Controling boost at the hit

I'm struggling with traction at the hit. BBC Blown Alcohol Fuel Altered 466", 14-71 HH set up. I use a 44 mag and a grid. 5800 stage RPM. About .25 to 1 second prior to releasing the clutch, the boost numbers go from 8-9 pounds to 20+. This hits the tires hard. Spikes the driveshaft speed at .6 seconds, .25 seconds, and .55 seconds so its bouncing the tires. We have raised and lowered tire pressures,( 4.8 to 5.7) raised and lowered the bar, but can't control spin. Got to looking at boost and see its way up there. thought I was using the grid to control max RPM while the blue wire is activated. Am I missing something in the grid??

We've been .996 - 60' at 8 pounds boost, but at 20+ were 1.03 to 1.06

Should I be looking at a throttle controller??

Any help would be appreciated.

Catman

 

What kind of tire ? More pressure more traction Use the grid to limit timing for first part of the run to control wheel speed .you should be able to have 20 plus lbs at the hit and control it........And we can go for pages on your clutch set up ....what kind do you have? whats your basic clutch set up

 

34.5-17-16 Hoosier, Taking 3* out at .1 into the run starting at 35*
10" triple, small, small 6 turns base, 53 grams total. No disc wear between runs. (.001 - .003) 5.0 rear gear, 1.94 low

 

We added fuel to the launch. We could tune our launch very well with launch enrichment. We set the high speed to open just after the clutch locked up. We tuned the low end separately from the high end. We simply varied the combination of main bypass and high speed bypass jet sizes to meet the low end and high end targets.

Bob Szabo
bob@racecarbook.com
airdensityonline.com

 

Try a different low gear.

What is DS at .1, .25 and .5?

 

.1 = 1075 .25 = 2145 .50 = 2091
driveshaft spikes at .06( 1189), then .25 (2145), then .54 (2130)

 

You could raise the tire psi 1/2 lb. or
raise wheelie bar 1/2 in
Or take 5 out instead of 3. But you need to take power out at shift to calm that spike down

 

Take some base out to see if the DS at .1 is lower. Next try more timing out at the hit. Also look at low gear change.

 

Thanks Will, you are right, we have an old style long bar currently. And yes, it flexes. Have the pipe and pieces to build another . Have held up building until we could get some answwers on correct length. So instead of a 7' bar, more like 5-6' ??? More like a fuel FC bar like TJ's or Capps??

 

I would take about 3 turns of base out of it.
-Dale

 

I'm kinda surprised by the responses here. It's sticking the tire and then not making enough power to smoke the tires when it bounces. You can get rid of the bounce a few ways, but more power seems like a potential option that nobody mentioned?

It worked better with a lower stage rpm but then I'm assuming he cranked it up in an attempt to go faster.

The problem I see is that he didn't crank it up enough and then got sidetracked because of the bar not being able to catch the squat. I can see the potential that a little less base would give him more rpm/power to stay up on the tire at 0.5, so are you already planning for that when telling him to take timing out?

 

35* and only 3* out at .1 (where the damage has already been done). Add in that low gear and the thing is on kill.

 

Max and Will are on to it. We had similar when we had the long bar. We put some bracing in it to stiffen it , and that helped , but the short bar is the go, and with your set up have it low , so its trying to smoke the tyres. Need base out as well.

 

We have a switch on the clutch pedal set at .000 travel so when the clutch is fully released it activates the launch retard

 

I would run a 4.56 remove 4 turns of base add 20 CWT 6.5 air in the tire drop 10 timing .1 into run ramp it back in @ 1.5

 

Made 3 passes on Saturday, 1st pass pulled 6* at the hit then ramped 4 back in by .7. Pulled the motor down pretty hard for
1.3. 1.02 60 and a 4.27. 2nd pass pulled 5, left higher(5800) and took 1 turn of base out. Improved.... 3 rd pass, 1. More turn of base out. 10 grams off the clutch, 1.06 60' but rear wheels tripped the lights Seems to be responding to less base, graphs looking better Still no clutch wear.