Hello all! I am in the middle of replacing the cylinder heads on my LS1 383 and I am after some advice on how far I should push my Static Compression and Quench specific to my build. I have searched and read lots but I am after some advice specific to my build as it is very unique in the camshaft department to say the least lol. The engine runs full time Pump e85 in Australia which most of my testing results have been between e85-e90. The unleaded they mix in over here is also "Premium Unleaded" which gives the fuel a theoretical 107 RON rating. The engine is an all forged alloy LS1 383 with CP Bullet flat tops. My camshaft is rather massive with a really late IVC point and lots of overlap so I would assume I would be able to run a fair bit of Static Compression as my Dynamic Comp is fairly low. But I have also read that Dynamic Compression is useless in a running engine which has confused me even more hence the thread.

Thanks in advance Cam specs below

Duration @ .050 248/258 112lsa
Valve Timing @ .050 Intake Valve Closes 54 degrees ABDC
Valve Timing @ .006 Intake Valve Closes 92 degrees ABDC
29 Degrees of Overlap

My pistons poke out 0.002 so I was thinking of running a 0.045 Cometic head gasket to get my Quench at 0.043

 

My $0.02:

I would go to .041 head gasket to get quench a bit tighter. Given the fuel you are running and those valve events, I suggest 13:1 static compression.

 

Hi TB92, I too agree with Jake.
There IS a need to "heat" the "E" fuels buy Compression Pressure/Squish, VERY good for quality combustion.
Thus I would fit a Felpro .041" HG for your case.

I would add a "tech" request about your piston design.

DID you fit an "offset" pin piston AND if so to which direction ?

Lance

 

Hi Lance, no offset pin. So a quench of 0.039 still plenty safe for an alloy rod street/strip engine? If so I'm all for it. Would be awesome if I could get to 13:1 with flat tops but I think I may have some PTV issues with such a small chamber. I do have decent valve reliefs but its also a lot of camshaft. Is there a way to estimate PTV or is mocking the engine up and measuring the only way to go? I would need a 61cc chamber to get to 12:1 comp with a .041 head gasket

Thanks guys

 

when you say alloy do you mean aluminum rods? i'd call the rod mfg and ask what the recommend. last I looked forged aluminum rods needed like .050"+ quench

 

Hey Lance, which felpro gaskets are .041 thick?

 

Hi All, I like the Fel Pro # 1041 with Welded O-Ring.

When the camshaft IS at Split Overlap, the P/V will be the largest distance.

State your Valve Drop, I could then use EAP for the P/V measurement.

Lance

 

Hi Lance, Took my old heads to the machine shop today and had them measured up. They said I had plenty of piston to valve and with the new heads I am looking at I will have ample clearance as well. But I will obviously check ptv once I get the heads on. With the new setup I will be sitting at 12:1 static comp. Cant really squeeze much more in with flat tops as clearance will start to get questionable. Will be a nice little bump up from my current setup which was at 11.5:1 static. If the e85 holds up to 12:1 maybe some dome tops in the future.

I am going to run a set of Dart Pro 1 heads that will be ported and setup by a top cylinder head builder here in Aus. Should help my 383 breath nicely considering the 241's I was running only had a mild bowl job and 40 thou milled.

 

Don't discount those "mild bowl jobs". That's where most porting gains are achieved!

 

I will agree! I made very good power with these heads a lot of people were surprised (480rwhp on a Dyno Dynamics chassis dyno which typically read low) . They have done me well but its time for an aftermarket casting to really take advantage of my cam and cubes.

 

So what is the general "Safe" rule for quench with an aluminum rod and a 2618 forged piston? I'm happy to tighten it up but I really don't want to have to pull this engine down again because I was getting greedy. Most are saying keep between .035-.045 and others are saying keep it at .050? Has anyone here touched a head with say .038?

Cheers

 

 

My bad I assumed I had aluminum rods for some reason. I have 4340 forged Lunati rods. With this in mind I'm thinking of either running a 0.045 gasket which will give me 0.043 quench or a 0.040 gasket with a quench of 0.038

 

Measure your valve clearance without a head gasket. That way, the gasket thickness will be in addition to whatever numbers you get.

As for the quench, I like to keep it in the .035-.040" range. It is optimal for fighting pre-detonation. So, I would go with the .040 gasket.

 

True! Never thought of measuring without a gasket. Seems like a good way to go and wont mess up a new gasket.

 

 

Even better point lol. I'll probably just use my old .051 gasket and subtract from there

 

As long as both surfaces are clean, The gasket should not be compromised until its heat cycled. I have used OEM and Cometic MLS head gaskets to take various measurements.

Never once was one been compromised or ruined.

 

On a side note I am undecided which cylinder head to go with. I'm tossing up between the Dart Pro 1's I mentioned earlier and a set of AFR 230. Does anyone here know what the valve springs that come on the AFR heads a like? I have a fairly aggressive lobe and Yella Terra Ultralite Pro roller rockers. Defiantly don't want to float again.

 

Took the plunge and settled on a set of AFR 1610 230cc heads. Should be a perfect match for my 383 will defiantly help it breathe better than the 241's I was running. Going to mill them to a 60cc chamber and run a .040 head gasket which will net me 12:1 static. I'm going to take the heads to the guys that machined my block for the milling and make sure they would be happy with me running .038 quench. If not I could run a .045 gasket and a 59cc chamber that would get me 12:1 also with a .043 quench.