MBC Racing

iTrader: (3)

I have a set of old school Cartek ported Stage IIX Ls1 heads from my original set up from 8 or so years ago. Currently they are milled at 57cc after the engine snapped a rod and did some damage.... I was going to use them on my Lq9 6.0 that I put in the car, but the compression was going to be WAY too high..... going to be ordering some PRC 227 soon.

I am contemplating putting them on my auto cross car with a stock 5.7 L.
I have two cams laying around that I could use....
224/224/.563/.563/113.5
or 232/237/.589/.589/113

I am thinking that the 224 cam would work better for auto cross since it would have more low and mid range AND I am concerned about pistion to valve issues on both.

So, the questions i have are what would my static and dynamic compression be on the two setups? Any experiance or opinions on the pistion to valve issues? Will I be able to run 93 or will I need oct booster, meth inj or race gas? Since it is a track only car, its not a big deal if I have to run something special, but prefer not to have to run race gas since I may not be available to me all the time....

thanks
Brad

mark21742

You will be pushing both compression for pump gas and ptv clearance. If I were you id clay the heads to find your ptv with the bigger cam, then flycut your pistons to give more room for the valves and slightly drop your compression. Keep your quench tight with a thin gasket to help reduce knock. Any thought of swaping to a small dished piston?

I'm running 57cc heads on my 408 with 12.5:1 compression, but my huge cam let's me run pump gas.....so that might be an option too, the later your intake valve closes the lower your dynamic compression and lower cranking psi.

MBC Racing

iTrader: (3)

this car is a complete budget car. Only reason it is getting heads is that they are laying around and I couldn't use them on my Z28 with the Lq9. So, I don't want to spend any more money than absolutly necessary. It runs strong now 360 rwhp with stock cam duration with .525 lift and stock 109k mile motor and heads. I just am looking to get some more hp since some of the other guys in my class are stepping it up this year. I know i can gain another 60+ rwhp over what i have now with the parts I have laying around.

What exactly is the procedure for checking PTV clearance?
thanks

91sonomast

Why wouldn't he use a thicker head gasket to help raise the compression a little? Don't understand why you would run a really thin one if you're already concerned with compression and PTV clearance, seem a thicker one would be more desirable. Explanation would be cool . Thanks, sorry to interrupt.

mark21742

No problem sonomast, yes if you run a thicker gasket you will drop compression, but very little volume can be gained by running the thicker gasket....it mainly has to do with "burn zones" if you keep your quench (area between the top of the piston and the flat part of the head) around .030" there is less of a chance of having detonation in this area...I'm not sure why .030" is the magic number other than maybe a safe gap to keep a heat swelled piston top from slaming the head face.... I have heard of people going closer, but less than that is really pushing it. Same with the piston to valve clearance, we are only talking .010"+- on most head gaskets, so this won't really get much more space between them.

MBC racing, its best to use a set of good used head gaskets for this and a set of reusable head bolts.
Get about a quarter size ball of modeling clay and lightly press it down on the top of the piston just under where the valves will be.
Place headgasket on and torque heads down, drop in pushrods, and bolt down your rockers.
Turn engine over slowly by hand a few times and pull the heads back off.
Take a precise measurement of how thick the clay is where the valve pushed into it and that is your ptv clearance.

Just remember you now have clay in the engine so if you are turning the engine over by hand and it gets tight stop turning it so you don't bend anything

mark21742

Also if you know all of your numbers to punch in I like to use wallace racing calculators. That site has calculators for just about everything

MBC Racing

iTrader: (3)

To measure current piston to valve clearance, I understand what you are talking about. However, how would I determine how big a cam would work and still HAVE piston to valve clearance? I can install the two cams I have and see how much I have, but if they don't clear, then how do I determine what i could use so I can buy one that works? What is an acceptable amount of PTV clearance?
thank you