Linear Velocity

iTrader: (1)

Hi guys, I got my Stage I heads back from West Coast Cylinder heads and am in the process of getting some head gaskets. My heads are .030 and I calculated the CR to be 10.77:1. I wanted to be right at 11:1 and with a Cometic .043 Gasket I'd be at 11.07:1 CR. My question is first off are there any issues with running a thinner head gasket with milled heads (p.v. clearance, etc.) and if not is it worth the extra $150 for .3 of CR. Thanks!

Linear Velocity

iTrader: (1)

bueller.......

felton316

Well, running a thinner head gasket on milled heads will reduce your piston to valve clearance.

Spinmonster

what cam/what lift/what lsa/stock pistons? I have .592 lift with a .027 cometics and shaved heads. I have a forged motor and have gone over 7k on revs with no P/head issues due to the tight quench. P/V for me is a different story since I have -2cc reliefs. The cometics are better for many reasons beyond CR. In general it is best to keep at least .025 quench and with the pistons comming out of the hole by .007 or so you could easily run .033's which is my recommendation. Some guys say that you need .03 or more quench but I disagree and I don't care what GOD said differently since I use half of that with crazy revs and it never touches. If your cam is 224/224/114 or bigger you can run 11.4:1 on 93 as I had done for over a year with a cam that size. .033's will give you 5rwhp more than your proposed .043's and much more TQ down low. If your cam is bigger then you should get the thinnest gasket they make if you clear P/V wise.

my vote: .033

strokedls1

iTrader: (1)

.043 will work fine or even .041 if you are talking about running them with the ls6 cam. Is it worth the added cost... probably not. Maybe a 5 rwhp difference. I have .041 that have worked out great from cometic with milled 5.3's, but I have a -19cc dish also. Should be good up to .570 lift. Just make sure that you clay a piston before final assembly so you know for sure if you go with a bigger cam.

Spinmonster

How can you make a statement like that not knowing what cam is in there?

If he is running a 230/230 .570 on a 110 or 112 then he will hit all 8 pistons. As far as is a MLS gasket worth it....yes even if you are running the stock thickness. Power increases from CR are far more than peak power.....5rwhp at the top doesnt even begin to tell what happeens to the area under the curve. Low end power is where the real difference is. The MLS cometics are also reusable (as per cometic and by personal experience) and I have done many head removals on the same set with no issues and it is eventually worth the money just in not having to scrape off the graphite crap from the stockers or not having to pay out for each head removal you make.

1-wont blow under boost or nitrous so easy
2-reusable
3-clean-up is non-issue
4-CR changes from gasket thickness changes are reversable unlike head milling
5-reducing quench area is more power while being less octane sensitive than milling heads where the quench area stays the same
6-most people run far too little CR especially for a motor that protects from detonation:
I have a laughathon watching guys put in huge cams like 231/237, Trex, all of these g5 cams and run the stock CR or near it. They wonder why it doesn't put down any power or at least near what the 'test' car did. Lou uses 11.45 for the G5X3 cam on a 114. Try running 12.2:1 + fot the Trex and gain 35rwhp on peak with gobs of TQ down low. Yes, all this on 93 due to overlap reducing the dynamic CR.

Linear Velocity

iTrader: (1)

Thanks guys for the info. Spin yes I am running an 02 LS6 cam specs are 204/217 .550/.500 117.5 LSA, also on a complete stock bottom end (pistons, rods, etc.) Head specs are 2.02/1.57 milled .030. I'm thinking of running the thinner cometics now for all their benefits, I'll call Richard at West Coast see what he thinks too.

strokedls1

iTrader: (1)

I guess because he is local and I know what cam he is running. I knew that he was not going 230 duration. Milling heads does reduce quench. Same idea as putting thinner gaskets on.

Spinmonster

The quench is the distance between the head and the piston where the flat part of the head is. If you do not use thinner gaskets the quench remains the same....if you mill the heads, the distance between the flat part of the head (which is now bigger in area if milled) is the same distance from the piston with the same gasket....quench is not changed. EXAMPLE: .054 gasket and unmilled head: distance to piston from the head is .054". Mill the heads .030 and the distance to the piston is still .054". Also the amount of reduction of the combustion chamber is the area not contained in the quench where in the thinner gasket is the full size of the bore X the reduction in thickness so a 3.905 bore in my case times the .027 reduction in gasket thickness is the same as milling the heads= .66(3.905)x.03618. So in my case I reduced the quench by 50% and increased the CR as if I had milled the heads an additional .03618".

Get other opinions on this if you don't believe you are wrong.

Mike TexaSS

iTrader: (2)

I had a problem with my 382 LS1 Stroker the block was decked too much and my heads are milled .30.So the piston is comming out of the hole. We lowered the compression with a cometic thicker head gasket. The car can still only run 20-21 deg of timing. The same as with the stock head gasket.

My question is since i raised the quench height is that why im still gettin detonation?
My car went from 460 RWHP 440 RWTQ @ 21 DEg of timing after adding the thicker head gasket the car made only 440RWHP and 412 RWTQ. At the same timing numbers.

Im wondering if im better off removing the cometics and going back to stock graphite and just lowering the timing.

Any opinions on this?

Spinmonster

Milling height from the engine block does reduce quench in that the distance from the piston to the head will decrease. You didnt say how much you shaved off. Assuming you used the exact same final thickness you should have no problem if the cause of the detonation was to high of a CR. There are other causes for detonation. If you are getting any misfire detection that could be caused by a huge cam the KR could be overly agressive.

If the quench area is too big: meaning you increased the quench area by going to a greater than .054" thickness in the P/H distance then you could be getting detonation from a second ignition front caused by too big a quench. For example: If you shaved the deck by .009 and the piston is .007 out of the hole then you have a P/H distance of .016. With the stock gaskets or any gasket with stock thickness that would be a quench of .038.....awesome. Lets say now to lower the CR you use cometics (or any brand with .071") you now have a quench of .055...too much and that can cause detonation, not from CR but from a second ignition source. Some people get away with it but some don't.

I am notorious for running high CR and never saw that severe a KR. I think you should check into:
1-knock sensor swap
2-A thinner gasket nearer to stock or thinner.
3-put in higher octane fuel just to test if your detonation is real or just being reported by a faulty sensor.

List the specs of your entire set-up like Cam, CR, heads, and tuning issues you had. I'll bet you can run the higher CR due to cam overlap and the detonation isnt real. The loss in power is from the loss in CR and the loss in TQ tells the whole story. Near 12:1 with a 230+ cam on a 112 should have no detonation problems.

Mike TexaSS

iTrader: (2)

The kit is a Lunati 382 stroker kit. That comes out to 10.6.1 with stock heads. I added heads milled 30. So it should be up around 11.8.1 add the block being decked we came up with a 12.2.1 comp ratio.

The cam is a MTI X1 on a 112 LSA. It does open the intake valve very late and causes high pressures. I assume that this doent help.

Basicly my car made 460 RWHP with stock gaskets and 21 deg of timing and slight knock.

Now it makes 440 RWHP at 21 deg of timing it has a slight knock.

Sounds like i might be better off going back to stock gaskets and lowering the timing to 20 deg and see what kind of power it makes.

Spinmonster

You have a bad knock sensor. I have a friend with that cam and 12.1 CR 93 octane and 28 degrees timing and he tuned with 92 for a nitrous set-up. Is your A/F ratio too high? Who tuned it?

Mike TexaSS

iTrader: (2)

MTI tuned it. The knock is real. You can hear it. Just a slight ping at WOT. And yes it does go away with race gas.

GrannySShifting

iTrader: (10)

bringing this up from the dead,but if you ran a mild standard split, I think youd be ok

GrannySShifting

iTrader: (10)

try a cam swap yet?