Need some ideas on this issue, if I am on a very well prepped track I typically do not have a problem, but when prep starts to go away a little or late rounds when not many cars are going down the track, my car will lose traction bad at approx the 330' area or if it hits any bumps. I know there could be a million things, but here is my setup and a little history: Tube chassis 55 Chevy, 2528 lbs. race ready, 54.7% front weight, 45.3% rear weight, 1070 HP, powerglide, 4.30 gears, 4 link I.C at 57" and 6" up, lower bars 1.5 degrees down, pinion angle 2 degrees down, 4 link has no pre-load, setup to squat, launches and drives perfectly straight, M/T 3084S 33x16.5x15 tires set at 6.7lbs., Strange front struts set at 1/2 turn from loose, JRI nitrogen rear shocks set 50 psi and at 3 compression (only have 5 clicks total) and 7 sweeps from soft (has 12 sweeps total) 100lb rear coil springs, car runs high 4.90 - 5.0 @ 137 mph. I've tried every shock/strut setting, multiple 4 link settings, multiple tire pressures, new tires, checked front end alignment, nothing helps and it costs me in late rounds because it will spin down track. My next step may be a set of Santhuffs or Penske rear shocks as I feel the JRI's do not have enough adjustment or will not keep the weight transferred, but don't want to throw money away if I have a different problem, any thoughts would be appreciated.

This message has been edited. Last edited by: Doug,

Increase pinion angle for traction down track. I typically run around 3 to 3.5deg down on diff

I have read if rear compressing, then softer compression and stiffer rebound setting. If rear separation, then stiffer compression and softer rebound.

If/when making 4 link AS/ IC changes, having rear shock travel sensor/s DA can help determine what is actually going on in the rear with each change.

My question is, “what is better at 330’, rear compression or extension?” My vote is extension, but I could be wrong.

quote:

Originally posted by Bob Payton:
Increase pinion angle for traction down track. I typically run around 3 to 3.5deg down on diff

Bob, that is something easy to try, Thanks!

Put a grid in it and take some timing away x sec from launch

PM sent also.

This message has been edited. Last edited by: ski_dwn_it,

Take compression out of the rear shocks. Let the car ride the bumps smoothly. You will be surprised.

any change you make will affect the starting line also, but you can adjust for that. Shorten the ic,less air in tires and compression midway or less providing internal shock settings are not stiff. If so go lower

What is your shift rpm? Have you played with that?

I am going to make the assumption the jri shocks are the sportsman series? Car may be too stout for those

Penske 8300 or JRI st08 will help. Give Dave a call at competitive suspension

When my altered had that problem a wing really helped and faster you went better it was. Made the car faster, more consistent and easier to drive. Do not know if you could put a wing on your car that would have much downforce but I think it would help if you did.

I THINK what radial tire guys are doing to fix same problem is using really long rear shocks with very tight extension and then on the fourlink they are using short, high instant centers. The short, high instant center wants to make car separate and tight extension on shocks slows it down so they are still getting separation almost all way down track. They may be using electronic shocks that are basically solid at hit and loosen up some as it goes down track? Separation is trying to plant rear tire. Maybe watch some of the radial tire guys that are going so fast and ask around. I think that is what they are doing.

Getting your car closer to 50/50% weight would help IMHO but would make your car try to wheelie more.

With four link setting same as weight when you move it around it changes how car reacts at the hit and at finish line. When you take away from one you add to the other. Longer, lower IC may help at finish line if you have enough traction at the hit. A wing does absolutely nothing on starting line but as speeds increase it adds weight to rear.

So what you are trying to do basically is get more of the weight of car on rear tires near finish line. To me that is basically physically moving weight bias more to rear, or moving four link or adding a wing or a combination of all.

And you want to do all this with out hurting on the starting line.

PM sent.

quote:

Put a Grid in it and take some timing away x sec from launch

I agree with this, and a plan “B” could be a great option that Grid could provide in a moments notice if desired. By this I mean you could activate the desired retard and time period with a simple toggle switch. Knowing what this will slow the car in advance would allow for accurate dialing if one wants to run all out prior.

This selective retard could also be accomplished with a delay box that has a timer output and analog ignition with retard input or digital with retard input.

This message has been edited. Last edited by: markemark,

Put a wing on it.
My buddy said it made a night and day difference down track on his 5.40's / 127-128 door car.
He had lost a lot of rounds having to peddle down track.

quote:

Originally posted by racerdude2054:
What is your shift rpm? Have you played with that?

I am going to make the assumption the jri shocks are the sportsman series? Car may be too stout for those

Penske 8300 or JRI st08 will help. Give Dave a call at competitive suspension

Yes, they are sportsman so I agree that I might be at the point of needing an upgrade. I'm shifting at 7000 rpm, I've tried a few different settings and it doesn't make any difference.

I changed out the rear JRI shocks for a set of Afco Big Guns 7" stroke with 100lb. springs and it made it much better, picked up in 60ft and was good down track and was able to pick up a win last weekend with it, this was a Top Sportsman/Top Dragster Q32 race where the 2 winners run off for overall series winner. I had absolutely no problems until that round where it spun a little after the 330 again, I was surprised because over 2 days, qualifying and eliminations, I had no issues and thought I found and corrected the issue, back to the drawing board. I went to the front of the car this time as the shock sensors are showing that the car porpoises down track, I have 8" 350lb springs on the front and the struts are not installed at the proper height, they are 2.5" travel and installed with about 1/4" extension left. I will have to change the springs as I cannot adjust the ride height enough to get the struts in the middle of the travel, the front weight is 1383 lbs. with driver, what spring rate would be best? Strange recommends 250 - 275 according to their chart and is it possible that the front suspension is at max extension causing this problem? Thanks for any advice!