I was trying to test my top speed in a 4 mile stretch and the car seems to get to 6400 very easily in 3rd and 4th gears but in the fifth it hung up at ~5600 at almost 165 MPH what could be the reason ??? Is it the aerodynamics? !! Have this scanned from my HPtuner that wouldn't go beyond 158MPH can you guys help me figuring out the problem.

 

I was told big part of it is wind resistance.

 

The 5th gear is more of a cruising gear. There is a calculation that shows how much power it takes to move a car at speed versus wind resistance and gearing. Basically, if you car made more power, it would definately push the car to a higher MPH...in 5th gear.

 

going with higher rear end ratio will help?? what ratio is the best??have 3.42 now

 

It may help a little but how many times are you going to be going 5,500+ RPM's in 5th gear? It's not worth the money for the small change it may make. You would see the biggest difference in how much power your motor makes. Add another 200-300hp and I almost guarantee that car will see 6,500+ in 5th gear.

 

good luck trying to kill your self

 

Silly question... have you raised your speed limiter?

 

my thougts exactly, its 165 the fuel cut off on a stock car with z tires
it may not have been changed

 

yes did that with hptuner

 

I would think that with your mods you should be able to see faster speeds than that. I would think a cam and boltons car would get into the upper 160s maybe even low 170s. Afterall they claim a stock b4c package is 170 MPH capable, and GM supposedly circle track tested a stock 98 f-car to 175. Those are under optimum conditions though. It looks like your motor just runs out of steam, not like it hits a wall (figuratively speaking) at 158. Have you had the car dyno'd? Did you try running in both directions? Tires fully inflated? Also, why are your LTFTs positive at WOT?