Jay Wellwood

Hey Gang-

As the topic above suggest, I am searching for information for an upcoming project.

Since the 928 4V heads are very similiar to the 944 4V heads, I figured I could get some easy answers here.

Some of us 928'ers have noticed that the 968 exhaust valves are a bit larger than the 928/944 exhaust valves. However, they also require that the seats be replaced - anyone here do this? If so, any part numbers/hints/tips that you'd like to share?

Also, who here has had head/valve work done by a shop and would like to recommend their work?

TIA-

keith

Without more extensive work I don't think you'd like the results. Seems to me the engine breaths to well anyway. For the bottom end that is. It would be different if it were a 9000rpm motor.

keith

Lets Turbo it!

Jay Wellwood

Hehehe....I hear ya. Bit of a problem with available real estate in the 928 engine bay though. I know of 1 turbo'd 928 (a Callaway job), so it IS possible, but again, very tight quarters.

Geo

It doesn't breath all that well. Have you seen how the dyno charts drop pretty fast between 5500 and 6000 rpm?

Jay, have you contacted Jon Milledge? I'm sure there are others such as Don Istook in Ft. Worth, but Jon seems to have done pretty extensive dyno testing. I'd be surprised if he hasn't played with larger valves already.

Danno

There's a magical number that's the ratio of intake to exhaust port sizes. The valves need to conform to this number as well. Then there's the cam with its lift, duration, and timing. A lot of the dropping torque-curve is due to the cam-timing on these cars. Retard the intake about 10-degrees and you'd be amazed at how much hi-RPM HP you'll pick up. Adding about 20-30 degrees duration helps too.

Geo

To really take advantage of this, wouldn't it require remapping the DME because wouldn't this retard the ignition timing as well?

It kind of bothers me that we cannot adjust the base ignition timing in these cars. A few years ago I went to a dyno day where every car picked up hp largely by playing with ignition timing. The low was 1 hp and the high was 7 hp. It strikes me that there may be noticeable free hp available if we could simply adjust base timing.

Jay Wellwood

Magical numbers - first I've heard of this approach Danno. That is not to say that I don't believe, just never heard it before.

Any additional info here? Just curious, maybe you could point me in the right direction. I'm all for mathematics!!!

In as far as breathing capability, folks - remember - this is an application of 944 experience/tech to the 928 motor. You guys have delved much deeper into your cars/motors than a vast majority of us 928 owners. We're trying to learn from your experiences.

That being said, there are only a few of the 'stroked' 928 motors out there, and one aftermarket group/supplier would like $25K for one installed out the door (you provide the car) that I know of.