Generation IV Internal Engine - Quench and Gasket size
11-13-2008, 10:23 PM
So we are trying to obtain an ideal quench distance, but our question is what thickness gasket should we use. With our calculations it seems like we would have to use a really thin gasket such as .020, but is that too thin for such a build? We are also planning on supercharging this build.
68CC Combustion chamber
.030" Piston to Deck (in hole)
-25CC dished pistons
44 ADV intake close angle
228 ADV intake duration
240 ADV exhaust duration
114 lobe separation
110 intake lobe centerline
Also, would like to keep compression around 9.5:1
.020" is thin, but would put you at about 9.43:1 and keep quench at about .050". If the shortblock isn't built yet, it really just needs the deck to be cut about .030-.040" and use a more conventional gasket thickness. Depending on how much boost you push through this thing, I would worry about gasket integrity. I have never seen .020" done, so I can't say whether or not it would hold up.
11-14-2008, 04:07 PM
^ +1 on decking the block if it isn't already assembled. Was the block decked originally? The LSx blocks are slightly taller than normal blocks.
11-14-2008, 06:16 PM
The block was not decked but only cleaned up by .003". Because the short block is assembled I may go with a .040" gasket and have a .070" quench and and keep my SCR/DCR lower. I'm thinking the compression is more a important factor than the quench in a forced induction application, I hope..... Thanks
11-14-2008, 06:44 PM
Don't lose any sleep over that thin gasket, Just use a MLS gasket like Cometic. keep the quench as tight as you can without the internals crashing together, It will help keep the dreaded detonation away
11-15-2008, 12:40 AM
Doesn't matter if you have forced induction or not, having good piston quench is never a bad thing.
First of all we need to find out if quench is even a concern for you.
What kind of pistons do you have? If the dish in your pistons looks like factory dish pistons (like a round bowl) forget worrying about quench because the pistons don't have a quench area to worry about. Good aftermarket dished pistons are made that only the valve relief area has the dish, then a flat area for the quench. Usually they have a bathtub shaped dish.
So if you have decent pistons like I described, usually 0.040" (including head gasket) is optimum. I've build motors with quench as tight as 0.030" (including head gasket), but that's getting risky. Anything above 0.050" quench and you've lost all benefit of having good a good quench.
So if you can get a 0.020" or less gasket or 0.00 deck the block you could run a 0.040" head gasket, either way you'd be in good shape.
11-16-2008, 02:24 AM
Thanks gents. I do have some aftermarket Mahle pistons with a relief and a flat surface ( bath tub as you described above). The .020" concerns me, I think Cometic would custom build me a MLS but the concern is still there.
11-16-2008, 03:50 AM
How much boost are we talking?
11-16-2008, 10:55 PM
I think Felpro makes a .027. Not sure on the bore size though. I know it's 4.0+ though
11-17-2008, 09:41 PM
Will be pushing 8 #'s of boost
11-17-2008, 09:56 PM
Will be pushing 8 #'s of boost
That's not too much to worry about. Just invest in ARP head studs and you'll be fine with a 0.020" head gasket.
11-20-2008, 05:19 PM