Engine angle and IRS Angle [Archive]

Tiger

03-08-2005, 03:34 AM

Hi all,

:help!:

At which angle I should mount the engine and transmission in my Chevelle chassis?
I know that most Dragrace cars have the engine at zero degrees and that most production cars are at approx 3 degrees (being lower in the rear), but I have understood that this is only to create clearance, am I wrong?

Using the Corvette IFS I'll move the engine rearward anyway to clear so I will in any case have to make a new floor and firewall, therefore I'm just interested in whats best.

Can somebody also please explain at which angle I should mount the corvette IRS in my chassis as well.

The IFS is setup for a 3deg rake of the frame if that matters.

Thanks!
André

paul67

03-11-2005, 12:42 PM

what engine are you using carb or injection the angle of the axle has to match the angle of the engine ie if engine angling down 4deg ie for carb to be level then the axle has to point up the same degree, if the engine is injection ie LT1 it has sit flat in car so axle has to match if this does not happen you get a vibration from the prop .I have fitted this combo in my car if you have a vette engine LT1 you need to change oil pan to camaro as the oil pan hits the cross member.
paul67

paul67

awr68

03-11-2005, 03:27 PM

Hummmmm? I was told to install my '96 LT1 motor at 2-2.5* so under hard breaking (front dive) the motor stays level and you don't have an oiling problem....

chicane67

03-12-2005, 05:12 AM

The angle has nothing to do with clearence and/or oiling problems.

The U-joint caps are loaded with small needle rollers and the angular difference (working shaft angle) is set to create the mechanical loading of more than one needle alone. If there is no angular difference, the joint will only load a few needles and will eventually flatten those few needles that are loaded. Also, having a two axis joint without any angular difference can induce vibration.

Most early (IE first gen) engines and drive train are installed (from the factory) with four degrees of angle. The differential housing is welded with four degrees of angle to set a mechanical difference to compensate for the drive train being loaded upon acceleration and common road going loads. The shaft is also skewed off axis laterally to compensate for engine loading (torque). This is more apparent when using factory/replacement rubber enging and transmission mounts. When using solid engine and ploy transmission mounts the number can be reduced, but I wouldnt reduce the number by more than half (2 to 2.5*).

There have also been some guidelines to follow when using an automatic or manual transmission as well. Here are a few differnt opinions on this subject and you will see from reading them that opinions do differ, but here are a few to read:

http://www.roddingroundtable.com/tech/articles/driveline.html

http://www.baselinesuspensions.com/info/pinionangle.htm

http://www.drivetrain.com/driveline_angle_problem.html

http://www.streetrodderweb.com/tech/0203sr_driving/

I have more if you want to go farther, into more detail.

paul67

03-12-2005, 07:21 AM

Just a quick note the links are for live axles, which moves up and down, he has asked for fixed axle which does not move so you get no movement under load, on the engine thats how i was told to fit it by street and performance and also fitted by GM in the vettes and camaros.
paul67

paul67

Tiger

03-12-2005, 09:37 AM

First off all thanks for replying.

would it be correct to put the gearbox rear down at eg. 3deg and at the same moment put the IRS center section front down at eg. 1deg (to compensate for lifting when applying power).
Thanks
André

chicane67

03-12-2005, 10:06 AM

What ever angle the engine is mounted, the differential needs to be mounted the same. If the engine is mounted 2 degrees, the differential needs to be at mounted 2 degrees.......no matter if it is a solidly mounted IRS or transaxle for that matter.

An articulating solid axle should see very little pinion angle change if the spring is constructed correctly, for the amount of suspension travel from static ride height to its loaded position.

We at ATS have recently installed an C4 IRS in a first gen and have located the engine and IRS at 3 degrees, because of the expected power from a relocated big block......but my point is, that it has to be equal of what the engine is mounted.

Tiger

03-13-2005, 01:44 AM

Ok, now I think I got it.
2 or 3 deg rear down at the engine and the same amount front down at the IRS.
It doesnt matter that one is front down and the other is rear down, right.

Thanks André

awr68

03-13-2005, 08:57 AM

So with my SBC (LT1) and a parallel 4-bar rear suspenion that calls for no pinion angle (front of housing plumb) due to the fact that a 4-bar susp. sees no pinion change threw suspension travel, I'm safe with the motor at 2-3*...correct??

chicane67

03-13-2005, 10:14 AM

Tiger

03-13-2005, 11:39 AM

Hey Chicane,
I am sorry to go on about this but I just want to do it 100% right the first time.
Should I go engine rear down at 2deg and IRS front down 2deg?

the fact that I have put the front suspension in the frame considering a 3deg rake of the frame doesnt matter as long as I measure both the engine angle and IRS angle with the frame level right?

Thanks
André

chicane67

03-13-2005, 03:17 PM

Sorry ? For what ? Man, this is why we are here.....the need to exchange idea's and information is paramount to doing things right the first time !!

In answer to your question, yes. Whatever the angle is at one end, it has to be the same at the other (with some exceptions to this rule, but not here). If you have 2* down at the tail shaft, you would need 2* up at the pinion yolk. You are correct, this is totally unrelated to frame angle. You just have to have, the same angle on both ends, regardless of any frame/chassis rake/rideheight.

On a side note, unless you are running solid bushings in the "batwing" of the IRS, and you are also using solid engine mounts......I would set an angle more around 3.5 to 4.0*. The only time I would set anything at that shallow of an angle is, if it has solid mounts that securely located the engine/ transmission and the IRS, limiting its movement under load.

awr68

03-13-2005, 09:02 PM

Now, why does it call for no pinion angle ? I dont believe that to be true, due to the fact that there is pinion angle change in its motion unless you links are like 85+ inches in length, through the required suspension travel from droop to bump.....

Secondly, the pinion angle in a four bar is what changes your 'forward bite' and locates the instant center. Not to forget to mention, that the u-joint still needs angle in itself so that you dont flatten the rollers in the caps.

But to answer your question, I would be totally comfortable with your engine angle being set to 2 to 3*.

Chicane thanks for the help!!!

Ok, now I'm going to have to do some homework, when I purchased the 4-bar kit from AME I thought I was told that when setting up an equal length 4-bar you want the face of the housing plumb...no pinion angle...remember this is not a 4-link where link adjustment is everything. The way I understand it, with the equal length bars the pinion angle never changes while going threw suspension travel, actually I just found this on AME's site:

"For many applications, the 4-bar suspension is preferred. Operating on the principal of a “constant motion parallelogram,” the design of the 4-bar is such that the rear end housing is always perpendicular to the ground—pinion angle never changes. This, combined with the lateral stability of the Panhard Bar, does an excellent job of locating the rear end and keeping it in proper alignment."

It's not that I don't trust what you are saying, and I totally understand the u-joint angle issue...but I'm getting conflicting info from two people I totally trust when it comes to suspensions....hope you understand.

chicane67

03-13-2005, 09:57 PM

For an initial set-up, I would agree with ~no~ angle.

But like I said. If I remember correctly your four link, lengths...... would have to be in the 'hood of somewhere around 63 to 65 inches in length for it to actually have zero (actual terms of 'minimal') pinion angle change throught its range of motion. With the practical arm lengths, that you can actually package into a 105 inch or so wheel base, it will have some angle change in it no matter how hard you try to dial it out. The links are just too short to geometrically make this a realistic possible.

Dont sweat it, I do understand. As "we" (the two you know) are both at an argueable point of splitting hairs..... but the geometrical answer does fall towards my side of the story. In reality, the change probably isnt going to be much, but then again we havent discussed your link lengths (and the rest of the set-up) to really determine (in your range of motion) if this is something that should be scrutinized.

The possibility still remain's. But we are going in the right direction..........

dennis68

03-13-2005, 10:27 PM

In answer to your question, yes. Whatever the angle is at one end, it has to be the same at the other (with some exceptions to this rule, but not here). If you have 2* down at the tail shaft, you would need 2* down at the pinion yolk. You are correct, this is totally unrelated to frame angle. You just have to have, the same angle on both ends, regardless of any frame/chassis rake/rideheight.
.
Tommy, are you sure about that? I have always set them up opposite. If you are down 2* at the tailshaft then set the pinion to 2* up, as long as operating angle is within a degree or so. That is how DCX wants their chassis set up and how I have always done it.

chicane67

03-13-2005, 10:45 PM

What do you call typing dyslexia ???

The answer is equal and opposite angles. Example given: 2* down on tailshaft, and 2* up on the pinion. Factory GM is 4* down, 4* up.

But they have to be equal. 2 up for 2 down, 3 up for 3 down......you get the idea......

**I will edit the above so as not to confuse myself or anyone else about my typing dyslexia**

dennis68

03-13-2005, 11:02 PM

I figured, didn't want to go cc.com on you though. :slap:

parsonsj

03-14-2005, 09:34 AM

Tom (and Anthony),

The AME 4 bar has *no* pinion angle change during bump or rebound. The upper and lower control arms are parallel to each other, such that the SVSA is infinite.

For the least amount of driveline vibration and longest life on u-joints, I agree with equal and opposite (3 down for engine, 3 up for pinion). However, that's usually not ideal for anti-squat behavior. Usually, for anti-squat, you want the SVSA somewhere so that you have anti-squat in the neighborhood of 50-60 percent. And that usually means a downward pointing pinion angle, or at least one that doesn't point up. Different solid axles geometries (and of course IRS) make for different settings, but the point is that optimum traction and braking behavior settings are usually not the same as the best vibration and u-joint settings.

jp

dennis68

03-14-2005, 10:14 AM

chicane67

03-14-2005, 10:24 AM

Different solid axles geometries (and of course IRS) make for different settings, but the point is that optimum traction and braking behavior settings are usually not the same as the best vibration and u-joint settings.

I agree with that. But.....

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.

And that was the point that I was trying to convey. You will induce pinion angle change with links as short as this, with this set-up (AME 4-bar). Now, with links in the 65 inch range you might get closer to zero angle change at 6 inches of articulation, but even that is being greatly optimistic.

And this is where we could (unnecessarily) start splitting hairs........... :naughty:

(and no I am not inciting any cc.com, knockdown, hardcore tech challenge at this one. my typing skilz will most likely get me spanked)

Tiger

03-14-2005, 10:41 AM

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

03-14-2005, 11:05 AM

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

03-14-2005, 11:45 AM

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... :bananna2:

parsonsj

03-14-2005, 12:39 PM

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

03-14-2005, 01:09 PM

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

03-14-2005, 03:28 PM

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

So what is SVSA??

parsonsj

03-14-2005, 05:56 PM

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

03-14-2005, 09:52 PM

Thanks!! :)

dennis68

03-14-2005, 10:06 PM

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

03-15-2005, 09:32 AM

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

03-16-2005, 04:06 AM

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

03-16-2005, 06:29 AM

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

03-16-2005, 11:38 AM

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