Visit The Dirt Forum for More Information

Author Topic:   HELP ! any ideas Jammin ?
rjs
Dirt Full Roller

Total posts: 38
posted March 25, 2001 10:53 PM
Here is the deal. WE build our own cars and love to try new stuff,but have experienced a problem and maybe someone can help. To set the stage: Molly car/metric frame,total weight 2200 w/o driver,59% rear weight,51%left,51.5 crossRF,LR , 3link, lower trailing arms 39 inches long up hill 18 degrees, Push bar 18inches long, rear end mt forward 3 inches of centerline of rearend, uphill rearward 23 degrees excessive rear end lift move down to 17 degrees lose forward bite. I know push bar needs to be longer but no room. Tried short trailing arms 12 and up hill 20 degrees and still no forward bite. Next we're trying a long pull bar with 3 rubbers. Tried solid and rubber push bars no help. Tried more rear weight 62% and will not turn. I mean we run top ten but that's not winning! Need better geometry. Also tried 90/10 facing rearward at different angels no help. New tires(2inches roll out) pleanty of side bite seems to have good antisquat, reacts quickly but short forward bite! Any ideas other than going back to base line. Try anything twice (first time could have been a fluke).

jammin
Dirt Administrator

Total posts: 3279
posted March 25, 2001 11:35 PM UIN: 16262997
with driver or without driver?

CUSTOMPERFORMANCE
Dirt Freak

Total posts: 213
posted March 26, 2001 12:46 AM
try shorter lower trailing arms in the rear around 20-22 inches long. have the mounts on the left side on frame so you can run up to 20 degrees uphill and on the right side so you can run as little as 0-5 degrees uhill. also what is the mounting distance from the center of axle to radius rod mount on the rearend mounts for the trailing arms? also how much lead in the rr tire you running? there is a lot more to this than just one thing

rjs
Dirt Full Roller

Total posts: 38
posted March 26, 2001 11:14 AM
With out driver and with a 20 fuel load, ride heights rf 6.5, lf6.0, rr6.25, lr 6.0. Run rear end square, have changed to lead rear end too tight, trail rearend need 120 lr to stick. Again forward bite not side bite. Good turn in, great mid turn, good off, but looses traction about15 feet down straight. Too much power for tires maybe but this is with a smaller motor. 355 steel bowtie heads, small 610 roller cam, Victor jr. We run UMP , Hoosiers. When track is dry run 12 rf,9 lf, 10rr, 6lr . last year with long pull bar only experienced a 3 lbs gain straight across rear so traction was evenly matched and the car took a good set, didn't scrub too much speed, and came off straight. WE even tried backing the timing down from 36 to 25 to take power out. If you don't try something new you will never know. Even went to a tall gear 5.43 on short 1/4 mile. May try a 29?

jammin
Dirt Administrator

Total posts: 3279
posted March 26, 2001 01:07 PM UIN: 16262997
It looks to me that your weights are way off....the 59 rear is the only thing saving you there. You will need more left side weight to get the car back down on the left rear tire off of the turns....this is why your breaking loose off of the turns, it is still laying on the RR tire out. Increase the cross just a bit to about 52 or so(maybe more with more motor) and with more left side weight. Part of the problem may be your roller cam is coming in too fast also...this is one of the reasons we usually dont run roller motors in a mod. But it looks to me that these are a couple of possible reasons for your bite problems...

MOD RACER#93
Dirt Freak

Total posts: 251
posted March 26, 2001 07:02 PM
This is just my opinion, i know others will and do vary... but i would take out the left rear. decrease cross weight.

the fact man
Dirt Roller

Total posts: 6
posted March 29, 2001 04:11 AM
we ran a car almost identical to your weights. we only ran 35lb of left rear but the pullrod was mounted about 12 inches to the left.car turned on a dime and was fast in the corners

speedster
Dirt Forum Racer

Total posts: 94
posted March 29, 2001 07:59 PM
i agree with jammin you need some more left try moving some of that rear in front of axle
and get your ride hieghts correct.

jammin
Dirt Administrator

Total posts: 3279
posted March 29, 2001 08:06 PM UIN: 16262997
it all depends on the track fact man.

GnarlyCar
Dirt Forum Racer

Total posts: 96
posted March 29, 2001 08:42 PM
Have to be another to agree with Jammin... Left side wieght was the first thing to jump out at me with the first post. Last year I had a car at the beginning of the year that had 52.5% left, 57% rear, and 53% cross... it did a lot of the things you're describing. Moved fuel cell from the far right to the far left, went from a 2" to a 4" wheel on the LR, which increased left wieght to 54%. Decreased wedge to 51% at 40 lbs LR bite, all changes over the course of about 6 shows. By the end I had a car that was fairly consistent in heats and features with minimal changes necessary from tack to slick, aside from 4-bar angles and RR tire compound.

If I had to do it again, though.. I'd build it so I could make all these changes between the heat and feature. On extreme dry conditions, this car would roll sooo much deeper into the turns than anyone else, and lose very little momentum getting thru, so it didn't need quite as much forward bite getting off. It was set up with the first numbers I gave, also with the cell on the right, the 4" wheel on the LR and yes, 3 1/2" stagger. It had a 29" panhard bar which was set 4" higher at chassis left. This car rolled over real hard, getting the fender into the RR even having set it static w/ 4.5" clearance. It worked well in the middle of the track when everyone else was hugging the bottom or running the cushion, but if you buzzed the tires even a little bit, you're out to lunch. I don't think I ever used full throttle on slick with this setup..a light right foot is a must.
The reason I changed away from this setup was simple... It sucked WICKED bad on tack, so bad that I had trouble making mains with it. Most mains I started from 18th thru 24th having made them mostly thru B's. My worst run in a main in 7 shows with this particular setup saw me passing 8 cars, the best having me run from 20th to 5th.

There's something to be found in there somewhere, but I think it needs a much bigger crew than I can bring to it to make all the changes from the good heat setup I changed to to the feature setup that I came from..

Food for thought,
Matt

rjs
Dirt Full Roller

Total posts: 38
posted March 29, 2001 09:39 PM
I'm going to try more left side weight about 53% and more cross about the same % wise. Also the Pull bar instead of the push bar just to try it again. We usually run a 4 off on lr for the heat and switch to a 3 off for the feature. Also we run a 3 off on rr for the heat and switch to a four for the feature. We'll see what happens if it stops raining down here! Appreciate the imput. Let you know the results!

Back to the Archives