wheel speed graph help/explanation - lovely commerce

need a little help getting down the lovely commerce track.

below is wheel speed data (started from g-meter movement) and graph snap shoots from lodrs race at commerce this past weekend. Tire shake got me both races and I have to go back to this great race track this weekend and try it again. Need some tuning advise from ITA. Below is what I'm doing.

Top Dragster, ohlins monoshock, 540 BBC 1471 HHR, Powerglide. Pulling 7* for .75s at the hit. 5.5#'s air in Hoosiers every pass.

Please look at the below let me know what is happening with the check mark at the hit. Don't really know how to interpret what is happening. I don't feel shake every run but people on the starting line always say my tires have got to be shaking. I noted where in felt some shake.

Question is what changes do I need to make to get down this great NHRA track.






thanks very much in advance.

 

I don't know about your type of car, horsepower etc. It really stands up on the graph in the first .25, .50 and .75. Then it completely reverses. That is a lot of tire pressure for a Hoosier in my opinion. Its pulling down and would run over the tire when it distorts at that point. I would try 4.5 or 4.7 to start. If it spins hard early you can try and control the launch rpm to slow the driveline speed down. Or you can change the pulley to give it some power ..lol One of those glass half empty or full statements. Of course I don't know what you are doing with the timing or if you have control on it. It has to free up the tire or you need power to keep it up on the tire. Black tracking cars haul ass and I know about TAFC and NFC. if you go from a track that is med good and go to a killer sticky track, with the same power....common sense says the track will make the tire the meat in the sandwich. You need less contact patch or more power......

thats my humble opinion
Dale

 

reply

thanks see below

This in on 6.40 TD.

launch 4200
stall 6600
msd power grid powered by MSD10
1.80 low gear
3.90 rear gear
34.5/17 tire

 

I have a pretty similar combo except 1.69 low gear. What is your base timing? I can go .990 60' with more timing pulled. When I've tried to go faster, it won't make it, but I dont have alot of runs under my belt yet. How fast are you going to 60'; how fast do you want to go?

 

Reply2

60' times are in first pic. Initial Timing is 30. Not trying to go faster just would like some advise on how to get those humps out of driveshaft graph at the lovely commerce track. This was last weekend LODRS and going back for nats this weekend. I don't have this issue at other places. Gators for instance and other tracks was a smooth arc every pass. Of course you get the occasional spin and 60' shows it as a +1.00 when usually .990. So this just happening every pass and 60's being less than 1.00 is why the questions. Also would like some education on exactly what is causing the check mark. Is spin/hook/spin/hook?? Is it trying to get up on tire then not able too?? Taking to much or to little timing or shorter or longer time so that doesn't try to hook up after the initial ramp up? Just a little education from those of you that know what your looking at.


Thanks

 

Worse track = more wheel speed; I would turn the power down farther. Checkmark the timing curve where the tire is standing up. Nothing wrong with going 1.05 if you need to.

 

Reply3

Finally had time last night to check old numbers. Typically a smooth launch curve has about 200 less at .25 and also .5. What I was concerned about was backing down power and shaking more since it seemed like I was on the edge and actually shaking causing lose of round in both races.

But I witnessed them start spraying track at the tree during the second race and this is exact place me and my neighbor starting shaking. I assume they did the same the first race. So basically that's bad track prep but will probably happen again at LODRS but probably not at nats??

So I could lower launch rpm about 400 rpm or pull 2-3 more degrees timing. Lowering the rpm would hit he converter stall harder and might pull the motor down harder and cause lower power shake. Or that may be what's happening now.

I guess I need to pull 10* instead of 7* and make sure it's back in just about the tree.

So new question??

Tree seems to be about 40 ft down track and I was ramping timing back over .75sec. It takes me 1 sec to go 60 ft. So assuming that's a linear speed I could plot and see where I am passing tree an make sure timing is back in. But let's say it's at .5sec. Is that to fast to ramp timing back in??

 

Revelations

Thanks all. The responses are making me anyalze my data thoughly.

I went back and looked at all me runs over several different tracks this year and found that I have a plateau at .4 sec even on the smooth graphs. EVERY ONE at .4 even when wheel speed is lower by 200 rpm at .25

So like Will indicates I believe it is either spin/hook or my concerveter is starting to lock up and drag wheel speed down.

The peak or plateau is not always at the stall speed but it's close. A few times it was at stall speed.

 

What does it do if you don't pull any timing? For what it's worth the smaller tire radial guys play around with the size of the converter feed hole as a means to delay the 'coupling' of the converter so they don't blow the tires off. I will tell you if you go too small on the hole, converter temperature becomes an issue if you have any appreciable power. Maybe your rear gear is pulling the engine down or maybe it's time to update the converter?

 

Casey

Hi Casey,

If it helps I tuned on basically the same engine at the same track and went 6.20's only with no suspension for what that's worth.

Old dragster chassis, 1.68 first gear, 4.11 rears, worn out 34.5" and 36" slicks with some kind of awesome spray call goat piss....? seriously that's what they called it but it worked very well for softening up the slicks. I didn't have timing control to work with so we just set it at 30 on a pro mag 20, 75% barrel valve, and let her go to see what happened To my shock it ran .970 60 ft's in 2600 ft density altitude and 6.20's in the quarter. Seems like commerce is a great track. Was only giving the old worn out LF K8 deal 38 percent o.d. and launched at 2600 rpm recorded. Motor never went over 8,000 rpm. I used one high speed lean out and timed lean out.

Let me know if I can help, I still have most of the data. The convertor is the only thing I don't have info on.

Best wishes,
Trevor Sherwood
Soldierboy0098@yahoo.com
727-364-4368