Tell me about engine twist...

[Turbo6Smackdown]

I heard, that if you run an engine tie down strap, and have a little bit of torque in your car, that strap will cause the engine to twist...unnaturally... to the point where eventually you'll start..uhhh help me out here. Twisting webs? Or causing cap walk? Does this sound right?
How true is this?

 

[bison]

This sounds like someones wet dream hypothesis. I doubt it could be proven with any simple testing. It would be hard to pinpoint what is being twisted at any one given time since the stock block is designed for about 400hp max. The stock crank flexes a lot over 550hp. If you ran poly or solid mounts and launched with a t-brake then you would shock the left side of the block where the mount attaches to it. With a steel strap you will move some of that load to the accessory bracket mounting bolts on the left side head. With poly/solid mounts i dont think a strap will do much since the engine wont be moving too much. My opinion is to run the poly/solid mount only and dont worry about it. I ran 650+hp through a stock bottom end for at least 5 minutes of WOT all together. Most of which was in 3rd gear. Car went 133.4mph weighing 3600+. Boost was 28.5 on that pass. I had it as high as 33 till i leaned out #1. Still did not hurt the bottom end.

 

[charlief1]

Kinda with bison on this one. Get some roses and plant them in this rumor. You'll have a pretty garden for sure.

 

[KL Mallender]

Block twist under load?

You heard correctly, use a mid-plate to restrain engine rotation, not the front of the block. :biggrin:

Kevin.

 

[Turbo6Smackdown]

I see... So which is which?

 

[JayC]

On a street car, about the best youre going to do is the HR Parts mounts. One a race car, you can use mid/motor plates. Thats what we do in our race car.

 

[Turbo6Smackdown]

So those motor mounts are better than a tie down strap? And, what about the theory of the mounts not being flexible enough, and causing false knock. Does this happpen?

 

[TurboDave]

So those motor mounts are better than a tie down strap? And, what about the theory of the mounts not being flexible enough, and causing false knock. Does this happpen?

Absolutely!!! They're WAY better than the hockey tie down strap.
No they do not cause false knock. Although you will feel a bit more engine vibration.
The problem with the tie down strap is not that it induced internal stresses on the engine but rather unatural "external" stresses. What I mean by that is: Think about it. Without a strap the engine naturally wants to rotate around the cranksaft. Driver's side wants move upward, passenger side wants to move downward. Now tie in the strap, the driver's side is restrained, so what happens to the passenger side? It of course is going to move downward, but even more than it normally would, simple physics dictates this, and you can see it. Ya it's less stress on the driver's side motor mount, but a LOT more on the passenger side mount. There's absolutely nothing good to come from using those stupid tie down straps.

If you've got any close tolerances with your downpipe, you're definately going to get things banging together!

 

[Just a Six??]

If using only 1 HR mount would it go drivers side? I know some guys only use the 1 side but not exactly sure why? Maybe less vibration than using 2 of them? Thanks!

 

[Turbo6Smackdown]

I see... hmmmm

 

[TurboDave]

If using only 1 HR mount would it go drivers side? I know some guys only use the 1 side but not exactly sure why? Maybe less vibration than using 2 of them? Thanks!

I've never been able to figure that out either. With the amount of twisting forces involved, it makes no sense to me to run one good mount and one softone. It's probably the vibration issue, with a dash of cheapness thrown in for good measure.

 

[charlief1]

I've never been able to figure that out either. With the amount of twisting forces involved, it makes no sense to me to run one good mount and one softone. It's probably the vibration issue, with a dash of cheapness thrown in for good measure.

It is a vibration issue as well as being cheap. The pass side will compress and the drivers side is the one that gets ripped apart most of the time so you put 1 on the drivers side to keep the engine from ripping the mount off and moving the engine agains the pass side frame rail.

 

[TurboDave]

If you don't think the compression on the passenger side isn't just as bad, you're mistaken. And with a torque strap on the driver's side you've now heavilly amplified that compression damage. The same twisting forces are still in effect. limiting the driver's side merely amplifies the forces on the passenger side.

If one is not to be racing, then a good set of stock mounts would be in order. However, hard driving or racing; common sensed dictates a pair of good high performance mounts. Replacing one side mismatches the forces just does'nt make any sense.

 

[67turboCamaro]

I ran with one poly mount for over 6yrs with no problems on my stock block/stock crank motor. I was running 10.0's with 1.3 60's off a trans brake.

 

[750H.P.V6]

I'd tell you that the block distortion theory has some merit. A decade or more ago and prior to the advent of decent motor mounts (Thanks HR parts) I had a low 11 second stock block with a stock crank and 2 steel main caps.

I flogged it pretty well for several years until it developed low oil pressure. When I disassembled the engine I found heavy main bearing wear on the #2 and #3 mains on opposing sides (ie: 1 was worn heavy on the passenger side lower bearing half and 1 was worn heavy on the drivers side lower bearing half).

Keep in mind I built this engine myself and the block had been correctly machined and measured prior to assembly. The only thing I could possibly attribute this to is block distortion due to running a tie down strap off the alternator.

Neal

 

[Turbo6Smackdown]

****....

 

[Turbo6Smackdown]

2 poly motor mounts for me