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Dynamohum Dynamohum is offline
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Join Date: Jan 2008
Location: Midland Ontario Canada
Posts: 173
Originally Posted by wanabe911 owner View Post
Just took my car for a ride and it started detonating really bad on the top end so I shut her down, so what do I do now? Do I have to install the IC, lower the boost level? Pull some timing?
Drop the boost or run a min of 107 Octane gas. I did some quick calculations using this calculator;

95mm Bore = 3.74
74.4 mm Stroke =2.92
Ve = 92% As suggested to me by another member here, I was told to reverse calculate known values from Porsche engine HP data to arrive at VE and subtract a few percent.
Standard U.S. compression on 3.2 = 9.3 to 1
Your boost pressure = 10 psi

This means that you are running a Boost compression ratio of 13.84 to 1 @ 10 psi boost and need a min of 107 octane if you want your motor to stay together

Also you need an IC or W/A to cool the charge air. Personally for both our applications W/A is the quick fix as this will have the same effect as increasing your octane and reducing the charge temp at the same time. Considering where you live I would do both the IC and the W/A

Try dropping boost pressure and see what you and your motor can live with. Without an IC or W/A its all dependent on the ambient temp and octane of fuel you can find your AF ratio and ignition advance. Also what plugs are you running?
You need to drop about 3 heat ranges cooler now that your increasing your compression pressure under boost! To hot a plug will cause pre-ignition which if far worse than Detonation and you motor will only last a few seconds.

Do yourself a big Favor and Do Not Run your engine into detonation, it will do major damage

Please go to this link and read All the pages.
Thank You for your time, Paul. We do because we can.
87 911 3.2 (Turbo conversion, build in progress, Thermal Barrier Coatings, High Pressure Dry film coatings) Modified heads, boat-tailed case, ARP hardware, OBX Header, 930 clutch disk, G50 Trans
89 5.0 Mustang convertible (For Sale)
Old 02-06-2009, 03:09 PM
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