Join Date: Jan 2008
Location: Seattle, WA area
Re: 351C results - jumpy curve
The biggest issue with giving advice on a single dyno sheet, is that no changes were made, which would have helped to indicate what was causing the anomaly. I realize you only did it for fun, but numbers from a dyno are not worth much unless they are used for comparison to each other with changes. It is quite dangerous to make a suggestion without more info, but my first hunch is over-advanced ignition.
I say this because your AFRs are quite rich from 3700 to 3900 rpm, yet the engine likes the extra fuel. It should not, and should have lost power (assuming the AFR sensor was properly calibrated). However, richer mixtures burn slower. Because it liked the extra fuel, this may be a clue that the engine could be over-advanced, and the extra fuel caused a retard effect. This retard effect could then increase power. Coupled with the momentary power drops (bucking) increasing from 5100 rpm and higher - this is my first guess.
Again, without comparative information, this is just a hunch. You can try driving the car, reducing your base timing 5° to feel if there is an improvement at higher rpm, confirming over-advance or not. Second is your fuel curve, which you want relatively flat, and at the AFR that the engine makes best torque (with correct timing). It would appear your carb needs a change of jets and probably PVCR tuning. If you experiment with changes, let us know what single changes help and what does not, and in what rpm ranges. Only change one thing at a time, or the information becomes confusing.
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Last edited by PSIG; 07-27-2014 at 01:39 PM.