# high compression 8v, have questions...



## salteatervw (Feb 27, 2005)

So I have a big valve digi head with a p&p job and a 1.8l 16v motor. I know the comp on the 16v is 10:1 and the digi motors had about 8:1. I hear different possible comp ratios after going to the 8v head. I've heard 13:1 or 12:1, has anyone actually be able to do the measurements and come up with a pretty solid answer for correct ratio? 

This is my 2011 project for a possible new Rabbit or Scirocco by falls end to start track racing for Spring 2012 at our local track.


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## Glegor (Mar 31, 2008)

salteatervw said:


> So I have a big valve digi head with a p&p job and a 1.8l 16v motor. I know the comp on the 16v is 10:1 and the digi motors had about 8:1. I hear different possible comp ratios after going to the 8v head. I've heard 13:1 or 12:1, has anyone actually be able to do the measurements and come up with a pretty solid answer for correct ratio?
> 
> This is my 2011 project for a possible new Rabbit or Scirocco by falls end to start track racing for Spring 2012 at our local track.


 first off, the 16v is closer to 11:1 stock.. 

digi engines were ALL 10:1 compression.. 

that aside.. 

an 8v head on a 16v block is going to make an ethanol, or race gas only engine.. your gonna have upwards of 14:1 compression.. 

what sort of fuel system you going to be running on this?


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## salteatervw (Feb 27, 2005)

Carb, like a weber. Also looking into running an MSD system for spark.


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## salteatervw (Feb 27, 2005)

Glegor said:


> first off, the 16v is closer to 11:1 stock..
> 
> digi engines were ALL 10:1 compression..
> 
> ...


 would doubling up the gaskets make it down closer to the 13:1 range to not have to always use race gas?


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## ABA Scirocco (May 30, 2001)

If you've got a 16v head and an 8v head, cc both, iirc, the 8v chambers are about 16cc smaller so just do the math. 

In any event, Glegor is correct, the resulting engine will not run reliably on pump gas, racing fuel or perhaps alcohol are absolutely required. 

We run an engine similar to the one you're thinking of on a 1/3 mile oval, the engine puts out about 195hp at the crank with a single side draft Weber carb. However, those engines are the result of many years of hard work and many disappointments if you're just throwing something together for the first time you could reasonably expect somewhere around 165-170hp. Making much more than that is rather difficult and requires a lot of time, experimentation and dyno testing.


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## salteatervw (Feb 27, 2005)

Nice! Well I don't expect the same HP as yours, thats amazing though. I was just hoping 150 crank, plus for me, this a year long project. So I'm not gonna rush into it and throw it in a car next month or nuthin.


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## Campbell (Nov 9, 2004)

*8v head on 16v pistons*

This is easy to run, even easier with the stock fuel injection. Few rules to follow: 

1) use head studs, head bolts will not keep the head down 

2) use an air/fuel mixture gauge - these can run lean quickly and melt the pistons, runs fine a little rich 

3) no problem with 110 leaded race gas 

4) if solid lifter, put in a mild cam and HD springs; you can run 7500 rpm no problem, hydr head not good over 6400 rpms due to valve float 

Have fun!!


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## scirocco8v1984 (Oct 18, 2006)

I've used 16V Pistons with a dish machined in the top for a total of 12.5-1 comp. it is good with stock injection & aviation gas 100LL ....Good port and big cam good for about 130 WHP or so! Ran 1.8 & 2.0 setups on this for drag Race\Hillclimb and work awesome! :thumbup:


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## Glegor (Mar 31, 2008)

salteatervw said:


> would doubling up the gaskets make it down closer to the 13:1 range to not have to always use race gas?


 i would never EVER stack head gaskets unless there was an actual spacer in between them.. 

why not just shave a 16v head and make it like 12.5:1? 

your gonna have WAY more power than if you used an 8v head.. 

and i would just run a stock VW knock sensing ignition system. your engine is gonna be really high compression, and very prone to detonation.. 

MSD ignitions dont have knock sensors.. they will keep the timing where its at till you melt a piston and blow the valve cover off your engine.. 

stock VW ignitions are way hot enough anyway, enough to make 5 or 600 hp IIRC..


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## ABA Scirocco (May 30, 2001)

Glegor said:


> i would never EVER stack head gaskets unless there was an actual spacer in between them..
> 
> why not just shave a 16v head and make it like 12.5:1?
> 
> ...


 Stacking head gaskets can work but it's most definitely NOT advisable as it's much more prone to failure. 

You can't shave a 16v head the way you can an 8v head, 12.5:1 is not attainable on a 16v merely by shaving the head. 

I agree with you about the MSD, not necessary, VW ignition components are easily up to the job. However, I wouldn't recommend a knock system for a racing engine as it can mask possible tuning issues, detonation should be controlled by using the appropriate fuel and proper tuning.


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## salteatervw (Feb 27, 2005)

Glegor said:


> why not just shave a 16v head and make it like 12.5:1?


 cause im sick of 16v's, Ive already built my MKI GTI with a 9A and Megasquirt. I want a new challenge and a new MKI to start out with. 

So back to my original question: 
* 
has anyone actually been able to do the measurements and come up with a pretty solid answer for correct ratio? 
*


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## scirocco8v1984 (Oct 18, 2006)

I'd Say go 9A or 3A Block with the 16V pistons maybe somewhere in the 12-13-1 comp. ratio just to be safe, stock CIS injection and 288 solid cam and use race gas "ALL" the time ....very easy & popular race setup! A good 120-130WHP will get you deep in the field! Good Luck ...:beer:[email protected]


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## Glegor (Mar 31, 2008)

ABA Scirocco said:


> Stacking head gaskets can work but it's most definitely NOT advisable as it's much more prone to failure.
> 
> You can't shave a 16v head the way you can an 8v head, 12.5:1 is not attainable on a 16v merely by shaving the head.
> 
> I agree with you about the MSD, not necessary, VW ignition components are easily up to the job. However, I wouldn't recommend a knock system for a racing engine as it can mask possible tuning issues, detonation should be controlled by using the appropriate fuel and proper tuning.


 my bad, wasnt awake all the way, forgot you cant shave them..


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## Willdue (Oct 14, 2007)

Campbell said:


> This is easy to run, even easier with the stock fuel injection. Few rules to follow:
> 
> 1) use head studs, head bolts will not keep the head down
> 
> ...


 this sounds interesting...


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## ABA Scirocco (May 30, 2001)

I missed the bit about hydraulic cams that Campbell wrote and I have to disagree, we've had pretty good results with hydraulic lifter heads, with good valve springs, we've experienced no problems with value float taking them up to 7500 rpm even a little more.


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## Shrttrackr (Oct 13, 2004)

with a 9a and JH head, my motor builder CCd the head ...he came up with 14.6:1 for this combo.

not sure if your motor combo has the same dims as the 9a/jh.


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## eurotrashrabbit (Oct 25, 2001)

14.6:1 is correct for a 2l with an 8v head. I have a set of 2l 16v 13.5 pistons for sale pretty cheap. Techtonics did them several years ago for me. I had to run 114 and it was fine. Right now I have 11.6:1 pistons which are modified Je turbo pistons with a bigger dish which they can make you what you want they just cost $650 a set. With the forged pistons and rods with 45mm throttle bodies and a 298 hydraulic cam it will go to 8k without blowing up. I missed a shift and it went to 9k and did not blow up. Fueling is very important to make the engine last with high coompression.







[video=facebook;1539621618243]http://www.facebook.com/video/video.php?v=1539621618243&comments[/video]


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## salteatervw (Feb 27, 2005)

eurotrashrabbit said:


> 14.6:1 is correct for a 2l with an 8v head. I have a set of 2l 16v 13.5 pistons for sale pretty cheap. Techtonics did them several years ago for me. I had to run 114 and it was fine. Right now I have 11.6:1 pistons which are modified Je turbo pistons with a bigger dish which they can make you what you want they just cost $650 a set. With the forged pistons and rods with 45mm throttle bodies and a 298 it will go to 8k without blowing up. I missed a shift and it went to 9k and did not blow up. Fueling is very important to make the engine last with high coompression.


Ive always loved your car man! Also thanks for the info!


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## eurotrashrabbit (Oct 25, 2001)

No problem here is a site that will help 
http://www.not2fast.com/vw/stuff/vw_engines.shtml#table


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