pinion angle change

[jerome]

I had originally planned for a 3link that had a shorter third link, but I really don't have any packaging issues or a specific reason to make it shorter, and I figure a single crossmember would be easier than two.

So, here's my question. How should the pinion angle change in bump and droop?
1. no change relative to ground
2. no change relative to driveshaft
3. tilt up
4. tilt down

are most of the third links that people make, just shorter because of packaging? or is it because the want the pinion to tilt down under bump and tilt up under droop?

everything I have read about pinion angle says that it is NOT a tuning factor for acceleration and you won't find extra tenths by changing it. however, I haven't been able to find what the ideal change or lack thereof should be. I have heard a rough guideline for the correct pinion angle change as the third link is 2/3 the length of the other two. But, I would rather just make the 3rd link the same length to make it simpler to construct. Any disadvantages?

Thanks,
Jerome

[Norm Peterson]

They may be shorter in order to make the change in anti-squat more stable, either gaining more A-S as the car squats under acceleration - or at least losing less of it. Keep in mind that 100% A-S and up numbers are more like dragstrip values, so you should generally plan on having some squat.

The other thing is that the arrangement that loses lots of A-S in bump also gains a lot of anti-lift on the rebound side (read: more likely to bring on brake-induced wheel hop).

For a positive value of anti-squat, along with a reasonable roll center height and a small amount of roll steer (in the vehicle understeer direction), you want the SVIC to be above the ground and ahead of the rear axle line, which corresponds to the pinion tilting down in bump.


Norm

[jerome]

If I am understanding correctly, pinion angle change doesn't matter much. The relative length of the arms is usually determined to make a favorable antisquat curve.

Did some more calculations, and here's what I came up with:

lowers 36" longitudinally (they are converging)
upper 16" long

that gives me a flat antisquat curve when static is set at 100%.


This is a probably a loaded question that cannot be answered without knowing alot more things, but...generally, is a flat antisquat curve optimal, or does it need to go in the direction of more antisquat in bump and less in droop?

[73ta]

Pro-stock chassis builder Jerry Bickel: Negative angle down
ladder bar suspension : 1/2 degree
4 link: 1-2 1/2
Leaf spring: up to 6-7
Quote: a straight driveline delivers the most power to the rear wheels.

Ray Currie:
Street car: 2 degrees
Quote: people increase the pinion angle to increase dragstrip bite, but he does'nt reccomend that for a street car.

**** Miller:
400 Hp: 2 degrees
500-650HP: 3 1/2-4 1/2
700+ HP: up to 7 degrees
Quote: the greater the pinion angle, the more horsepower the driveline will consume.

The just of it all is that you want the driveline, rear and trans as straight as possible under full power. Nose down degrees are to compensate for flex in the rear suspension and the nose raising under power

[MonzaRacer]

Ok to clear things up on pinion angle:
A leaf sprung car can use as much as 4 to 4.5 down angle sitting at race weight. this is max any more and you will be buying pinon yokes take that from experience.
A 4 link is measured differently as you have to know where your cg is.
Center of Gravity is you take a the center point of the canshaft and run a diagonal line down to the frame rail and when you (in theory) lift the car with a triangle block at that point and the car balances perfectly (ie no teetering like a teeter totter) draw that line down.
Then you take the straight line through the lower arm piviot points forward and then the upper arms pivot points forward.
This will tell you where they meet forward and the relation ship of the cars lifting(ie launching force) causes the rear suspension to try to "grap " the handle of the front of the car and pull it up.
Now in a properly balanced car the proper point is where the front tires just skim the ground and the rear tires are loaded so as to deliver ALL of the available power on launch without spinning or slipping.
Now a coil sprung car its given to run in the 1.5 to 2,5 range and basicly the pinion should not go up.
To measure this get a digital level from Sears for about $50 and you zero it on the drive shaft then I use a machined slug to sit on the pinion ujointand I use regualr inside spiro locks inplace of the stop ujoint clips (if its and outside cliped ujoint) or if you have a nub in the yoke to hold the cap in. There are several ways I do it ,its car dependednt. but assume the drive shaft is "level plane" and the pinion should be down, one for lube purposes and another as under power it should be static (ie 0 ) under heavy load.
as for the big degress in big power cars ,,MAYBE if its light enough but if you do that much in heavy cars and it breaks parts.
Chrysler did the next best thing they added the degrees to the pinion angle but used a pinion snubber to keep it from going over zero at launch. A crutch maybe but it also saved weaker diffs.
Besides you wont need that much on take off in a road car.
I assume your using coil overs with a three link I would set my static9at rest in the 2.5 degrees down with full tank of fuel, i never dial a car in with half a tank I tune it as it lowers. And I am by no means a perfect tuner but I helped a buddy set up his 73 Camaro and we gave it 4.5 down pinion angle ,we built the bars from and old set of $39 slappers and some metal ewe had laying around and some cheap spring cups in place of the factory spring mounts.
The car with a worn out 283 and a old th350 and a cheap converter would give us 1.81 60 foots on street tires and 1.70s on slicks.
We had no power and hooked!
this car had the 456 taken out after he sold it and the guy put in 3 somethings, a small 350 and drove it and added some 17s on back and its a very stable on turns from what i saw(they did pullout the race prep shock bar and went with stock mounts.
heres a lisst that I use"
4 link generally 1 to 2.5
coil sprung and certain coil overs 1.5 to 3.5
ladders depends on the spring used, you use more on leaf cars.
Leaf cars in the 2 to 4.5 and maybe use a pinion snubber.
IF you add or use more pinion angle on the street you can nad will trash ujoints and and yokes.
My max would be 4 deg down on street.
Pinion angle is the adjustment used for bit EXCEPT for a 4 link. The 4 link is the traction the pinion angle is simply ANOTHER tuning tool.
I like to take a 4 link at first I start with the (provided I am doing from scratchI set my meet point directly above the CGthen I move it down till it has no improvement then move it forward till it slows.
The meet point of the uppers and lowers is your tuning for launches and and a set pinion angle.
Then I use the pinion angle to tune for tracks, power down ,more bite,,well ferocity is the best word for it.
I also like to get new drivers to start with my spec engines and good chassis cars and train them from thier then let them up grade the power ,then getthem to max the chassis tune out ,then bring the chassis back into hooking. I have put several guys in slapper bar cars and got them from stock engines to modded engines and now 5 to 10 yrs later they have nice pro built race cars and are going fast.
Good luck
Lee Abel
AFTERMARKET PERFORMANCE