# C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer?



## slc92 (Feb 9, 2005)

I'm in the process of swapping the Corrado to obd2 and I'll be running C2's 42# tune. Turbo is a TO4E .69 and I'll likely be pushing it to it's max ~20-22psi.
C2 rec. for pump gas:
9:1 up to 15psi
8.5:1 over that
Throwing some MS109 in at the track is not a problem. I'm thinkin I'll make a bit more power w/ the 9:1, but wont be able to run as much boost on 93 octane on the street. I'm aware of the positives and negatives of each, but I guess I'm looking for experiences to sway me one way or the other. No Meth and IC is on the smaller side 27x7.5x2.5.
Which spacer would you run and why? Thanks in advance http://****************.com/smile/emthup.gif


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## PjS860ct (Dec 22, 2002)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (slc92)*

9:1 here @18psi is no problem with 93oct and some water/meth
-- its when i turned it up to 25psi w/ 93oct with alot of w/m and the inline pump decided to loose connection is when i had my problem... lol


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## flatsix02 (Aug 23, 2004)

whats your goals? If youre going to stay with this setup forever, 9:1 is fine, but if you think you may want more in the future, just go with 8.5:1.


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## TBT-Syncro (Apr 28, 2001)

*Re: (flatsix02)*


_Quote, originally posted by *flatsix02* »_whats your goals? If youre going to stay with this setup forever, 9:1 is fine, but if you think you may want more in the future, just go with 8.5:1.

the difference in overall power delivery possibility is miniscule. on a good tune, its going to be the difference of being able to run 25 psi rather than 23 psi (arbitrary numbers).
my vote is 9:1


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## pimS (Jan 7, 2009)

You guys reccon 20psi on 95 or 98 pump gas with 8.5:1 wouldn't give any problems? On C2 42# tune


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## KubotaPowered (Jan 27, 2005)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (slc92)*

8.5:1 you can alweay compensate with more boost.


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## slc92 (Feb 9, 2005)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (KubotaPowered)*


_Quote, originally posted by *KubotaPowered* »_8.5:1 you can alweay compensate with more boost. 

Not true in every case. Think about reaching turbo maximum flow and or inj. safe max. This turbo's done at ~20psi IMO.


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## KubotaPowered (Jan 27, 2005)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (slc92)*

Difference between 8.5:1 and 9:1 is ~15whp. That can be made up with boost. Just safer to run less compression, less worry


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## slc92 (Feb 9, 2005)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (KubotaPowered)*


_Quote, originally posted by *KubotaPowered* »_Difference between 8.5:1 and 9:1 is ~15whp. That can be made up with boost. Just safer to run less compression, less worry

What I'm saying is that at some point I'll be maxing this setup's flow capabilities. Both the inj. and the turbo. I don't run Meth. At that point turning up boost wont make anymore power. 
If I had a bigger turbo and larger injector then sure.


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## FaelinGL (Nov 28, 2004)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (KubotaPowered)*


_Quote, originally posted by *KubotaPowered* »_Difference between 8.5:1 and 9:1 is ~15whp. That can be made up with boost. Just safer to run less compression, less worry

x2. 15 whp is about 1 psi of boost, maybe a bit more on your turbo.
Mike


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## crzygreek (Jul 8, 2005)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (FaelinGL)*

I'm in the same boat and really don't know which to pick. I do a lot of highway driving so anything that will boost fuel mileage is a plus in my books but there is no concrete evidence that the 9:1 produces better mpg's than the 8.5:1. 
A lot of people are making 400whp with a 9:1 without w/m and don't even think twice about it, but then again more are doing it with the 8.5:1. The more i think about it the more undecided I am


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## GinsterMan98 (May 19, 2008)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (crzygreek)*

If you are going to upgrade later I would go with the 8:5:1. If you don't see a bigger turbo in the future then go with the 9:1. It will make the same power with less boost. Running at near max of the turbo and inj is a recipe for disaster IMO. If you can make your power goal with less boost it will equate to cooler intake temp reducing the chance of Detonating, there by negating the need for a lower CR. Also a solid tune will allow you to keep the CR high, sometimes people use a HS as a band aid for a substandard tune. You have a MK3, so you can't control timing manually like on a MK4. Keeping a cooler intake temp is the way to make safe power.


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## slc92 (Feb 9, 2005)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (GinsterMan98)*

Basically it's do you want to limit yourself on pump gas to make a little more power on race gas at the track.
9:1 at 20psi will make more power than 8.5:1 on 20psi, w/ race gas prevemting detonation, will it not?


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## Weiss (Jun 21, 2004)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (slc92)*


_Quote, originally posted by *slc92* »_Basically it's do you want to limit yourself on pump gas to make a little more power on race gas at the track.
9:1 at 20psi will make more power than 8.5:1 on 20psi, w/ race gas prevemting detonation, will it not?

Sure will. More compression does make more power. Why do we see pro mod guys running 14:1 compression ratios? Theyre making tons of power but also have a very effective way of controlling spark advance and watching knock, but they usually use alcohol or nitromethane.
It's pretty scary to see the actual compression numbers when in boost. According to Weiand starting at 10:1 and 10psi of boost I think I remember it was over 18:1 compression!








That's all besides the point... as others have stated it's far easier to start safe and always add boost later. You will "usually" make more power with less compression and more boost vs more compression and less boost. If that makes any sense. 
I'm redoing mine in January... I'll be buying a 8.5:1 spacer.


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## slc92 (Feb 9, 2005)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (Weiss)*

Thanks for all the help guys.
Pretty sure I'm going 9:1 and here's why:
1) It'll make more power at the track than 8.5:1 w/ some MS109.
2) I'll still be able to run ~15psi on the street on 93 octane which is plenty.
3) Slightly better off boost response and gas mileage.
4) Less of a change in cam timing w/ the thinnner spacer.
It's all about maximizing the 42# setup. If I want more then it'll be forged pistons and rods anyway so the 8.5:1 spacer would be coming out as well. I'd also need a bigger turbo, intercooler, inj., management, etc. People keep saying more boost, but I'll max the turbo and or inj. at or just north of 400whp. More air isn't an option on this turbo.
At the end of the day I know I'd kick myself for leaving something on the table at the track.







I can't afford to drive fast on the street. If I get points or lose my license I lose my job.
Who's the fastest C2 42# car? I know Mikebobelak went 11.5X's. Anybody know of anyone faster? I'm coming for them


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## PjS860ct (Dec 22, 2002)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (slc92)*


_Quote, originally posted by *slc92* »_Thanks for all the help guys.

Who's the fastest C2 42# car? I know Mikebobelak went 11.5X's. Anybody know of anyone faster? I'm coming for them









http://****************.com/smile/emthup.gif








[email protected] i cant wait to see your times this coming season with the 42# set up!!!


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## sp_golf (Nov 28, 2007)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (slc92)*


_Quote, originally posted by *slc92* »_
Who's the fastest C2 42# car? I know Mikebobelak went 11.5X's. Anybody know of anyone faster? I'm coming for them









Quickest I know of ran 11.2


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## slc92 (Feb 9, 2005)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (sp_golf)*


_Quote, originally posted by *sp_golf* »_
Quickest I know of ran 11.2

That's pretty respectable http://****************.com/smile/emthup.gif 
Any details?
I'll make it interesting for sure


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## marat_g60 (Mar 5, 2003)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (slc92)*

Pretty sure he's talking about this car 
http://www.youtube.com/watch?v...lated
I believe on that run he was running around 25psi on the kinetic t3/t4 turbo, probably why the mph is a little low.


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## slc92 (Feb 9, 2005)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (marat_g60)*


_Quote, originally posted by *marat_g60* »_Pretty sure he's talking about this car 
http://www.youtube.com/watch?v...lated
I believe on that run he was running around 25psi on the kinetic t3/t4 turbo, probably why the mph is a little low. 


Thanks. What was the mph? Anymore details on the car?
11.34 is nice http://****************.com/smile/emthup.gif


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## marat_g60 (Mar 5, 2003)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (slc92)*

mph was 122 on that run.
Its a stock vr6 with a headspacer, not sure 9:1 or 8.5:1
c2 quickflow
kinetic stage 3 kit,
24.5 slicks
cant remember if its on stock shafts or dss
car is gutted


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## quadcammer32 (Jan 20, 2007)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (marat_g60)*

what would you guys recommend for a c2 36# setup? im going to be running a gt3076r, i think the limiting factor will be the injectors/ tune 9:1 or 8.5:1


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## TBT-Syncro (Apr 28, 2001)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (quadcammer32)*


_Quote, originally posted by *quadcammer32* »_what would you guys recommend for a c2 36# setup? im going to be running a gt3076r, i think the limiting factor will be the injectors/ tune 9:1 or 8.5:1

injectors
9:1
if you havent bought it already. i'd suggest a 3582 over the 3076. the spool is almost the same, but the 35 has a lot larger top end.


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## Weiss (Jun 21, 2004)

Just placed the order for my 8.5:1. I'm tired of blowing up these engines. It's starting to get expensive...


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## sp_golf (Nov 28, 2007)

*Re: (Weiss)*

I'd go 8.5:1 on software, you can max out the fueling on 9:1 but I wouldn't trust it without WMI


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## quadcammer32 (Jan 20, 2007)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (TBT-Syncro)*


_Quote, originally posted by *TBT-Syncro* »_
injectors
9:1
if you havent bought it already. i'd suggest a 3582 over the 3076. the spool is almost the same, but the 35 has a lot larger top end.

i got a 3076 for REAL cheap off my friend so im going to run that. how much boost can I run n the 36# file?


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## TBT-Syncro (Apr 28, 2001)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (quadcammer32)*


_Quote, originally posted by *quadcammer32* »_
i got a 3076 for REAL cheap off my friend so im going to run that. how much boost can I run n the 36# file?

3bar or 4 bar fpr?
i'm guessing on that turbo in the 18-20psi range.


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## Nuzzi (Oct 18, 2001)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (TBT-Syncro)*

im no expert in FI, but will the cam size also be a deciding factor? meaning if you ran 9:1 but with a 268 cam it would be as safe as 8.5:1 with a 256? im probly way off here...


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## TBT-Syncro (Apr 28, 2001)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (Nuzzi)*


_Quote, originally posted by *Nuzzi* »_im no expert in FI, but will the cam size also be a deciding factor? meaning if you ran 9:1 but with a 268 cam it would be as safe as 8.5:1 with a 256? im probly way off here...

cam size will definitely effect fueling. the cam will allow more air in, which of course means you need more gas.


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## slc92 (Feb 9, 2005)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (TBT-Syncro)*

I was just looking at the TO4E 60 trim's compressor map today. That turbo is done on this motor at 19-20psi. I should be fine at 9:1 and some VP MS109 at that psi.
It's only ~7psi more than I run now at 10:1.


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## quadcammer32 (Jan 20, 2007)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (TBT-Syncro)*


_Quote, originally posted by *TBT-Syncro* »_
3bar or 4 bar fpr?
i'm guessing on that turbo in the 18-20psi range.

i was gonna run a 4bar, i also have cat 263 cams that are already installed if that will change anything. Its not worth taking them out.


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## marat_g60 (Mar 5, 2003)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (quadcammer32)*

4bar on the 36# software runs too rich out of boost, you'll get high off the fumes. Id suggest sticking to the 3bar unless its not a daily, but then again, you dont want the engine running rich all the time either.


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## quadcammer32 (Jan 20, 2007)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (marat_g60)*


_Quote, originally posted by *marat_g60* »_4bar on the 36# software runs too rich out of boost, you'll get high off the fumes. Id suggest sticking to the 3bar unless its not a daily, but then again, you dont want the engine running rich all the time either.

what about an adjustable one or a 3.5 bar?


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## TBT-Syncro (Apr 28, 2001)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (marat_g60)*


_Quote, originally posted by *marat_g60* »_4bar on the 36# software runs too rich out of boost, you'll get high off the fumes. Id suggest sticking to the 3bar unless its not a daily, but then again, you dont want the engine running rich all the time either.

if you have a newer version, with a properly working 02, then the 02 should be able to dial the fuel back to stoich.


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## quadcammer32 (Jan 20, 2007)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (TBT-Syncro)*


_Quote, originally posted by *TBT-Syncro* »_
if you have a newer version, with a properly working 02, then the 02 should be able to dial the fuel back to stoich.

my software is C2s latest version.


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## marat_g60 (Mar 5, 2003)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (TBT-Syncro)*

I had the latest version, brand new o2. the A/f was spot on at idle and cruise, but it wasted so much more gas and smelt like ass inside the cabin.
It may work for him, but didnt work out for me.


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## Weiss (Jun 21, 2004)

*Re: C2 42# 12v VRT: 8.5:1 or 9:1 Headspacer? (Nuzzi)*


_Quote, originally posted by *Nuzzi* »_im no expert in FI, but will the cam size also be a deciding factor? meaning if you ran 9:1 but with a 268 cam it would be as safe as 8.5:1 with a 256? im probly way off here...

Yes it does. Not only more air but also dynamic compression ratio as well. Depending on how many degress ATDC the intake lobe closes, that can change the compression a notable amount.


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