Peter,

Calling what I have wrote 100% is a true statement when applied to the wrong torque location. Maybe I didn't make it clear enough in all the earlier postings so let me try again. I know this thread is getting very long, and most might not take the time to read everyone of the postings. So, to summarize, this all start (at least for me) with the diagram from Josh to explain how their new rear differential mount/brace works. The diagram shows an arrow with presumed torque from the propshaft. I could not understand where this torque he was showing was coming from. I know about inertia and how that generates a torque while the engine rpm is accelerating or slowing at a rapid rate, but brake torque isn't there to twist the body of the car laterally because of the torque tube. The twisting load is not communicated to the engine mounts. Peter, what I was talking about had nothing to do with the reacting torque from turning hot sticky tires on pavement. You are correct about the torque reaction from the wheels tries to lift the front of the car and will put both engine mounts in tension. As seen in some of the drag strip photos the transfer of torque to the wheels is high enough to carry the front wheels of the car off the ground for some distance. In all of these vehicles that have the power and traction to carry the front wheels off the ground and have kept the basic powertrain design of a propshaft rotating in an outer torque tube, you will see a number of advantages over non-torque tube cars. You will see that the lift is even laterally and that the body isn't twisted.

All I've been trying to point out in all of these postings are some of the very unique features that make the corvette special when compared to any other production vehicle. It works well for track and it can work well on the drag strip. Can we change things to bias its performance better at the track or drag strip? Sure! Even a stock Corvette will do well in ether event compared to most any other production vehicle. Are there other vehicles that will perform better? Sure there are, but get ready to spend substantial more money.

One of the other forum members made a statement that has stuck in my head ever since I read it. I'm really sorry I can't remember who posted it, but it went something like “the corvette is the only vehicle that was designed by engineers without accountants, or lawyers messing it up.” This statement, even though I know it's not true, I wish it were and believe the Corvette comes as close to it as any vehicle out there.

Chip,

I agree with you 100% that the “drivetrain moves around a lot”. I don't agree that “locking it down” is better. It really depends on what you plan to use the car for. If you have a daily driver you most likely will want to maintain a stock powertrain mounting configuration. If you're a track freak you may want to increase the durometer of the mounts some. If you are a drag racing fanatic you may want to increase the durometer of the mounts a lot.

Hey guys, if you agree or disagree it is all fine with me, however keep posting your thoughts as I enjoy learning and I'm not ashame if I have something wrong. I've ate plenty of crow in my days!

Regards,

Eric D

 

Here's a simple experiment to show that torque loads don't cause the engine or differential to rock from side to side:

Take the car on the freeway, put you hand on the shift lever, and alternate between full throttle and no throttle. You'll notice that there is almost no movement from side-to-side in the shift lever. Since the shift lever is mounted to the torque tube, which is rigidly bolted to the engine and rear end, any rotational movement would show up in the shifter.

So there's not really any "wasted motion" in the power transfer.

I can see how stiffer engine mounts might be an advantage for someone like an earlier poster, who was having problems with the shifter moving under high G loads from fast cornering on the race track, but that motion has nothing to do with engine torque reaction.

 

I still think it may apply from a dead stop though, like on the drag strip.

 

Looking fwd to it Tim,

I would have done the July event at summit point with the Northern Virginia Corvette Club but my car wasn't ready, it was, but the new clutch didn't live up to claims, so it wasn't....

Next time the BMW CCA or NVCC are running we'll touch base, it'll be a great experience for you as they have great safe and conservative instructors, of which HRTRacer here is an excellent instructor, and will definately take you for the ride of your life if you just want the best 20-30 min ride ever if you want to come up and see what it is all about.

I'm hoping to get my instructors liscense next spring.

The fall is a great time for motor sports!!!!!!

Eric

No problem buddy, I knew an engineer would like the SWAG....

I failed to post motor mount pics too. I have to figure the whole posting pics out today.... There's a stick on that somewhere around here....

 

Open an account on Photobucket.com http://photobucket.com/

Copy the img code link and paste it in.

 

Sheesh,

I don't look at this thread for like a day and a half and half way through it turns into WW3 ..... and usually I'm the moron with the gas can fueling the fire !!!

BUT, I have learned a ton from the posts from Eric D and Warp Factor (who I believe in an earlier post said he was not an engineer - dude - you are one).

Never thought about how the torque tube distributed torque forces before .... but Eric's posts and Warp Factor's incisive questions (and answers) have opened my eyes to another part of how well engineered the Corvette platform really is (well, with the exception of the column lock engineers, I still believe the death penalty ought to apply for them).

Thanks guys ...

I love this forum .....

 

Oh geez, now I have to go out and do some holeshots and burnouts!

Might not have time for a couple of days.
Might need to find a new spot too. The people at the church up the road haven't been taking kindly to using their parking lot for this lately.

I believe you're right though. How much the power train twists on launch should depend on how much the engine "bogs", or changes rotational speed on the launch.

If it moves a little, I don't see why it would hurt anything. In fact, it might help by reducing shock loads to driveline parts, much like drag tires with high, flexible sidewalls do.


Yes, BlackZ06, death to the column lock engineers!

 

There has been some confusion about what and how this mount actually works. Well here is a quick diagram that shows what is actually going on.



Josh,

I need some clarification.

Is the above diagram looking forward or rearward in the vehicle?

 

I'm back, holy crap did this thread take a nose dive and its a shame because I felt we were trying to understand the product being made by an outstanding vendor (Pfadt).

Eric,

After reading your post the light bulb went on (took me a while ). I guess the next question I would have is lateral support at the differential. I think the Pfadt brace would provide more constraint in the transverse directions (in my world fore/aft and athwartship ). Would there not be any benefit in this, especially in the case where a driver is hard in and out of the throttle (road racing) in a possibly not stock car? Seems to me that the Pfadt brace with DTE brace would be an excellent combination to aid in keeping things together as we modify the cars well beyond the design parameters that GM likely used to bring the car in at a price point.

 

Ok, so there really is little force trying to roll-over or twist the driveline? that means this Pfadt brace is pretty much completely useless then. A good stiff poly mount holding the diff in it's location would work just as well.

Peter

 

Peter,

This was why I had hoped that Josh would come back and respond to this thread. The diagram he showed really confused me. From what I could make of it, it seemed to indicate it would react to the inertia response from the engine. In my opinion this force is small and I'm not so sure that any brace for it would be needed. As VetteNuts pointed out, with increased engine power there may very well be something else the bracket does that we are missing, but without input from Pfadt we may never know.

VetteNuts,

Though I have no experience with the DTE brace, looking at it I can see where it would help with the transmission to differential joint. I do know that the differential case went through design changes. I believe this change was to improve the case strength due to the later model Corvettes having increased engine power.

Eric D

 

At the drag strip, with a manual transmission and sticky tires, the most common thing to break seems to be the driver's side output shaft. Another point of failure is the flange where the differential and transmission connect. The torque reaction which lifts the front of the car via the torque tube puts a huge tension load at the top of these flanges. The DTE brace, when properly adjusted, puts that area in compression, and is designed to transfer the lifting forces (and compressive force at the bottom) past that joint. It may also serve somewhat as a "case girdle", making splitting the diff case and side covers less likely.
I don't know if loading the case differently, by adding a more rigid mount like the Pfadt, would help or hurt when it comes to the case staying together. That's assuming that there is enough differential rotation to load the brace.

I have the hardened driver side output shaft, and the DTE brace, because I could understand the value of those parts. Haven't gone any farther than that (like a complete built rear end) because I'm only at about the 500hp level, and only go to the drag strip a couple of times a year. I was mostly concerned about preventing breakage during wheel hop, which I get into somewhat regularly. Happened most recently on a power shift to second (with drag radials). That's like putting the mother of all impact wrenches on the driveline! You can get off the throttle when it happens, but there's no way to know you need to do this until it's already happened.

Still, I think it's amazing what abuse the Corvette will handle, given what people do with them versus the intended usage, and that keeping the weight down must have been a design priority.

 

I talked to Pfadt yesterday and Josh is on vacation until next week.

I think all of the doubting Thomases need to watch the video that Pfadt has on their web site several times.

After you have watched that video, please explain to the rest of us what is causing the powertrain judder.

 

If we saw the same video, the "before and after" was motor mounts, not the brace.

I still don't understand what they describe as "powertrain judder". It sounds and looks exactly like what I get with wheel hop, and I've never had anything remotely like that unless it was wheel hop.
Whatever it is, it's still there on the video after the new motor mounts are installed. You just see less drivetrain movement when it happens.

I've been able to get rid of it on other cars by replacing the rear control arm bushings with metal spherical ends, but I don't want to spend the money, give up the road noise and vibration isolation, and take on the higher maintenance unless I know it will work on the Vette.

 

Please watch the rear tires while the powertrain is moving. I don't see any wheel hop taking place. I have driven vehicles when the wheel hop caused the tires to bounce off the pavement.

Do you see wheel hop at the tires?

 

Yes, I believe I do, but it's hard to tell because of the low-res on the video. I think I see it on one tire at the beginning, and on the other tire later.
On one of my cars, there wasn't much up-and-down motion. It was most noticeable from the side, and showed up mostly as fore-and-aft motion of the wheel in the wheel well. That's why I thought "solid" control arm ends would help on that particular car.

Edit: The tires don't need to completely leave the ground to call it wheel hop. All they need to do is come up far enough to unload slightly, starting a cycle of more traction/less traction/more traction etc. On a narrow sidewall tire, this wouldn't require much vertical motion.

I guess one way of defining whether "driveline judder" is really a different animal from "wheel hop" would be to ask whether it ever occurs when tire speed is the same as road speed. If not, I think those wheels are bouncing around, on one axis or more, due to a resonance starting with tire spin.

 

I am at a lower hp level, but when I had DTE build my differential I went all the way (Stage IV) since I only wanted to do it once and am planning more modifications that will further increase power levels. I still believe that providing a better anchor to the differential would aid in keeping the drive line together in not normal street driving conditions. I think this brace would also help with any overall drive train wind-up that might occur with rapid application/removal of power (in and out of clutch, etc.).

 

I went directly to the You Tube web site and watched the video in their full-screen mode.

I see zero wheel hop. In fact, the most significant powertrain movement is not during acceleration. It happens before the Vette accelerates.

Your thoughts?

 

That's where I watched it too. There are two places on the video where I think I see wheel hop, despite the poor resolution. At about 2 seconds into the video, on the tire on the left side of the right split screen segment (the tire you can barely see), and at about 44 seconds on the other tire, on the right of the screen. Judging from the sound of the rpms, I'd say the tires were spinning both times.
I found it easier to watch the shiny wheel rim on the barely visible wheel at 2 seconds, and the actual tire itself (right of screen) at the 44 second spot. At the 44 second spot, the tire may be bouncing completely off the ground.

Whether or not you agree that the video shows wheel hop, what else would cause such a beating on the drive train, and that kind of noise?

 

The Video is of a C6 not a C5.

Read the title.

http://www.youtube.com/watch?v=LczzhRrwhR4