L24 head gasket choice

jonbills

jonbills

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Hi all,
I've had the head of my car (replacing inlet valves) and I'm about to put it back on.
I've got a stock head gasket from Mr.F ready to go, but I'm wondering if there's an easy ( & affordable) option to bump the compression up a bit.

Its L24 with 83.5 bore, e88 head. measured at 43cc combustion chambers..
By my calculations, stock head gasket is 1mm thick with 88 mm bores giving CR around 9.2.

I saw MSA offer a Nismo 0.6mm gasket, and all things being equal should get me to around 9.6 CR.

So - what are my options, and what would you do?

(yes, I did do a search, and found lots of great info, but didn't get me to a conclusion!)
 
Hi Jon,

Make sure this doesn't affect your timing chain and make it too slake, you're probably fine as it's only a 0.4mm difference but maybe best to check to be sure in case your heads been slightly skimmed also.
 
Using a gasket to alter compression is an **** about way of doing it and should be used as a last resort as you risk reducing piston to head and piston to valve clearance to unnacceptable values (measure)

Plus, the change from 9.2 - 9.6 will be unnoticable

Whilst the head is off......skim it
 
One other thing, what bore is the Nismo gasket, if it's more than 88 then the compression ratio will be lower then 9.6.
 
SKiddell said:
Using a gasket to alter compression is an **** about way of doing it and should be used as a last resort as you risk reducing piston to head and piston to valve clearance to unnacceptable values (measure)

Plus, the change from 9.2 - 9.6 will be unnoticable

Whilst the head is off......skim it
Click to expand...

Does ''****' stand for 'good'?

Surely both skimming the head 0.6mm and using a 0.6mm thinner gasket give exactly the same piston to valve clearance, all other things being equal?

And although the thinner gasket does bring the piston nearer the head, skimming the head means the head has less dish by the same amount, thus the chance of the piston to head contact is the same, no? (I'm less sure of this than the valve bit!)

I could however buy an argument that a thinner gasket is less tolerant of head & block straightness.

George, I believe the Nismo gasket has diameter around 89, but still this will give CR of 9.6:1. I've attached my spreadsheet that I'm using. Do you think I'm missing something?

I think now the stock gasket is 1.2mm - so that takes my current CR down to 9.0

View attachment compression-ratio.xls
 
Slightly O/T but why don't you machine the head/deck the block for 10.5:1 ratio, I know the yanks struggle with low grade fuel but we in the developed world should be fine?
 
I haven't checked the maths but I think the Nismo gasket is a 91mm bore so that will knock the figures out already.
 
Mr.G said:
I haven't checked the maths but I think the Nismo gasket is a 91mm bore so that will knock the figures out already.
Click to expand...

Even with 91, still CR is 9.6. A few mm here or there on the radius doesn't make much difference, even though they're squared. (compared to halving the height).
 
franky said:
Slightly O/T but why don't you machine the head/deck the block for 10.5:1 ratio, I know the yanks struggle with low grade fuel but we in the developed world should be fine?
Click to expand...

Mainly because I want to be finished and driving it :)
but rationalising it, I have half an idea that in a few years I might reuse the head on an L28 block, and skimming the head now might result in too high CR on that.
 
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