaskets is because they are 7 layers and are supposed to provide better clamping force. I'm building a car that is going to be making around 17-19lbs of boost.

Is there a reason why I wouldn't want to be around 8.5:1?

 

Based on the info you supplied and figuring "0" deck - 8.2:1

If you are going to be running at 19 lbs of boost on a regular or sustained basis you need to ensure proper head-to-deck clamping - take a look at ARP's L19 head studs as well and aftermarket, thicker deck head.

 

I'm pretty sure those are the head studs I ordered since I paid 430 for them. My builder addressed them as ARP 2000 head studs.

Do you think it will be a bad idea to run my compression that low? I'm only going to be running around 12lbs on 91 and 17-19lbs on 109. Most of the time this car will only be on 12lbs.

 

Sorry but the head gasket is not providing any clamping force. If you have a MLS gasket, which all of the stock ones are, you want to use the proper gasket for your application, not just one that someone said he better than another.

I use stock gaskets, the correct one for the bore size, etc for my application. This is all information your engine builder should have discussed with you BEFORE you bought any parts.

Running around on 12 pounds and occasionally making 17 is not high boost and I would run 9.5:1 for that setup. Just a preference but you are going to get all the torque from the bigger cubes anyway.

If you are running 19 psi on that stock thickness head you will likely end up pushing coolant anyway, but you can try it.

I spoke with him before about it... as you can see that is not what I would call a high boost engine.

I think too many times people get caught in the discussion of this part is great, that part is nice, but all of the parts have to work together, if you just buy a random bunch of parts that are not correct for your specific application you are just going to end up with a bunch of nice parts, not a nice package.

Hope that makes sense.

 

A 7 layer gasket will help with sealing more than 3 or 5 layer gasket will. I don't see what would be so bad about running a 7 layer MLS gasket please help me understand your train of thought here. Is the ZR1 gasket not going to fit properly or something? If that were the case how come everyone is telling me to use them?

I would honestly say that running 17-19lbs of boost on an LS motor is considered a lot of boost. Most the guys on here making 800 plus are only pushing about that.

I don't understand why you think I would be better off running at 9.5:1 vs 8.5:1? With a lower compression I should be able to make more power since I would be able to run more boost before detonating.

 

I took your advise and decided to go with a Cometic head gasket instead.

 

Smart guy, Nick will not tell you wrong here man. He has build a few motors in the past.

 

OK.. I did not say that a ZR-1 head gasket would not work or would not work properly. The reason that they have 7 layers is not for better sealing over a 5 layer gasket. The reason there are more layers is provide a thicker gasket to lower the compression of the engine.

I think you have kind of missed my point so I will say it one last time.

You should have a complete plan for your build BEFORE you start buying parts. You should know what heads you are going to use and what the other components are BEFORE you buy parts. I always buy shelf pistons and shelf (GM) head gaskets if I absolutely can. I would use a correct gasket for your application and decide on a target compression ratio and cut your 72 cc heads to get there with a standard GM gasket.

Point being that there is no reason to spend $200 on a pair of head gaskets because you need a certain gasket for a specific compression ratio when you can buy a set of GM gaskets for $50 and have the heads shaved for another $50.

If I was putting an engine together that ZR gasket was the right gasket, I would use it.

I don't understand if you have an engine builder putting an engine together why you are shopping all of these parts? If he is building you an engine you guys should decide on a compression ratio and he should be able to tell you what you need to get it there.

I would say that 19 pounds is a lot of boost on an LS engine. I don't know what you FI setup you are running but if you have an 8.5:1 compression engine it probably will take that much boost to get to 800 plus. I am not sure what your experience is but again 800 plus on the street is a lot for any street tire, more driveable with a SC setup but much tougher on a TT setup.

Hope that helps you a bit, but again, if your engine builder cannot help you spec this stuff and is letting you just randomly buy parts for him to put together, you might want to find someone else to put your engine together.

 

My engine builder has gave me a lot of suggestions it's just that I don't want to follow his exact build. I want this motor put together with the parts I pick out. I've already decided on which pistons I want to go with since I got a good deal on them. I already have heads and rods that came off my last motor. All I'm trying to do is make a few changes to my last build to support my new power goals.

With the ZR1 gasket it would put me right near my target compression ratio but I'm sure I can get there with Cometics too. I really don't want to mill my heads down (don't want to loose any thickness to my deck).

So here is what I have so far:
LS2 402 w/Manley 29cc pistons, Manley I-beam rods, billet main caps w/ARP studs, clevite bearings, custom grind turbo cam, Callies Dragon slayer crank, C5r single timing chain, Melling high volume oil pump, 317 heads (72cc), PRC dual springs, ARP L19 head studs, cometic head gaskets and Cadillac racing lifters.

My goal is to get the motor as close as I can to 8.5:1. I don't see any reason I wouldn't be able to make 850-900rwhp at 17-19lbs on a twin turbo setup, my old motor made 750rwhp and 800tq on only 14lbs and 100 octane with my compression at 9.0:1.

 

im running 8-10 psi boost on my ls2 402 its making 600rwhp low compression pistons stock ls1 241 heads i think im @8.5:1 i did a compression check it was 135lbs what do you think it is? im adding 5lbs of boost to it this week.

 

You should pick up around 130rwhp give or take on the tune. How much timing are you running and what octane?

 

93 octane! my tuner does the timing and he always says i cant believe how much timing it can take! i wish i knew what compression I'm running any clue

 

DO NOT use the cadialac lifters!!!! I aswell as many others have them fail causing a good amount of damage, stick with some LS7 lifters or some good aftermarket ones.

 

I had Comp R and they failed on me. I'm having a hard time finding some good lifters other than $500 Morales. What do you think about Comp OE replacements?

 

What is the dish on your pistons? Are you on stock 64cc heads? What head gaskets? Stock deck height?