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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Paul,

Good suggestion, on the Google. I am very much in the learning stage as to cams and will do so.


There has been much conjecture as to why Porsche put such small intake ports on a 930 compared to most normally aspirated or turbo cars.

I heard it referenced once that someone had talked to a Porsche Engineer asking about this and was told it was to purposefully to limit power. Not sure I buy it.

My guess is it has mostly to do with creating velocity for better air fuel mix to help with emissions at idle. (Note the SC piston crown is also for this.)

For what ever the reason, it would seem that the 930 would respond to any thing that improves cylinder filling with such a restriction.

You can only force so much through a small hole. But why force it.

No argument that a longer duration cam might help some.

However, I suspect until the intake port restriction is addressed the potential that should come with a cam change will not be well be limited from what I think I am seeing.

Forgetting cam timing as it relates to where the TQ and HP peak's are going to be, the existing cam has the piston sweep area covered pretty well.

That is, when the piston is best moving during the intake stroke, the intake valve is mostly fully open and the port is the restriction. Not valve lift or duration.

It looks like increasing the duration is going to have the valve open longer at that point where the piston is stalled at the top or bottom of the cylinder. That can not have much of an impact.

Along with increasing duration comes about a half point loss in effective compression, earlier opening of the exhaust valve such that more energy is lost out the exhaust, and more residual exhaust pressure will remain in the cylinders when the exhaust valve dose close.

If we are going to time our SC cams to make peak HP at 5500 rpm where the stock cam dose, I suspect much of its improvement is going to be lost.

Having said that I recall Brent 930 making over 430whp through stock sized ports. He did however run a lot of boost and had ported his intake manifold substantially and nicely transitioned his injector blocks.


I have lots to learn about cams.

My biggest question is why should an SC cam improve off idle, pre-boost, or even boost onset on a 930 when a 930 cam seems better suited to be a better choice in those areas?

Last edited by 911st; 02-01-2010 at 05:33 PM..
Old 02-01-2010, 05:29 PM
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