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copbait73 copbait73 is offline
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Join Date: Nov 2003
Location: Chesterfield IN
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Originally Posted by beepbeep View Post

My comment was maybe a bit hasted, I wrote it after few beers. Sorry.

Engine was a turbo-converted 964 N/A 3.6 with hot cams, twin Garrett GT35R's, twin huge intercoolers, cams hotter than GT2-evo and Rochester 1000cc-ish injectors. Pistons were 993tt stock pistons and it had H-beam steel rods. It was dynoed at 2 bar using standard (?) race fuel...I forgot which sort. On ordinary 98 octane RON fuel, boost could be upped to around 1.6 bar w/o knock. It had twin plugs as well (having N/A 3.6 heads)

I belive the graph is accurate but I suspect graph assumes 100% VE and low air temp. What I'm trying to say is that typical working installation is going to have different dynamic C/R at different revs, despite constant boost pressure.

As turbochargers go trough their different efficiency ratios, so does discharge temperature. The more heat in the air, the less oxygen is introduced into combustion chambers. Also, VE is going to vary wildly depending on cams, runner length etc.

Of course, Porsche aircooled heads aren't as good when it comes to knock as modern pent-roofed 4v designs with plug in the middle, but there are numbers of tricks one can use to prevent knock despite soaring dynamic C/R ratio. Ignition retard, twin-plugging, high octance juice and efficient intercoolers are some of them.

P.S. It's quite amazing what kind of boost you can run on modern engines. I have an old Audi UrS4 (93' model) that boosts 1.5 bar of boost on the top of it's 9.3:1 C/R.
Goran, no problem on the comment. I often wish I wasn't geograhically displaced from ALL you guys so I could buy you all a few rounds.

Thanks for the information about this engine. Is this going to be a street engine?

We have talked of the importance of flowing, modern turbos and their efficiency (I like the name Garrett) and killer bar/plate charge air coolers (Garrett also).

Now assuming this engine has one other enabling technology, knock sensors, (only shown on the 3.6N.A. data point) how much have they entered into your moving this motor to very high TURBOcharged power levels?

Last edited by copbait73; 03-09-2008 at 01:45 PM..
Old 03-09-2008, 01:40 PM
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