9 inch rear end questions

[CobraV8]

I'm building a custom 9". As far as I understand, the pinion angle should be at +3degrees. Does it also make sense to center the differential under the car, or should it be offset with one axle tube longer than the other? Axles have to be custom made anyway, so that wouldn't be a problem.

Thanks, Simon

btw does someone have a set of the weld on brackets for the axle housing left over and wants to sell it?

[Double Venom]

CobraV8-
First and formost your piniion angle should never be "positive" (Pointing upward-massive wheel hop problems!) under any circumstances! You can cut both axles to center the pumpkin but that really isn't necessary. The car is originally built to the stock 8.8 rear and it is offset to begin with.

When I order a custom 9" from "Currie" or whomever I tell them to weld in the exact same brackets as the 8.8 and in the exact locations, including shortening the one axle tube to the same as the 8.8.

When done your 9" will look just like an 8.8 except you will have the 9" pumpkin.

Pinion angle should be a minus 3 degrees, +/- 1/2 degreee. Again depending on your HP, TORQUE numbers, traction and how hard and long you intend to -stay in it- at launch. The higher the torque/HP, the more traction you get, and how hard you launch- (I.E.;1/4 mile racing) can equate to a full 3.5 degree negative angle.)

Scott is in the middle of correcting his engine and pinion angle right now. It might help to glance over his thread.
DV

[CobraV8]

Thanks DV, a lot of good advice! If there is no benefit from centering the differential, I won't do it.

Is there a source for the brackets at a reasonable price? It would save me some time measuring and fabricating.

[Double Venom]

Fella,
I hate to say this but I don't know of a supplier for the bracklets. Plasma cutter and a blown up rear end??

How about getting hold of Terry Gattrell at http://sebring-mx.com/ , Terry is the one trying to salvge CR's and is a pro at the Sebring/MX's. What parts he doesn't have he makes them in house.
DV

[bobcowan]

>> As far as I understand, the pinion angle should be at +3degrees. <<

Pinion angle is a complicated subject, and easy to get wrong. The first thing is, what is pinion angle, exactly? The pinion angle is measured against the drive line, not the horizon. This is a key point. Maybe the most important points. Before setting pinion angle, you have to install the drive line and measure the power angle.

The second thing is, what are you tryng to accomplish? Under power, you want the drivce line angle and the pinion angle to be exactly the same. When they're not the same, it costs you power. Street cars do well with 1.5-2.0*, drag racers do well at about 3-3.5*. IRS cars get 0*. Again, all compared to the power angle, not the horizon.

When you let out the clutch, the tires want to spin one way, and the differential wants to spin the other way. That changes the pinion angle, and brings it closer to the power angle. It may move a lot, or just a little, depending on how the car is built and used.

Do a google search on pinion angle, and you'll get lots of info with pictures.

On the other Cobra forum, we've discussed this quite a few times, with some excellent info and pictures.

[Double Venom]

Bob,
In other words you think the angle should be UP? Your point on the turning of the wheel rotation forces the pinion to re-act in the opposite direction? Exactly! If you dump the clutch so to speak the tires are obviousloy turning in a clockwise rotation, this forces the nose of the pinion to rotate to a "plus setting". This is/was the gratest problems with FFR's a few years ago. Wheel hop was so bad in some of the cars it would knock the dash loose. (I have fixed them.) FFR changed to the new control arms about 5/6 years ago. One FFR with one of the broken loose dash's found his pinion to be over 12 degrees positive with their stock arms.

And a perfectlyt straight line, I am assuming you mean tail shaft,driveshaft and pinion? Or are you just talking about being under power? I would seriously like to see a professional link from any custom car builder to a factory OEM unit that has a "flat non-horizon" set drive line angle?
This old dog is never to old to learn!
My point is, the CR's with a beefed 351-even a 302 under full load, with their or like kind control arms the pinion will go up either adding to a problem with a plus setting or go toward -0-. I.E.; With the Double Venom cobras, Viper V-10 powered and MT Street Slicks, I was lucky enough to have the Honda Engineers (Marysville, Oh.) not only helped check out one of my first DV's, they came to National Trails drag strip in Columbus and not only watched me race they filmed it in slow motion so they could see what all the suspension was doing at launch. From how high the nose lifted to how long it took for it to settle down and how much squat the rear end had.

They did a skid pad test on their track and I will do a little bragging, with their help my DV pulled a plus 1.7 G, almost formula numbers! (Front roll bar disconnested, stock CR's rear sway bar, tubular front suspension with coil-overs, 275lb rear springs also with with
coil overs.

They and "Jegs Coughlin" (JEGS) were at National Trails Drag Strip for the '99 Viper Classics which Chrysler had invited the Double Venom to, to race the Vipers. (Four years and the DV was never beaten-I have the plaques on the wall.....except for the last year.
For three years I beat the same Blue and White Viper. Every year he came with the intention of beating DV. The last race , he (Paul Fischer of Akron) and myself ended up going against each other once again for the Title.

At the last yellow I dumped the clutch hard.... the DV came off the ground and I jumped out in front of Paul by a good car lenght, I slammed second (This car pulled +2.3G's at launch and almost 2 G's going into second. Then it happend, Paul went by me like I was standing still! Well I almost was.....Per the Honda guys, JEGS, and the Chrysler guys that came down to the track and looked at the car all stated my pinion angle must have gone level or even positive as I had actually "Ripped the Ford 9" housing in half! Driveshaft,U-joints,pinion and gears were all fine and actually re-used. The housing itself was litterally ripped in half. You can actuaslly see from the "spli" that the rear end had split from the top down.

I'm serious if you have a link showing a plus pinion angle I would like to see it. Hel, I've eaten Crow before!

Not Enough NEGATIVE/DOWN angle!

[bobcowan]

>> In other words you think the angle should be UP? <<

Yes, as compared to the horizon. Like I said, the pinion angle is measured against the power angle, not the horizon. That is the key point.

In most cars, the power angle is about 5*. That's why the pad on many 4 barrel intake manifolds is milled at an angle. That keeps the carb flat, even though the engine is tilted. It seems that many CObra's have a power angle much lower, like 1-2*.

Under power, you want the power angle/ driveline angle to be the same as the pinion angle. That doesn't mean they'll be perfectly aligned with each other, just at the same angle. The greater degree of disparity between the two angles, the more power loss you have. And the greater probability of wheel hop.

Think of the drive line and pinion as a side view. The drive line is angled at 5*, pointed up toward the front. The pinion is also angled, pointed up toward the front. Under power, you would want them to both be pointed up at exactly the same angle. In this case, 5*.

Under launch, the pinion angle will change, moving upward. The trick is to figure out exactly how much. So, lets say 3*. Since you want the angles to be the same under a load, you set the pinion angle at -3* in relation to the drive angle. Which is actually +2* from the horizon.

An IRS car has a fixed differential. That makes it easy. Measure the drive line angle, then set the pinion angle exactly the same. The easy way to measure the drive line angle is across the face of the front pulley or balancer.

Also, don't confuse pinion angle with offset. U-joints need a little offset to keep the bearings lubed and alive. As the rear moves up and down, the angles of the u-joints will change, which keeps them alive. With IRS, The odds of getting a perfectly straight line from the pinion to the trans is pretty slim, but I suppose it could happen. If it did, probaly the easiest thing to do would be to cock the driveline 1* to the left, and the pinion 1* to the right. Angles would still be equal, but it would have a 2* offset.

Carroll Smith's series of books starting with, "Engineer to Win" are an excellent resource for this sort of thing.

Go to the other Cobra site and do a search on "pinion angle" and you'll get about 18 results from the last year.

Also, do a google search, and you'll find some excellent resources, complete with pictures and diagrams.



"Ideally, the angles between the transmission output shaft and driveshaft, and between the driveshaft and the pinion will be equal and opposite."
http://www.carcraft.com/howto/91758/index.html

"Pinion angle is the difference between the driveshaft angle and the pinion angle on the differential."
http://www.wolferacecraft.com/pinionangle.aspx

I especially like this one: Myth #3: The garage floor is the correct reference point for
measuring the pinion angle.

Straight Scoop: You've got to be kidding, right? The garage floor
doesn't have anything to do with anything. http://www.buickperformance.com/Pinion.htm

[Tugboat]

CobraV8

Try Brian at Lone Star Classics in Texas. I am pretty sure he gives the brackets to Currie to install on the 9" that we put in out Lone Stars. The Lone Stars use 4-Link.

Larry

www.lonestarclassics.com

[tcrist]

[quote=bobcowan;901659]>>
"Pinion angle is the difference between the driveshaft angle and the pinion angle on the differential."
http://www.wolferacecraft.com/pinionangle.aspx

Bob,
Scroll down to the bottom of this link that you provided. It looks like it says minus to me. I think DV and yourself mean the same thing just saying it different. Although I could be wrong. It's happened before.

Terry

[bobcowan]

You could be right. Pinion angle is always expressed as a negative, or down angle. That's because it's properly measured against the power angle.

But if you incorrectly measure it against the horizon, it becomes a positive or up angle.

[Andrew Teal]

Simon,
DV got it right, I also have a classic rd. with a 9 inch and 427 side oiler 4 speed toploader. The rear should be off center just a little as DV said, now I dont know if you inside frame rails run back like mine as mine is a 1993 Classic and there is very little room for the drive line between the inside rails. I had custom 4 link bars built as the stock one did not center the rear in the wheel archs. I dont remember what I set my angle at but I could look in my notes. I have no wheel hop and the car goes strright runs low 11. I did built a custom coil over for it also.

Andy

[ratsnst1]

Just for thought shell valley sells the brackets you need, but it depends on your 4 link bars, that you are using, shell valley also has some nice allum, 4 bar set up, as far as your drive line angle go any time you have multible angles, what I mean by that is up and down and side to side, I used a currie housing and lined it up pretty close so the only angle I had was top to bottom, I didnt wanna take a chance of having a vibration, I can not remember my pinion agle though.

[Double Venom]

OK,
"Car Craft", "How To Set Pinion Angle
Ask 10 Guys About Optimal Pinion Angle And A Lively Debate Will Ensue".....
Bob, I do see exactly what you are talking about, We used Carroll Smiths book on how to set up DV II's, front and rear suspension, At one time I had the Hot Rod article you are talking about so I know how/what you speak.

I have tried to keep this whole thing simple because most guys simiply do this once and I am referring to strictly a guy building his CR's in his garage. I'm not getting into the physics of the driveline thing, but the way a CR's motor is normally set into the frame. The only thing I explained to Scott was to set the car while it was on the ground with fully loaded suspension. (Yes I am assuming his garage floor is as level as most garage floors.)
I Intentionally did not talk about the 'Horizon plane' or IRS- (IRS= level as possible).
Every article you posted was basically for a street car with one chart for various cars.
My point was to help build CR's as simple and correctly as possible. Not to give lessons on building a virgin driveline.

Forgive me if I misssed it but I did not see one word about the pros or cons on the pinion angle (as I am referring to.) See the above picture of a Pinion/Rear end that went way over-in my words "positive"* under a major load.)

I absolutely have no doubt that you are well knowledgeable and or experienced in setting up rear ends so please do not take my debate as a negative. A good debate is good for all.

*General consensus from the Ol' Man, (Jegs Coughlin) and Honda Engineers on my rear end splitting in half was; My launch was harder than normal, around 4,400/4,800 RPM vs 4,200 RPM the shift from 1st to second was quicker, or traction after the Funny cars had run- traction was greater than normal. When I slammed Second gear, ( the nose was still up or airborne, the pinion had not had a chance to drop back to "close to normal". This apparently caused a major "wheel hop as the pinion went to a Plus angle and snapped the housing immediately." This, in my explanations is where I should have had the pinion set at Minus 3.5, there by not letting the driveline angle-pinion to go over or in the plus range. Race and learn!
DV