Power Grid timing curve on blown Hemi Pro Mod, shifted, 2 disk clutch

Marco email me at mike.c@mindspring.com

 

Marco,

I'm sure you will get a bunch of different answers on this because there are a number of different theories on timing curves.

I don't think there's one 'right' way other than what works best with the rest of your combination and the way you are trying to run the car. Gearing, fuel system and fuel management, car set up all come into play, and the timing curve is trying to get the most out of the combination of those elements.

Also, I think too often we focus too much on the "number," that is how much timing we have out at a given time, without remembering it is relative to what we are pulling from. Pulling 10 degrees from a combo that has a 165 degree head and already at 800 degrees by 30' is going to be a lot different from a 135 degree head that is only 700 degrees. Camshaft profile, heads etc., also come into play because it affects where the engine makes torque. A lot of the technology out there today is aimed at making upper rpm power, so even though it may be a more powerful engine, it may make less torque at 7500 than what you ran 4-5 years ago. This all goes back to the 'relative' aspect of it, especially if someone tells you 'well I take 15 out at .4.' Same concept can be applied to leanout jets, but that's another discussion.

Now here's my theory on ramps. The shorter the wheelbase, the more important it is to ramp the power out (with the exception of at the initial hit). I think if you knock too much power out too quick, you run the risk of setting the front end down and getting the car flat footed, unloading the rear and/or sticking the tire, driving over it into weak shake. Now it doesn't have to be a huge ramp, but any slope is better than a "step" straight down.

I think throwing all the power back in in a flat step up is problematic for several reasons. If you are at a stop sign on a wet road, are you going to stomp the pedal to the floor or are you going to ease back in. Same concept with what we are doing with the aggressive ratios we try to run these days. Every blown alcohol combination generally has a range from 1.5 to 2.0 that, depending on the track conditions, you are not going to knock the tire off no matter how much power you throw at it. Obviously with an all-in step, you have to be on the other side of that line. I think this all-in step leaves some on the table, because a ramp could have been started much earlier, gradually putting power in where you had power out. Often times you will have an earlier point to get the power in this way vs just shoving it all back in at 'x' seconds.

Another thing that we see with these big swings in timing to get it through the shake zone is even with a ramp, it will flare the clutch or converter when you ramp it in. If it doesn't it usually will try to hike the front end up.

All of this said, I have heard of some pretty fast cars in Pro Mod and Top Alcohol having step timing maps instead of ramps. These are just my opinions based on my years of power management. If anyone wants some further help, shoot me an email at will.hanna@insidetopalcohol.com.

 

Something has to give to get the car going. Either the clutch/converter or the tire. If you run a real tight converter or a lot of base, you will see minimal flare of the motor, and it will lay over and 'angle' up to the shift more so than a looser set up that will 'flash' to a certain rpm, then kind of flat line over to the lock up/coupling point where it ramps to the shift.
I don't know that you could achieve total lock up, but there are certainly teams that are trying to get real close to that. That's why some TAFC teams are leaving north of 8000 now to get that plate load from the counterweight up (along with boost/inertia).

Running a lot of ratio and having a good amount of clutch, I prefer the motor get a little ahead of the clutch/converter early so it's slipping there, and not just trying to spin the tire. Don't get me wrong, I love a 'controlled' spin as much as anyone, but the more static or with a tighter pump/stator combo, you have less of a buffer there and any miscalculation will result in it smoking the tires at the hit or very early.

There's plenty of times I have a great idea on paper and the car just wants something else.