Peter,

I really appreciate your post and you ask some very important questions, however it seems we lost our Pfadt rep, Josh, I expect due to some bad behavior of someone that think they need to represent Pfadt for some unknown reason.

You point out something that I am starting to believe many people think happens with torque in regards to the C5 Corvette. Your statement about the car wanting to lift the left wheel at launch is absolutely true for many vehicles, but not the case with the C5 Corvette. One of the most unique features of the C5 is how it handles torque. All the torque produced by the engine is put through the propshaft and the reacting torque returns to the engine block by way of the torque tube that the propshaft turns in. It doesn’t need to use any other path; most important, the body of the car isn’t used to return the reacting torque. This means that the net torque that travels through the engine mounts is zero. In the C5 unlike other vehicles, the engine mounts, left to right see almost the same loading. During a launch at maximum power, the left engine mount does not go into tension and the right does not go into compression.

In regards to the Pfadt mount, I doubt there would be much risk of it damaging the differential. I would speculate it may very well help with reducing torque tube vertical deflection during a car launch. This is why I started my conversation with Josh. It is really sad that he has been run off. I still hold hope he will return with more input on the subject of their new mount.

Regards,

Eric D

 

I made my own engine mounts out of 2.5 inch galivinized pipe from home depot, 1/8" steel plate, a 2.75" hole saw to cut 4 Circles to weld on either end of the 2 pieces of Galvinized pipe.

Drilled a hole through the center of the steel plate and welded a 6" piece of 5/8" threaded stainless steel stock where the threaded rod passed through the steel plate.

It took me about 6 hrs to figure out and fab but it only cost me $20. Of course I already had the welder and drill.... But it saved me $300 and they work great! No vibration very solid feel.

It looks equally as easy to take a piece of square stock and make a trans axle mount, but for $129 I wouldn't have to recreate the wheel. It has a little bit of Poly in it to dampen vibration. Where I am in the build, I'm tired of creating the wheel so this price point works for me.

 

If you have a chance I wouldn't mind seeing a photo of your fab'd mount.

Thanks,

Eric D

 

Read the entire thread. Very interesting!

Questions to Eric D:

Are you saying that there is no transfer of forces to the engine mounts in a C5 because all the torque the engine produces is transferred/absorbed by the torque tube?

I don't know about your vette, but when the throttle is mashed on my vette the engine twist around a bit. How can this be if the above statement is correct?

Other than the fact that the C5 has its transmission in the rear, how does the C5 differ from any other rear-drive, independent suspension car with the transmission behind the engine? For example, say the Viper. I ask this question because Vipers don't seem to have the drive line problems that the C5s and C6s have even when they put out gobs of power (800+ rwhp).

Looking forward to your replies.

Thanks

 

Until Eric comes on with a better answer.......

The engine mounts will see a minor amount of torque from changes in the speed of engine rotational mass, like when you wing the throttle in neutral. I believe that's what you're seeing. What the motor mounts don't see is a torque reaction from power applied through the driveshaft.
In other words, if you were to "power brake" an automatic Corvette, you won't see the engine "torque over" like a conventional car would.

On a conventional car, the torque return path is through the frame/body, through the engine mounts, and back to the engine block.
On the Corvette, the return path to the engine block is through the torque tube. The frame and engine mounts aren't involved.

It's a neat concept, because there's no twisting force on the chassis to bend it, and mess up corner weights for the road racers.

Eric will explain it better.

Can't answer your question about differences between the Vette and the Viper.

 

Warp Factor,

Nice job! I'm not so sure I can add much, but will try.

Tim,

Excellent question! Thanks for asking it. You are absolutely right in your observation that “the engine twist” when you rev it up. This is caused by the change in speed of all the rotating masses in the engine. It only occurs when the engine is changing rpm. Once the engine is at a constant speed this torque returns to zero. This is way different from the torque generated driving the vehicle down the road. They are two different things. Most are familiar with the term Brake Torque, like when you hold your foot on the brake while increasing the throttle. In a vehicle without a torque tube this load is reacted back to the engine mounts. Without the engine mounts the engine would try and rotate raising the left side can compressing the right side mount. The inertia torque is short duration and only while the engine is changing rpm. The torque influence in the engine will be one direction while accelerating and the opposite while slowing the engine, zero when at a steady rpm.

Sorry, I really don’t know anything about Vipers.

Eric D

 

^^Thanks for the reply.

If I am understanding what you are saying correctly (I'm no engineer ) when the engine is in a steady state (no rpm changes) then no, or only a negligible, amount of engine torque is being transferred to the engine mounts. However, when the engine is being accelerated or decelerated then engine torque is being transferred to the engine mounts.

Am I even close?

With the Viper question I was trying to get at the issue of why the C5s seem to have a lot more transmission/differential issues than the more conventionally laid out independent suspension cars. We keep being told there are these deficiencies in the design of the C5 that make it more prone to breaking the transmission/differential, and the anecdotal evidence you see on this site seems to support this view.

I can understand why the high horsepower (and high torque) vettes need to take additional steps as I don't think the GM engineers designed the cars with those kind of power numbers in mind. But in my time on this site I have seen a lot of cars, including stock, that are not super power houses break something back there. Wheel hop seems to be a factor in these cases, but not always.

Would be really nice to see some objective tests carried out to answer these questions.

Thanks again.

 

I'll try to post up some picts of the motor mounts when I get to that computer later today.

Here's my SWAG based on road race experience for the HP required for upgrade:

-Anything Z06 like, 400 rwhp and under swhould use OME replicated or upgraded parts.

-A good head and cam car putting down 500 RWHP-400 rwhp should look for extreme duty replacement parts.

-Anything going significantly over 500 rwhp would need re engineered parts.

Now, apply common sense. If you are doing burnouts on dry pavement and you have 488 rwhp and your reving it up to 6K rpms and continually dropping the clutch, Upgrade to the re engineered parts.

I think the corvette suspension and transaxle set up is pretty bullet proof. Ive seen cars launch off turtles at the track, get completely airborn and not miss a beat. It wasn't even out of alignment and it was a stock 01 Z06.

I think people are overly paranoid about the dependability of two very proven components in the t56 trans and the 3.42 geratag rear. These things have been handling high hp for years and been fine. Think of how may corvettes are running around out there. Your going to see posts like my diff blew up or trans shfting problem 100% more than My axle worked great or my trans shifts great.

I knew I wanted to upgrade my motor and trans mounts when I would be comning out of a corner and want to shift coming out of third and into forth. The problem was with the torque, high rpms, and g forces comingout of the turn finding second was ambiguous because of all those forces maximising the displacement of the drive train to which the shifter is attached.

Bottom line I found myself having to double check to make sure I was in 4th and not second.... I even have a short throw shifter, but I just wasn't comfortable with the feel with all the driveline movement. It was obvious to me that when I had the chance I would upgrade the mounts. My car at the time put down a very healthy 370 rwhp and 380rwtq out of a stock 97 mn6 with lgpro headers and bolt ons. I knew when I added the head and cam the 11 yr ome mounts wouldn't cut it.

I'm glad to see everyone is benefitting from this....

 

^^Good post!

I expect my car to have somewhere north of 400 rwhp when I finish it, and it will be street-driven only. Within the limits of reason I will push on it a bit.

Not a drag racer, so no clutch dumping for me! More into road racing aspects. So handling is my main focus.

I have the heavy duty stuff out back including a DTE brace, but am sticking with the stock engine mounts so that the ride quality is not too adversely impacted. Since the car is all apart and won't be ready till next spring won't be able to say any time soon how it all works out.

Hope you are doing all your shifting on the straights, as shifting on the corners can upset the balance of the car.

Looking forward to pictures of your engine mounts.

 

My main experience with shifting in a turn was on the tri oval at pocono North. Coming out of the infield in second or third and you wind it up going around the big NASCAR turns. Eventually I end up in 5th. 5th is more fun. Also up through the "S"'s at watkins.

I would always shift on a straight if I could, but I'm not power shifting and dumping the clutch. As experienc and skill levels increase, you'll know when to shift and when not to as a comfort level of knowing your machine. I'm not saying shift at the Apex of a tight turn. Think of shifting from 3rd to 4th coming out of a turn, that's ~ 100mph turn, so it's not a hair pin. You tap your brakes to make the front plant and get lined up for the entry then use the throttle to plant through the rest of the turn.

I dont like to wind my car up to a sustained 6K through a turn. All the rotating moment of inertia has that entire car wound like a top. That's what is very unsteady. One bump that makes your throttle foot move a little can unsrettle the car a lot. Where being able to shift to 4th with a lot of low rpm torque coming out of the turn or going into the turn makes the throttle position very forgiving.

For me it's resulted in hiogher lap times to try to stay in a higher gear around the track even if I'm not screaming the engine (except on the straights so I can hit my power band on the shift).

 

dmiz0420,

Great post, I really enjoyed reading it. I think you are spot-on with your swag! I can understand the need for stiffer mounts when putting the car through the lateral "g" forces at high speed turn. I wonder what the new ZR1 is using for engine mounts. I could be wrong, but I seem to remember reading they are getting up to 1 "g" lateral turns. Man, that would be the same as running the car on its side!

Eric D

 

Your not only close, I think you are seated right on it!
I believe dmiz0420 post covered this very well and I agree with his "swag".
Some point when I have sometime I'll try and put some information on this subject together. I'll be on the road the next few days and might not make it back here for a while.

Regards,

Eric D

 

^^There are a number of people who are pulling greater than 1.2gs laterally in their cars who run the HPDEs. Of course they are running on racing slicks to achieve these numbers.

I believe the stock C5 Z06 were around .97gs. With a little suspension work and better tires would be pretty easy to exceed 1g. Even though my car is for the street I am hoping it can pull better than 1g laterally.

Thanks for all the good info.

 

^^I happen to have a great interest in road racing myself although I have not had an opportunity to get to the track yet. If you get a chance I highly recommend reading Speed Secrets 1 & 2 By Ross Bentley, and also Drive to Win by Carroll Smith. Just fantastic books. Learned a lot from them, and still learning.

Maybe we will bump into each other at a track sometime.

Tim

 

Sorry, but I have to call on that, 100%.

Then engine is producing torque around a front to rear axis or it's producing torque around the axis of the drive line. The diff changes that into a side torque to drive the wheels. The gears in the diff will resist the torque direction change and attempt to roll over the drivetrain instead. The only think keeping the drivetrain from rolling over is the engine mounts. Just because everything is connected together front to rear doesn't mean that you change Newtons 3rd Law. The force reaction in a straight axle car also tries to lift the drivers side wheel. That's why a straight axle tends to spins the drivers side wheel.

The Vette will also still try to lift the front end under acceleration. The differential is trying to twist the wheels forward and the reaction to this is that the differential is also trying rotate front up. This force will transfer right to the engine and try to lift it but because it's held to the chassis by the mounts the whole front of the car will lift. Look for the pictures of the 9 second IRS Vette here with the front wheels off the ground at launch.

Depending on which force is bigger (engine trying to roll over vs diff trying to lift front of car) the drivers side mount could be in tension lifting the whole nose off the ground while the passenger side mount could still be under compression. Likely though, the drivers side mount is doing most of the lifting and the passenger side just a little. I don't really know how these forces balance, just that they exist.

Peter

 

No, he's right. At full throttle, as long as the engine isn't gaining or losing rpms, there will be no rotational engine load on the motor mounts
Newtons 3rd law can remain intact for now.
You have a force applied to the driveshaft. When this force reaches the differential, the diff applies an opposite and equal force to the torque tube, which returns it to the engine. These opposite and equal forces conteract each other. The result is no rotational force on the engine, and no "torquing over" of the engine.

Imagine it this way:
If you take a conventional drivetrain and put it on the floor, power up the engine and resist the engine with the rear brakes, the rear end will pick one side up off the floor, and the engine will tip over on its side if you apply enough power.

Do the same with a Corvette drivetrain, and you can give it as much power as the rear brakes will hold without the engine tipping over, or the rear end moving.

 

Torque or no torque, the drivetrain moves around a lot.

Locking it down gives a mechanically more efficient transfer of power.

Peace
Chip

 

How so, if torque isn't moving the drivetrain, only G forces?

 

API Standard 541 Third Edition, Form-Wound
Squirrel Cage Motors - 250 Horsepower and Larger
Washington, D.C., 1995

NEMA Standards Publication No. MG 1-1993
Rosslyn, VA, 1996
60 65 70 75 80 85 90 95 100
% Full Load Speed
Vibration Amplitude
Vibration at Rated Voltage and 100% Full Load and Speed
Mechanical Unbalance
Resonant Structure

Sommers, Ernest W., “Vibration in Two Pole
Induction Motors Related to Slip Frequency”
Transaction, AIEE, (April 1955), pp. 69-72

Alger, P.L., “Induction Machines,” Second Edition,
Gordon and Breach Science Publishers, New York,
1970.

Finley, W.R., and Burke, R.R., “Troubleshooting
Motor Problems,” IAS, 1993, IEEE Transactions of
Industry Applications, 1994, vol. 30, no. 5

Finley, W.R., “Noise in Induction Motors – Causes
and Treatments,” IAS, 1991, IEEE Transactions of
Industry Applications, 1991, Volume 27, Number 6.

Costello, M.J., “Understanding the Vibration Forces
in Induction Motors,” Proceedings of the 19th
Turbomachinery Symposium, Dallas, TX, pp 67-76,
September 1990.

Hodowanec, M.M., and Bezesky, D.M., “Field Motor
Testing: Procedures which Limit Amount of Risk
Involved, IEEE IAS PCIC Conference Records, pp
79-90.

Berry, J.E., “How to Track Rolling Element Bearing
Health with Vibration Signature Tracking,” Sound
and Vibration, pp 24-35, November, 1991.

Taylor, A.G., “Computer-assisted Diagnosis of
Instability Problems: Four Case Histories,” Orbit
Publication, Bentley Nevada, Vol. 8, No. 1, pp 5-13.
February 1987.

Good reading

Peace
Chip

 

Thanks, I think you've pointed out some of the challenges of vibration isolation versus power transfer. The thing about the Corvette drivetrain is that it has already solved these challenges rather well.

Coincidentally, that happens to be one of Eric's automotive engineering specialties.