comp ratio... sorry guys

[kingcorolla]

i know u have herd this all before, but i ran a search and couldnt be fukkd lookkin through all of them. I want the formula to work out comp ratio. i know its in ure bore + stroke etc etc.

or one of u could do me one better and answer this...

im shipping my short block off to reconditioners for bottom end work on mon, and wanted to increase my BLUETOP compression ratio while im at it. Bluetops are 9.4:1 factory, and i want to increase to red/silvertop comp ratio (10.3-5:1,) for a little more bang.

so can anyone hook me up with a good amount to shave off the block? or at least the formula so i can try and work that mother out for myself?

[JasonZE]

You are better off giving them the head and block and have them work it out as you need to cc the combustion chambers in the head to work out the ration between bore and chamber
You can deck the block but you need to plane the head or get a suitable trd metal gasket to achieve the right ratio as you can only take a tiny amount from the block to get the piston deck height right.,
A good reconditioner will be able to do this easily and it would take you for ever as measuring the combustion chamber volume is a slow process.

[kingcorolla]

u think if i send my head to a specialist, told him the cc rating of the engine, and the comp ratio, they could take off the rite amount?

[Drifter4ag]

take 1mm off the head and bang .. your done .. 10.4:1

[kingcorolla]

cheers drifter4ag! thats wat i wanted to hear

[CozmoNz]

you know i really hate you for forcing me to type this out....... but i gotta do this

i hate typing btw, so be thankful

Compression ratio:

A compression ratio is the comparison of the volume above the piston when the piston is at BDC to the volume above the piston at TDC.

The volume above the piston at BDC = v1 = swept volume + clearance volume (SV + CV)

The volume above the piston at TDC = v2 = clearance volume (CV). Compression ratio = v1 : v2 = (SV + CV) : CV = (SV + CV) / CV

It can be shown that the same numerical answer can be obtained from an alternative formula: compression ratio = (SV / CV) + 1.

got it?

Example:

Determine the compression ratio of an engine if the bore is 80mm, the stroke is 100mm and the clearnance volume is 70 cm cubed.

Solution:

Bore = 80mm = 8cm.
Stroke = 100mm = 10cm.
Swept volume = area of bore X stroke
Therefore = (PIE D2 X Stroke) / 4
Therefore = ((PIE X D X D) X Stroke) / 4
Therefore = ((3.142 X 8 X 8) X 10) / 4
Which = 502.7cm Cubed

V1 = SV + CV = 503 + 70 = 573
V2 = CV = 70
V1 : V2 = 573:70
= 8.19 : 1

and that annoying alt soloution:
(SV /CV) + 1
= (503 / 70) + 1
= 7.19 + 1
= 8.19

got it? ^_^ ezy pzy

[Al]

i hate typing btw, so be thankful

thankful you can cut n paste?

[kingcorolla]

thanx cosmoNZ

that "...sorry guys" in the title was directed to people like you!

*cuts and pastes to desktop*

[RedMist]

Because I am truly lazy.

http://www.hotrod.com/techarticles/54258/

Aint google grand!

[4agepwr]

Drifter4ag wot headgasket would you use after planing 1mm off to get that comp ratio?

[CozmoNz]

i hate typing btw, so be thankful

thankful you can cut n paste?

excuse me? i typed that out from my notes in my power efficenty papers....

did not cut and paste damnit

[qik20v]

[/quote]
Bore = 80mm = 8cm.
Stroke = 100mm = 10cm.
Swept volume = area of bore X stroke
Therefore = (PIE D2 X Stroke) / 4
Therefore = ((PIE X D X D) X Stroke) / 4
Therefore = ((3.142 X 8 X X 10) / 4
Which = 502.7cm Cubed
[/quote]

isnt the area of a circle pi * radius squared

not pi*diameter^2 ?

[jayznz]

Bore = 80mm = 8cm.
Stroke = 100mm = 10cm.
Swept volume = area of bore X stroke
Therefore = (PIE D2 X Stroke) / 4
Therefore = ((PIE X D X D) X Stroke) / 4
Therefore = ((3.142 X 8 X X 10) / 4
Which = 502.7cm Cubed
[/quote]

isnt the area of a circle pi * radius squared

not pi*diameter^2 ?[/quote]


first of all hehehe 'PIE'

Secondly, qiky you forgot about the little' /4' tacked on the end
r^2 is the same as (d/2)^2
which is the same as d^2/2^2
or d^2/4
Hence the '/4'

So, Cozmoz formula is correct i think

Now children that will be on your end of year tests so i hope ur writing this down

[qik20v]

ok my appologies to CozmoNz

didnt really look at formulas just saw pi*d^2 and was like wtf?

[Spannergal]

take 1mm off the head and bang .. your done .. 10.4:1

not completely sure coz i hate working things out but don't think its as simple as that. but the specialist is supposed to know how to change the cc and comp ratio

[RedMist]

Which is a good question.. has anyone CC'ed a 4age head and piston dome?

[ChaosAD]

I cc'd a red\blacktop piston dish. It was 5cc but I dont know what it would be in the engine, that would depend on the piston height.
In the wiseco catalogue it lists the 16v 4age head at 39cc.

[Drifter4ag]

if your gonna take 1mm off the head just run a std ae92 gasket which is the best of the lot
otherwise get a TRD one .. they plenty good and can be used again and again

[CozmoNz]

Yeh, i was pretty sure my formula was correct, its what we use...

looks quite complicated, but if you follow it through, its pretty damn easy