60ft questions

[Alky V6]

Don,

Are you saying that this is what it should be ? based on your experience.

George

The GN examples I've seen in the sims that I run spec out the weight over the rear axle at 43%.

My race car, that I did bother to take to a truck scale and weigh, calculated out to have 44.2% over the rear axle. It makes sense. The engine bay is stripped down. No a/c, p/s, etc.

 

[oldtimer]

The GN examples I've seen in the sims that I run spec out the weight over the rear axle at 43%.

My race car, that I did bother to take to a truck scale and weigh, calculated out to have 44.2% over the rear axle. It makes sense. The engine bay is stripped down. No a/c, p/s, etc.

my car has 43% weight on the rear presently ( Longacre scales ) so those numbers should be close for my situation I would suspect as a starting reference point .... do ya think ?

George

 

[Alky V6]

my car has 43% weight on the rear presently ( Longacre scales ) so those numbers should be close for my situation I would suspect as a starting reference point .... do ya think ?

George

For the CG, yes.
For the control arm mounting points, I think the riding height on the stock GN example in my sim might be too high. I would use Blazer406's numbers or make your own measurements. If you'd like, post the numbers you get and I'll run them through the sim and get the results back to you. The more people that volunteer their pickup points for the control arms, the better chance of coming up with a dependable spec to use for our cars.

 

[Blazer406]

I PM'd KevinS to see if he might weigh in.....I think he is the one that told me that the no-hop bars moved the I/C too much....

Incidently.... his measurements and my measurements on our own cars were off from each other... as to the I/C location.... enough so I wanted to go re-measure with a plumb bob and string..... thinking I would be more accurate....

 

[Alky V6]

I'm wondering how much spring sag is in the picture. I mean, our cars are over 20 years old. If everyone has varying amounts of spring sag, that's going to give different ride heights and pickup points for the frame. This could be a very individual kind of thing. If the tires are stock diameter, then the axle pickup points should be very close to the same from car to car. It's just the frame points that I see possibly varying due to spring sag. And, differing ride heights will definitely affect the resultant IC calculation. Even just an 1/8 of an inch will make a difference.

 

[Blazer406]

I'm wondering how much spring sag is in the picture. If everyone has varying amounts of spring sag, that's going to give different ride heights and pickup points for the frame. This could be a very individual kind of thing. If the tires are stock diameter, then the axle pickup points should be very close to the same from car to car. It's just the frame points that I see possibly varying due to spring sag. And differing ride heights will definitely affect the resultant IC calculation. Even just an 1/8 of an inch will make a difference.

Very good point Donnie.... my car had over 150k on the clock when I measured it....that 1/8" 2' from the rear end is loads more than 1/8" out at the I/C.....

I'll re-measure mine after I get the engine back in....this time with a string and a plumb bob...

 

[Alky V6]

Very good point Donnie.... my car had over 150k on the clock when I measured it....that 1/8" 2' from the rear end is loads more than 1/8" out at the I/C.....

I'll re-measure mine after I get the engine back in....this time with a string and a plumb bob...

Another measurement that should be carefully done is the length of each control arm. Not from center of bolt to center of bolt, but from the rear axle centerline vertical plane to the center of the front mounting bolt. Your upper control arm length measurement was quite a bit off from the dimension I have. Not saying mine is right. It just needs to be rechecked.
One other measurement. The distance of the upper and lower, rear control arm mounting points, forward or behind the rear axle centerline vertical plane.

 

[Blazer406]

Another measurement that should be carefully done is the length of each control arm. Not from center of bolt to center of bolt, but from the rear axle centerline vertical plane to the center of the front mounting bolt. Your upper control arm length measurement was quite a bit off from the dimension I have. Not saying mine is right. It just needs to be rechecked.

I can't remember... I probably did... bolt to bolt....

 

[Alky V6]

I edited my last post. Please read again. Thanks.

 

[Blazer406]

I edited my last post. Please read again. Thanks.

I did re-read.... just re-iterates... I need to do it again... as I don't remember exactly how I did it.... but it took some thought how to draw these points in AutoCad... to get the correct answer for the data that was measured.....

 

[KEVINS]

I got your PM and I have some info to add but I'm at work right now so I don't have much time. I have plotted several G-body cars lately and at stock ride height the IC seems to be BEHIND the car. You can see a graph on my www.baselinesuspensions.com site if you go to G-Body link. I am in the middle of developing an UCA suspension kit to fix all of this, too..=)

ks

 

[Mike Washington]

That car is a definite candidate for some adjustable shocks!!!! The car from the video angle hits the tires then unloads and bounces. Shocks will eliminate that problem. Double adj are $$$ but well worth the tuneability. Single adj do not offer the flexability to truely fine tune suspension.

My 2cents

Laters
Mike Washington

 

[oldtimer]

I just came out of the shop with a concern. I dropped the GN down on blocks to start taking some measurements and I thought I'd check the angle of my rear upper control arms before I started.

Here's what I found; the passenger side is 9* down ( front mounting point ) and the drivers side is
6* down, so I know my instant centre or centres is/are going to be forward "somewhere". Is this variation in angles a common thing ? Rear is a Moser 9".

Now the question; Am I going to have 2 different instant centres

My car drives to the right on launch . All things being equal, could this be the cause ?

I just stopped everything until I posted my findings. Where do I go from here ???



This is a very informative (great) thread !

George

 

[KEVINS]

I just came out of the shop with a concern. I dropped the GN down on blocks to start taking some measurements and I thought I'd check the angle of my rear upper control arms before I started.

Here's what I found; the passenger side is 9* down ( front mounting point ) and the drivers side is
6* down, so I know my instant centre or centres is/are going to be forward "somewhere". Is this variation in angles a common thing ? Rear is a Moser 9".

Now the question; Am I going to have 2 different instant centres

My car drives to the right on launch . All things being equal, could this be the cause ?

I just stopped everything until I posted my findings. Where do I go from here ???

This is a very informative (great) thread !
George

Hi George,
If the angles are accurate then, Yes, you will have two different IC's. But instead if measuring the angle of the control arms you should measure the distance from the ground to the center of the control arm bolts while the car is on the ground and race ready. You will need to be within 1/8" for accuracy. This will give you more accurate numbers.

KS

 

[lazaris]

There is no one specific spec to fit all cars. Depending on each cars power, weight, weight distribution,ride height, etc etc. will determine whats best. One of the best ways to determine this is to watch the car launch and review it.

 

[KEVINS]

Here are a couple links to IC's plotted out:
The first one is stock GN at a fairly stock ride height.
http://www.geocities.com/kdslaby/BUICK4LINKSTOCK.pdf

As you can see the IC ends up behind the car. Not Good.

The next graph is a jpg on my website from a Malibu with a Chevy 12-Bolt installed. FYI, the 12-Bolt and the GN 10-Bolt bolt heights are nearly identicle but the lateral angles are way different. The car was lowered to get the LCA horizontal with the ground which is desireable and the IC still ended up behind the car:

http://www.baselinesuspensions.com/gmplot.jpg

I currently have a kit to correct the geometry when a 12-bolt is installed and I have a few other kits in the works too.

When taking measurements of the control arm lengths you need to measure the perpindicular distance to the axle centerline. Not the true control arm length.

Back to the original poster: If those slicks are 4 years old then that should be the first thing to replace. There are probably other concerns in the suspension but it's best to eliminate those as the culprit first.

ks

 

[Super6]

pinion angle

Raising the rear of the transmission didn't make a lot of difference on the angle but i did have to re-adjust my downpipe and the engine looks more level now...i probably raised it a good 3/4" and the driveshaft clears the loop. i am real close to the floor board but it doesn't touch and probably have about a 1/4" of clearance on the left side and about 1/2" on the right..more clearance on the right putting the tires in the front on blocks didn't make a difference but i guess it better to be safe then sorry. i am at 3 degrees down(neg) on the tailshaft and now the pinion is at 1 degree up(pos). i am at -2 now. the Metco upper adjustables made this adjustment very easy . i took a pic of how i raised my trans with flat washers. i am not sure if this is safe. the bolts in the trans were plenty long but not sure of the strength i might have lost by doing it this way. i have a welder and can take the crossmember off and relocate the mounting pad if ya'll think this could cause a problem. here is a pic...tell me what ya'll think
i will be using these slicks at least a couple more times out...i have my eye on some Pheonix slicks and some shiny wheels .....thanks Bob

 

[Alky V6]

You'll be fine.

 

[Alky V6]

There is no one specific spec to fit all cars. Depending on each cars power, weight, weight distribution,ride height, etc etc. will determine whats best. One of the best ways to determine this is to watch the car launch and review it.

That is true. But, there are some guidelines that can be used to setup the car with a baseline. For instance, I see no reason at all, if you're serious about drag racing your car, to start off with a baseline chassis setup where the IC is behind the car. Just call me silly.

 

[oldtimer]

There is no one specific spec to fit all cars. Depending on each cars power, weight, weight distribution,ride height, etc etc. will determine whats best. One of the best ways to determine this is to watch the car launch and review it.

Thanks Laz,

I realize this. I was just checking out the ears on the Moser 9" to see if they were raised and how much from the stock position. I saw that they were and just wanted to see how much of an angle the UCA's had. I was just surprized that they were different and wanted to check with the experts.

I'll now proceed in the recommended fashion to get it close ( in theory at least ) and I'll fine tune it at the track. 60 foot time slips will be my report card. I'll be happy if I can get into the 1:20's This will get me well into the 8's.

George