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Old 05-15-2002, 06:33 PM   #1
tonytiger
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Question Thinner head gasget, bigger compression ratio?

As we know changing the head gasgets to thinner ones increases the CR a bit. How much it changes depends on the current one.

Well, have anybody changed theirs?

The stock head gasget looks pretty thin already, how thin is it actually when bolted on?

How big is the EJ18 combustion space? I mean the burning space in the heads? Knowing this I could count the produced CR with the thinner gasget.

Any material suggestions?

I doubt changing it will cause self detonation

That's it for the start.

Thank you.



tony
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Old 05-16-2002, 12:57 AM   #2
Jademonkey
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Wouldn't a thicker gasket accomplish this?
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Old 05-16-2002, 01:10 AM   #3
RawCode
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A bigger head gasket would lower compression because it would create more volume in the cylinder.

RawCode
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Old 05-16-2002, 02:57 AM   #4
HndaTch627
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FWIW you are going to get .1 compression out of this and SEVERLY increase your risk of valve train damage should you snap the timing belt.

Jeremy
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Old 05-16-2002, 04:04 AM   #5
Kevin Thomas
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Exclamation I thought

I thought at one time Cobb Tuning was offering thinner headgaskets to up the compression ratio of the EJ25.
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Old 05-16-2002, 04:37 AM   #6
tonytiger
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The thinnernes of the stock gasget was the thing I was woried about, it can't be much more thinner that it is currently. As you HndaTch627, Jeremy said the increase of CR might only 0.1 it's not worth the money - at least here where I live.

By the way, why does the timing belt have a bigger risk to snap? I'm not familliar with the issue...

But since COBB has offered them, forget everything what I've said, that must be a really good mod then Ads tons of HP

Thank you for the responces.



tony
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Old 05-16-2002, 11:13 AM   #7
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The compression ratio is the ratio of the maximum volume in the cylinder over the minimum volume in the cylinder. So, by increasing the stroke of the cylinder head by putting a larger gasket on, you increase the compression ratio.

What this does to the stock engine parts I'm not sure of, but I'm going with what's been said already.
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Old 05-16-2002, 11:38 AM   #8
proecm
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Tony,

I would encourage you to do what you are planning on doing, the CR could probably be increased quite a bit without risk of detonation, considering being in Finland you should be able to get 100 octane out of the street pump, right?

If thinner hed gasket is not enough increase in CR, just plane the head 0.5 mm or so and you should be fine. Keep in mind that you will not see as much improvement in power as you will in mileage.

/David
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Old 05-16-2002, 01:18 PM   #9
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midnx,
I think you have that backwards. Let's exaggerate things to make it a little more obvious. Let's say that our imaginary piston moves back and forth 9 inches in the cylinder. At the peak of the cylinders compression there is a 1" airspace from piston to valve, and when the piston moves back 9" you have a 10" airspace. This would be a 10:1 compression ratio. If you moved the valves 1" away from the piston by putting in a REALLY thick gasket, you add 1" to both airspaces. Now you have 11" to 2", or 5.5:1 compression ratio (much lower compression).

Does this make any sense?
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Old 05-16-2002, 01:40 PM   #10
HndaTch627
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Quote:
Originally posted by tonytiger
The thinnernes of the stock gasget was the thing I was woried about, it can't be much more thinner that it is currently. As you HndaTch627, Jeremy said the increase of CR might only 0.1 it's not worth the money - at least here where I live.

By the way, why does the timing belt have a bigger risk to snap? I'm not familliar with the issue...

But since COBB has offered them, forget everything what I've said, that must be a really good mod then Ads tons of HP

Thank you for the responces.



tony
LMFAO!!!! haha that's great man ....i was just stating that the EJ25 is designed to have the cams free spin and stop at a certain point before it bends valves....by effectively lowering the clearance between the valves and the piston you are increasing your risk of valvetrain damage SHOULD a failure occur.

jeremy
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Old 05-17-2002, 02:53 PM   #11
AJ711
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Thanks for the clarification BugBomb, I was going with my general knowledge from my Thermodynamics course I just got done taking. I see what you're saying too, and understand where my thinking was wrong. Thanks.

AJ
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