Quench.... Do i dare go with .030's?
 

Alright, here is the setup...

Shortblock = HPE Forged Iron block 408. -8 CC dished wiseco pistons
Heads = Patriot Stage 3+ heads milled from 65 CC's down to 63 CC's
Cam = Custom ground by Thunder.. 250/255 615/619 on a 110.9 LSA


Current compression W/GM mls 6.0L Head gaskets comes out to be : 11.381:1

the squish on those gaskets is .051 though... leaving a very undesireable quench. so lets put some Cometic MLS 4.030 bore .030 thick gaskets in the equation...

Compression with .030 Cometics come out to be : 11.8205:1



Would it be worthwhile to swap them out to the cometics when i pull the heads to install the new valves?? am i going to see much better dyno results or is it pretty much negligiable?

also this is a daily driven rain/shine non weekend drag stip car. it MUST be able to run on 91 octane with no detonation problems. I can run race gas for when i wanna spray but other than that its a pump gas car.


any input would be VERY appreciated!! especially from some of your veterens that really know your stuff!! :drive: :chug: :chug: :chug:

i dunno know about that on 91 octane

currently with my .051's im running 31 degrees of timing and cant hit detonation... not gaining any power but the car wont detonate... we have tried and tried and it just holds strong lol :jest:

Try a .035 gasket,thats enough quench, no need to go much lower really. Once it goes low enough you risk the piston hitting the head deck at TDC from it rocking if the piston to cyl wall clearance isnt tight enough..

does anyone make .035's??? all i see is .030's and .040's... thats why i asked about the .030's.... if i could find some .035's id be all over them :chug:

btw, need to be MLS and or cometics.

Cometic makes .035's, call cometic and ask just in case.

No one has asked the right question yet... What is your current deck height? That will be your first consideration when choosing head gasket thickness. Common rules of thumb put .036" at the minimum piston to head clearance figure for a steel rod motor. I've seen LSx based motors with as much as .015" positive deck height... this would put you at .036" quench which is the minimum... :)

Shane

he said in another thread deck height is zero.

deck height is zero, i forgot to mention that in the first post..

Sorry guys I didn't see the other thread... Well, the numbers I gave still hold. You can go with the .040" gasket as long as long as you verify deck height before you put the heads back on. As far as the compression ratio question, With the proper tune, you can get by with that much compression with a good combustion chamber and excellent quench. Back in '02 I had a 408 solid roller with .030" quench... the pistons were just barely kissing the heads on cold startup. The motor made crazy power for the day. 12.0:1 compression on pump gas LS6 intake and stock TB and MAF I made 523 RWHP through a 9"...:devil: I still think the tight quench had at least a little to do with it! :)


Shane

I know on my set up The pistons are .010 out of the hole and I run a .040 gasket which would yeld .030 quench. Usually when you run the quench on the tighter side it has less possibly of detontation, because it forces all of the air fuel molecules toward the spark plug.

well.. just talked to chuck... hoping that erik will answe my PM here quick... come to find out what i was originally told is not true.. they are not zero decked... pistons are out of the hole from .005- .010... gotta have erik check my build sheet and see exactly what they are at.

if thats the case then some .040 cometics will work SWEET.. anybody know of anybody who stocks .040 cometics??? i need this car back up and running ASAP.

Thats a big gap for deck, better get the right number for deck. Thunder stocks .040 cometics, they will be out same day that you order them.

well with the pistons .010 out of the hole and .040 cometic gaskets that puts me right at

11.8379 : 1 compression worst case scenario... that gives me a .030 quench as well which i think will work freaking sweet!

the benefits of running it on the very edge of clearence I dont think are worth it for most guys. Its the 10% deal, getting within 90% of the tightest quench w/o hitting the heads is worth a good bit, but that last 10% is hard to come by and not worth as much. Id run a .035, or a .040 even. 5 thou isnt going to pick you up a magic 15 lbs of torque, and if your 5 wrong, you have problems, about 8 of them :)

Looks like a stout setup you have coming there either choice, 550 easy on a Djet I would think it could make

hehe depends on if i ever upgrade my intake :jest: i put down 480 RWHP on the local dynojet but now it seems as though i was down or at least handicapped on that cylinder... (see other threads :jest: )

I just dealt with this today with my 408 L92 build. I decided to go with a .040 quench to be on the safe side even though it will be race motor more than a street motor :drive:

I had a 347 w/.030 quench and it spun a few rod bearings, yeah that was sweet :barf:

Had nothing to do with your quench.

I would assume your pistons are .008 out of the hole like mine are from HPE. I run a Cometic .040 gasket with a .032 quench. To me and many other people, that's perfect.

I assume your actual CR will be lower than the calculated number due to your altitude (~4300 ASL)? or is your number the actual CR?