Need your advice - Dyno tuning a rebuilt 87 motor

[Pchip]

After a two year (more actually) backdating project I will bring my ‘87 911 to a local dyno shop for some tuning. As a reminder, we completely rebuilt the motor, leaving it as a 3.2 but it has been “enhanced” with higher compression Euro pistons, a 993 Super Sport cam, a Clewitt EFI conversion kit with 46MM PMO’s and high performance coil. Up until recently the motor was running VERY rich but we have sorted that out.

My questions are around how best to fine tune the engine mapping when we get on the dyno. Given the engine mods how should we program the motor through the rev band? I am a rookie with this part of the project but I know many of you have already done this and know a lot. Any suggestions will be appreciated.

[jpnovak]

Your tuner manning the computer on the load dyno should know how to do this...

For known basics...

Rule #1. Give the engine what it wants.

Otherwise.

AFR 13.1 for maximum torque per given rpm. Switch to 12.8 after engine peak torque reduce torque dropoff due to reduced time of combustion. Run as lean as you can under light load conditions to improve fuel economy. These target numbers may shift as you add more ethanol (E5, E10 and E15 fuels)

Tune ignition for peak torque in a given load cell. Once you set ignition your AFR will likely change as you optimize combustion efficiency.

Make sure all your transitions are smooth so that the car is driveable.

Make sure your temperature corrections for timing and air density are properly scaled.

Otherwise, have fun optimizing your engine.

[icarp]

switch to 12.8 or 13.8 after peak tq?

[Pchip]

Very helpful; thanks.

[jpnovak]

Originally Posted by icarp

switch to 12.8 or 13.8 after peak tq?

12.8.

at higher rpm time for fuel atomization is reduced. trend toward rich to make sure to use as much of the ingested air as possible. Fuel can not be limiting factor here. I.e. you don't want to go lean under load at high rpm.

BTW my targets of 13.1 is at heavy load up to WOT. That is way too rich under partial load.

There are two books by Greg Banish on EFI tuning and setup. And another by Batt Cramer and Jerry Hoffmann. Read them. There are also many online descriptions of EFI tuning. Read and learn and then practice to see what your engine wants. The beauty of EFI is that you can experiments with a few keystrokes on a laptop (PDA, tablet, smartphone) and immediately know if you get better or worse.