G50/50 gear ratios and speed per 1000rpm in 5th.

[shithotfast]

I "inherited" my gbox from a family member who raced an ultima a few years ago. The gbox had just been rebuilt with quaife gears. I have 17 inch rear wheels.

I was once told that I could expect 29mph per 1000 rpm when in 5th gear. My standard zz4 revs to 6k so thats 174 mph. max. I notice my car is slightly less than that. EG 3,000rpm in 5th shows around 80 mph. (speedo could be slightly out) Question is what do others get? Not sure if the gears in my box are non standard? What speed do you guys get at 3000 rpm in 5th? Was thinking of changing the 5th gear to give more "legs" and higher top end. Dont think I should rev a zz4 past 6k or it will go pop!

[B1 ECC]

Hi Paul,
Your bang on correct, 70mph-- 2700rpm, 80mph--2999rpm, top whack @ 6000rpm (but you know you shouldn't rev your ZZ4 past 5800) is 160mph.
Hope this helps!

Ian

[bluesatin]

mine does 165 at 6400 rpm

[GT4T]

You can get a copy of my Excel gearspeed calculator here:
www.gt40s.com/ubbthreads/download.php?Number=61845

Regards,
Lynn

[andygtt]

changing 5th will cost about £500 for the gear plus fitting....... you really need to know what you have first so you can work out what you need.

[shithotfast]

thanks guys.... so the Ultimas doing high speeds (eg 210mph) are the gear ratios differant, or just high reving engines? I guesstimate to do 210mph you need to rev to nearly 8k! Will look at a higher 5th during the winter. PS nice GT40 Lynn!

[andygtt]

well mine did 212mph at 7000rpm, at brunters I got 184mph at 6100rpm.... its all in the ratio's which vary depending upon which spec gearbox you buy.

What I suspect is that you have a lower CWP ratio that is giving you the lower top gear than some others...