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930turbo 930turbo is offline
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Join Date: Jul 2006
Location: Valrico Florida
Posts: 200
I've had experience with two examples of twin-plugging engines. The first was a slightly modified 1.9 liter 914. I discovered the ability to reduce the timing from 7 to 28 degrees down to 0 to 20 with much more reliable power delivery. Horsepower gains, probably not. However, there was a noticable difference through the middle of the usable power range - around 2500 to 4000 RPMs. ( I had the ability to swith from single to twin with timing adjustments from the driver's seat)It just plain felt stronger. It had a mild cam, 9.0 CR, Kerry Hunter header and Dellorto 44 carbs. I drove it almost every day and to and from Sebring to participate in several PCA DE events without a failure. The car had 25,000+ miles on that engine build when I sold it and I never had any service issues other that the usual maintenance. I was the least expensive and most enjoyable Porsche I ever owned prior to being spoiled by turbo power.
The second example was a '77 Triumph Bonneville 750 which is notiously prone to pinging. I used the experience gained to determine the advance curve which was similar to the 914, although I don't recall the exact numbers. It was nearly impossible to make it ping with the second plug and revised timing. It had to be insanely hot, such as idling in traffic for a while before it would make any unnerving noise.
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'77 930 turbo Garretson I/C 1 BAR spring, (2) '82 Triumph Bonneville Royal Wedding Edition
Past rides: '74 914 1.9 liter twin plugged track car, '83 928S, '87 924S, '75 911S w '78 ROW 3.0, '72 911T, '70 911T and various other insignificant domestic examples. Happiness is a grey tailpipe! Turbo lag......it's worth the wait!
Old 03-04-2008, 06:14 PM
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