Frame Flex on High hp Cars

[Marshall1]

This was posted by GJ a while back.

I have some slips from last year, I will post one, it is a mid 11 second pass at 123.94 mph on street tires(275/30/19 bridgestone SO3's) on this pass I had to lift off the gas in 3rd and 4th momentarily to keep the car from going into the other lane from frame flex, the NSX was not made to handle the power that it is getting from the turbo or other power adders, I am very surprised that some people that have posted times are not seeing the same problems. I tried the ET drag slicks on the car and couldn't even complete a pass because the car was impossible to keep straight after going into 3rd gear.

Anyone have comments on this? I just don't see an $70k supercar chassis flexing to the point of uncontrollability -especially when the acceleration probably wasn't more than .5-.6g (less than cornering forces)
Perhaps he was spinning the street tires? I know ET drags are VERY loose on the top end.

 

[sjs]

I’d like to hear from some engineers who really understand the kinds of stresses involved with an auto chassis. But my first thought, besides the fact that I’m inclined to put stock in what GJ says, is that the NSX chassis was designed to be very rigid on the directions stressed during cornering, but perhaps not with regards to the type experienced when the engine tried to twist it like a pretzel. That may be in different planes and they wouldn’t add weight to stiffen where it isn’t needed stock.

 

[RP-Motorsports]

I think there is another factor involved here. Eddie Bello from NY has a 911 turbo monster and due to the rear drive and rear engine, the front end actually pulls and rides wheelies in the first 2 and sometimes 3 gears. I know the NSX is not rear, but mid-engined, so a wheelie won't happen, but with the driveline pull beeing off by even 5%, can allow for rear steering overpowering the front wheel steering due to no weight up front. Just a thought. Maybe he needs some lead in the front bumper!

 

[NSXTASY_MD]

Eddie Bello !? I haven't heard that name in years...is he out of jail yet ? I remember he was arrest for running a chop shop or something to that extent


...he is/was probably the baddest street racer of all time though....at that time his STREET porsche 911 was faster than any RACE supra. At some point i think he was doing 9.1@163 MPH trap in it...just ridiculous for a street car on DRAG RADIALS....rear-engine Porsche's, no substitute

 

[RP-Motorsports]

I don't know? He was missing for a few years, and now just heard his name pop up within the last year again??? I met and talked with him in Atlanta back in 98, and he was kind of a thug, but a fast one at that!

 

[titaniumdave]

The NSX has the motor mounted transverse and any torque which is put into the frame should be transmitted in line with the direction the car travels unlike the torque twist one would associates with American cars where the motor is mounted perpendicular to the centerline of the car and the motor tries to twist the body. An increase in power should have little or no net effect on the stability of the car where frame flex is concerned. Weight transfer is another issue, plus alignment can make a major difference in stability. The NSX is very sensitive to minor changes in ride height and the weight transfer could effect the ride height, making the rear end squat enough greatly change alignment and I am not sure what effect this would have on the stability.

My $.02.

 

[sjs]

True enough that the transverse engine means it is not subjected to some of the frame twisting through the mounts seen on other cars, but it still needs to transfer all that torque from crank to the road through transmission and drive shafts. Parts of the car are stressed by that at levels not intended, but I really don't now how significant it is. Also, the rear equivalent of torque-steer seen in many FWD cars is not normally an issue because it has an intermediate shaft on the passenger side to yield equal length half-shafts, but pushing two or three times the normal torque through it may uncover (normally) minor issues.

But I do think the point about weight transfer making the front light is a good one, and the combination of independent rear suspension and limited slip isn't exactly typical for drag racing either. Do the hard-core drag guys normally run a welded diff?

 

[titaniumdave]

Hard core drag racers will run a rigid rear end with a locker differential. I think I have seen dragsters with out any rear suspension, just the differential bolted to the rear of the frame?! They are designed too run on a pretty smooth surface so my guess is you just want to put the power on the ground as efficeintly as possible.

I wonder what effect the different styles of differentials in the NSX would have on the straight line performance of the car. I always think about going around corners when I think about the performance of my car. I seem to want to make my car turn into a corner quicker, and that seems like the opposite of what you want in a drag car.