cant get down the track

I have just bought a full chassised 37 chev with a 417 donovan in it. The engine is approx making 1400hp. It weighs 2570 with me in it. It has a 4 speed lenco with a 10in 2 disc crower pedal clutch. Has 34.5 x 17 M/Ts. 4.3 rear gears. My Data logger is stuffed and I can now only get drive shaft rpm(have been onto Autometre to get it sorted almost every day). I have taken the car to the track 3 times now and have done 11 passes. The tracks I run on are not 100% great but arnt to bad. My problem is I get about 80 foot out and it either unloads the tyres or shakes the tyres but not in a big way. The car goes a bit sideways and I have to get off then every time I try to get back on it it just wheel spins and throws me every where and I have done many big changes to the clutch and it makes next to no difference other than with more base I have got my wheel speed up more and 60 foots have dropped. I have tried many things. I have to admit I have never had a blown car and never had anything to do with lencos and clutches. With beadlocks I have tried tyre pressures from 5.25 - 6.25 with 6.25 probably being the best pass. With the clutch I have gone from 12 grams on all 6 fingers to 0 grams on the fingers. I have had 2 1/2 base at the start and now 4 turns. Im doing 1.13 60ft with a wheelspeed of 1435. I dont think the tyres are great but they are not bad on the start line. I was having a staging rpm of 4000 and have brought it up to 5000. My front shocks are on full tight and rears are on the middle setting with are 4 on the strange shock. About 1.5-1.6 sec into the run is when it happens. I even did a pass and took off in second gear and it happened at the top of second gear. I turn the engine to 8000rpm and Im having the problem at about 7000 approx. Like I said when it happens it dosnt go up in smoke or shake me to peices(cant actually feel shake) it just sends the car in the wrong direction. Can any one please give me any ideas. What am I missing. Its not that hard is it. Im not after the car to be on kill Im just want to have it going down the track and running a number

 

shake

You will get alot of ideas, but try to fatten it up around the shift point then take it away. also timing just try and keep it as simple as possible. Mike Canter is really a smart guy, maybe if you e-mail him, he might give you better ideas. Don

 

a car that heavy probley needs more clutch make the base around 750-850 lbs and 60grams on the fingers 10 one each and change 6 grams at a time either way to see what helps and dont make to many changes at once one at a time loosen the front end up so the car can work some gookd luck

 

The motor may be going lean put more fuel in main and block hi-speed untill you get it down the track, try backing down the timing a few degrees.
Ricky

 

you wouldn't happen to have any videos....would you? they can really help with tuning. also, how much is the clutch wearing per pass? what are your gear ratios? trans/rear? the more info you can provide, will definitely help your cause.
Darren

 

I have 1020 lbs of base with my 4 turns from memory. As I dont really fully grasp it all as yet, how would loading up the counterweight help? I have been told to stiffen the front shocks so that the car dosnt nose down and then unload the rears. When I back the timing off the wheel speed drops and it dosnt get a chance to get up on the tyre. Im trying to get my hands on a video tomorrow. All the videos I have arnt any good as there not on the tyre and no zoom. The clutch is getting about 2-3 thou per run. There is a bit of clutch dust out the back of the car on launch. I have a 4.3 rear gear. When I got the car I was told that it has a 2.86 1st, 2.07 2nd, 1.44 3rd and 4th is 4th. It seems to go about 100feet in first gear though. The best wheelspeed I have had is 1435 at .5sec. Can it be tyres, 4 link, shocks? Ive been told many things today what is wrong. Here we go.
1) The 4 link is out and when the counterweight grabs it is hitting the car and throwing it right 9/10 times.
2) still to much clutch counterweight, take off fingers
3) rear shocks are off and the car is bouncing at the top of gear
4) tyres are off and there slipping once there stood up and going

http://www.youtube.com/watch?v=9-RvAZN6ke4
not any good though.

 

No idea if this will work

 

Track Problems

I would baseline the rear shocks by backing off the compression all the way (soft) and crank the extension all the way up (stiff) That will help with the bouncing, plus it will limit the tire hit untill you know what the car wants. Just keep softening the extension a click at a time untill your 60's drop off. If the shock runs out of clicks before this happens then move your bars. You should really map your rear suspension to know where your instant centers are, makes it much easier if you have to make a move. Also you should check your suspension for square and eliminate any preload (if any) this may be causing you to go sidways.

I would also loosen the front shocks as a baseline as well.

MY 2 cents
Corey

 

Part of the problem is in the 4-link and suspension. Soft rear cars with a lot of horsepower are tricky in the sense that the harder you load the tire, it will want to smack the wheelie bar back down on the ground and unload it. Bead locks make it even more fun. If you're only knocking 2-3 thou off the clutch on a full pull, you're not working it(by working it, I mean sliding it) hard enough. Does it feel nice and violent at the hit and then fall off a little? Take a really close look at what the wheelie bar is doing. In the video it looked like it was hitting bump stops. It should have one clean smack to get your line wheelspeed up like a rocket, then when it falls back onto the tire the car should be moving pretty well, but the added resistance should knock the clutch loose, which I don't think its doing in your case. Most roots style cars run more like a regular door car and considering your weight and power, clutch lockup should be somewhere around .6-.8 secs into low gear. You should be closer to 8 thou on wear, not that it is gospel, but right now it sounds like the clutch isn't working right.. too tight.

Now that being said, with it being that light on clutch and still tight. you need to work the 4-link and suspension to plant that tire harder and keep it from rebounding so hard after the hit. The clutch and tranny were in the car before? Make sure the 4-link bars aren't the super shortys made for a convertor/PG setup.

 

What do you boys think of the tire wrap up in picture 3?

 

Track Problems

Had another look at the video, it looks like your rear spring rates are a little to high as well, what are they? Plus the car drops at the hit then bounces back up, you really want the car to rise slightly (plant the tire).

Corey

 

with that low of a first gear it would seem to me it would be on the wheelie bar through low gear if the front wheels are up and it going to the right a slight four link adjustment will correct that when adjusting the four link just adjust the upper right bar a 1/2 of turn at a time unless your changing the whole set up for me if ist just drifting to the right it wont need much shorten the upper right bar 1/2 turn but it has been several years since i had a four link car it shouldnt take long to figure it out patience is the key

ps bad ass looking ride good luck

 

Michael,
I am the first to admit that l know jack about suspended set ups, never having had one, but 6.25 lbs seems a little low for pressure in that size tire. I would increase the pressure a bit (???) until it blows the tires off at the hit, and then dial it back from there.
Maybe check the wheeliebar height as well. A lot of squat in that sidewall going by the photo.
The beauty of this board is there are lots of smart racers on it. Mike Canter leads the pack. Give me a call if you like.
Damien Scully.
0410 221 272.

 

I dont no if this helps but on the weekend it was shaking the tyres in the burnout about 40-50 into it. Why dus it do that? 7500rpm in burnout.
I just gave the 4 link a quick measure up. It seems that it has squat in it. The instant centre is about 3in down and about 3in forward of the neutral line. The bottom 4 link bar is pointing down hill a bit. Could this be my problem. I have the wheelie bar up about 4in and it is on the wheelie bars for about 12in

 

Another thing you may consider along with the 4-link is trying a 33.5" tire instead of the 34.5". I only say this because of your horsepower and weight. It may open your window up a little. Granted you've got a slightly different combo going and this may get me slaughtered for saying it, but you're basically in the same horsepower range as a modern Pro Stock with less gear, wheelbase and more weight and I've never seen one of them use a tire with a rollout much bigger than 104". Just another thought anyway.

And I agree with Jim, that is a badass ride.

 

Just going to throw my opinion out here.

It doesnt look to me that you are that far off, one thing thats making it tricky is the big tire, a little too much traction and too much tire wrinkle. Give them some more pressure and see if you can spin them a little.

 

I just took a look at the video and it looked like the car was pourposing up and down at the hit of the throttle. From the tire wrap it looks like it is dead hooking the tire like a converter car. The wheel speed is way low. How far out is your instant center (intersection point of the fourlink) and how high is it? I have never had any luck with the bars pointing down.

 

The IC is 63in forward and 7in up
http://www.youtube.com/watch?v=su8PMY6O0xg

 

In just reading page one - you need more air in the tire - and the wheelie bar is to low.
At that weight you need 7 pounds of air to compensate - wheelie bar height - every guy measures em different - and diameter of wheels vary but shoot for 7 1/2 inches centerline to ground - high enough to say - wow that front ends up there to far - then back down - some. Once launched you should carry the wheels 60 to 100 feet. Adjust 4 link pre load to keep the car striaght.
RIGHT NOW - get on the Jerry Bickel website and order their chassis book - its the best $60 you will ever spend - I guarantee it. It is the best ever book about door slammers with easy to understand teminology and pictures. It will save you thousands of dollars - and hours of headaches. I've been racing blown suspended doorslammers for 15 years - with 1400-2500 HP. 7.20s to 6.40s - heavy cars - medium cars - Bickels book will get you close - right off the trailer - WR

 

sounds like the IC is too far forward. I would try to find someone who really knows what they are doing with suspension and get the 4link plotted and get the car scaled. you need all that set. you will want 51% on the front wheels. my IC in the vette was 48 out and 7 up. how much pre load is on the right rear? you can chase the power and clutch all day but if the suspension is off you may never be able to put power in it.