acceleration help

see timing map below.



see dip in rpm and g meter when converter locks up pulls motor down and quivers tire i assume because wheel speed is building and then drops and tire starts to roll over itself a little.


question is to stop the quiver and keep g meter climbing should i change timing map?

60's are .988 and wheel speed at 1 s is 2800

top dragster converter car 1471 chevy

thanks ITA

 

What rear gear do you have ? My own thought is the wheel speed is to slow

 

389 gear for 1/4 mile racing.

Have the ability to pull some fuel with electronic lean out but not currently in use.

 

Why a 3.89 gear. ? 4 speed?

 

What’s the end goal? Consistent back to back runs? Go faster? Quit shaking the tires?

 

3.89 gear to get motor rpms where I like...shift 7600 cross 7800. 2 speed PG 1.80 low.

End goal is to stop the quiver. Assume the acceleration dip is causing it??

Mike-turn the lean out on while on 2-step and leave on for how long? What about turning on again at bottom of high gear? Again for how long? Another question: shifting on rpm is somewhat variable it seems. So would i need to switch to time shifting. If wanted to stay on rpm I think I could use a relay and I believe grid shifter pulse width is adjustable to activate lean out as well??

 

FWIW Casey, I don't pull any timing till .1-.15 out to get wheel speed.

You might try to bring more timing back in sooner......looks like about .4 out it wants more power.

 

what Brian said^^^
hit it with full timing for the first .1(tenth) and then ramp it in faster.
I bet it will take it all by 1.0sec without a problem.

 

Last two posts are good advice, then you can play around with rolling the timing up or down after that to suit your needs. There are other ways to accomplish what your trying to do, like blowing a jet open or using a converter dump. Maybe you get a good base timing curve and then play around with opening and closing some jets.

 

I tried to PM you, doesn't seem to be available. Is it a "lockup"? Looks like a gear change occurring.

 

No lock up

 

What tire are you running?

 

Not sure I understand? With his current timing curve, the timing is out while he’s on the brake.

But I think you’re saying that after he puts the first dot at 0 retard then the grid has a .030 latency vs the programmed curve? Is that a known limitation of the grid? Is the latency the same no matter how far you are from brake release?

I could see if you put a dot at .001 after brake release that there could be some latency, but I would expect it to be at the third decimal and that anything after .01 would have 0 latency.

 

Will, have you considered that the pinion is rotating much, much slower than the crankshaft at the hit and shorty thereafter? I'm not arguing your point about the timing delay because you would know from experience. Just thinking the crankshaft speed would make for an accurate resolution compared to the driveshaft.

 

While I'm thinking about it, do you have any idea why I have to static set my crank trigger pick about 6-8° before the point I want my timing? RCD hub and the long skinny pick up, MSD 8+ with the Grid.

 

If I’m on the chip at 4000 rpm, the next spark plug will fire less than .003 after button release. As the motor accelerates, this time goes down. There should be no reason (other than crappy design) that the grid can’t fire that cylinder at the prescribed timing for .003 into the run. Feel free to check my math on the .003 number, I haven’t had my coffe yet this morning.

I’m not doubting Wills experience, just saying that if there really is measurable delay these are the possibilities I can think of.

1. MSD cheaped out on either the design or construction


2. The instrumentation Will was looking is inducing a time shift in the recorded firing pulse

3. the grid data and racepak data are not properly time aligned for one or more reasons