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Originally Posted by Blown353
15 degrees is VERY low timing. I would keep bumping it up and keep a close eye on the power numbers and the plugs. I'd be willing to bet it will run best somewhere between 24 and 30 degrees under boost on 91 octane. You're probably leaving 75-100hp on the table running only 15 degrees of timing under boost.
What heatrange plugs are you running? Keep an eye on that too as you bump up the timing.
With my blowthrough carb setup on 91 octane I was running the distributor locked at 36 degrees, plus another 14 degrees possible with vacuum advance. The BTM box pulled it down to 27 degrees at 15 psi of boost. That's with 15 psi of boost, no intercooler, 9.25:1 compression, and water injection.
Another thing, don't trust the knob on the BTM. Start the engine and run it and use a hand pump with an accurate gauge to apply pressure to it to the BTM simulate your maximum boost, then adjust the knob to your desired timing number while watching the pointer with a timing light. The numbers on the knob aren't really that accurate. In the ballpark, yes, but not exact.
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I agree with the knob, but I do have fast burn heads. Do you think that the fast burn heads require less timing under boost? I heard that they do under N/A.