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NoDOHC · 01-01-2012, 08:40 PM

I would look into leaning the fuel mix in vacuum.

You should have a wideband on the car anyway with a turbo, it can give you advance warning before you damage the engine if something in the fuel supply fails.

In the summer my 4-port gets mid-30s on the highway (although I have never logged a tank over 33.6 MPG - due largely to my right foot having a problem on certain onramps, etc.) In the winter it gets about 30 MPG highway.

In my opinion, your timing in vacuum is 20 degrees retarded. However, you should read my transmission failure posting before you advance yours.

At 2500 RPM I run 30 degrees BTDC at 0kPA vacuum (WOT). I run 60 degrees BTDC at -61.3kPA (weird spot for a data point, I have a 3-bar MAP sensor) - the curve is linear between these two points. Porting is conservative, no changes to stock port timing, idles at -52 kPA, 14.2:1 AFR, 5 deg BTDC @ 900 rpm.

Typical cruising vacuum (-45kPa) at 2500 rpm = 62MPH on my 0.72 overdrive and 4.1:1 diff. I am running about 52deg BTDC and injecting about 2.5ms duration with 550 cc/min injectors.

01-01-2012, 08:40 PM	#7
NoDOHC The quest for more torque Join Date: Sep 2008 Location: Sheboygan, Wisconsin Posts: 855 Rep Power: 17	I would look into leaning the fuel mix in vacuum. You should have a wideband on the car anyway with a turbo, it can give you advance warning before you damage the engine if something in the fuel supply fails. In the summer my 4-port gets mid-30s on the highway (although I have never logged a tank over 33.6 MPG - due largely to my right foot having a problem on certain onramps, etc.) In the winter it gets about 30 MPG highway. In my opinion, your timing in vacuum is 20 degrees retarded. However, you should read my transmission failure posting before you advance yours. At 2500 RPM I run 30 degrees BTDC at 0kPA vacuum (WOT). I run 60 degrees BTDC at -61.3kPA (weird spot for a data point, I have a 3-bar MAP sensor) - the curve is linear between these two points. Porting is conservative, no changes to stock port timing, idles at -52 kPA, 14.2:1 AFR, 5 deg BTDC @ 900 rpm. Typical cruising vacuum (-45kPa) at 2500 rpm = 62MPH on my 0.72 overdrive and 4.1:1 diff. I am running about 52deg BTDC and injecting about 2.5ms duration with 550 cc/min injectors. __________________ 1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers) 1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic) Last edited by NoDOHC; 01-01-2012 at 08:46 PM.