WTF

[cronin49]

Hey guys, I got a crappy surprise today. I was on a long long stretch of blacktop, no cars around, so I decided to go for it. I hammer up to about 122mph redlined in 4th gear, I then shifted into 5th and the RPM's dropped to 3500 and nothing happened. I kept it froored for about 5 seconds, and the speed actually dropped to 118. I then got off of it. So I guess I have 120mph car, I find that crazy , I am putting down over 430hp. Take a look at my Sig. How can I cure this? The car is a Paxton 2000 Supercharged 2003 Mustang Convertible. Maybe a new tranny? If so, what do you suggest? I know 5th is an overdrive gear, but I thought going to 373's would make it less so. Before I had her Supercharged, I had her at 140mph redlined in 4th gear. That was with the stock 327 gears. If I remember right the gears with the 327's went 1st 40, 2nd 70, 3rd 110, and 4th 140 mph. What gives.
Is 5th gear really that much of an overdrive?
Of course, it took me 14.1 sec. to hit 100 mph when I was stock,
and now I hit 100 mph in about 9.5 sec.
But that's another story, guys.
Thanks for any advice,guys.

 

[trinity_gt]

Hey guys, I got a crappy surprise today. I was on a long long stretch of blacktop, no cars around, so I decided to go for it. I hammer up to about 122mph redlined in 4th gear, I then shifted into 5th and the RPM's dropped to 3500 and nothing happened. I kept it froored for about 5 seconds, and the speed actually dropped to 118. I then got off of it. So I guess I have 120mph car, I find that crazy , I am putting down over 430hp.

What was your AFR doing during this run?

How can I cure this? The car is a Paxton 2000 Supercharged 2003 Mustang Convertible. Maybe a new tranny? If so, what do you suggest? I know 5th is an overdrive gear, but I thought going to 373's would make it less so. Before I had her Supercharged, I had her at 140mph redlined in 4th gear. That was with the stock 327 gears. If I remember right the gears with the 327's went 1st 40, 2nd 70, 3rd 110, and 4th 140 mph. What gives.

If you do the math: 3.27/3.73 == 0.8767...140*0.8767 = 122.

So your MPH in 4th gear with 3.73s is correct.

The fact that the car was unable to pull 5th -- and in fact to lose velocity -- suggests to me that you're not making 430rwHP after an extended high-speed run.

You should check the AFRs and fuel pressure.

 

[2002BLGT]

Load can almost double when boosted and go even higher when placed in 5th gear , so depending on how it is tuned the spark is usually dependent on load and RPM , so when the RPMS drop once you put it in 5th it might be so low that its not really boosting much since you are using a very large centrifugal blower and spark is probably pulled WAY down in this part of the tune to account for the boost which will cut HP dramatically so its probably just not going to accelerate at that high of a speed in 5th gear unless its retuned which could possibly be harmful for the engine if you are not VERY VERY careful