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 Post Posted: Wed Aug 19, 2009 10:27 am 
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Seems we're having traction problems again with my Camaro. Only change from last year was the camshaft swap last winter and so far this year this thing as been impossible to dial. We've changed tires thinking that the Hoosiers were on the way out but that didn't help. So, I made a 4link adjustment last weekend moving the IC out about 2 inches and up about 2 inches so we'll see what happens this Friday.

Was talking to Jason Kowalsky yesterday about this and he told me that Vanishing Point Race Cars gave them some info on which holes to use on the rear housing brackets, something I've never even considered before. Accorging to them, engine HP output is directly related to which holes you use on the rear housing. Lower HP likes holes further away from the axle center line while high HP likes holes closer to the axle CL? If you look at the geometry of those holes, it kinda makes sense that low or high HP would like different mounting points?

Anyone ever hear of this and or experimented with different combinations taking this into consideration?

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 Post Posted: Wed Aug 19, 2009 8:23 pm 
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Top bar maybe.... but from what I was taught, the bottom bar is usually set as close to the same height as the rim as possible. This information came from a well known Prostock team a while back.

How far out is the IC of the car after you changed it? How high is it now aslo? Springs and shock settings? Car weight? Estimated HP@rpm? Torque@rpm if you have it also?


Don

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 Post Posted: Thu Aug 20, 2009 9:57 am 
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want-a-be wrote:
Top bar maybe.... but from what I was taught, the bottom bar is usually set as close to the same height as the rim as possible. This information came from a well known Prostock team a while back.

How far out is the IC of the car after you changed it? How high is it now aslo? Springs and shock settings? Car weight? Estimated HP@rpm? Torque@rpm if you have it also?


Don


Car is 2450 lbs WET and on methanol it's making somewhere around 775HP. No dyno numbers available but the gear change is made at 7600rpm and it's trapping just over 7300 in the eight mile. Converter flashes up over 5900 and dead stalls on the brake just over 6200. Fall back RPM at the shift is 6320. On gas this engine will probably be down about 40hp from methanol. Rear corner weights before I changed out the aluminum center section for a nodular one were 600 driver side and 613 on passenger side with me in the car.

Went from 51.1 out and 3.6 up to 54.1 out and 5.0 up. The car is 108 wheelbase.

AFCO shocks with 125lb springs. 10 clicks on compression and 5 on rebound (they have about 30 clicks available on both).

5:14 gear 1:80 planetary with 100" roll out tires that are 14.8 wide on 15x15 wheels. These are MTs in the L8 (soft) compound. Been running 10.5 psig but tried 8.5 psig last time out and it blew the tires off at the hit. Noticed when I had the tires off the other day that the mold marks are still in the center of the tires after about 20 passes? Plan this week includes trying higher tire pressure up around 12.5psig.

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 Post Posted: Thu Aug 20, 2009 5:38 pm 
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How did the car react when you mmoved the ic from 51" to 54 "?

When you changed out the center section.....did you reuse the same internals? Rotating mass may have changed for the worse if you didn't. :-k

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 Post Posted: Thu Aug 20, 2009 6:18 pm 
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want-a-be wrote:
How did the car react when you mmoved the ic from 51" to 54 "?

When you changed out the center section.....did you reuse the same internals? Rotating mass may have changed for the worse if you didn't. :-k

Don


RE: The new IC? Won't have any data on that change until tomorrow, if it doesn't rain out! They're calling for 69% chance of storms so we may not get to go.

But yeah, I moved the IC out some to try to slow the hit a bit so maybe the tire could catch up. Been reading Morgan's Doorslammer book and just decided to try this to see how it reacted. The guy I bought the car from had the IC out at 58 and up 10+ for 103% on the antisquat line. He was running 4.80s with this car and had done a 1.09 short time with it. I had to move it back to make my "junk" engine work with it.

RE: Housing? All that was changed was the housing and the gearset. Used the same pinion suport and spool.

Anywho, we may have some data tomorrow night. I'll post the results on the board.

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 Post Posted: Thu Aug 20, 2009 8:00 pm 
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Ken,

I'd consider the 58" @ around 4"-6" off the ground. I'd at least have it mapped out in case you want to make the change at the track. Thats a good starting point that I like for BBC type torque. But you do have a known starting point from last year. If you do go to the longer ic (58") you might need to lighten up the extension of the shocks on the rear. I'm thinking by making the hit a little milder with the longer ic you might need to quicken up the hit with the shocks a bit. But I would not try them at the same time.

How many inches are you running? What was the old cam specs and what are the new ones. Might have made a pretty good difference. What is the whole engine combo actually.

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 Post Posted: Thu Aug 20, 2009 8:16 pm 
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Never seen any mid 5 second 2450lb car require that much air pressure, you have other problems somewhere. JMO

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 Post Posted: Sun Aug 30, 2009 9:34 pm 
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I moved my top bar down a hole at the housing and the 60' picked up a little , but I know my tires are done. The reason I moved it was because mine was hitting the tires hard (1.09-1.10 60' ) and the tires quit hooking about 30 passes. I am suspecting it beat the side walls out of them and I wanted to remove some of the instantaneous hit . My ic setting was 49.3" @ 5.7" high , it is now at 60.9 @ 5" high. That is on a 110" wheelbase.

Moving the top bar down is supposed to slow the instantaneous hit and apply more leverage as the car moves out. It makes since to me because the closer you get to the housing the arm is getting shorter , it should slow it down and let the housing apply more pull on the chassis.

I would almost agree with Want a bee on the bottom bar , but I feel the overall height of the bar in reference to the cog is more important than just a generic height with out weighing out the ride height of the the car itself. There are lots of back half and chassis cars that set considerably higher than an all out chassis car , it would only make since to me that the cog is higher.

I would also say in most cases the housing brackets are going to be about the same height in both styles of cars, how could a bar the same height work the same in both cars ? I am not knocking the theory just curious .

Will the top bar setting band aid a bottom bar that is too low by pulling up on the chassis ?

Great discussion guys I am always interested in suspension threads to try and learn all I can .


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 Post Posted: Mon Aug 31, 2009 5:46 pm 
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ky mustang wrote:
I moved my top bar down a hole at the housing and the 60' picked up a little , but I know my tires are done. The reason I moved it was because mine was hitting the tires hard (1.09-1.10 60' ) and the tires quit hooking about 30 passes. I am suspecting it beat the side walls out of them and I wanted to remove some of the instantaneous hit . My ic setting was 49.3" @ 5.7" high , it is now at 60.9 @ 5" high. That is on a 110" wheelbase.

Moving the top bar down is supposed to slow the instantaneous hit and apply more leverage as the car moves out. It makes since to me because the closer you get to the housing the arm is getting shorter , it should slow it down and let the housing apply more pull on the chassis.

I would almost agree with Want a bee on the bottom bar , but I feel the overall height of the bar in reference to the cog is more important than just a generic height with out weighing out the ride height of the the car itself. There are lots of back half and chassis cars that set considerably higher than an all out chassis car , it would only make since to me that the cog is higher.

I agree with you on this. But the car I was talking about usually has a ride height of 6" or less.

I would also say in most cases the housing brackets are going to be about the same height in both styles of cars, how could a bar the same height work the same in both cars ? I am not knocking the theory just curious .

Actually...you're more right here then you may know. Most 4-link brackets are designed for lowered cars. When buying a new 4-link you need to consider the ride height of the car, then ask the 4-link manufacturer if his brackets are designed for that height.

Will the top bar setting band aid a bottom bar that is too low by pulling up on the chassis ?

As a rule of thumb, that I use for a starting point, on small blocks & lower powered big blocks I'll go with the upper bar being as far from the rear end housing as can be had. On big blocks I'll start out closer to the housing.

Great discussion guys I am always interested in suspension threads to try and learn all I can .


Same here.

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 Post Posted: Sun Sep 20, 2009 8:42 am 
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This post will undoubtedly upset some of you. I assure you that is not my purpose. I'm just trying to encourage some further thought with regard to instant centers, antisquat, suspension geometry, etc.

We all know how to draw lines through upper and lower links of a 4link and find the instant center. We also know that the instant center for a ladder car is simply the front pivot for the ladder. With a ladder bar car, the forward push at launch must act at that pivot point. With a 4link, the instant center is equivalent to the pivot point for a ladder bar. In other words, if a ladder car had its pivot point at the same location as the plotted instant center for a 4link, the performance would be the same. And, why would it be the same? It would be the same because the forward push is acting at the same point...the instant center.

Going back to the ladder car: The ladder bar is solidly attached to the rear axle housing. As a result, the ladder and housing act as if they were one member. The shape or slope of the ladder bar is totally unimportant. The ladder could be formed in the shape of a pretzel and, so long as the pivot point remained in the same place, the performance would be unchanged.

Just as the ladder bar could have any shape without affecting performance, so could the links of a 4link be moved all over the place, SO LONG AS THE LINK LINES CONTINUE TO INTERSECT AT THE SAME INSTANT CENTER. The rest of the car doesn't know whether it's a ladder bar suspension or a 4link. Or whether the rear link mounts are close to the axle housing or far. All it "feels" is a resultant force acting at the instant center.

But, here's where it gets really interesting! That forward push is generated at the rear tire patch, which means that the resultant force acting at the instant center must have a line of action which also passes through that same rear tire patch. This line is a line of constant percent antisquat. If it has a slope equal to the center of gravity height divided by the wheelbase, it's the 100% antisquat line (often called the "neutral" line). If the slope is greater, the car will have "hit" or "separation" or, in other words, the rear of the car will rise on launch. If the slope is of a lesser value, the car will squat.

This will seem silly, but consider balancing a pencil on your finger. The force is acting vertically upward through the center of gravity. Then, tie a thread to the pencil at the same point and suspend it by the thread. If you've tied the thread at the center of gravity, the pencil will again be balanced. But, the force is now being applied above the pencil. The force line of action is the same...a vertical line..., but the force is being applied at a different point along the line. This is a VERY important principle. The effect of a force is unchanged when it is moved anywhere along its line of action.

So, with a force line of action that passes through the rear patch and the instant center, we can move the point of application of the resultant force...the instant center...anywhere along that line and the rest of the car will not know the difference. An instant center that is 60 inches out and 10 inches up is EXACTLY equivalent to one that is 120 inches out and 20 inches up. Or, 60 FEET out and 10 FEET up. In other words, what's important is the antisquat percentage and NOT the actual location of the instant center.

A dramatic example is found with the 4bar suspension. With the end brackets keeping the upper and lower bars parallel at all times, it is impossible to construct link lines which intersect for an instant center. But, as I'm sure you're aware, parallel lines meet at infinity. So, if the 4bar is installed with the bars parallel to the 100% antisquat line, the car will have 100% antisquat, EVEN THOUGH THE INSTANT CENTER IS AT AN INFINITE DISTANCE FORWARD AND AN INFINITE DISTANCE UP. Again, it's the percent antisquat that's significant, NOT the actual location of the instant center.

Yes, I know you've all heard explanations about "lifting" effects of link positions and you've seen pictures of a refrigerator being pushed around, but, when it comes to working with numbers, those explanations fail.

I'm certain I've ruffled some feathers, but, again, that certainly was not my intent.

If you have further questions, you might want to take a look at Page 38 of my site.
http://www.racetec.cc/shope


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 Post Posted: Sun Sep 20, 2009 5:03 pm 
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Billy you have not ruffled my feathers one bit. I do have some questions though.

Why are ladder bar brackets designed with the bottom rod ends significantly lower at the housing than the top rod ends if the shape and size makes no difference ?

What if the bottom rod end on a ladder bar was only 1/2" from the housing center would it work the same as correct laid out design in the same front bracket setting ?


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 Post Posted: Sun Sep 20, 2009 7:16 pm 
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ky mustang wrote:
Billy you have not ruffled my feathers one bit. I do have some questions though.

Why are ladder bar brackets designed with the bottom rod ends significantly lower at the housing than the top rod ends if the shape and size makes no difference ?

What if the bottom rod end on a ladder bar was only 1/2" from the housing center would it work the same as correct laid out design in the same front bracket setting ?

Static preload should not be confused with the instant center and its importance. The brackets are designed to allow both static preload adjustment and adjustment of the pinion angle. But, whether static preload is used or not, the resultant force still acts at the pivot point (the ladder bar instant center).

What I was getting at is that there is no significance to the angle of the ladder bar relative to the ground. The ladder bar could be vertical at the front pivot and then be formed like a pretzel before attaching vertically to the bottom of the axle housing. All that's important is the location of the front pivot point. There must still be some bracket spread at the axle, however, if provision is to be made for static preload and pinion angle adjustment.
http://www.racetec.cc/shope


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 Post Posted: Sun Sep 20, 2009 9:50 pm 
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ky mustang wrote:
Billy you have not ruffled my feathers one bit. I do have some questions though.

Why are ladder bar brackets designed with the bottom rod ends significantly lower at the housing than the top rod ends if the shape and size makes no difference ?

What if the bottom rod end on a ladder bar was only 1/2" from the housing center would it work the same as correct laid out design in the same front bracket setting ?


They have to fit under the body as well, more room available below the axle tube.


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 Post Posted: Mon Sep 21, 2009 7:36 am 
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BillyShope wrote:
What I was getting at is that there is no significance to the angle of the ladder bar relative to the ground. The ladder bar could be vertical at the front pivot and then be formed like a pretzel before attaching vertically to the bottom of the axle housing. All that's important is the location of the front pivot point. There must still be some bracket spread at the axle, however, if provision is to be made for static preload and pinion angle adjustment.
http://www.racetec.cc/shope


So it does not matter the least bit how high the bottom bar on a ladder bar is in relation to the housing center line as long as there is room to add preload ? The angle of the ladder bar in correlation to the chassis has zero effect on squat /anti squat its all dictated by the height of the front link ?


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 Post Posted: Mon Sep 21, 2009 8:55 am 
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ky mustang wrote:

So it does not matter the least bit how high the bottom bar on a ladder bar is in relation to the housing center line as long as there is room to add preload ? The angle of the ladder bar in correlation to the chassis has zero effect on squat /anti squat its all dictated by the height of the front link ?

You got it!
http://www.racetec.cc/shope

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