Hey guys, Its getting to be about time for a new head gasket, and a while ago I bought a Cometic Head Gasket with a .030" thickness. I now have plans to turbo my car sometime in the near future and am just wondering if I would be able to safely run anywhere between 6-8 PSI with the .03" gasket. Does the thickness really make that much of a difference? Or should I try to sell it and get the .074" thick one instead?
What's your static compression now with the .030 gasket? If it's 9.5:1 or less then you should be fine but if it's higher than that I would get the .074 gasket.
2000 Z24 5spd header & catback for now.
I have a stock bottem end right now so I think the compression ratio is 9.7:1. I guess I will just play it safe and get a .074" gasket
The thinner gasket is ALWAYS better. Don't worry about your static compression, it's a minor detail, but not important in the grand scheme. Just make sure your piston to head clearence is adequate (as long as you're not running custom pistons, you're fine).
fortune cookie say:
better a delay than a disaster.
If I remember right, the .030" gasket puts you in the 9.9:1 range......
The .074" gasket should put you at about 9.3:1
SPD RCR Z -
'02 Z24 420whp
SLO GOAT -
'04 GTO 305whp
W41 BOI -
'78 Buick Opel Isuzu W41 Swap
is that with stock pistons 9.7:1 compression ratio?
yeah I have a 2000 ld9 with the 2.4, im pretty sure the compression is 9.7:1
Hmm, Im not sure if I would run boost with compression that high.. Its just going to be harder to tune I think.. My pistons are 9:1 with the N/A .030 headgasket.
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You will get more detonation with the .074 than the .030, guaranteed.
fortune cookie say:
better a delay than a disaster.
Actually the.074 gasket will drop your compression a full point, my engine builder just did the calculations for me so I'll know where I stand cr wise. The custom Wiesco dished with valve pockets pistons I have would give 8.4:1 with the stock .041 head gasket and stock LD9 head. and with the .074 gasket the cr would be 7.4:1 which combined with the 086 head I'm using should put me at 9.3:1 cr so I can run 18# - 20# of boost on pump gas. And OHVnotec you would be correct about detonation on a wedge head motor such as yours but with a 4 valve semi hemi or pent roof like the LD9/Quad4 head we don't have that problem.
2000 Z24 5spd header & catback for now.
According to the Compression Ratio Calculators I've been using, my Wiseco .040"+ Pistons (9.5:1) + .074" gasket + head shaved .013 (58cc combustion chambers) = 9.3:1
When I plugged my stock numbers in (9.7:1 pistons, 60cc head) + the .074" gasket, I belive it was 9.3:1 also...... (my Wiseco pistons have just over a 2cc dish to them)
I also did it for the .030" gasket, and it was damn near 10:1
Usually I agree with OHV notec, just not on this.
SPD RCR Z -
'02 Z24 420whp
SLO GOAT -
'04 GTO 305whp
W41 BOI -
'78 Buick Opel Isuzu W41 Swap
Dale Young wrote:And OHVnotec you would be correct about detonation on a wedge head motor such as yours but with a 4 valve semi hemi or pent roof like the LD9/Quad4 head we don't have that problem.
Do you have pictures of your pistons? Most modern pentroof designs still implement some type of squish pad, so I'd be suprised if the LD9 didn't. Custom pistons may have neglected the feature of course.
fortune cookie say:
better a delay than a disaster.
SpeedRacerZ wrote:If I remember right, the .030" gasket puts you in the 9.9:1 range......
The .074" gasket should put you at about 9.3:1
which compression ratio pistons you got to make it like that? the 00-02 9.7:1 cr?
OHV notec wrote:You will get more detonation with the .074 than the .030, guaranteed.
would you mind providing your reasoning behind that?
Blew it up, build numbers coming soon
98redcavz24 (LD9Stunner) wrote:OHV notec wrote:You will get more detonation with the .074 than the .030, guaranteed.
would you mind providing your reasoning behind that?
That's how it works on 99% of motors on the road. Post up some pics of piston tops and combustion chambers for a 2.4L and I'll do a lil write-up if it applies. Piston deck height would be necessary to determine 'ideal' gasket thickness.
fortune cookie say:
better a delay than a disaster.
2.4 is a
0" deck height.
Stock headgasket is .040"
'96-98 2.4 pistons have a slight dish to them
'99-02 2.4 pistons are flat
'96-98 2.4 head
'99-02 2.4 head
'96-98 head top
'99-02 head bottom
'086 2.3 head (just cause I found the pic)
as you can see, in the '96-98 combustion chamber there is an extra 'pad'.... which the 99-02 doesnt have. This will effect chamber CC. I know my '02 head, shaved .013", is at 58cc's (stock was supposed to be 60cc)
Edited 1 time(s). Last edited Thursday, May 24, 2007 2:28 AM
SPD RCR Z -
'02 Z24 420whp
SLO GOAT -
'04 GTO 305whp
W41 BOI -
'78 Buick Opel Isuzu W41 Swap
0 deck height? It would be impossible to run a .030" gasket with a stock block...that can't be right if they are actually selling them. Also, no OEM would risk .040" piston to head clearance on a factory lo-po motor. Can anyone verify the deck height?
Anyway, although the piston and chamber designs are far from optimal, there is a good squish pad (or two) on the head, and around the piston. When these approach eachother at TDC they create MASSIVE amounts of cylinder turbulence, which speeds flame propogation, creating a more complete burn and helping ward off detonation. The closer they get, the more turbulence they create, and vice versa. So, ideally you want .001" clearence at your maximum RPM. Due to rod stretch at TDC after the exhaust stroke, and thermal expansion of the reciprocating assembly, you have to allow extra static clearence. This is standardly stated as about .040" (that's for you geforce) for a mild performance motor using mostly stock parts, or lower quality aftermarket and usual tolerences, or for forged pistons which require a larger bore due to their higher expansion rates. An OEM wouldn't do .040" because it would require a well-kept motor (which 85% of buyers don't qualify for, leading to "reliability isues").
Using something more towards the .07-.09 range would decrease efficiency, performance, and increase potential detonation due to the more dormant chamber.
fortune cookie say:
better a delay than a disaster.
From everything I have read, it is 0...... and the 3 2.4's in my garage agree with me......
If I get a chance, I'll find a straight edge and my feeler gauges.
SPD RCR Z -
'02 Z24 420whp
SLO GOAT -
'04 GTO 305whp
W41 BOI -
'78 Buick Opel Isuzu W41 Swap
it's 0 man.... come on now.
-Trailblazer SS - not so custom 6.0L - custom intake - custom tune
- (1) 2.4L on an engine stand (1) blown trans (2) good quad trans (1) eco trans = party
So, has anybody actually used a .030" gasket on the stock (or modified even) LD9 then? That gives .030" clearance, and certain death... How could a company knowingly sell that?
fortune cookie say:
better a delay than a disaster.
yep...... no valves hit pistons either...... even when using larger then stock LD9 lift cams (and duration).
I guess its a DOHC thing, you just wouldnt understand
SPD RCR Z -
'02 Z24 420whp
SLO GOAT -
'04 GTO 305whp
W41 BOI -
'78 Buick Opel Isuzu W41 Swap
I have the .030 gasket and i had ZERO issues with clearance. I even have 1mm oversize valves and larger cams
When i put my built motor back together again ill clay it to make 100% sure
I don't think he's talking about piston to valve clearance so much as piston to head clearance. High RPM rod stretch and piston growth...
"The FACTS are always subject to CHANGE once the TRUTH is applied"
"In the entire history of man the only stupid questions are the ones that don't get asked"
john317(AKA Gary the Old guy) wrote:I don't think he's talking about piston to valve clearance so much as piston to head clearance. High RPM rod stretch and piston growth...
Yeah, all ICE motors are the same in this respect, regardless of valve layout. I know ge_force hit at 5400 rpm w/ .022", so how high are you .030" guys revving your motors? Also, what is OEM piston-bore clearance?
It's amazing the stock LD9 can get away with a 30, that's rare. Definately take advantage of it and run the tight quench, it will help more than the slightly lower compression of the .074 gasket. It also allows you to run less timing, which obvioulsy decreases negative torque, bonus.
fortune cookie say:
better a delay than a disaster.
