8 second OEM 4 link drag race chassis setup
- Thread starter Alky V6
- Start date
Welcome!
By registering with us, you'll be able to discuss, share and private message with other members of our community.
It looks like I should be able to use the existing #1 axle bottom bracket hole on the right side, and the #3 axle bottom bracket hole on the left side. With the 1.81 x .53 numbers you gave me to reposition the chassis top bracket, that should provide;
Left side IC: 44.2" length, 11.1" Ht, 125.9 AS%
Right side IC: 43.5" length, 11.2" Ht, 129.6 AS%
I'm interested, Kevin.
Left side IC: 44.2" length, 11.1" Ht, 125.9 AS%
Right side IC: 43.5" length, 11.2" Ht, 129.6 AS%
I'm interested, Kevin.
oK. This will take some time and a little work from the both of us to make sure I get the hole in the proper position so the UCA's aren't too long/short.
I want an IC length of around 36".
Using the 1.81" backwards dimension (I'll call this the 'X' dimension) what Virtical dimension (Y dimension) do I need measured down from the UCA chassis hole?
Once the X,Y dimensions are figured out I need you to make a template like you did for the LCA's then mark the X,Y spot on the template then measure the length that the control arm needs to be. The template doesn't have to be as exact as you did for the LCA's if you don't want to.
If the hole is too close to the factory torque box and you can't get a hole there then move the holes to a position that will clear it.
ks
I want an IC length of around 36".
Using the 1.81" backwards dimension (I'll call this the 'X' dimension) what Virtical dimension (Y dimension) do I need measured down from the UCA chassis hole?
Once the X,Y dimensions are figured out I need you to make a template like you did for the LCA's then mark the X,Y spot on the template then measure the length that the control arm needs to be. The template doesn't have to be as exact as you did for the LCA's if you don't want to.
If the hole is too close to the factory torque box and you can't get a hole there then move the holes to a position that will clear it.
ks
Kevin, are you sure you want to go for 36" with the IC length? I'm already seeing separation on the left side with the IC position I'm using now. If I shorten the IC length to 36, I'm going to end up with an AS% of 149 on the left and 155 on the right. That will just make my separation problem even worse. I'm already doing a good job of killing the sidewall. Stiff sidewall slicks.
The above AS% numbers are with the right LCA level and the left LCA angled slightly downward at the front from level.
Traction at the launch is not really the problem. Traction from the 1-2 shift on is.
The above AS% numbers are with the right LCA level and the left LCA angled slightly downward at the front from level.
Traction at the launch is not really the problem. Traction from the 1-2 shift on is.
Yep, 38" would be the max length for that much power. Anything much longer the topend stability becomes an issue and the less loading the rear tires get.
Can you control the separation with the rear shocks, are they double adjustables? Never Mind, I just saw that they are. You would use the rear shocks to stiffen the rebound if they are separating too fast.
Also, you may be able to raise the rear of the car to lengthen the IC and lower the AS so I'm thinking this would be real good to try.
ks
Can you control the separation with the rear shocks, are they double adjustables? Never Mind, I just saw that they are. You would use the rear shocks to stiffen the rebound if they are separating too fast.
Also, you may be able to raise the rear of the car to lengthen the IC and lower the AS so I'm thinking this would be real good to try.
ks
That will give AS% numbers of 144.6 left, 150.6 right. That still seems like a lot to me.
Kevin, if you think the shocks can control the extension, I'm willing to give it a try.
I'm going to double check all the pickup points before I do anything else.
Kevin, if you think the shocks can control the extension, I'm willing to give it a try.
I'm going to double check all the pickup points before I do anything else.
Just to give an idea of the amount of separation and sidewall crush I was getting with the car, the AS in this picture was closer to 100% than what I'm using now with the car. In fact, it was around 96% for both sides, and the IC lengths were 60-70". I'm presently at 115-120 AS% with the IC lengths at 53-62".
Attachments
Some more recent launch pics with the higher AS% can be found here Pete Liebig Photography - Snapshots!! Go to Drag Racing, then West Coast Altered and test tune, then pages 65, 66, and 103. Hurry. I don't know how much longer these pics will be posted up.
The front tires are not lifting as much, because the front shock extension is tighter in these photos. If you could see the right side, there is a little squat going on. The left side, a little separation. Most of both has to do with the slight amount of body roll going on. I think if you were to remove the body roll from the picture, the squat/anti-squat would be fairly neutral.
I can see where there is room to add some AS%. I'm just worried about the amount of tire sidewall crush we might be adding.
Will stiffening the rebound to control separation at the launch be counterproductive to trying to achieve better traction down track?
The front tires are not lifting as much, because the front shock extension is tighter in these photos. If you could see the right side, there is a little squat going on. The left side, a little separation. Most of both has to do with the slight amount of body roll going on. I think if you were to remove the body roll from the picture, the squat/anti-squat would be fairly neutral.
I can see where there is room to add some AS%. I'm just worried about the amount of tire sidewall crush we might be adding.
Will stiffening the rebound to control separation at the launch be counterproductive to trying to achieve better traction down track?
Did you ever try controlling the separation with the rear shock rebound?
FYI, ladder bar cars have an IC of 32" and will load the tires a LOT more than a 4link car so the rear shocks are used to control the separation.
I don't know about those rear shocks but the $$$ have a high speed valving that's stiffer that reacats on the launches while the slow speed valving controls the shock going down the track.
I've never had anyone have issues by stiffening the rebound and there have been a lot of cars where the AS was around 140%. I admit 150% is getting up there in AS, but it looks like you have good shocks and since they are double adjustable, if they can control the separation then everything else may fall into place. The topend stability issues "usually" start getting worse around 43" and usually after the IC gets moved back to 36-38 the tires are loaded better and the car is more stable on the topend and everyone has been able to leave harder.
ks
FYI, ladder bar cars have an IC of 32" and will load the tires a LOT more than a 4link car so the rear shocks are used to control the separation.
I don't know about those rear shocks but the $$$ have a high speed valving that's stiffer that reacats on the launches while the slow speed valving controls the shock going down the track.
I've never had anyone have issues by stiffening the rebound and there have been a lot of cars where the AS was around 140%. I admit 150% is getting up there in AS, but it looks like you have good shocks and since they are double adjustable, if they can control the separation then everything else may fall into place. The topend stability issues "usually" start getting worse around 43" and usually after the IC gets moved back to 36-38 the tires are loaded better and the car is more stable on the topend and everyone has been able to leave harder.
ks
Man, I hate measuring the control arm pickup points. Every time I do this I get different numbers. This time I put weight in the driver's seat to simulate my weight. I still have to double check the projected length for the UCAs.
So far, it looks like the AS% numbers are higher and the IC lengths are shorter than I previously calculated. The AS% difference between the left side and the right side is also greater.
Without the UCA lengths being double checked yet, the new numbers look like this;
Instnt Cntr Lengths: 48.9 left, 43.8 right.
Instnt Cntr Hts: 12.4 left, 11.9 right.
AS%: 126.9 left, 135.8 right. And going straight. Interesting. This is for a calculated CG of 21.7", which could be on the low side.
Instant center lengths hovering around Dave Morgan's box for a 3200 lb., 8.50 car.
So far, it looks like the AS% numbers are higher and the IC lengths are shorter than I previously calculated. The AS% difference between the left side and the right side is also greater.
Without the UCA lengths being double checked yet, the new numbers look like this;
Instnt Cntr Lengths: 48.9 left, 43.8 right.
Instnt Cntr Hts: 12.4 left, 11.9 right.
AS%: 126.9 left, 135.8 right. And going straight. Interesting. This is for a calculated CG of 21.7", which could be on the low side.
Instant center lengths hovering around Dave Morgan's box for a 3200 lb., 8.50 car.
These numbers were with the last tested LCA settings (LCAs angled upwards). To clarify, a couple posts back where I stated, "And going straight", I meant, 'and the car is going straight'.
I measured all the choices of holes, and came up with some proposed top frame holes too. I'll post up the tables showing all the possible combinations for you soon.
But, before I do that I will be checking those projected UCA lengths. If this goes true to form, some numbers are going to change.
As I expected, I was off on the UCA lengths by 1/4". Projected length is 8.125" from axle centerline.
The new numbers for the current setup are;
IC length: 47.8 Lt, 42.8 Rt
IC Ht: 12.3 Lt, 11.8 Rt
AS%: 129.2 Lt, 138.3 Rt
Proposed new top frame mount location would give;
IC length: 39.1 Lt, 35.9 Rt
IC Ht: 10.8 Lt, 10.6 Rt
AS%: 138.7 Lt, 147.4 Rt
The new numbers for the current setup are;
IC length: 47.8 Lt, 42.8 Rt
IC Ht: 12.3 Lt, 11.8 Rt
AS%: 129.2 Lt, 138.3 Rt
Proposed new top frame mount location would give;
IC length: 39.1 Lt, 35.9 Rt
IC Ht: 10.8 Lt, 10.6 Rt
AS%: 138.7 Lt, 147.4 Rt
I will need to add another right side LCA axle mounting hole to get that control arm closer to level. The left already has a hole that will work. Both LCAs will be lower in the back by .062" from level.
I'm working on the x y coordinates for the new UCA frame mount holes to see it you think they'll work before I get under the car to see how they fit.
I'm working on the x y coordinates for the new UCA frame mount holes to see it you think they'll work before I get under the car to see how they fit.
Yea, for the initial measurements let's use the 1.81" for now since thats what the arms are made to work with on the 10bolt. That hole position should clear the existing torque box which is the biggest concern.
I can make longer or shorter ones if needed once you measure where that hole will actually be located on the chassis.
Just to clarify why I would need you to mark the hole position on a piece of cardboard then measure the desired length of the new control is b/c my c.arms are designed for the 10bolt which has the UCA bushings lower than the 12bolt. In order to mount these arms to the taller mounting ears of the 12bolt I may have to make longer arms in order to reach the higher mounting points.
Also, if you drill new holes to level the LCA's and the IC gets moved back round 43" then I would test that setup before installing these buckets.
ks
