Hey guys, building a 572 (4.5 x 4.5), however, pistons are in hole .006.
I happen to have two sets of Cometic gaskets, one set is .040, which leaves me not enough quench for my liking, and the other set I have is .030 thick.
Do you guys think I would be safe with the .030 set???
Just wondering with the big bore how much of an issue piston rock will be.
Will be street car (4-speed), rev limiter probably set at 6200ish.
Scat crank and rods, Ross pistons.

Thanks!!!

I have .035 quench and for peace of mind I sure would have liked an extra .010 !!!

piston rock depends alot on bore clearance. I worry more about actual gasket thickness being what it is supposed to be. I wouldn't think a 572 would be a high RPM screamer & I'd be OK with a confirmed/measured three times! .035. when done I would see if I could measure the space between the head and the deck anywhere on the outside of the block & more important, on assy with 1 head gasket on, with the block upside down, loosen a rod cap then turn crank till the piston is at TDC & see how far you can push the rod/piston further in till it contacts the head (that is the bottom line that it will see when operating). if its too close you are only out 1 gasket assuming all measurements on both decks everywhere are equal.

It should work fine with the 0.030 gaskets at that RPM. If you were going to spin it a lot higher then maybe it would be an issue. Next time you pull the heads you might want to order the 0.036 gaskets.

Andy, is the difference in quench effectiveness between .046 and .036 significant enough to make a change to attain the tighter number?

What compression ratio is this bad boy at?

There are many factors that need consideration before running that tight of clearance at that bore and stroke.Then throw in the 4-speed factor.I think you already know the answer since it is a street build and the gain of the quench benefit is certainly not worth the risk.Theoretically it is recommended that clearance should be set at .055 with all the factors,we can list many,taken into consideration.We have run race engines as tight as .038 but don't recommend it.

Compression will be at about 13.6 to 1 with .040 quench.
Will be running on E85. Cam is solid roller street grind 267/279 .640 lift.
Heads are EZ'z with MCH cnc porting.
Also will be running HP EFI system. I think this should make a nice street engine, I would think 650hp shouldn't be an issue.


I suppose I could get the .036 gaskets, maybe that would be the way to go ($450 laying around in head gaskets, ouch).
I'll still ponder on it, thanks for all the replies so far!

I'm in the middle of assembling a pump gas 340 stroker motor with SRP pistons that have right at .0035 piston to cylinder wall clearances, those pistons rock from .0050 to .0080 on the cam side at the edge of the cylinders with a small screwdriver holding the piston tops towards the cam My old pump gas 400 srtoker motor had .035 with a .042 thick head gasket on both sides of the pistons, it was touching both head on both sides a tiny bit It didn't touch with .047 thick head gaskets after that
To many people on here preach things that don't work for me when it comes to clearances in motors we beat on .0010 to much clearance are way safer then .00010 to little
Be safe

[quote=Kelob_pie]Compression will be at about 13.6 to 1 with .040 quench.
Will be running on E85. Cam is solid roller street grind 267/279 .640 lift.
Heads are EZ'z with MCH cnc porting.
Also will be running HP EFI system. I think this should make a nice street engine, I would think 650hp shouldn't be an issue.


My I would run the .040 gaskets you have and be happy.

572",e85(lots of fuel volume), over 13.5 comp, street motor, 4speed. I agree with Cab.

At that C/R and the added information we would recommend you use at least use a .040/.041 head gasket.E85 is not always E85 it could be less and sometimes garbage depending on the source.Save yourself a lot of grief.

You might be able to get by with the Quench that tight, but I would make sure every cylinder has the same quench. Production tolerances may give you less on some cylinders. I have run them as tight as .038 and had no trouble. Seen one set at .030, and you could read the part number of the piston on the cylinder head when they took it apart, ran for a season, didn't see any damage but it was set a .040 when it went back together.

Check how much piston rock you have, stick a clean wooden dowl on the bottom of an installed piston and push up and measure that way on both sides. Bore size, piston to bore clearance, piston skirt height, bearing clearance can all add up to a supprise, basing it off a calculated clearance is silly or even a static center of the bore measurement. Useing this method I run pretty much any motor at .020 clearance and never had an issue. Measureing this way will give you more of an actual running minimum clearance than taking rod center to center-piston heaght-stroke-deck height or even more acurate than measureing at the center of an idle/static unloaded piston. My only disclaimer is I have only built one aluminum rod engine and it had no quench to speak of so if your useing an AL rod you need to consider that.

On my 440/493 street eng I am using the basic EZ heads and I use a dished piston to have a 10.6 comp ratio. I run about .046 quench and it runs fine on 91 to 93 pump with 36 total timing all in about 1800 rpm. I use the felpro .039 gaskets and my piston flats are about .006 to .007 down in the cyl. You are running more comp then me but I have had no eng ping at all as I run a full exh and would hear it if it had any ping or spark knock. My cam is 264 & 270 @ .050 with .585 & .592 lift. And if its a street eng you plan to put alot of miles on as I do I would feel better at the .045 quench. Ron

I find it interesting you're building a street engine at 13.6:1 CR? Guess I need to get out more...

Hopefully the motor will never have problems, but a little bore ware, rod bearing going south, and you might hurt a piston or worse. Better to have a safety margin than what, five extra hp?.

To that add crank flex. AndyF has a lot of dyno time under his belt and he's probably right, but I'm thinking a piston that big and a crank that flexible (because of the lack of overlap due to the long stroke and small pin diameter) would push me to add the extra clearance. You'll never notice the tiny drop in performance.

R.

Well, I guess you guys convinced me, I'll go for the .036 gaskets.
I believe I'll still retain the quench benefits at .042.

its an E85 motor.

You already have a set of $150 .040 Cometics and you are willing to spend $150 more just for .004?

Man, I'd run the .040's, but yea, I'm cheap.