Head Gasket Compressed Volume
Turbo Mini Forums

Anyone know a typical volume in cc's for the head gasket when compressed? I am trying to accurately calculate the CR of my engine, I know piston and head volume, will assume pistons flush with block for now until I can measure it.

Std gasket volume? Or volume for the Gp A gasket if anyone knows as that is what I am using?

grp A = 4cc

bk450 = 3.8cc

http://www.afracing.com/cr.xls

Alex

AlexF

Sorry Alex, the BK450 is 2,8cc

Not my figures...

Is the grp A one right?

Alex

AlexF

Nope, the GpA is 3,1cc :)

I've just messed about with these trying to achieve 11,4:1in my Mini, that's why I noticed.

Quoted from the Minispares catalogue.

Edited by Vegard on 7th Apr, 2005.

Arr ok...

I use somelse's figures off the net...

I'll update that spreadsheet at somepoint!

Alex

AlexF

i have one here in front of me - so pull rank and makes me the leader of the gang !-or maybe not!
its used and now measures 0.84 thick and 71 mm bore dia (.88 thick and 73.2 mm bore when new ), pye r squared x hieght gives us the volume :
35.5 x 3.14 x.84 divde by 10 to get cc's =SEE BELOW
-if in doubt check it yourself-
group A should be around 70 mm when compressed and same base thickness so: SEE BELOW

Edited by stuart gurr - vmaxscart on 7th Apr, 2005.

thats thrown all my figures out! I have no idea what my CR is now, 29cc head, 10cc pistons? what do you make it ?

Team www.sheepspeed.com Racing

yeah but wont it relax a fair bit when uncompressed even if its not new?

nope... or you couldn't measure the gasket thickness full stop!

AlexF

yeah you could

just need to measure something static and torque the head down with no gasket, then add a gasket and see the difference is. hence get your compressed gasket in situ size

We do it on our parts to calculate stack ups and the gaskets do relieve themselves a fair bit.

Just wondering if anybody had checked thats all.

good point iain!

Alex

AlexF

Hmmm interesting!!! I always thought that the head gasket volume figures were in the order of magnitude 2.5-5cc's depending on the gasket, those are the kind of figures I have always used.
Calculating for my engine assuming piston crowns flush with deck gives me 8.08:1 using 3.1cc, or 7.24:1 using Stuart's figures.
I think that Iain has got a good point about the gasket material relaxing when un-compressed, thinking about it there must be an area of elastic deformation which the gasket recovers to, and then the plastic deformation which is visible between a new and a used gasket. Surely if all the deformation when torqued down were plastic, there would be little or no sealing effect between the gasket and the block faces?

think your math is wrong Stu!

I use (pi * d^2) / 4 to calculate area - same as pi r^2 mind...
Also, lets keep it in cm to avoid confusion,
Hence 0.84 thick and 71 mm = 0.084cm thick and 7.1cm dia.

So, pi * 7.1^2 = 3.142*50.41 = 158.367

now divide by 4:
158/4 = 39.592 cm^2

Now multiply by thickness:
39.592*0.084 = 3.325cm^3 which = 3.325cc



You wrote:
pye r squared x hieght gives us the volume :
35.5 x 3.14 x.84 divde by 10 to get cc's = 9.363 cc

You wrote formula correctly, but forgot the ^2
eg
pye * r squared x hieght
(3.142* 35.5^2 ) * 0.84

= (3.142 * 1260.25) *0.84
= 3959.192*0.84
=3325.721

To get from mm^3 to cm^3 you have to divide by 1000, hence
3325.721/1000=3.325cm^3 = 3.325cc

Edited by TurboDave16V on 7th Apr, 2005.

and the prize goes to dave , i posted it , drove up to london thinking doh!!!!!!
but i'm now thinking :
35.5 x 3.14 x 3.14 x 0.84, divideby 100 =
2.940 cc std bk 450 ,and turbo is :2.898cc
i was a cse grade 2 at maths so open to suggestions , and sorry to throw the preverbal spanner in the works !

So now 8.12:1 using Stu's mark 2 figures!!!

Ah well whatever, its around the 8.0:1 mark, thats the kind of region I was aiming for anyway.

Well I'll throw another spanner in the works... The gasket isn't completely round is it (or at least not on the middle two) as I recall?

Stu - You're 'squaring' the pi (3.142) - you need to be squaring the radius... Pi R^2

Easiest thing is to forget that Pi R^2 and remember this one:

Pi * D^2
----------
4

And also, work in cm, not mm, as it saves doing the conversion into cc...

I recently did some CR calcs for my engine, and I measured the gasket thickness by cutting a notch out the side, fitting it and measuring the gap beteen the block and head with a feeler-gauge. Haven't got the figures handy, but it's an easy measurement to do.
Hugo

Hugo

*** 1989 Jet Black body stripped for resto ***
*** 1988 Metro engine undergoing turbo conversion ***
*** 1989 BMW 318iS as daily run-a-wreck ***

good simple aproach Hugo

Team www.sheepspeed.com Racing

WOW i have used my head gasket 4 times now think its time for a new one

slap it together works every time

SON, WHATEVER FANCY SHIT YOU'VE GOT UNDER THAT BONNET, SEEN IT A MILLION TIMES

was it new when you had it?

Team www.sheepspeed.com Racing

Standard factory turbo head gasket - average 3.5/3.6 cc
Group A last time we checked was a nominal 4cc

http://www.avonbar.com

So now 7.95:1

Any more offers on head gasket vol!!!!!!!!

hmmmm, anyone care to work mine out for me? i don't have excel on me comp at home so cant use alex's table thing.

head is 29cc, 1293cc block, 11cc pistons, pistons sit 20 thou down the bore, normal head gasket.

Think karl worked it out to roughly 8:1 for me before but cant remember exactly.

Cheers, Nick.