Need Advices to Setup Rear Suspension

[68dodge]

Good news guys! My car has made his best ET so far. I could drop 60ft from 1.54 to 1.50 and the problem with tire boucing is almost solved but the car still boucing tires on start.
I'm sending below a video from my GoPro camera that I installed under the car. Sorry for the quality but was darken when I made the video.

Are you starting at a higher RPM? The car lifts nice which is what you want. I think the front end may still be to stiff on the lift when you launch. My car will raise in the back once I stage, then stay up as I come off the line.

 

[famous bob]

Good news guys! My car has made his best ET so far. I could drop 60ft from 1.54 to 1.50 and the problem with tire boucing is almost solved but the car still boucing tires on start.
I'm sending below a video from my GoPro camera that I installed under the car. Sorry for the quality but was darken when I made the video.

that didn`t look too bad .

 

[360tripleblack7]

Are you starting at a higher RPM? The car lifts nice which is what you want. I think the front end may still be to stiff on the lift when you launch. My car will raise in the back once I stage, then stay up as I come off the line.

View attachment 1715127164

At footbrake I keep the car around 2500RPMs and When a leave brake and WOT the flash stall goes up to 5000RPM. I agree with you. Front end looks like too stiff yet. Looking at your car picture the behavior is so similar then my car... Look at this picture of my car on launching...

 

[68dodge]

At footbrake I keep the car around 2500RPMs and When a leave brake and WOT the flash stall goes up to 5000RPM. I agree with you. Front end looks like too stiff yet. Looking at your car picture the behavior is so similar then my car... Look at this picture of my car on launching...View attachment 1715127305

Now that looks good to me. If your stall speed is 5000 RPM, it's hitting the the rear tires pretty hard. Tires look good in picture. Could be the track, some of the tracks prep better than others.

 

[Cudafever]

First of all congratulation on your improvement!!!!!
So what did you change from the first video to this one and...........
I still think you have too much air in the tires .........
Do you have screws in your rims? if so, let some more air out and see what it does.

 

[Cudafever]

I went back and look at your first 2 videos and the front isn't getting much rise under launch.
I think that you need more travel up front.
See how the wheel well all most covers up the top half of your rear slick? The top of the front wheel well molding should cover at least half of the rubber of the tire.(taking about from the top of the tire to the rim) HOWEVER, if you drop the front that much, you will need to have it re aligned or at least re set the toe.

 

[yellow rose]

At footbrake I keep the car around 2500RPMs and When a leave brake and WOT the flash stall goes up to 5000RPM. I agree with you. Front end looks like too stiff yet. Looking at your car picture the behavior is so similar then my car... Look at this picture of my car on launching...View attachment 1715127305

Are you using torsion bars? If so, what bars do you have? To me, it looks like the front is sprung a bit too stiff and a shock won't fix that.

If it's a coil over do you know the spring rate and front end weight?

 

[360tripleblack7]

First of all congratulation on your improvement!!!!!
So what did you change from the first video to this one and...........
I still think you have too much air in the tires .........
Do you have screws in your rims? if so, let some more air out and see what it does.

Thanks Man! The first thing that I did was improve more front end travel. At first video I had 4" of travel so I lowered front of car to have 5" of travel. Only with this change car went from 1.54 to 1.51 and checking the video made by my wife I can see that I still having bouncing on the start so I stiffed rebound to 14 and compression to 5 on the rear. Car went from 1.51 to 1.50. About the tires, I was running with 13PSI and I haven't screws in my rims.

 

[360tripleblack7]

Are you using torsion bars? If so, what bars do you have? To me, it looks like the front is sprung a bit too stiff and a shock won't fix that.

If it's a coil over do you know the spring rate and front end weight?

I totally agree with you. Front looks like too stiff yet. Because I'm using shocks almost full soft at front (rebound 2, and compression 12). I'm running with OEM torsion bars and this bars has 0.896" of diameter. Do you have any recomendation of what torsion bars I should use to make front softer?

 

[Cudafever]

For drag racing, with stock suspension, 6 cyl front torsion bars is the trick, because they are weaker, requiring you to twist them up more for the same ride height(stored energy)Brazel my be a tough place to find some. I don't have 6 cyl torsion bars on my car. I have the nose on the ground(almost on the bump stops) so i get as much up rise as i can. If its a daily driver, i wouldn't recommend setting it down on the bump stops.

 

[Cudafever]

O and i don't think i would lower the air pressure any lower, without, some screws in the rim.tire bead area.

 

[RockinRobin]

just a casual observance - you're not squatting enough on launch.. might be weight transfer - the back end seems to need to come down some.. with that much stall and that kind of HP - you should be doing wheelies!

Remember, leaf spring cars do NOT squat on launch, they rise. Rear Tires appear to bounce slightly. Try 1 or 2 clicks less rebound on rear shocks. Wait, looks like you've got that part solved, now more weight transfer. Try lowering front end all the way down to the bump stops for maximum front end travel. Also experiment with lower launch RPM. My Duster has 5500rpm stall and I have to leave at 1500rpm on footbrake to get good weight transfer. Assuming we're talking about a car that is not driven on the street...

 

[360tripleblack7]

Remember, leaf spring cars do NOT squat on launch, they rise. Rear Tires appear to bounce slightly. Try 1 or 2 clicks less rebound on rear shocks. Wait, looks like you've got that part solved, now more weight transfer. Try lowering front end all the way down to the bump stops for maximum front end travel. Also experiment with lower launch RPM. My Duster has 5500rpm stall and I have to leave at 1500rpm on footbrake to get good weight transfer. Assuming we're talking about a car that is not driven on the street...

You told a thing that make sense for me. Maybe try to leave in lower RPM. I was seeing some videos of my car and I can see that at footbrake around 2500rpm front suspension looks like too much high and this can harm launching. Anyway finally I'm ordering my Calvert monoleafs and installing this new springs should help me on start.

By the way, the car still running at street... lol

Thanks for your advice man!

 

[RockinRobin]

You told a thing that make sense for me. Maybe try to leave in lower RPM. I was seeing some videos of my car and I can see that at footbrake around 2500rpm front suspension looks like too much high and this can harm launching. Anyway finally I'm ordering my Calvert monoleafs and installing this new springs should help me on start.

By the way, the car still running at street... lol

Thanks for your advice man!

The other nice thing is adjusting launch RPM requires no wrenching so it's an easy change. Good luck!