wow, Neff...seems like you lean out quite a bit at the end...8lbs and 14.2 A/F? That's dangerous, isn't it?

 

ha ha, yeah Randy it would be if he didn't let off of the gas pedal. The car is going to vacuum at that point and it looks like it's about to explode but in reality it's not.

One more reason why I just love my gauges. Wideband and boost gauges both reassure me that what you're reading ONLY happens at vacuum (when you lift off of the throttle). This is a common phenomenon with ALL FI applications. When there is no boost, back to vacuum and high A/F's.

BTW, they never took my car to redline (or they didn't bounce off of the rev limiter). As soon as the car stopped making power, they let off of the throttle. Notice how the rpms never got to 6800? In fact, the rpms start dropping as he lets off of the throttle.

 

6100 384.2 331 90.5 11.3 0.77 8.3 PSI 102
6125 385.1 330 90.6 11.2 0.77 8.4 PSI 102
6150 386.3 330 90.6 11.2 0.77 8.4 PSI 103
6175 387.2 329 90.6 11.1 0.77 8.5 PSI 103
6200 387.8 329 90.6 11.0 0.76 8.5 PSI 103
6225 387.6 327 90.6 11.0 0.75 8.5 PSI 103
6250 387.3 325 90.6 10.8 0.74 8.6 PSI 105
6275 386.4 323 90.6 10.6 0.73 8.8 PSI 105
6300 385.8 322 90.6 10.6 0.73 8.8 PSI 105
6325 385.0 320 90.6 10.6 0.73 8.8 PSI 105
6350 384.2 318 90.6 10.6 0.73 8.9 PSI 106
6375 383.5 316 90.7 10.6 0.73 8.9 PSI 106
6400 382.8 314 90.6 10.5 0.72 9.0 PSI 106
6425 381.8 312 90.6 10.6 0.73 9.1 PSI 107
6450 373.6 304 90.6 11.1 0.76 9.0 PSI 106 Here he is letting off of the gasoline.

The momentum allows the car to keep generating rpms but the car begins to go into vacuum and starts 'leaning out'.

6475 349.5 284 90.7 12.5 0.86 8.5 PSI 106
6475 335.2 272 90.7 13.1 0.90 8.4 PSI 107 This is where the rpms peak but it is under vacuum at this point
6450 322.6 263 90.7 13.4 0.92 8.5 PSI 107
6425 309.9 253 90.7 13.7 0.94 8.6 PSI 107
6400 291.5 239 90.7 14.0 0.96 8.4 PSI 107
6375 271.9 224 90.7 14.2 0.97 8.0 PSI 107 This is the rpms falling back down and the car going to vacuum

 

if that was the case, why wouldn't the PSI column show vacuum? You know, a negative number...

Awww...forget the statement above...I see it's going down and thus vacuum is being acheived...

 

Neff,

Have you tried removing the front sway bar at the track?

That should allow for a significant amount of front end travel, resulting in much better weight transfer to the rear tires.

This is a proven track aid!

 

Only a very very small fraction of the weight transfer to the rear comes from movement of the center of mass rearward from suspension deflection (look at the wheelbase, estimate the suspension compression, look how much a point near the center moves towards the rear). Regarldess, the sway bar has virtually no effect when both wheels are in jounce or compression. It's there to add roll stiffness.

 

What you really need is some drag shocks that you adjust and they allow the rear end to go down when you launch resulting in better traction. And some traction bars would help as well. Removing stuff up front does not help.

 

The fact that the rear end comes down does not significantly impact the weight transfer to the rear (seems non-intuitive, I know). However the added force necessary to slow down the rotation of the car as it compresses the rear and then hits the stop might give you some noticeable additional force on the rear wheels for that instant. Again that's more from dissipating the car's built-up angular momentum and is not directly related to the suspension deflection really. But in steady state, 90+% of the weight transfer is due to the vehicle acceleration alone, not the deflection of the suspension.

I actually wrote a technical paper and did detailed dynamic simulation of cars accelerating from a stop (including detailed tire slip models) to characterise the effect of weight transfer on FWD versus RWD cars for a final project in a graduate vehicle dynamics class, so I am painfully familiar with it.

 

Well, technical paperwork and real world racing are two different things. I have raced many cars and been part of many 6-8sec 1/4 cars to know the setups that work.

 

All this technical thinking is not helping the original poster here on this thread.
He totaled his car when hit a taco cart. Happy new year, Neffster!

 

Don't knock it 'till you try it. Knowing that some given setup works is very different from knowing why it works. But it doesn't matter, I agreed with you that softer shocks in the back will indeed increase traction for a few instants off the line as the vehicle pitches and is slowed by suspension forces in the rear.