# 8v compression ratio



## bradlesp (Jul 20, 2006)

I am starting on my 8v turbo build on my obd1 aba and am wondering what compression ratio stacked head gaskets results in. I have read everything from 8.5 to 9.5 so if anyone has acutally had it checked and knows the true answer it would be greatly appreciated. http://****************.com/smile/emthup.gif


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## jezzag60 (Aug 26, 2006)

Haven't done it but fearly sure it's like only 9.5-1.


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## GTijoejoe (Oct 6, 2001)

*Re: (jezzag60)*

Its actaually more 8.75-9:1 http://****************.com/smile/emthup.gif 
I'll show you the math if requested


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## bradlesp (Jul 20, 2006)

*Re: (GTijoejoe)*

here we go with more different results. if you could explain to me how to determine the compression ratio mathmatically it would be greatly appreciated. but 9:1 is good news since ill be shooting for 10-15psi.


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## clarksongli (Nov 4, 2003)

*Re: (bradlesp)*

9:1 would be a result of a SS gasket such as c2 or eip's.......im pretty sure with a stacked oem gasket, your lookin at just under 9.5:1, but it depends on if your head has been decked ever, and which gaskets your gunna use.....stack 2 and call it a day, or just buy a premade sized one so you know for sure


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## GTijoejoe (Oct 6, 2001)

*Re: (bradlesp)*


_Quote, originally posted by *bradlesp* »_here we go with more different results. if you could explain to me how to determine the compression ratio mathmatically it would be greatly appreciated. but 9:1 is good news since ill be shooting for 10-15psi.

Here ya go: These are the parameters that were given to me a while back, I am NOT saying that they are 100% correct, but mathmatically some of these numbers that are used check out to give the ABA stock compression ratio of 10:1 which the bently states. So I take them to be 98% correct
This is what I was using to calculate an ABA block with 16v head, so I'm just going to copy and paste it. This was written and used with MATLAB, because its my friend








Parameters and Equations units are cubic centimeters for the most part:
There maybe some info here that you actaually dont 'need, pay attention to the equations and you'll be set.
% 16v head volume + valve dish
sixV= 48+14.5;
% 8v head volume + valve dish
eightV = 32.5+14.5;
% 1 aba gasket volume
g=8.5;
% aba block & rod displacment per cylinder 
cyl=1984/4;
cyl2 = 1974/4;
% cylinder parameters aba block and rods
stroke= 9.28;
bore = 8.25;
% difference in volume with 9a pistons if they sit 1.5mm above aba pistons
v9a=(.15)*pi*bore^2*.25;
sixV_9a= sixV-v9a;
% 8v head with aba block & pistons 2 HG
CR8v2HG=(cyl+eightV+g+g)/(eightV+g+g)
% 8v head with aba block & pistons 1 HG (stock setup)
CR8v1HG=(cyl+eightV+g)/(eightV+g)
% 16v head with aba block & pistons 1 HG
CR16=(cyl+sixV+g)/(sixV+g)
% 16v head with aba block & 9a pistons 1 HG
CR16_9a=(cyl+sixV_9a+g)/(sixV_9a+g)
Answers:
This is ABA block and internals with 2 HG
CR8v2HG = 8.7500
This is ABA block and internals with 1 HG (stock)
CR8v1HG = 9.9369
This is ABA block and internals with 16v head
CR16 = 7.9859
This is ABA block, ABA rods, 9a Pistons, 16v head
CR16_9a = 8.8753

For those who don't like math and don't really understand that.
CR = (Entire volume of the cylinder at BDC) / (Remaining volume at TDC)


_Modified by GTijoejoe at 10:29 PM 11-8-2006_


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## ABF Jeff (Nov 16, 2005)

*Re: (GTijoejoe)*

Depending on what turbo you run, you can handle 10PSI without even stacking gaskets...
It's all about air volume... I ran 22PSI from a T3 super 60 on stacked gaskets.


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## TheVolksracer (May 26, 2004)

*Re: (ABF Jeff)*

well if you were smart you would do this..
go to http://www.eiptuning.com and buy the low compression head gasket. its only $130, and that one wont leak liek the stacked ones will.
Then go to http://www.parts4vws.com and buy the ARP head stud kit. 
Assemble then you are set for 20 ish psi. 
Your compression will be 8.5:1 if its an OBDI engine.
If its OBDII then you will be at 8:1
http://****************.com/smile/emthup.gif * Ignore every other post after mine.. cause these are the facts and i am %100 sure of it. *


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## bradlesp (Jul 20, 2006)

*Re: (TheVolksracer)*

I all ready have head studs and two multilayer head gaskets so i figured if they would be as effective as an EIP at lowering compression and making a good seal then i should use them.
It is an obd1 aba and i will initially be running an m24 .42 .48 which i believe is a 40 trim 
also a 268/260 boost cam if that makes any differance
abf jeff: what type of management/injectors did you run? any numbers?
thank you for the mathematical way to figure it out it acutally is helpfull.
from what i have researched my turbo i have will only support about 15-16psi but up to only about 5500 rpms from what i read. not sure how valid the information is.
anymore help or suggestions would be much appreciated seeing as how i am going to be taking the head off this weekend. http://****************.com/smile/emthup.gif


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## bradlesp (Jul 20, 2006)

*Re: (bradlesp)*

clarksongli, also the head has not been decked so right now the engine is bone stock as far as compression.


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## ABF Jeff (Nov 16, 2005)

*Re: (bradlesp)*

42# injectors, RRFPR... Not too sure about the actual numbers, but it bent a tie-rod from torque-steer in third. Shifting into 4th with a heavy foot would get the tires talking to you as well. http://****************.com/smile/emthup.gif


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## bradlesp (Jul 20, 2006)

*Re: (ABF Jeff)*

that sounds a little more intense then what i will be running. how long did it run before it broke?


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## ABF Jeff (Nov 16, 2005)

*Re: (bradlesp)*


_Quote, originally posted by *bradlesp* »_that sounds a little more intense then what i will be running. how long did it run before it broke?

I broke it fast... Cracked the turbo housing, but no hickups or anything for a couple hundred miles, but it never saw anything other than full throttle.


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## bradlesp (Jul 20, 2006)

*Re: (ABF Jeff)*

mine is be a daily driver with a 020 in it until summer at least thus only 10-15psi tops. sounds like stacked head gaskets are the way i am going to go. any reason they woudlnt make as good of seal with some rtv sealent as an EIP copper headgasket would?


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## ABF Jeff (Nov 16, 2005)

*Re: (bradlesp)*

just use copper sealant on both sides of both gaskets and make sure to add an extra 40-45 degree sinch to the head torque ritual to make sure you atequitely cruse both gaskets.


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## GTijoejoe (Oct 6, 2001)

*Re: (ABF Jeff)*


_Quote, originally posted by *ABF Jeff* »_just use copper sealant on both sides of both gaskets and make sure to add an extra 40-45 degree sinch to the head torque ritual to make sure you atequitely cruse both gaskets.

That is basically exactly what i did. copper gasket sealant between the gaskets, and top gasket and the head. A little higher torque squish and you should be good to go http://****************.com/smile/emthup.gif


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## bradlesp (Jul 20, 2006)

*Re: (GTijoejoe)*

will do, ready for the boost monster to get under way


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## epjetta (Sep 19, 2006)

*Re: (GTijoejoe)*

so 8.75:1-9:1 is for using two gaskets (about .120in) on a 10:1 motor?


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## Salsa GTI (Aug 29, 2000)

*Re: 8v compression ratio (bradlesp)*

I would do the stacked gasgets for price sake..as long ase you get Victor Rienz gasgets or similer there will be no worries.......I currently run stock compression with C2 42# injector software package.
12 psi with a t3 48/60...Have fun


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## rhussjr (Aug 7, 2000)

*Re: 8v compression ratio (bradlesp)*

The compression ratio will be between 8.3:1 - 8.4:1 with two gaskets.


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## bradlesp (Jul 20, 2006)

*Re: 8v compression ratio (rhussjr)*

rhussjr how do you figure that the compression is that low? i am considering sticking with stock compression and running low psi


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## rhussjr (Aug 7, 2000)

*Re: 8v compression ratio (bradlesp)*

Stock ABA compression is 9.6:1 (not 10:1) and by adding an extra gasket (metal gasket) for double stack the added cc's in the total volume is 8.21 cc's. This is enough to drop the compression down and equal 8.3 - 8.4:1.


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## TheVolksracer (May 26, 2004)

*Re: 8v compression ratio (rhussjr)*

obd1 engine are 9.5:1
obd2 engines are 9:1
dont be cheap and stack gaskets.. they leak
Buy the eip spaced one and also use the arp headstuds


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## bradlesp (Jul 20, 2006)

*Re: 8v compression ratio (TheVolksracer)*

might just stick with stock compression and head studs then, seems like a lot of people have had good luck with stacking head gaskets but i have also heard of people blowing their engines in 2 days, maybe its the tune


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## GTijoejoe (Oct 6, 2001)

*Re: 8v compression ratio (rhussjr)*


_Quote, originally posted by *rhussjr* »_Stock ABA compression is 9.6:1 (not 10:1) and by adding an extra gasket (metal gasket) for double stack the added cc's in the total volume is 8.21 cc's. This is enough to drop the compression down and equal 8.3 - 8.4:1.

What is the head volume chamber with the valves on an 8v head?


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## rhussjr (Aug 7, 2000)

*Re: 8v compression ratio (GTijoejoe)*

29-30 cc's


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## GTijoejoe (Oct 6, 2001)

*Re: 8v compression ratio (rhussjr)*


_Quote, originally posted by *rhussjr* »_29-30 cc's

Do you also have the CC for a 16v head and valves?
I'm going to rerun my numbers and see what I get when I get home and re post em up.


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## papichulo7 (Dec 3, 2006)

*Re: 8v compression ratio (bradlesp)*

Bump from the dead -- just want to see if there is any updated info. Going through the same research ... thinking about running low (max: 14) PSI w/ STOCK compression on a turbo ABA swap. Thanks


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## Agtronic (May 14, 2001)

*Re: 8v compression ratio (rhussjr)*


_Quote, originally posted by *rhussjr* »_Stock ABA compression is 9.6:1 (not 10:1) and by adding an extra gasket (metal gasket) for double stack the added cc's in the total volume is 8.21 cc's. This is enough to drop the compression down and equal 8.3 - 8.4:1.

I *think* this is right.
I got a compression ratio of 8.48:1 using two stacked gaskets.
Here's how I calculated mine :
Calculator primed with _correct_ numbers for a stock ABA : LINK
Now, add another gasket into the "change CR section". (put 1.57 into spacer thickness and 83.5 into spacer bore).
When I did this calculation a few years ago, using this very same calculator, I actually got 8.33:1. I don't know what is different this time. It's confusing, and all this is assuming that the ABA really is 9.6:1 as it says in the Bentley manual.
I also don't buy the "OBD1 was 9.5 and OBD2 is 9:1". If that were the case, the HP ratings would be different, no? They seem to all dyno the same.


_Modified by Agtronic at 12:54 PM 3-3-2007_


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## GTijoejoe (Oct 6, 2001)

*Re: 8v compression ratio (Agtronic)*


_Quote, originally posted by *Agtronic* »_
I *think* this is right.
I got a compression ratio of 8.48:1 using two stacked gaskets.
Here's how I calculated mine :
Calculator primed with _correct_ numbers for a stock ABA : LINK
Now, add another gasket into the "change CR section". (put 1.57 into spacer thickness and 83.5 into spacer bore).
When I did this calculation a few years ago, using this very same calculator, I actually got 8.33:1. I don't know what is different this time. It's confusing, and all this is assuming that the ABA really is 9.6:1 as it says in the Bentley manual.
I also don't buy the "OBD1 was 9.5 and OBD2 is 9:1". If that were the case, the HP ratings would be different, no? They seem to all dyno the same.

_Modified by Agtronic at 12:54 PM 3-3-2007_

my bently manual states 10:1 compression... I dont understand all these numbers be screwy....
Taking the bently's dimensions for the cylinder etc.... other key volumes are needed.
~head chamber
~valve dish

and taking the gasket thickness from the link Ag provided is still similar to the calculations i've done a while ago....
If I get the stock CR to be 10:1, ~stacked gaskets is 8.75:1
and if I get the stock CR to be 9.6:1, ~stacked gaskets is 8.5:1


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## Ghetto-8v (Jun 3, 2001)

*Re: (ABF Jeff)*


_Quote, originally posted by *ABF Jeff* »_Depending on what turbo you run, you can handle 10PSI without even stacking gaskets...
It's all about air volume... I ran 22PSI from a T3 super 60 on stacked gaskets.

I ran 21 on the way home from inital install No problems.


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## Agtronic (May 14, 2001)

*Re: 8v compression ratio (GTijoejoe)*


_Quote, originally posted by *GTijoejoe* »_my bently manual states 10:1 compression... I dont understand all these numbers be screwy....

My Bently states 9.6:1 ... there is so much confusion with this stuff! I don't get it!

_Quote »_Taking the bently's dimensions for the cylinder etc.... other key volumes are needed.
~head chamber
~valve dish

and taking the gasket thickness from the link Ag provided is still similar to the calculations i've done a while ago....
If I get the stock CR to be 10:1, ~stacked gaskets is 8.75:1
and if I get the stock CR to be 9.6:1, ~stacked gaskets is 8.5:1

I don't get why I get such lower numbers using that same calculator.








I get the following :
9.6:1 motor = 8.48:1 with two gaskets. 
10:1 motor = 8.78:1 with two gaskets.


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## GTijoejoe (Oct 6, 2001)

*Re: 8v compression ratio (Agtronic)*


_Quote, originally posted by *Agtronic* »_
My Bently states 9.6:1 ... there is so much confusion with this stuff! I don't get it!
I don't get why I get such lower numbers using that same calculator.








I get the following :
9.6:1 motor = 8.48:1 with two gaskets. 
10:1 motor = 8.78:1 with two gaskets.


I've never seen that Calc. before... I made my own Ag with MATLAB








MATLAB is my friend http://****************.com/smile/emthup.gif 
But from that calc. at least I got a good representation of valve dish volume and head chamber.... Of course when I use their numbers I don't get EXACTLY 10:1..... its rounded its very very close to it, and when I got 9.6:1 its like 9.632.... its just all really close....
So our over all stacked numbers are still very similar.... I like to calc it myself, because I know what exactly is really happening.... I can't see behind the interface of that calculator, or how far they take the decimals out too..... http://****************.com/smile/emthup.gif


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## sumpsfast (Jun 21, 2004)

*Re: 8v compression ratio (GTijoejoe)*

If you can afford it, pick up some custom JE pistons and create the CR you want. There is a GB going on over on the Audi forums, great buy!


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