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  #16  
Old 10-28-2007, 10:06 PM
Myxalplyx's Avatar
Myxalplyx Myxalplyx is offline
XT6 is SVX's Daddy
 
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Back from Dead

Bringing this ancient thread back up. Noticed that stock pressure is 36psi and people have been bumping them up to 43psi.

Let us say that your air fuel ratio is 13.6:1 and you want to bring it down to 12.8:1 for WOT horsepower purposes (Just because in your head for some reason you think it will make more power in the 12.5:1 to 13.0:1 range being naturally aspirated). Just a guess but how much of a pressure increase will you need to make this happen from the stock fuel pressure of 36psi? I am curious as to if there is a formula for this (Ex: +2psi fuel pressure increase = -.4:1 air/fuel ratio drop or richer fuel). If not, then just will have to do it by trial and error. I wish I could do a cool graph like Chike put up. Thanks for any input!

Also, is there a how-to for installation of a fuel pressure regulator here somewhere? I have a fpr regulator and gauge from my Subaru RX turbo in my garage. May as well put them to use.

BTW: Browsing the internet I ran into an interesting before and after air/fuel ratio tuning article on a Honda.
http://www.turbomagazine.com/tech/02...ing/index.html
I am not saying we can expect similar gains but it does show what proper air/fuel ratio tuning is capable of.
Wish an SAFC could be used on an SVX.
__________________
Kevin Thomas
1997 2.2ltr Subaru Impreza Outback Sport Wagon (AWD/Auto) 13.03@100mph
1989 2.7ltr Subaru XT6 (AWD/Auto) 15.912@85.93mph
1996 3.3ltr SVX (AWD/Auto) 15.070@91.38mph
***R.I.P***
2010 RAV4 AWD Sport (13.717 @ 99.19mph )
2015 Honda Fit LX CVT (15.2 @ 90mph)

Last edited by Myxalplyx; 10-29-2007 at 04:47 AM.
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  #17  
Old 10-29-2007, 10:01 AM
cdigerlando cdigerlando is offline
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Location: Longwood, FL
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Quote:
Originally Posted by Myxalplyx View Post
Bringing this ancient thread back up. Noticed that stock pressure is 36psi and people have been bumping them up to 43psi.

Let us say that your air fuel ratio is 13.6:1 and you want to bring it down to 12.8:1 for WOT horsepower purposes (Just because in your head for some reason you think it will make more power in the 12.5:1 to 13.0:1 range being naturally aspirated). Just a guess but how much of a pressure increase will you need to make this happen from the stock fuel pressure of 36psi? I am curious as to if there is a formula for this (Ex: +2psi fuel pressure increase = -.4:1 air/fuel ratio drop or richer fuel). If not, then just will have to do it by trial and error. I wish I could do a cool graph like Chike put up. Thanks for any input!

Also, is there a how-to for installation of a fuel pressure regulator here somewhere? I have a fpr regulator and gauge from my Subaru RX turbo in my garage. May as well put them to use.

BTW: Browsing the internet I ran into an interesting before and after air/fuel ratio tuning article on a Honda.
http://www.turbomagazine.com/tech/02...ing/index.html
I am not saying we can expect similar gains but it does show what proper air/fuel ratio tuning is capable of.
Wish an SAFC could be used on an SVX.
If you start pushing your fuel pressure up, you are going to run very rich at idle, unless you tune. Bottom line is you need to be able to tune your injectors to do any useful and safe air/fuel ratio changes. I've had to run stock fuel pressure on my new setup with the nismo injectors and Tec 2. Anything less is not tunable (the injectors can't flow less). The FPR increases the pressure on the fuel rail 1:1 with an increase in manifold pressure so if I were running 20 psi of boost the pressure would rise from 35 psi to 55 psi. But this is all tunable.
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Chuck D.
1992 Subaru SVX LS-L - Heavily modded turbo
2002 Subaru Impreza WRX- Turboxs stg3 & Susp. Mods
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  #18  
Old 10-29-2007, 08:42 PM
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Myxalplyx Myxalplyx is offline
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Quote:
Originally Posted by cdigerlando View Post
If you start pushing your fuel pressure up, you are going to run very rich at idle, unless you tune. Bottom line is you need to be able to tune your injectors to do any useful and safe air/fuel ratio changes.
I plan on using what I have lying around. I have a Jumptronix digital air/fuel ratio meter on my FWD XT6 over my sisters house. That was a very reliable tool to use on an N/A engine and it worked well on 'tuning' the XT6 when Gary Gross installed Delta cams in it. What I did was raised and lowered the fuel pressure to get a flat line on 13.0:1 at WOT. Once this was established, I was gold.

However, I plan on doing the same thing with the SVX but need to use the SAFC to trim fuel down during neutral and light throttle conditions. This worked well on my Outback Sport so I figured why not try it on this. There are two important setup info about the SAFC that I need to find out. I may need to post this in an SAFC thread.

What is the Sensor Calc and Sensor Number settings to use the SAFC on an SVX? Does anyone know? I only think I need to adjust the fuel. I will know after tomorrow.
__________________
Kevin Thomas
1997 2.2ltr Subaru Impreza Outback Sport Wagon (AWD/Auto) 13.03@100mph
1989 2.7ltr Subaru XT6 (AWD/Auto) 15.912@85.93mph
1996 3.3ltr SVX (AWD/Auto) 15.070@91.38mph
***R.I.P***
2010 RAV4 AWD Sport (13.717 @ 99.19mph )
2015 Honda Fit LX CVT (15.2 @ 90mph)

Last edited by Myxalplyx; 10-29-2007 at 08:45 PM.
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