Engine angle and IRS Angle

[Tiger]

Now I'm confused again, I always thought that the pinion would have to point down to compensate for a bit of climbing under power, or does whats written in the first website not mean that it has to be pointing downward but mean that it should point one degree further down than the trans to compensate for climbing?

Example.
trans 4deg down, pinion 3deg up (to gain 4deg while under power).
Is this right?

BTW. I have poly bushings at the engine and trans and rubber in the batwing.

I'm starting to feel really stupid now :o(

Thanks André

[parsonsj]

John, I fail to see how pinion angle has an impact on AS. AS is determined by the SVSA, which has no bearing on pinion angle (well maybe an inch or 2 but not enough to be a determening factor).

All suspension designs will have some pinion change throughout travel, it is virtually impossible to move the axle through a 6" travel and have 0 pinion change. Minimal perhaps but you can't say *no* change.

Sorry, I wasn't being all that clear. In the real world, it's the other way around. Setting up the SVSA for AS will change the pinion angle. Change the lengths or connection points of the linkage arms of the suspension, and most likely you'll change the pinion angle. This will be true unless you can rotate the housing mount points around the centerline of the axle ... which doesn't occur in the real world.

There is no change in pinion angle using the AME 4 bar. The upper and lower control arms are equal length and parallel. The connection points on the housing and the crossmember are equi-distant, and parallel. They form a perfect parallelogram. The SVSA is infinite. The pinion angle does not change through 6" of travel, and wouldn't change through 12" of travel (if that were possible in the real world).

jp

[dennis68]

Sorry, I wasn't being all that clear. In the real world, it's the other way around. Setting up the SVSA for AS will change the pinion angle. Change the lengths or connection points of the linkage arms of the suspension, and most likely you'll change the pinion angle. This will be true unless you can rotate the housing mount points around the centerline of the axle ... which doesn't occur in the real world.
jp

Well, were getting a little off topic but for future reference purposes I'll explore this a little. Shortening SVSA for improved AS does have to increase pinion angle. On stock pick ups yes, but if you are building from scratch there is no reason SVSA has to have any affect on pinion angle at all. Just change where you weld the mounts to the housing or the frame.



Or run a full floater birdcage...

[parsonsj]

On stock pick ups yes, but if you are building from scratch there is no reason SVSA has to have any affect on pinion angle at all. Just change where you weld the mounts to the housing or the frame.

Yup. We're in agreement.

jp

[dennis68]

PS, I see where you went with the parallel 4-link....the sytem would run into full bind way before the pinion angle changed.

[awr68]

Thanks for all the input guys and Andre sorry to steel the thread....we kinda needed the same info.

So what is SVSA??

[parsonsj]

SVSA: side view swing arm. The virtual connection point of the uppper and lower control arms if they continued forward. It is measured by the distance from the virtual connection point to the axle centerline. SVSA in conjunction with the center of gravity (CG) of the vehicle determines anti-squat. Anti-squat is the term that deals with how a vehicle squats during acceleration. If the vehicle has over 100% AS, it will actually lift during acceleration.

jp

[awr68]

Thanks!!

[dennis68]

Go check out the suspension section for guidelines on setting up the back half. Having really high AS may seem great but it has a downfall.......go research.

[Jim Nilsen]

To get the full picture you have to include the height of the ends of the driveshaft too. Pinion angle is directly related to driveshaft angle and both have to be moved accordingly. Just look at some of the rock crawlers.

My trans is angled down a bit and my pinion is down a bit but because they are at different heights the driveshaft angles should be ok. A lot of cars are setup this way and don't have problems, but you never really know till you drive them.

Just make sure to go more by the driveshaft angle for vibration control and and pinion angle for deciding how you want the car to handle depending on the setup. You can change a lot with 3 inches of height difference at the trans tail shaft.

Jim Nilsen

[Tiger]

Thanks.
If you were to install the engine and trans in the frame before installing the IRS at which angle would be correct to mount it?
Or
should I do the IRS first ?

thanks
André

[Salt Racer]

I don't know who told Anthony to set the pinion angle at zero, but...

It really should be determined by crank centerline/tailshaft angle as well as how much compliance you have in your suspension.

Theoretically, the pinion should have zero angle relative to crank centerline, ie, they need to be parallel to each other. However, nothing in this world is rigid. Everything behaves basically like springs.

In this case, rubber/poly bushings have noticeable deflection under hard acceleration. Axle housing reacts to the torque resisted by traction, and pinion will try to tip up. AME's current poly bushings have durometer of Shore A95, which is on relatively stiff side but they still deflect quite a bit.

You want pinion centerline to be parallel (or close to it) with crank centerline under hard acceleration b/c that is when U-joints are subjected to highest loading.

I'd set the -2.0~-2.5* static pinion angle (pinion angle 2.0~2.5* down from dead parallel) if you have poly bushings. You can get by with slightly less with rod ends, and you'll probably need more with rubber bushings, soft leaf springs, etc.

[paul67]

there are loads to think about, what engine are you using, I would fit the engine first if you intend to put a new fire wall and tunnel, also have the car sat at the angle and height that you want it to sit at . If you are using a carb engine the carb has to sit flat so this will depend on angle of the manifold used but this can be machined to suit if the cars angle alters after, if you are using the LT1 engine and gear box it comes with an alloy torque strap that runs from the engine to the diff this will show you that this engine runs flat in the car and meets the diff at the same angle if you want confirmation look under 1 camaro and vette or look a service book , need to know what engine
paul67

[Tiger]

Hi,

I have a SBC (carb) with a D&D Gm converted Viper T-56 and a Dana 44 Corvette C4 rearend and its all to be mounted in a 1968 chevelle frame.
I think I got it now.
pinion centerline and crank centerline parallel and then the pinion some degrees down to compensate for raising under power.

André