4-link/swing-arm dragster burnout

[johnracer]

My buddy finally got to run his dragster for the first time and I have a question. Its a '00 Fritz, 235" swing arm, 565 ReherMorrison, 1.80 glide, 4.10 gear and 33x16 Goodyears. In Denver, ran 8.02 @ 169 w/1.18 60's.
The problem is the burnout. The car shakes hard in the burn out unless it's VERY short. I'm talking about barely a 1 sec burnout. My only dragster experience is with fed's and mine would shake if I made the burnout too long, but not like this. It does have a burnout limiter on a button set @ 6500rpm. I suggested trying it without the limiter. Is this common with a suspended dragster, or is there something we're missing? Any suggestion/thoughts would be appreciated He's running 5psi in the slicks.....
Thanks,
Johnny

[hammertime]

A few things, what brand of rear tires and how many passes on them ?
Some good years are hell in the burnout box, old tires will do this also.

Roll through the burnout box, back up and go through it again, always gets enough water on the tires. Some places dont put nearly enough water. Burnout chip should be fine. I had one set of new goodyears, I actually had to stop and footbrake the car up to around 2500rpms then let it loose.

[johnracer]

Good to know. They are Goodyears and are the spares for my Vette. They have approx 100 passes on them and are 2 years old. It looks bad when it rattles and he says it hurts bad too....other than that, he loves it! I'll relay the info.
Thanks David,
Johnny

[shawnp]

The famous GY shakes. You can try to get more water on the tire but the only way to cure the GY shakes is to put Hoosiers on it. :lol:

[johnracer]

Any suggestions what compound to use for Hoosiers or Mickeys? He's limited to a 16" wide tire due to the wheel offset. We're comsidering going with a 33.5-15 or 33.5-16 tire.....

[hammertime]

I run a 18700 Hoosier, which is a 33.5 17x16 with a c06 compound. Id look at the 18400 with a d06 or c07 combo. c07 need lots of water on them most the time in the burnout though.

I had terrible luck with the mt I bought for mine.

[johnracer]

Cool David, thanks. We were leaning toward the 18400, just not sure on the compound. I'll suggest the d06 and let him take it from there.
Later,
Johnny

[shawnp]

x2 on the compound and skip the mt's. Too many problems with the small tire.

[johnracer]

Update..He went with the Hoosier 18400 in the c07 compound. Ran it yesterday and 60's went from 1.18 best to 1.15 on the first pass and stayed in the 1.15-1.16 range the entire day with a 7.96 @ 169 best et in 7400' air. It's still beating him up in the burnout though, even keeping it short. He's got bruises on his back today as proof and understandably is hesitent to run it again.
While inspecting the car today, we found the slipyoke splines worn sharp. The trans output is fine so we suspect the slipyoke was that way when he bought the car. We didn't really look at it when we put it in. Any chance that could be causing the problem? It just shakes when coming off the throttle after the burnout. Basically severe wheelhop.
Also having some rt issues. He runs around 1.090 in the box to stay in the mid teens which won't cut it on a pro tree in Supercomp. I'd think a car like this should need 1.130 or more on a full tree. He may just need more seat time. He only has around 10 passes in the car.
I'm planning on making some laps in it on Friday to get a better feel for what's going on and would like some suggestions to make it more fun and less pain.
Johnny

[hammertime]

I doubt that was causing a issue, is he getting the tires really wet the co7's are known for crappy shaky burnouts, thats why most get the c06.

Try footbraking the car upto 2500 rpms then letting it rip, it may work. my old goodyears shook bad but nothing like your saying he has. Id bet something else is wrong, does it have a vibration or anything going down the track ?

[johnracer]

When he lifts at the traps there's a slight vibration, but it doesn't last long. I'm pretty sure the slip yoke's causing that. Otherwise it's smooth....
Do you think a shock adjustment might help? If it was shaking on the launch, I might try stiffing the compression a little, but I don't know if it would do anything in the burnout.

[hammertime]

I guess if the shocks had no compression at all it may hop on him, but they would have to go full extension to make the car hop id think.

Wish we were closer I could see exactly what its doing.

[johnracer]

If I can borrow a digital video cam, we'll get some video and post it. It isn't as visible as it was with the Goodyears so hopefully we can get some closeup shots of the tire & suspension when it's shaking.
The shocks are pretty stiff now, the rear of the car isn't near as springy as my Vette. In fact you really can't bounce it much at all. Of course I've never messed with a suspended dragster so maybe they're all that way....
Johnny

[hammertime]

They normall can be moved by pushing on them a little bit, does it have a shock stuck on it ?

[johnracer]

I know that the rh shock is fine. We had it off Sunday, removed the spring and made sure the adjustments worked and how they work. Can't say about the left one though. You can move the rear suspension, but it takes all my weight (170lbs) and it doesn't move much no matter how hard I try to bounce it. I'm talking maybe 1/2" or less. I assume that's more than pushing on it a little bit? I'll see if I can convince him to remove both shocks tonight, move the suspension through it's travel to check for bind and check the lh shock.
Johnny

[johnracer]

Well, wasn't able to borrow a digital cam, but we got rained out on Friday anyway. He made 2 time trials on Saturday on the stop for Supercomp and loaded up before first round. I watched as closely as possible and couldn't see any shake, and 2 others said the same, but he says it just as bad or worse. Car ran great, just can't cut a light on a pro tree yet. His lights are consistent, but slow. He ran 9.47 @ 164 on only the second run on the stop on the 9.50 SC index in Denver......personally I'd have pounded a pot of coffee and taken a shot at it!!

He's getting a pad made for the seat, and we moved the pedals and steering wheel farther away in an attempt to make him more comfortable in the car. Hopefully that'll keep him in the car so he can get seat time!

David, last fall when he got the car, I mentioned the ballast box in the nose. I'm guessing it's got 30-50 lbs of shot in it. It also has 2 batteries about 3ft back from there. I think you said that a suspended car shouldn't need any ballast. Could that account for his reaction time issues? Just a thought.

I think the car is pretty light for a swingarm dragster. Even with the additional weight, it weighs 1895lbs full of fuel and him....

Johnny

[hammertime]

Unless it has major power (1200hp +) it shouldnt need the weight in the front of it. When you say reaction time issues, you mean its just very slow to react or inconsistent reactions also ?

Does the driveshaft have a lot of slop in it? Like if if the car is sitting in park and your push the rear tires how far does it chuck ?

[johnracer]

His 565 has 970hp. His reaction times are getting more consistent as he gets used to the car, but they're slow on a .4 pro tree..in the .040-.050 range. Full tree isn't a problem, but runs 1.060-1.070 in the box to keep them decent.
With the old slipyoke, it'd roll quite a bit. In fact, he put a line lock on it to prevent it. It's wired into the box and releases with the trans brake. With the new slipyoke, very little.....we tried unhooking the line lock, but it didn't seem to help rt's much.
Johnny

[hammertime]

Does it have a pro tree brake in it ?

[johnracer]

Yes it does. TCI, same as mine...

[shawnp]

It sounds to me like your buddy is trying to drive thru the burnout. What I mean is that the tires are trying up quickly and he is trying to be John Force. What he is feeling is not shake but the tires are trying to grab traction.

[hammertime]

Yes it does. TCI, same as mine...

whats the car 60ft and run et wise ? thats very slow delay

[johnracer]

Shawnp, his first couple of burnouts were pretty long, but even after making them VERY short, he was complaining about the shake. I think youre correct though. It's the tires biting coming off the throttle after the burnout. Hopefully padding the seat will help.

David, it 60's in the 1.15-1.16 range, 5.0's @ I think 138 at the 660 and 7.90's @ 169 at the 1320. Agreed, it's very slow delay. I run 1.117-1.126 in my Vette now that it's sorted out and figure this car should take that and more.....

[johnracer]

I'm hoping if we can get him focused instead of tensed up and trying to crush the button, his lights will improve. If weather permits, we'll find out tomorrow.....

[hammertime]

Them 60fts are slow also. He should have around 1140 delay with a probrake. I am 1100 right now with a non pro brake. Converter ?

[johnracer]

Man, I thought those 60's were pretty good! How quick should they be in a high 7 sec dragster? He's running 5psi in the slicks now and we could certainly go lower. Convertor is a JW and stalls at 6000 behind the 565. It was set up for the same engine in his 72 Chevelle running 9.0's at 148 @ 2800 lbs.....

[hammertime]

Man, I thought those 60's were pretty good! How quick should they be in a high 7 sec dragster? He's running 5psi in the slicks now and we could certainly go lower. Convertor is a JW and stalls at 6000 behind the 565. It was set up for the same engine in his 72 Chevelle running 9.0's at 148 @ 2800 lbs.....

1.12 atleast but when I ran 8.0;s with my bb it'd go 1.10
6000 is a touch tight also, which would normally 60ft faster. Is it a 8 or 9" converter? Setup for a heavy door car vs a light dragster though. I assume JW said it would work good ?

I think you may of just stumbled on to slow on the reactions. I have several different converters for my car, one that will go 1.02 60ft, or as slow as 1.12 both run 7.50ish or faster. Delay is about 35 different between the 2 of them.

[johnracer]

It's an 8" converter. Didn't check with JW, he just wanted to save some $$ and we figured it would "work" as it is. It does, but could certainly be better set up for the dragster. I didn't realize that the converter could have that much effect on rt's. Of course if it 60'd quicker, in theory the rt's should be quicker too....I'll relay the info.
Thanks,
Johnny

[johnracer]

No runs today, got blown out. 30-50mph winds at the track and they called it........

[shawnp]

John

You racing in Denver? I would think with a single carb on that motor that 1.12-1.13 would be right for up there with a low 7.90 ET. The correct converter for the application is going to help a bunch here as far as the ET and reaction time but also remember the delay box adjust as everyone reacts differently. Had a buddy that was lucky to see delay at 1050 on a good day but he was very consistent on the tree.

As for the burnout shake, I would bet he is just feeling the tire grab when lifting. Padding will help with some of that but it will still be there. No way around that.

[johnracer]

Yes we race in Denver and in Grand Junction Co a lot. In Denver with the Goodyears he ran 8.02 @ 169 with 1.18 60's in 7800' air. About the same in GJ with the Goodyears. The Hoosiers picked up the 60 a solid .03 and pushed the et to a 7.96@169 best. Only runs in Denver with the Hoosiers have been on the stop, so really can't compare.

If all he did was bracket race it, the delay wouldn't be a problem. He's one of the most consistent leavers I know. I've personally witnessed the guy go .000 3 times in a row in eliminations, and go between .001 and .009 all day, race after race in his Superstreet Chevelle, but he want's to run Supercomp on a .4 pro tree and the best he can do there is .050 or so. Gonna be tough to go many rounds that way...

Hooked the practice tree to his car yesterday, to experiment. With the same delay, same button in his car, he go .030-.040 on the tree and I'd go -.003-.008 on a .4 pro tree. We tried a few different release methods and got him down to consistent .015's so hopefully he can do the same on the track...I'm sure he'll send the converter in this winter or buy a new one built for the car.
Johnny

[shawnp]

What's the launch RPM when running Super Comp?

[johnracer]

5600 rpm

[shawnp]

One thing I caught in reading is the PSI at 5 lbs. My guess is the thing is wadding that tire up horribly. I would recommend going up in air pressure. I ran 6.0-6.25 in the Hoosier 33.5x17x16. That may help. The other thing you may look at doing when running super comp is stiffening up the suspension to make the car react harder.

[johnracer]

We tried them at 6.5 in an attempt to help the shake and the 60's fell off to 1.19-1.20. 5-5 1/2 psi produced the best 60' times with the Hoosiers and the curent 4-link/shock/ballast combo. Any idea of what IC combinations work on a dragster? The current setting doesn't appear to have been changed since the chassis was built. The powdercoat on the brackets isn't marked at any other holes.....I can measure is up and figure the IC if it'll help.
Johnny

[shawnp]

A lot depends on the total set up of the car for IC. I would spend some time on the phone with the chassis builder. I would think that a little more tire hit would be wanted when super comp racing.

Also, have you checked the pinion angle of the dragster?

[johnracer]

No, haven't checked the pinion angle. We talked about it but never checked it. Should it be the same as any other 4-link car? 1-1.5 degrees negative?

[shawnp]

Yes it should be the same.

[hammertime]

No, haven't checked the pinion angle. We talked about it but never checked it. Should it be the same as any other 4-link car? 1-1.5 degrees negative?

yes ...

[johnracer]

Finally got around to checking the pinion angle. It was at .8 degrees negative. We reset it to 1.5 negative.......planning on testing Thursday night.
Johnny

[dparker]

Whats the best way to check pinion angle on a 4-link dragster...

[hammertime]

Whats the best way to check pinion angle on a 4-link dragster...

I use a degree finder, they sell cheap ones with a needle gauge or they sell digital ones. Either will work but to be spot on the digital is best.

[johnracer]

Testing went great! The seat pad made all the difference.....didn't like the pinion angle though. Vibrated from the hit, so we moved it back to 1 degree neg and took care of it.
The track set him up on a .4 pro tree and he went .019, .016, and .001 on the last run with no time in the box. I know he'll get better from there now that he doesn't hate the car.....on all burnouts he brought it up to about 2500 then just nailed it and it worked just fine. 5.5psi in the Hoosiers, all runs in Supercomp trim on the stop and 60's were 1.538, 1.541, 1.536....9.50@163 at 8200ft....he's a happy guy!

Thanks for the help guys,
Johnny