[Formulajones]

Originally Posted by JLMounce

One thing to keep in mind is that as the cylinder bore increases, the flame propagation slows down, which requires a bit more timing lead to reach maximum power.

I've been doing a good bit of tuning on my engine this summer and most of what is working well for power and heat management has been almost exactly the reverse of what many people believe is what needs to be done with these cars. Including myself.

My combination is a +0.040 455 with the factory 4.21" stroke. It uses KRE D-ports with a 2.11/1.66 valve arrangement with Jeff's 310 cfm port. Port matched Torker II, a moderate 240/248 on 112 hydraulic roller and a FiTech system fuels and provides spark.

What I've found is that having more timing in the curve, while simultaneously slowing that curve down has resulted in the best power and street manners. I've also fattened it up more than I did in the past. I'm not saying that works for every engine, but it's working well for mine.

I idle the car around 13.5:1 afr with 22 degrees of timing in it. at 1100 rpm and increasing MAP, I don't drop the timing down further. I command 25 degrees at 1100 rpm and 95kPa MAP readings. At 3000 rpm the spark curve is around 34 degrees and between 3000 and 6000 rpm another 3 degrees is added. This puts my 36 degree total timing figure right at around peak torque that occurs at 4600 rpm.

My engine is very knock tolerant and it will handle a lot of timing, which is one of the reason I'm able to have a bit more in it everywhere. But in my case a slower curve is working a bit better. At cruise, I'm only adding around 5 degrees of additional advance and I'm targeting between 13.7-14:1 AFR. Fuel mileage has actually picked up a bit even though I'm running the engine a little richer.

For WOT AFR I command 12.5:1 that tappers richer to around 12.3:1 by 6000 rpm.

I've explained a lot of that in the past. Leaner AFR's don't mean better fuel mileage. And with today's fuel mixed with 10 percent ethanol stoich is only 14:1. Typically anything with camshaft overlap wants to idle richer anyway cause the fuel gets diluted. I usually idle my stuff in the mid to low 13's AFR as well. That's just where they end up for best vacuum and idle quality, along with 25-ish degrees of timing give or take.

I find on the dyno the engines respond well to more timing at the higher rpm ranges just like you described. That's where electronic timing control has an advantage, I can put an additional 2 degrees above 4000 or 4500 rpm. As long as it's above where peak torque occurs it's usually worth a little power.

Generally speaking where peak torque occurs is where detonation is most likely. In that area I'm more careful with total timing and a little richer in fuel, then add timing and less fuel after that. That's where EFI and timing control is nice as I can tweak this area. You can see it on your ve table.

All my tuning at the track and dyno are at sea level but I live at high elevation. Although higher elevation tolerates more timing and wants less fuel I generally don't touch the tune because I frequent lower elevations and race down there anyway so I just find it easier to leave alone. It's not like they get stupid rich at 6000 feet anyway and a pinch more timing won't bring all the power back you lose at elevation anyway. With EFI closed loop compensation adjusts the fuel as well which is a nice benefit.