Thread: EFI cam choice
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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
You could re-time the cams for even more low end.

If you wanted you could bump compression about a half a point by having the rods rebuilt and offset bushed about 1mm. Or buy JE turbo pistons.

Just a note, the effective compression ratio is about 1 full point higher with the stock cams longer compression stroke duration compared to a 964 cam. That is, the stock cam has a compression stroke that is 153 deg in duration, the 964's lasts 124 deg's.

Twin plugs speed up low compression ignition and can help low end in some ways more than on boost where there is not as much power gain to be had as ignition is already pretty fast. TP's also may alow running more boost with less sensitivity to detonation.

Anything you can do to reduce exhaust back pressure before or after the turbo and or restriction before or after the turbo's cold side inproves its response and extends the HP effecency range it will support.

The biggest opportunity is to manage boost by rpm. With this you might be able to run say 1.2 bar by 3500rpm. If needed you could pull some boost as you approach TQ peak where you will be most sensitive to detonation to say 1 bar, then tapper boost to keep HP withing the limits of your turbo. Porsche and other makers have been doing this for years on there EFI cars.

You should be able to use an ATM boost solenoid with your EFI. See this thread for some info about this. ELECTRONIC CIS fueling & BOOST control

If you can wade through it there is also some clues on running a lot of boost at low rpm in this thread. Cis monster

Lastly, based on comparing the area under the intake valve seat to the cross section of the intake port, I believe CIS motors are a 'port restricted motor'. Thus, opening the intake ports should help. I think opening the ports can increase air flow potential per stroke as effectively as running a more aggressive cam with the stock ports. However, more agressive cams can make there power at a hight rpm which let's them more more peak HP.

Again, this is a non tradational approach to tuning a 930. However, others have gone this way and it seems a be a very good fit with the stock wide ratio 4 speed. It trades peak HP for greater average HP.

Could be fun.

Last edited by 911st; 10-18-2010 at 08:13 AM..
Old 10-18-2010, 07:52 AM
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