Ideal weight distribution for ladder bar car running 9's ?

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cudabin · #1 Post by **cudabin** » Mon Oct 16, 2006 9:50 am

We have a 67 Cuda Notchback that weighs 2,995#'s with driver and including a 125# ballast bar in the trunk. Rolled the front tires off the scale, and the rear axle weighed 1,335#'s, so the front must weigh 1,660 lbs. This gives 55% on front and 45% on rear.

The car runs a 9.94 at 136.2 mph with a 1.43 60 foot. It lifts the front end up evenly, and carries it out past the 60 foot, but does not quite pull the front tires off the ground...

Ladder bars are in the bottom hole, and appear to be 2 degrees down in front.

I need to lower slicks down to 8 psi or else it spins after the initial hit. I want to be able to step up the combination, so need to improve traction!

What is best weight distribution front to rear? How much do i have to slide the motor back to make a difference ??

Thanks for any and all advice.

Arnie

#2 Post by **John_Heard** » Wed Oct 18, 2006 1:49 pm

I've been waiting for one of the other guys to post on this, but since nobody's jumped in I'll give it a shot. I've seen quite a few cars with weight distribution similar to what you have and it doesn't seem to have been a problem for them. Most of them are backhalfed cars which takes a lot of weight out of the rear.

What kind of car is it? I mean are you bracket racing, heads up/index, test n'tune for fun? What size tires?

I kinda have the feeling that your at about that point where more power might help the car hook better. When you step the combo up are you going to spray it, different motor or what?

cudabin · #3 Post by **cudabin** » Wed Oct 18, 2006 3:41 pm

We are running a 10.5W -31 which is as big as possible in the minitubs!

The car is basically a Bracket car, but we enjoy test and tune sessions to learn how to go faster...

The car should 60 foot better, and once the cage is done and we are legal to run 9.s' we will remove the 125# ballast bar from the trunk to offset the 40 # gain from the cage. then we can try tuning for a better 60 foot.
We never set it up to run all out yet, so I think it could run 9.89 with just a little better launch!

The heads are unported 440-1's which have potential for 50 more cfm through a CNC port Job from Jeff at Modern Cylinder head... this should take it to 9.70's ???

We are also running a 950HP which we could trade for a 1050 Dominator.

Strange as it sounds, I would like to be able to yank the front tires every now and then just for Fun! With the double adjustable ladder bars and double adjustable Strange coilovers, i thought I would be able to dial in the right amount of traction and weight transfer. Apparently i have more to learn.

Thanks for any ideas.

Arnie

Mike Peters · #4 Post by **Mike Peters** » Wed Oct 18, 2006 4:25 pm

Wow, this post looks familiar. Not that there's anything wrong with soliciting ideas wherever you can -

http://speedtalk.com/forum/viewtopic.php?t=4197

cudabin · #5 Post by **cudabin** » Wed Oct 18, 2006 4:40 pm

Exactly, The thread did not go very far on that board, so I thought I would try this one !!

Any one have some ideas ???

Cheers,

Arnie

#6 Post by **John_Heard** » Wed Oct 18, 2006 4:41 pm

I'm kinda at a loss where to start here. Let me make sure I understand, it's not spinning if you run the tires at 8psi right? That seems a bit low but I'm not used to 31" tires and 3000lbs.

If you're wanting to get the car to wheelie, there are a number of things you can do, more gear, looser converter, loosen the front shocks up and put as much travel as you can in them, raise launch rpm, etc. Those things will probably help it 60' better too. Sounds to me like the car launches soft - probably has a tall gear and somewhat tight converter for a N/A setup?

cudabin · #7 Post by **cudabin** » Wed Oct 18, 2006 5:38 pm

It hooks off the initial hit at 8 psi. Mickey Thompson tech said min of 6 psi with my 12" rims, and that 8 - 9 should be ideal. The car feels loose out of the hole, but stable at the top end. At 10psi it breaks the tires loose!

Gears are 4.56 and od of slicks is 31.3"

It has 90/10 shocks in front.

I was most interested to learn if i need better weight distribution as the traction is on the edge, and I didn't want to start spinning again if i stepped up the power.

I tried to stall it up past 2,000 rpm on the launch but it wants to push the car forwards and red light! Perhaps the drum brakes need adjusting...
The 8" Coan convertor seems to flash to around 5,200 rpm and the shift recovery rpm never falls below 5,700 rpm according to the playback tach.

I will try to post a launch pic attachment.

Mike Peters · #8 Post by **Mike Peters** » Thu Oct 19, 2006 6:25 am

An 8" converter that you can only bring up to 2K in the beams? I think you've found your problem. Plus, if it were my car, I'd move the ladder bars to the upper hole and set ride height so the ladder bar is parallel to the the ground.

cudabin · #9 Post by **cudabin** » Thu Oct 19, 2006 4:24 pm

Regarding the convertor, If you are very careful and pump the brakes and hold pedal firm, then sneak up the RPM's you can get over 2,800 rpm before it pushes... but if you hit it, it will push just over 2,000

Coan says this is normal for a "tight 8" and it flashes over 5,000... It has less than 5% slippage on the top end.

What do you think it should brake stall to???

If I raise the bar back to the middle hole and then crank up the ride height to get the bar level, does that help the weight transfer just through the higher center of gravity? Or some other advantage ?

Thanks for the input,

Arnie

Mike Peters · #10 Post by **Mike Peters** » Thu Oct 19, 2006 4:38 pm

Moving the bar to the upper hole will give a more favorable geometry to lift the front of the car as you desire. If the bar is pointed down now, how much higher do you think you have to raise the car to get the ladder bar level at ride height? I would think you could actually lower the rear of the car once the ladder bar is moved.

Footbraking works but, loads the suspension and it's components. When you load these components, you're using suspension travel which could be used to help the car work better. Have you thought about a transbrake? Is this a leaf spring car or coil-overs?

cudabin · #11 Post by **cudabin** » Fri Oct 20, 2006 10:31 am

Was not planning on a transbrake at this time. Just put a new Cheeta manual valve body in the 727 and had the trans freshened...

I thought that the lower holes transferred more of the cars weight to the ladder bars and the upper hole hit the tires harder ??? Based on the large wrinkle of the sidewall at the initial hit, I figured I was hitting it hard enough already ???

Please educate me, or point me in the direction to read some more info if you can.

Thanks,

Arnie

Mike Peters · #12 Post by **Mike Peters** » Fri Oct 20, 2006 10:50 am

I will tell as I have told many who are looking to educate themselves - please order a copy of Dave Morgan's "Doorslammers". There you will find what you seek...........................

Yes, the upper hole will hit harder. I would suggest you look for a way to lower the car so the bottom of the ladder bars are parallel to the ground at ride height. In restrospect, if your bars are only 1-2 degrees down, they may well be parallel to the ground during launch. This is why I asked you if it was a coil-over car or leaf spring car. What kind of shocks do you have?

cudabin · #13 Post by **cudabin** » Fri Oct 20, 2006 2:04 pm

Strange double adjustable coilovers w/ 110# Hypercoils.

I definitely will buy Doorslammers book as I need to learn more...

Any pictures explaining your observations ???

Thanks again for helping!

Arnie

Mike Peters · #14 Post by **Mike Peters** » Mon Oct 23, 2006 7:18 am

I will apologize and retract my previous statements concerning your ladder bar set up. After doing some reading over the weekend (since i didn't feel well enough to go to the MAKO race

), I will agree your positioning of the ladders at 2 degrees down is correct. I haven't thought much about ladder bars for quite a few years as they haven't really existed in any of the classes I have focused on in recent years. Ladder bars are unique in the fact they transmit the forces of the rear end housing through one point rather than 2 like a 4 link. This situation delivers a large amount of anti-squat, so the 2 degrees down in front should work well. Of course, anti-squat means you are not lifting the front of the car which is what you are desiring. However, the anit-squat may provide the traction you want to enable you to lift the front end. I agree with John H. in that you may be at a point where more power is needed with your current set-up to obtain the wheelies you want. Once again, I apologize.

cudabin · #15 Post by **cudabin** » Mon Oct 23, 2006 10:54 pm

No Worries Mike !!

At least you are trying to be helpful... I have not got a lot of feedback from others on this topic.

I guess I will try again next May and just keep testing... The worst part is it is so hard to get a bunch of passes back to back to learn anything.

I was told to check my crank centerline and ensure it is 14 - 16 inches from the ground as the height of the motor affects weight transfer as well.

I will also attempt to slide the motor back an inch or two as it can't hurt!

Thanks again,

Arnie

Ideal weight distribution for ladder bar car running 9's ?

Ideal weight distribution for ladder bar car running 9's ?

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