If you have solid motor mounts, will a spreader bar do anything? Won't the engine block act as a spreader bar? Just curious....

 

I put a spreader bar on my car with factory rubber mounts a few years ago. I just recently put solid motor mounts on and noticed a pretty significant difference even after the spreader bar in the front end

 

Ive run both for so long i dont remember.

 

Any downsides to solid motor mounts? I just recently installed the spreader bar and can't believe the difference! Still waiting for the shark bar behind the seats attached to the seatbelt mounting points for even more rigidity!

 

I am just guessing but the motor mounts are well back of and somewhat independent of the front cross-member and A-arms. It would seem that the spreader bar is addressing suspension/frame flex that is divorced from engine movement vis-a-vis the frame.

 

Certainly solid motor mounts would introduce additional rigidity to the front of frame but the points between which the spreader bar connects are well away from the the motor mounts location.

So I would agree that they would not completly eliminate any benefits to a spreader bar, they may contribute to the effects of, or partially offset the lack of, a spreader bar however.

 

Distance is the problem. The bending forces are caused by the spring and shock being compressed.

Also from and engineering stand point don't believe that the low mounted aluminum spreader bar going under the mechanical fan is anywhere as effective as an higher mounted ridged steel bar

1978 & 79 vettes had more ridged frames because of known cracking problems in the earlier vettes.

Also from and engineering stand point don't believe that the Shark bar bolted behind the seat to the body would do much of anything. I've lifted the vette body off the car with five guys and walked it over and set it down. The body is not at all ridged. It is the frame that is stiff. The rubber body mount donuts allow some frame movement without effecting the body.

 

I will let you know about the shark bar on my 78 when I get it installed but what from others have said about the shark bar it will add rigidity since the mounting points for the bar are the seat belt mounts which have to be much stronger than just the fiberglass body. The manufacturer also assures me that the shark bar will definitely add rigidity-we will see!

 

I would agree theoretically. The VB&P bar for example (for electric fan equipped cars) mounts its bar about an inch higher and being made of steel and a larger diameter I cannot imagine the suspension forces being able to cause any deflection in the bar.

All that said, the aluminum bar in its present location I really cant see deflecting either, even under high suspension loads. I dont know how much the upper A-Arm point might deflect from its static position when unrestrained by a spreader bar but I doubt its very much.

All the bar has to do is restrain that upper mount. It may be marginally less effective but your phrase "anywhere as effective" implies a vast differential in perfomance which I'm not sure I agree with. but yes, a higher mounted bar with greater strength would theoretically do a better job.

As for the shark bar, I dont know enough about it to judge. If it mounts between seat belt mounts I would be suspect. The seat belt mounts are part of the body's birdcage if I remember correctly and thus are divorced from the frame due to the rubber body mounts. I could definitly see some reduced flex in the birdcage though and thus squeaking and flexing of t-tops and the like would be reduced, certainly giving the impression that things are tighter.

 

Maybe it was somebody like Norvals home made the spreader bar I was thinking about from the pictures. The cross bar was mounted an inch or two above the upper A-Arm.

 

THANK YOU guys! I guess I'll start fabricating my own. I can't justify spending 100 or more for a steel or aluminum rod and two brackets. I can make this myself. Thanks again!!!!

 

Yeah, If youve got fab skills and tools, make your own its a pretty simple device.

 

I don't know for sure but I doubt that the upper seat mount is just free floating in under the fiberglass-it has to be seriously bolted to the frame-the birdcage that is, since the roof would instantly collapse in a roll over otherwise which is not true for the coupes.

I know you said that you were not familiar with the shark bar but you should check out "vettes on line" to see that the bar is actually attached on each side not only to the upper seat belt mount but a solid bar connects each upper mount to the lower seat belt mount on the floor-the whole assembly is tied together from the floor to across behing the seats-it will definitely strengthen the whole assembly like a rollbar

 

I have had them both at different times. My previous 406ci I installed solid motor mounts and you could feel everything was significantly tighter up front.

My 427ci I used poly mounts and after a few months installed the VB spreader bar I can't really say I noticed anything. If I was racing on road course them perhaps they are needed more. I'm not taking it out though

 

If you have rubber body mounts, stiffening the birdcage wont net you much (if any) chassis stiffness.
The claim that it increases chassis stiffness could be for early vettes with solid body mounts, but even then the increase would be marginal.

 

I miss Norval and his skills at innovation. Anyone know if he still drives Corvettes?

 

I think the answer on the question is wery dynamic.

I think it depends on what forces you put on the car.

I belive that a street driven Vette is a very good roadcar and the amount of flex one may se in the frame and suspension is something most people can live with.

However, if you go one step further and take your car to the track, maybe with som sticky tyres and some stiff suspension, the pressue is on.

The solid engine mounts will help making the frame stiffer, so will to finish off the welding of the frame that GM once started..

The "spreaderbar" (between the spring towers) will help this part of the frame from twisting during hard cornering and to remain proper wheel alignment/angles when the pressure is on.

The engine mounts are located quite low and the spreaderbar several inches higher, together those form a "box section" that i belive add strength in square (i hope you understand my english..).

If you emagin a "box" consisting of the front member (low), the solid engine mounts (middle) and the spreaderbar (top) then i belive you have done what you can to get a stiff front end frame/suspension.

Ergo, the higher up you are able to mount your spreaderbar the bigger box = stiffer frame/suspension.

Personally i couldnt mount my spreaderbar so high due to bigblock and Meziere electric waterpump but you can still make out the difference in height (box).

 

This is how i made the brackets for mine if that may be of interest.

The shape of the bracket is to give room for the lower radiator hose.

 

This is how it ended up when installed.

If the engine could do without the waterpump it would have been easier to mount it higher up.

 

A lot of good comments already.

IMCO anyone earnestly seeking to reduce chassis flex up front should install both the spreader and solid mounts. No down side as far as I can tell, but those with less priority than myself on performance have been known to bitch and moan about extra noise/vibration due to the mounts, not that I could (or would) speak to the validity of such complaints. In any event, DO NOT install a solid transmission mount unless you really get off on breaking things. My $.02