Toyspeed.org.nz Message Board

by **4000GT** » Mon Jul 10, 2006 7:00 pm

This seems to be a pretty common mod, but on a stock engine I dont see the point, but its often recommended. So I thought maybe it raises compression?

by **Jebus** » Mon Jul 10, 2006 7:10 pm

Yeh its thinner, 0.5mm and 0.8mm available. Not recommended on 20V's on pump gas.

by **4000GT** » Mon Jul 10, 2006 9:32 pm

Jebus wrote:Yeh its thinner, 0.5mm and 0.8mm available. Not recommended on 20V's on pump gas.

Whats the stock gauge?

I can tune it on the dyno, and use 98 octane, so I am not too worred about tuning for det. Anyone have a calculation to determine the .5 and .8 gasket compression ratios?

by **Mr Revhead** » Mon Jul 10, 2006 9:39 pm

stock gasket is 1.2 mm
i havnt done the maths to work it out
cant find the exact cc of the chamber

by **4000GT** » Mon Jul 10, 2006 10:11 pm

Mr Revhead wrote:stock gasket is 1.2 mm
i havnt done the maths to work it out
cant find the exact cc of the chamber

Ok, dropping .7 isnt going to raise compression that much. It would be interesting to see what gains come from it. May be worth a try for giggles. Can you send me a price and availability Warwick on the .5. Cheers mate.

by **Mr Revhead** » Mon Jul 10, 2006 10:16 pm

the 20v ones only come in 0.8mm.
how ever u can remove a layer (they are 3 layer)

the other advantage is they are steel

by **Jebus** » Mon Jul 10, 2006 10:59 pm

This is assuming all stock gaskets are 1.2mm (Revhead??)

And is not 100% accurate, so dont bet your mothers life on it.

by **Quint** » Mon Jul 10, 2006 11:01 pm

Just remember to use ARP bolts and torque them down nice and tight.

by **DXROLA** » Mon Jul 10, 2006 11:11 pm

do u have to run 96 octane with the new headgaskets?

Details of car here · by **AE85coupe** » Mon Jul 10, 2006 11:11 pm

hmm so when i took 45 thou off the head of my smallport how much did i raise the compression?

whats 45 thou in mm?

by **Mr Revhead** » Mon Jul 10, 2006 11:13 pm

you should run at least 95 on the bigports
and 98 on the others

by **DXROLA** » Mon Jul 10, 2006 11:19 pm

sounds good , what is a disadvantage of doing it

by **CAMB01** » Mon Jul 10, 2006 11:32 pm

45 thou or 45 thousandths of an inch is just over 1mm.

by **Jebus** » Mon Jul 10, 2006 11:34 pm

$&#$%

by **AceSniper** » Mon Jul 10, 2006 11:51 pm

.4mm off and it puts blktop to that? I thought 0.3556mm skim would give 11.5:1

Details of car here · by **AE85coupe** » Tue Jul 11, 2006 12:03 am

CAMB01 wrote:45 thou or 45 thousandths of an inch is just over 1mm.

dam.. guess i've got enough compression then heh

by **4000GT** » Tue Jul 11, 2006 12:23 am

Jebus wrote:

This is assuming all stock gaskets are 1.2mm (Revhead??)

And is not 100% accurate, so dont bet your mothers life on it.

Jesus titty christ, how did you compute those figures? I cant believe .4mm raises the ratio by over 1. Thats insane.

by **Jebus** » Tue Jul 11, 2006 12:32 am

Hmmm...Ill go over it again, might have computed wrong by the looks of it, will update tomorrow.

by **sergei** » Tue Jul 11, 2006 2:18 am

I did a few calculations for cynos, so starting with 9.8:1 cr, and 1.2mm gasket, with 2.4mm gasket I got 8.8:1 cr. All those values highly depend on combustion chamber size, but there is no actuall need to know the size of it, it can be calculated from bore, stroke, head gasket thickness and compression ratio.
Here is the break down:
Find max bore volume of 1 cylinder (excluding gasket volume or cmbst. chamber):

PI * ( ( BORE / 2 ) ^ 2 ) * STROKE

Find volume of stock gasket:

PI * ( ( BORE / 2 ) ^ 2 ) * S.G. THICKNESS

Define compression ratio:

C.R. = TOTAL MAX VOLUME / TOTAL MIN VOLUME

Total Maximum Volume:

Maximum Bore Volume + Stock Gasket Volume + Combustion Chamber Volume

Total Minimum Volume:

Stock Gasket Volume + Combustion Chamer

Hence:

C.R. = (Maximum Bore Volume + Stock Gasket Volume + Combustion Chamber Volume ) / Stock Gasket Volume + Combustion Chamer

Replace Combustion Chamber Volume with X and introduce parameters and simplify:

C.R. = ( ( PI * ( ( BORE / 2 ) ^ 2 ) * ( STROKE + S.G. THICKNESS ) + X ) / ( ( PI * ( ( BORE / 2 ) ^ 2 ) * S.G. THICKNESS + X )

Calculating X (jumping few steps, oh my math teachers hated that):

X = ( ( PI * ( ( BORE / 2 ) ^ 2 ) * ( STROKE + S.G. THICKNESS ) ) + ( ( PI * ( ( BORE / 2 ) ^ 2 ) * S.G. THICKNESS ) ) * (1 - C.R. ) ) / ( C.R. - 1)

Skipping a few more steps:

X = ( ( PI * ( ( BORE / 2 ) ^ 2 ) ) * ( STROKE + ( S.G. THICKNESS * ( 1 - C.R.) ) ) ) / ( C.R. - 1 )

Real neat formula...

by **Adamal** » Tue Jul 11, 2006 8:16 am

Yea, learnt that one in kindy!....

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