# aba 16v Compression Ratio



## GTijoejoe (Oct 6, 2001)

i'm sorry, but I did search, and I know I've seen the answer before but can't find it.
Looking to know the CR with a 16v head on an stock ABA block, because I want to know what it will be with aba JE 9:1 pistons
Thanks in advanced


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## OstTrefftWest (Sep 28, 2002)

*Re: aba 16v Compression Ratio (GTijoejoe)*

IIRC, it's about 8.5:1 (with pistons that yield 10:1 with an 8v head). Sounds like you'd be at about 7.5:1 with those pistons. JE also makes a forged 9.6:1, which is what I have, which should give about 7.8:1 with a 16v head (which is my pipe-dream for lots of boost eventually)....


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## GTijoejoe (Oct 6, 2001)

*Re: aba 16v Compression Ratio (OstTrefftWest)*


_Quote, originally posted by *OstTrefftWest* »_IIRC, it's about 8.5:1 (with pistons that yield 10:1 with an 8v head). Sounds like you'd be at about 7.5:1 with those pistons. JE also makes a forged 9.6:1, which is what I have, which should give about 7.8:1 with a 16v head (which is my pipe-dream for lots of boost eventually)....

wow, 7.8:1 would require a lot of boost, and would be a lot of fun....
Thanks for the good info, very much appreciated.


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## ABA Scirocco (May 30, 2001)

*Re: aba 16v Compression Ratio (GTijoejoe)*

With stock ABA pistons, the compression ratio would be about 8:1. If you want to do the math, here are the numbers you need.
Stock ABA: 1984cc displacement
32.5cc head chamber volume
14.5cc piston dish volume
8.5 cc gasket volume
and the head chamber volume of a 16v head is 48cc.


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## OstTrefftWest (Sep 28, 2002)

*Re: aba 16v Compression Ratio (ABA Scirocco)*

Cool -- the calculators I'd run used 30cc and 45cc as chamber volume for the 8v and 16v heads, respectively. The extra few cc's sure explains the difference in numbers.
Guess this means that my current pistons would probably be down more like 7.5:1 with a 16v head over top of them....


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## jettaflair (Jan 7, 2006)

*Re: aba 16v Compression Ratio (OstTrefftWest)*

could you shave the head enough to bring the CR back to 10:1, or would there be valve interference? What about higher CRs? Or, would one have to buy 16v pistons to run 10:1 or higher CR?


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## OstTrefftWest (Sep 28, 2002)

*Re: aba 16v Compression Ratio (jettaflair)*

You'd need 16v pistons. My 16v-driving friend has found that the 16v heads have VERY little extra material to be decked -- I think the limitation is getting into coolant passages....


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## ABA Scirocco (May 30, 2001)

*Re: aba 16v Compression Ratio (jettaflair)*


_Quote, originally posted by *jettaflair* »_could you shave the head enough to bring the CR back to 10:1, or would there be valve interference? What about higher CRs? Or, would one have to buy 16v pistons to run 10:1 or higher CR?

Unlike an 8v head, the intake valves are at an angle with respect to the surface of the head and as a result the valve seats are quite close to the surface. So, you can't shave a 16v head very much at all before you starting cutting into the valve seats.
Normal 9A (2.0L-16v) pistons give you a compression ratio somewhare around 9.0:1 in an ABA block with a 16v head because the wrist pin is closer to the top of the piston than stock ABA pistons meaning the piston wouldn't come all the way to the top of the cylinder at TDC rather, they'd be about 1mm below the deck. Also, the 9A pin diameter is different so you'd need to rebush the ABA rods to fit them. To increase the compression ratio, a small amount call be milled off of the heads and a bit more off of the block, I'm not sure but you could probably get back up to 10:1 or at least close.
I think a better route for a NA ABA/16v, is to order up some custom pistons. To order them, you need to know the bore diameter, pin diameter, pin height and dome (or dish) volume, with those 4 numbers, a piston manufacturer will be able to give you exactly what you need to get the compression ratio you want. Another option is to order some ABF pistons, Techtonics, among others, sell them but they'll probably cost as much or more than custom pistons.


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## GTijoejoe (Oct 6, 2001)

*Re: aba 16v Compression Ratio (ABA Scirocco)*

If 9a pistons yeild a 9:1 CR with 16v head on ABA block, then what would 9a pistons yeild with a 8v head?
or what volume of the clyinder does the 9a pistons take away in cc's over the aba pistons.


_Modified by GTijoejoe at 6:25 PM 4-7-2006_


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## GTijoejoe (Oct 6, 2001)

*Re: aba 16v Compression Ratio (ABA Scirocco)*

OH did the math, well actually MATLAB did








sixV = 62.5000
eightV = 47
g = 8.5000
cyl = 496
CR8 = 9.9369
CR16 = 7.9859
cr8 = 9.9383
cr16 = 7.9869
that would be the stock compression on an 8v, and then what the compression is with the 16v head. According to your numbers. The second number for compression is calculated with the bore and stroke parameters.
heres the math:
sixV= 48+14.5
eightV = 32.5+14.5
g=8.5
cyl=1984/4
stroke= 9.28
bore = 8.25
cylinderarea= pi*bore^2/4
displacement= cylinderarea*stroke

CR8=(cyl+eightV+g)/(eightV+g)
CR16=(cyl+sixV+g)/(sixV+g)
cr8 = (displacement+eightV+g)/(eightV+g)
cr16 = (displacement+sixV+g)/(sixV+g)



_Modified by GTijoejoe at 6:14 PM 4-7-2006_


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## jettaflair (Jan 7, 2006)

GTIjoejoe, i'm pretty sure that 16v pistons shouldn't be used with 8v heads. the pistons have quench for 16v versus a dish for 8v, it could screw up the flow, or something.
i have an aba i'm rebuilding with ITBs. i was considering going to 16v, even though i would have to buy twice as many valve guides, seals, cams, etc. however, the price of new pistons has convinced me to stay with 8v!


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## ABA Scirocco (May 30, 2001)

*Re: (jettaflair)*

Actually, an 8v head works pretty well on top of 16v piston except for the fact that the compression ratio is very high which means you need to run the engine on racing fuel.


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## GTijoejoe (Oct 6, 2001)

*Re: (ABA Scirocco)*


_Quote, originally posted by *ABA Scirocco* »_Actually, an 8v head works pretty well on top of 16v piston except for the fact that the compression ratio is very high which means you need to run the engine on racing fuel.

OR i run 2 head gaskets or a custom spacer to reduce the CR with the 9a pistons


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