Larry Parker

Looks like my SC rally build will begin sooner than later. I recently purchased a '81 SC for stage rally use with the intentions of starting the build later this winter. While doing a valve adjustment yesterday I stumbled across two broken head studs on the exhaust side. With this in mind, I plan on tearing into the motor soon. Right now I am trying to make plans to build a strong reliable motor with good torque and power in the upper 200's. Im partial to a high compression engine with twin plug and PMO carbs or ITB's. Based on initial reading, im not finding many people with twin plug running over 10.5:1 on twin plug despite the 964 and 993 motors running well in the 11's on pump gas.

Thanks
LP

pu911rsr

LP,

I don't think you want to go over 9.5:1 with a single plug ignition and 10.5:1 with twin plug with the SC motors on pump gas. The 3.6's had much more sophisticated engine management control systems. The good news is the big port SC motors will make very good power w/o resorting to really high CR's. Ping Steve Weiner- he has forgotten more about this than the rest of us know.

Phil

Reiver

The 930-10 ROW I have has the stock 9.8:1 single plugged "But" also has a some different CIS elements that deliver more fuel (fuel head?) and a different dizzy....also the larger runners and cooler plugs are required.
I'd guess that would be the max with a single plug and pump gas.

Larry Parker

No intentions here on running CIS... It looks like the SC/RS ran MFI, single plug and 10.3:1 which seems like a possibility...

Steve Weiner-Rennsport Systems

We have an SC/RS here for restoration, 2nd one we've done.

Those cars needed to run reliably on local fuels, hence the moderate CR. If you need high compression for whatever reason, plan on using 110 octane leaded race gas and you'll certainly feel the difference.

Larry Parker

Steve,

Rally-america rules limit us to running 100 oct unleaded... The rules don't govern motors closely like the PCA, so I can run just about what ever I want. If 10.3:1 and single plug is an option, then that's one possible direction. If going twin plug is a must and higher CR's are safely achievable, then maybe that's an option too. I see that Wossner sells a 95mm 11.6:1 piston and that's what peaked my interests.

Thanks

Larry

Steve Weiner-Rennsport Systems

With 100 octane, you should limit your CR to 10.5:1 & twin-ignition so you can run sufficient ignition advance for good throttle response & acceleration.

JE (and others) can make you whatever you need.