Cam timing on custom engine

[hbrand]

I have a 1982 Porsche 911, Euro 3.0, 9.8:1 compression, big intake and correct fuel distributor and distributor, 964 cams.
I had all the heads rebuild and would like to set the cam timing to decent torque and still good RPM.
Using stock exhaust with cat bypass.
What would be a good cam timing considering my engine specs?
Thank you for helping, Harold

[Classic 911]

Hi. With the exact same spec’s as yours included SSI’s I used 1,35 overlap on my previous build. The engine made very good torque all over the powerband and revved very good. HP at the cranck was 250 and torque 298Nm / 220 ft lbf.
It would help your engines performance quite a bit using SSI’s instead of original exhaust.


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[AndrewCologne]

@ Classic 911
A 3.0 ROW with 9.8:1 CR ... all stock ... and here just SSIs and 964 cams will bump up the power of about approx 50 HP?

@hbrand
964 cams will be set on intake to 1.25 at overlap per default, ... but you can advance a bit more like Classic 911 did. To achieve even more torque you can advance even a bit more, .... but all advancing approaches beyond the factory specs makes it necessary to check the valve piston clearence over all 720° of the crank.

[hbrand]

Thank you for your help
Harold

[Classic 911]

Originally Posted by AndrewCologne

@ Classic 911
A 3.0 ROW with 9.8:1 CR ... all stock ... and here just SSIs and 964 cams will bump up the power of about approx 50 HP?

@hbrand
964 cams will be set on intake to 1.25 at overlap per default, ... but you can advance a bit more like Classic 911 did. To achieve even more torque you can advance even a bit more, .... but all advancing approaches beyond the factory specs makes it necessary to check the valve piston clearence over all 720° of the crank.

Sorry, forgot to tell that my build had 46MM PMO ITB’s


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[targa72e]

My experience dyno testing cam timing (3.0 big port stock intake, cams and headers) showed that best power was with most advanced timing you could run and still have appropriate valve clearance. The trade off was a few HP over 6Krpm for more Torque (thus power) everywhere else.

john

[mikedsilva]

Originally Posted by targa72e

My experience dyno testing cam timing (3.0 big port stock intake, cams and headers) showed that best power was with most advanced timing you could run and still have appropriate valve clearance. The trade off was a few HP over 6Krpm for more Torque (thus power) everywhere else.

john

This has been my experience too.
I normally run the 964 cam set at 1.5mm min. You really need to check your valve-to-piston clearance and from memory, the intake valve approx 12-15 deg ATDC is the critical point.

Next question is "how much clearance is enough"?

[Zuffenwerker]

Mahle says 2mm intake 2.5mm exhaust is minimum clearance. I remember reading in the early WSM though and Porsche said 1mm minimum. Interesting how most specs like this have changed overtime.

Daniel

Originally Posted by mikedsilva

This has been my experience too.
I normally run the 964 cam set at 1.5mm min. You really need to check your valve-to-piston clearance and from memory, the intake valve approx 12-15 deg ATDC is the critical point.

Next question is "how much clearance is enough"?

[AndrewCologne]

With much timing advanced 964 cams on 3.0 Engines I would suggest using pistons with valve pockets (like the 10.5:1 from JP or Woessner) to have more clearence to play with, but with these higher premium fuel octane is mandatory.

[hbrand]

I did set the overlap to about 1.5mm
Engine started on the first try. Now running in. Then checking valve play
Thank you for your tips.
Greetings, Harold