3.0 EFI Cam Choice

[1972_911T]

Whats the best cam for use on a 3.0 engine with EFI. Engine will be 9.8:1 twin plugged and run on ITB's is 964 profile the best choice using the original CIS pistons?

Steve

[Scott R]

for my bitz kit the 964 had a rough idle below 1100, hard to say if it was the CAM, however that was the big change I made during my rebuild. Well, that and higher compression.

[kenikh]

The sky should be the limit on ITBs with that CR. You have no need to mitigate reversion problems with that set up. I'd run Mod-S cams of Mod-Solex cams. Lots of fun.

[jpnovak]

A 964 or Webcam 20/21 grind is about as aggressive as you can get with stock CIS pistons. You could have valve pockets cut in them, loose a few tenths of compression and then run whatever cam you want.

I am sure John Dougherty (camgrinder) might have another suggestion. give him a call or email since you are across the pond.

[kenikh]

Good call, Jamie. Totally forgot to mention the piston relief cuts. Still shouldn't drop CR below 9.5:1. Still a very, very good CR.

[1972_911T]

Originally Posted by jpnovak

A 964 or Webcam 20/21 grind is about as aggressive as you can get with stock CIS pistons.

Are the webcam 20/21 grinds similar to DC21? or totaly different. Will wilder cams cause problems with MAP signal at idle for MS or is this what Kenik means with his port reversion comment and ITB's?

Steve

[jpnovak]

Any cam with a narrow lobe center (lots of overlap) will cause reversion issues at low rpms. This means you might have problems getting a good MAP signal at idle. Are there ways around it? Sure. A few examples would be: increase idle speed, run alpha-n at low rpm and switch to SD off-idle, use a ballast tank for the MAP signal , and have custom cams made with a wider lobe center. The obvious answer would be to just keep your foot in it.

I am currently using a ballast tank for the MAP signal and it really works to quite the noise. Think of it as sending the vacuum lines to a tank that mimics a common plenum. I am in the process of having cams made with John. I am getting a DC40 made on 108 lobe centers. This will broaden the torque curve and reduce the reversion issue. Similar tricks can be played on other cam grinds.

BTW, with MS you w ill want a MAP_dot signal of less than 40 at idle. Mine was almost quadruple that until the ballast tank was installed.

[Jeff Alton]

A for MAP signal, I am using a custom made vacuum manifold that each throttle links to. My 3.4 has DC44's on the 108 lobe center and my load signal is rock steady, no pulses at all.....

Cheers

[safe]

Originally Posted by Jeff Alton

A for MAP signal, I am using a custom made vacuum manifold that each throttle links to. My 3.4 has DC44's on the 108 lobe center and my load signal is rock steady, no pulses at all.....

Cheers

Do you have any pictures of that?