Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > 911 / 930 Turbo & Super Charging Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Registered User
 
Join Date: Sep 2002
Location: texas
Posts: 863
Garage
AFR for Supercharged 3.6

Tried searching the forum but didn't return anything.

What's a good (and safe) AFR to run on a supercharged 3.6 engine with 11.5-to-1 compression running about 5.5lbs of boost?

I want to tune the car. It's running a rich but safe 11 AFR right now. Should I increase AFR to about 12 to 12.5?

thanks,
anthony
Old 11-19-2011, 05:25 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Registered User
 
Join Date: Mar 2011
Posts: 471
When you tune for max power, 12.5 is typically the AFR to aim for I believe.

Bosch state that most spark ignition engines develop their maximum power at air/fuel ratios of 12.5:1 - 14:1, maximum fuel economy at 16.2:1 - 17.6:1, and good load transitions from about 11:1 - 12.5:1. However, in practical applications, engine air/fuel ratios at maximum power are often richer than the quoted 12.5:1, especially in forced induction engines where the excess fuel is used to cool combustion and so prevent detonation.

Given you are running a blower on a non decompressed motor, I'd stay between 11 - 12.5 AFR. you also have the advantage of twin plugs, which helps too

Please correct me if I'm wrong anyone

Edit: are you running an intercooler?! If not, I'd highly recommend it! If your motor is a 964, you have heaps of meat on the crown to machine down to a more boost friendly CR, and then you can run more boost

Last edited by 911TT33; 11-19-2011 at 07:09 PM..
Old 11-19-2011, 06:57 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Registered User
 
Join Date: Sep 2002
Location: texas
Posts: 863
Garage
I am running an intercooler and water/meth injection. But the water meth is small and mainly used to further cool the charge.

As for AFR....I should then shoot for 11-12.5 throughout the rpm? Including the lower 2K-4K rpm?
Old 11-19-2011, 07:14 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Registered User
 
Join Date: Mar 2011
Posts: 471
Are you tuning on a dyno and monitoring AFRs as you tune?

When you say lower rpm range, are you referring to AFR at cruise? If so, then 14-16 is fine, but watch your EGT as well.

I'd shoot for between 11-12 under load.

Last edited by 911TT33; 11-19-2011 at 07:34 PM..
Old 11-19-2011, 07:24 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Registered User
 
Join Date: Sep 2002
Location: texas
Posts: 863
Garage
I am using a wide band O2 sensor with data logging and a good run or two in 2nd gear.

Lower RPM is the lower range of RPM when I am doing my WoT runs and measuring AFR.

BTW, this is a motronic 993 engine, so under cruise, it is closed loop controlled by the computer and 02 sensor.

I am seeing 1100F to a max of 1300F for my EGT.
Old 11-19-2011, 07:59 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
Registered User
 
Join Date: Mar 2011
Posts: 471
Interesting, how are you tuning the Motronic fuel/ignition tables? Do you have the software?
Old 11-19-2011, 08:13 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
 
Registered User
 
Join Date: Sep 2002
Location: texas
Posts: 863
Garage
The system is TPC which uses a unichip piggy back computer. It intercepts various engine signals, and can manipulate them.

As for motronic, there is Tuner Pro, but only the 964 mapping is available. No 993 one is publicly available that I know of.
Old 11-19-2011, 08:47 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
Metal Guru
 
911nut's Avatar
 
Join Date: May 2001
Location: Michigan
Posts: 2,511
Garage
Those of us that use CIS are in the habit of quoting a range of AFR since the system leans out by .6-.8 points by max engine speed.
Is your system able to deliver enough fuel such that your AFR is steady throughout the rev range?
As for the best value of AFR to obtain max torque, a dyno session would be the best way to determine that.
__________________
Paul B.
'91 964 Turbo
Port matched, SC cams, K27/K29 turbo, Roush Performance custom headers w/Tial MV-S dual wastegates, Rarlyl8 muffler, LWFW, GT2 clutch & PP, BL wur, factory RS shifter, RS mounts, FVD timing mod, Big Reds, - 210 lb
Old 11-20-2011, 04:31 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #8 (permalink)
Metal Guru
 
911nut's Avatar
 
Join Date: May 2001
Location: Michigan
Posts: 2,511
Garage
Quote:
Originally Posted by 911TT33 View Post
Given you are running a blower on a non decompressed motor, I'd stay between 11 - 12.5 AFR.
You can only get so much phase change cooling before you get the fuel wetting the cylinder walls and killing power. I think the boost pressure is a more important value since his static compression ratio was meant for n/a oeration. Crank up the boost enough and he'll have an intake charge temp rise that no extra fuel and meth will cool.
__________________
Paul B.
'91 964 Turbo
Port matched, SC cams, K27/K29 turbo, Roush Performance custom headers w/Tial MV-S dual wastegates, Rarlyl8 muffler, LWFW, GT2 clutch & PP, BL wur, factory RS shifter, RS mounts, FVD timing mod, Big Reds, - 210 lb
Old 11-20-2011, 04:36 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)
Registered User
 
Join Date: Sep 2002
Location: texas
Posts: 863
Garage
Quote:
Originally Posted by 911nut View Post
You can only get so much phase change cooling before you get the fuel wetting the cylinder walls and killing power. I think the boost pressure is a more important value since his static compression ratio was meant for n/a oeration. Crank up the boost enough and he'll have an intake charge temp rise that no extra fuel and meth will cool.
Yeah, I am running only 5lbs of boost. Anymore and the supercharger will just produce heat.

At that boost level, surprisingly, my liquid-to-air intercooler and two radiators+fans are capable of holding the avg intake temperature to +15F of ambient temperature even in Texas summer. With the aw injection in place, the intercooler & end pipe is cold to the touch.
Old 11-21-2011, 08:11 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #10 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 10:10 AM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.