Need Help with Door Car Suspension.

I am kind of stuck with my 4-link setup... It worked fine when the car had a nitrous motor...

The problem I am having now is the car is hitting the tires really hard, then jumping the rear of the car off the ground on the launch. It also seems to be driving the passanger side rear harding, causing the driver front to come off the ground more.

I am running 1022 Goodyears with No Liners.

I have tried tires pressures all over the place, and I have adjusted the shocks... When I go stiffer, it seems to have less bouce, but spins the tires quicker.

I am thinking it has somthing to do with the extra weight of the blower motor, and how hard the blower motor hits the tires.

What should I have my tire pressure set at? Where should my imaginary 4 link lines come together for the best weight transfer? Should I keep the shocks stiff to remove the bounce, or will changing the angles of the 4 link bars take car of that problem.

Car goes straight once it hooks up, but I just cant seem to get it off the line.

I will say that after dumping the clutch and the tire spin... It usually hooks up fine when I get back on the gas.

Anyone have any good starting points?

 

Suspension tuning

The problem with attempting to give you a good starting point for your chassis is, without knowing the weight bias and the center of gravity. Which you probabley did change with the blower motor, is very hard to say where your instant center locations should be. If you have been or have a method of mapping your instant centers start by moving the IC lower and longer this will hit the tires slower. But without wheel scales and a lot of testing it's pretty hit and miss. If you don't have an anti-roll system, put one in, that will get the car launching a lot more flat.

You may want to go the Performance Trends website, they have a very good software program for mapping 4-links. Just get the pro version not the sportsman.

I hope this helped a little.
Corey

 

I have an anti roll.... It seems to be pretty flat until it unloads.

Here are some pics.

Start of launch.



Starting to unload.

 

There are a few more details that would be nice to have. You also need to remember that unless the person giving you the info is there, it’s going to be a guestamation at best, so here is mine............

When you changed engines, did the crankshaft dist from the C/L to the ground stay the same? Do you have a clutch or a converter and is it the same unit as the previous combo? Look under the car and see where the bottom bar is. Whose shocks and struts do you have and are they Double adj. and are they Elec. or Pneumatic? Do you have an anti-roll bar? Whose chassis is it? Do you own 4 corner scales, or have access to them? Does the car have a data logger?


I can’t imagine if the car makes it down the track that the 4 link is too unhappy. Does the car try and drive you from the 660 to the finish line? The shorter the IC is, the more violent the launch is going to be.

Sorry I started writing this and got interrupted. Corey seems to have answered a lot of your questions.

I personally wouldn’t spend the time to map the 4-link. If you don’t have the NESS 4-link set up, you will probably find that you will only use a fraction of the holes. And no, I don’t think that you need that set up. The last thing for now, WRITE EVERYTHING YOU CHANGE IN A LOG BOOK. You will need it once you get it sorted out. That should keep you busy for a while...


Good luck and report back

Pirate

 

I will admit, I dont know much about a 4 link or how to get one to work.

I will say launching a blown motor is alot different than a NA motor, when I switched to a blower I had to add ballast, add preload to the driver side, lower tire pressure, and im not done tweaking it yet.

 

there is an excellent book called Door Slammers: The Chassis Book by Larry Morgan. I highly recomend it. It will really help.

 

Highly reccommend Jerry Bickels book on chassis tuning, his logic is well tested and works for many.
cheers

 

Video of the pass.

http://www.youtube.com/watch?v=3MHnbGSbnEg

 

Pardon the correction, but the book is by Dave Morgan (former National Dragster tech editor), not Larry Morgan (Pro stock racer). And the book is excellent.

http://www.jegs.com/i/Chassis+Book/622/CHASSIS/10002/-1

Chris

 

Yeah, Morgan's book is good but it is dated. The Bickle book is excellent.

 

Agreed I have read both and Bickels is a lot more up to date and also a lot simpler to understand.

Gavle

 

try long low intersection point of 4 link ex(60" 3"of ground)

 

I am using my foot to control throttle... lol.

They are QA1 double adjustables... Both settings in the middle.

I have a thread about this in the chassis and suspension section on yellowbullet.com and I am getting a lot of varied responses.

I am starting to come up with a conclusion.... First is that my IC is out a bit to far... Second is I could probably use better shocks.... Third is that I am launching a 4 speed in first with a 2.49 low... I should probably be launching in second.

It is hard to tell because there are soo many opinions on what the car is doing.

 

x2. That sucker really pounded at the hit. Another thing changing your first gear ratio would allow in your clutch tune-up would be better big end lockup.

 

what is the deal on the starting line sounded like you lifted the run looked good curious about what its doing at the hit i didnt see tire smoke like it blowed the tires off your probley not that far off just a few bugs to work out cool ride

 

Digging into the rear suspension I found the problem... My driver side rear shock housing broke...

But yeah, I let off when it spun, then got back into it... 1.47 sixty foot time and ran 7.76..... lol.

Should be fun when I get the bugs out!

The engine itself is very mild... 498", unported canfield heads, 10.7 to 1 compression, shift at 7200, low 20's for boost... Steel rods.. Goes thru the traps at 7300