Lowering C/R on a race motor
 

Let's say that you had an 11.2:1 compression ratio 3.8L twin plug race motor with motec engine management, TMW throttle bodies, etc. It’s tuned for race gas, but you need it to run on CA 91 octane. What do you do so it can run it on pump gas, at least from time to time?

A few things crossed my mind, including headwork, shims to space the heads up, tulip valves, an engine remap, and finally new pistons. Anyone know how the options would stack up?

Try first with running less aggressive ignition map and see if it pings. It's just a software hack.

For reference, I have a little over 12 to 1, twin plug, M48 with TMW's. I also run it on pump gas. Different MAP for race fuel. Although, I can get 93 readily available.

And yes, ignition map change is required between the 2 fuels! I have also found that fuel map differences are needed to keep desired AFR.

I'm not sure I'd recommend this by design. One may better off designing at lower CR, moving ignition and therefore better power/torque than at higher C/R with more potential for disaster.

hth

hth- couple questions:
Is your motor a 3.8L as well, or is is smaller?
The M48- do you have to load a new map from a PC, or can it store the different map in so that you can switch between them?

I agree with you by design, but this motor is already built...

dwight, how rich do you run it with the 93? do you have any closed-loop running with an 02 sensor?

TIA

3.6l
Load a different map from laptop
Target .88-.95 lambda under load (higher load, lower AFR) .95 to .99 light load-cruise, a little higher lambda trailing throttle. It's been tricky determing Alpha-N points translated to loads. All open loop at the moment.
Constantly monitoring lamda via MDD. Review data logs periodically.