Continuing ignition timing debate from the 416 thread.
Isn’t 30 a compromise between best power and torque? Didn’t you say earlier that it made a little more hp and a little more tq with different timing and you split the difference? But in your opinion it was negligible.
It is negligible. But for reasons I can’t explain other than what I’ve been told about how many cycles it takes to affect a change if you steady state test for MBT (or for LBT because you do fuel and spark the same way) it will take different timing than what a sweep says it wants.
When I was dealing with a chassis dyno where I worked the single biggest complaint was once the timing was set on the dyno it would take less timing at the track.
I now know that sweep testing for a curve changes what the engine wants in the car at the track.
I suspect (especially on a water brake where the sweep rate is controlled by the dyno) that is because in the car the engine gains rpm at far faster rates (especially in first and second gear) than it does on the dyno.
In the case of the wheel dyno, you are testing in high gear (usually) where the acceleration rate is far slower than it would be in lower gears.
Somewhere on speed talk Larry Meaux posted some acceleration rates for several different engine/chassis combinations and IIRC some of them were close to or at 2000 rpm/second in the car.
You can test on a water brake dyno at close to those acceleration numbers but the test is so short the data acquired would be at best too small a sample and probably they would be useless.
There are compromises in every type of testing we do. The best we can do is research what we are doing and test what we can in every different form we can.
I have not yet performed any deceleration tests because I’m not doing something I’ve never done on a customers engine. When I get my junk together I will get it sorted out and then I will do some deceleration testing and see what I get from that.
I’ve been told I will be surprised at what I see. I’ve asked several other dyno operators if they’ve ever done them and it one has said they have. Maybe that’s true or maybe they don’t want to give something away, but if the software is capable and it’s in there, someone, somewhere is doing it.