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BlkBird BlkBird is offline
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Join Date: Feb 2002
Location: Atlanta, GA
Posts: 938
Question Excess gas consumption & bucking

Hello all,

I notice that there is another thread involving bucking but I have a 1989 Turbo 911 that has an interesting problem.

First off the modifications:
• GHL header & muffler
• Kokeln intercooler
• 1 bar boost spring
• Andial fuel enrichment system
• Modified K27 7200 turbo

I’ve also installed additional gauges to show the A/F ratio and the boost levels (replacing clock).

The car ran great when I was using the standard K27 7200 turbo putting 389HP to the rear wheels. But not being satisfied and forgetting my car is a “street” car, the turbo was modified to flow more air. It works very nicely and now puts out close to 422HP to the ground.

But the car is in no way as pleasant to drive. It’s a gas hog now and can buck like crazy when under partial boost. Of course it doesn’t always buck everytime. The shop that worked on the car says I need to drive it full throttle to avoid the bucking syndrome but to be honest that isn’t my style of driving. According to the A/F gauge the car is running much too rich but again my shop states it is better to run rich than run lean. True I suppose but my thinking is I have the Andial system in place to prevent running lean when under heavy boost. When not in boost, the enrichment system isn’t on and I thought I should get pretty good gas mileage.

So to my questions.

1) I was told that part of the Andial system was to replace the size of the CIS injector. And that even when the enrichment system was not in use (boost less than 0.65 bar), the bigger injectors would put more gas in than the old “stock” injectors for the same period of time. In effect the CIS injection pulses are can only be made so small in duration, and with bigger injectors I’ll always have more fuel in the motor. The metaphor given was it’s like pulsing a garden hose vs. a fire hose. The pulses can only be made so small and the fire hose will therefore dump more gas in to the motor. Is this true? Is this how the system works?

2) I’ve asked numerous times to have my engine leaned out and was always told its part of owning a Turbo. But according to the new boost gauge I’m not in boost all that often, and when I do go on boost black smoke comes out the rear of the car. Do I need to always run rich?

3) Why did the car run so much better with no bucking when it was using the “stock” K27 7200?

I realize it is hard to diagnose a car remotely but I’d appreciate any suggestions. I keep thinking I need to unmodifiy the K27 but I don't know if that is really the root of the problem. Maybe a faulty wastegate or a wastegate that can't keep up to the new turbo?
Boost Addiction - honestly, I have it under control
1989 911 Turbo Cabriolet
Mods include: Kokeln IC, GHL Headers, Hooligan muffler, Modified K27 7200, BL WUR, LC-1 & XD-16, Bilstein Sports (4), TRG sway bars, Oversize torsion bars, Strut brace
Old 07-20-2007, 11:39 AM
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