FOUR LINK ?

[curtisreed]

I have always been told that you want the bottom bar to be level or slightly down. Why? Why can't it be up some to get the IC you want? Sometimes a lot of repeated info gets passed around and I was wondering if anyone had any empirical evidence on this. Thanks guys.

Curtis

[altailites]

My bottom bar is slightly up so I could get the ic where I wanted it to be car works fine 1.03 60ft . what kind of car are you working with ? and where do you want the ic to be at?

[curtisreed]

I have a 27 roadster. I can get the IC that I want right now but I might need to go a little higher, not sure without a little more testing. This is just something I have been told and have read in other tech posts but never have seen why.
My car hooks initially but sometimes gets loose about 100-200 feet out. Tough to dial not knowing if it will stay hooked or not. Not a very fast car so it suprised me that I could spin 16.5-33s only running 6.0s with a sbc.

Curtis

[johnracer]

I have a 27 roadster. I can get the IC that I want right now but I might need to go a little higher, not sure without a little more testing. This is just something I have been told and have read in other tech posts but never have seen why.
My car hooks initially but sometimes gets loose about 100-200 feet out. Tough to dial not knowing if it will stay hooked or not. Not a very fast car so it suprised me that I could spin 16.5-33s only running 6.0s with a sbc.

Curtis
That sounds to me like it needs to be a little lower & longer to keep it hooked down track, but may be a tire pressure issue. What pressure do you run? My Vette roadster did the same with a sb & bb. Found out my tire gauge was reading 1.5lbs low. New gauge, problem solved. Mine likes 4.5-5lbs....

[curtisreed]

This car was set up really short and low. 30.460 and 6.480 I am going to move it to 47.675 and 8.375, I think being so short it is not keeping enough weight on the back and it's not getting enough seperation. Been running 6lbs. I don't know the actual weight but should be right at 2,000lbs. I'm going to put a data recorder on in the next couple of months so I can get some better info.

[johnracer]

That's pretty short but not terribly low. I'm no chassis expert, just have made many mistakes on my own. Personally, I wouldn't make big changes. I'd try a longer ic at about the same height, maybe 40-45", soften the rear shocks on extension, and lower tire pressure. I wouldn't be hesitant to try 4.5-5lbs in a 2000 lb car. Mine, with a sbc, spun bad at 6lbs....

My Vette weighs 2180 with a bbc, 30lbs of rear ballast & me. I run 4.8 lbs most of the time and run fairly fast (5.60's @ 125 in the 1/8 and 8.60's @ 157 in the 1/4 at 8000ft) and it drives great at speed.

What brand tires do you run and how many runs are on them? With my sbc, Goodyears were good for about 120-150 runs before they went away. I've heard that Hoosiers die sooner, but have no personal experience.
I chased my 4-link all over the place, and made many other changes with little improvement, only to find out my tire gauge was bad. Seriously, get yours checked and good luck.

Hope this helps,
Johnny

[curtisreed]

I think you might be right about making to large of a move. I checked possible ICs again and I think I will try 39.85 and 8.375 first. Have checked tire guage. Running Hoosier C07 with about 100 runs on them. On our dragster they have been good to at least 225-250 runs in our experience. Kinda slow dragster 5.29 @130. Shocks are on the softest setting, (single adj. QA1s). I will try a lower air pressure also.

At 8000' I'm not sure my little motor would get out of the 8s. :lol: Is your car a chassis car? I don't get much front end travel compared to the travel of a back halve car (pinto front).

It does help having someone to bounce ideas off of, thanks Johnny.

[johnracer]

Yes, it's a moly SG style 63 Vette roadster, strut front. It doesn't have much front travel either, but lowering the spring seats as much as possible and setting the struts to full soft helped too.

With my ol 408, it only ran 9.60's @ 146 up here @ 2015 lbs, 4.86 gear and 33x16 Goodyears....

I'd bet that REALLY short ic and tire pressure is most of the problem. An ic that short hits the tire really hard at launch and that's it, done....

Keep me updated ok?
Later,
Johnny

[itsabird]

yep that 30.4 is really very short, the 39.85 should be better, don,t forget to factor in the distance from the axle centerline to the top bar on rear houseing bracket. i would stiffen shocks at about half, for a start and go up or down from there, prob... up. watch any bouncing.. or listen for any waa waa, of the engine. heck i can,t belive i typed that, :? anyway good luck and keep posted.

[curtisreed]

Thanks guys. My racing partner is going to start driving a blown alcohol nastalgia F/E dragster and is going to rent the track to practice. I plan on tagging along to get in some testing. You never know he might trip and stub a toe and need a fill in driver. :D

My old heap only says waa waa when I run it through the 1/4. That's because it is crying the cam I have in it is done by 1000'. :lol: :lol:

Curtis

[itsabird]

hey doorracer in tube chassis car, with double adj.. shocks had to stiffen rebound quite a bit, eliminating hook a little, but you will love how fast the car reacts, hammer down man. :)

[itsabird]

should have said with that ic set up, brain cramp huh. :oops:

[johnracer]

Thanks guys. My racing partner is going to start driving a blown alcohol nastalgia F/E dragster and is going to rent the track to practice. I plan on tagging along to get in some testing. You never know he might trip and stub a toe and need a fill in driver. :D

My old heap only says waa waa when I run it through the 1/4. That's because it is crying the cam I have in it is done by 1000'. :lol: :lol:

Curtis
Lucky dog!! I'd love to get into a fed again, especially blown. I sold mine to buy the Vette. Really miss it. It just had my 408 in it but was a hoot to drive!! The Vette's quicker & faster but not as much fun......not even close.

[BillyShope]

http://i78.photobucket.com/albums/j89/BillyShope/linkage.jpg
This came up in another forum and I put together a spreadsheet based on the picture above. Using the dimensions indicated with a 3250 pound car (250 pound rear axle assembly), I calculated the moment (torque) about the front tire patch when the car is accelerating at 2 g's. I did this 3 ways: I used the force resultant at IC location A, the force resultant at IC location B, and the upper and lower link forces acting at their location points on the chassis. In all cases, the moment ends up exactly the same.

In other words, so long as the IC falls on the same constant percent antisquat line, the car can't tell the difference.

Since it's a spreadsheet, it's very easy to try other combinations. So, I pushed point A along that same percent antisquat line until it was about a quarter mile ahead of the car. Again, the moment comes out exactly the same!

[ken0069]

I have a 27 roadster. I can get the IC that I want right now but I might need to go a little higher, not sure without a little more testing. This is just something I have been told and have read in other tech posts but never have seen why.
My car hooks initially but sometimes gets loose about 100-200 feet out. Tough to dial not knowing if it will stay hooked or not. Not a very fast car so it suprised me that I could spin 16.5-33s only running 6.0s with a sbc.

Curtis

I chassed my tail for the better part of a year and a half, spent about $1500 in parts and cost of testing only to find out that the rear springs were too soft allowing the suspension to bottom out about the 330 timers. Put a tie wrap around the shock shaft and check to make sure that you're not hitting bottom down track as that's cheap way to verify this. If I would have done that last year I could have saved myself a bunch of time and money!!

[curtisreed]

Ken,
Good tip. How did you determine that it happened at the 330 and did it not do it at the starting line? Data recorder or??

Curtis