rpm ?

ok im kinda stumped on this.
i race on a 1/4 mile track last year i ran a 659 final in a mustang and turned 7900 to 8100 rpms
now i have a pro 4 the same track same final and only turn 6500...
any ideas on why this would be????
tire sizes are the same on both cars..

is this the same motor or a diff one. if its the same one something is wrong somewhere a bind or something. but if this is a diff motor, you might have to run a diff gear but with that much change in rpm something in the engine is prob off, wrong cam, cam not setup right, carb bad, bad valve springs, or something along that line. does it get to that rpm and quit pulling or does it pull all the way down the straight to the corner. if it quits pulling might want to check dist, grounding, tach, ign switch, fuel pressure

but wat r ur lap times mabe u aint spining tires in the pro4

same eng same trans...only thing diferent is the rear end it has a 9inch. if i put a 749 gear it turns 8400 on the same track...

would a 9inch drang down that much so you have to gear it lower....
i figured a pro 4 would go faster so youd have to gear it high but dont seem to be working out that way.....

I would bet either the trans ratio or rear gear ratio is different from what you thought on your mustang or pro-4. That big of a difference has to be gear ratio related or different sized tracks, recheck your ratios and final drive numbers.