Diff ratio and speed
Discussion
If you alter the final drive (diff) ratio, then this will also throw out the speedo reading by a similar amount - ie going from 3.31 to 3.45 will cause your speedo to read about 73mph at a true 70mph.
You could use a satnav to check what your speedo reads at a true 70mph and then record the revs.
As a rule of thumb, a high number diff gives a lower top speed and increases revs while cruising but accelerates quicker.
A low number diff will give a higher top speed, lower revs while cruising but accelerate slower.
Drag cars mostly run 4.11 or 4.56 gears, giving lower top speeds, but quick accleration.
Hope this helps?
You could use a satnav to check what your speedo reads at a true 70mph and then record the revs.
As a rule of thumb, a high number diff gives a lower top speed and increases revs while cruising but accelerates quicker.
A low number diff will give a higher top speed, lower revs while cruising but accelerate slower.
Drag cars mostly run 4.11 or 4.56 gears, giving lower top speeds, but quick accleration.
Hope this helps?
black and green said:
If you alter the final drive (diff) ratio, then this will also throw out the speedo reading by a similar amount - ie going from 3.31 to 3.45 will cause your speedo to read about 73mph at a true 70mph.
You could use a satnav to check what your speedo reads at a true 70mph and then record the revs.
As a rule of thumb, a high number diff gives a lower top speed and increases revs while cruising but accelerates quicker.
A low number diff will give a higher top speed, lower revs while cruising but accelerate slower.
Drag cars mostly run 4.11 or 4.56 gears, giving lower top speeds, but quick accleration.
Hope this helps?
I`m buying a new BTR with GKN to BTR fabricated brackets ,so will fit straight in .. What will i need to get You could use a satnav to check what your speedo reads at a true 70mph and then record the revs.
As a rule of thumb, a high number diff gives a lower top speed and increases revs while cruising but accelerates quicker.
A low number diff will give a higher top speed, lower revs while cruising but accelerate slower.
Drag cars mostly run 4.11 or 4.56 gears, giving lower top speeds, but quick accleration.
Hope this helps?
the speedo to work . I`m aware the toothed wheel is in a different place .
If a 345bhp Chimaera takes me to 60 in less than four seconds with a 331ratio i wonder what time it would take with a 308 .
Seen some 308 crown wheel and pinions advertised on fleabay from Australia .
I don`t know if to fit the 345 or have the 308 crown and pinion installed . Everyone who has gone to the 308 have been very pleased
.
0 to 60 times will be slower but maybe quarter mile drag races may be faster .
I can confirm that 0-60 and the 1/4 mile will not be affected by fitting the 3.08.
I know because ive done it and tested it out a lot.
The best part of running a 3.08 is the cruising on the motorway off cam at 3000 rpm.
The gearing is very very close to 30 mph per 1000 rpm. I run 265/35/18s.
I know because ive done it and tested it out a lot.
The best part of running a 3.08 is the cruising on the motorway off cam at 3000 rpm.
The gearing is very very close to 30 mph per 1000 rpm. I run 265/35/18s.
A pal of mine did this on a Cobra but went the other way for better acceleration. All i can say is it was noticeable.
Just read your opening post again Daz, I suspect the difference in ratios you are mentioning would hardly be noticeable accerelation wise.
Just read your opening post again Daz, I suspect the difference in ratios you are mentioning would hardly be noticeable accerelation wise.
Edited by carsy on Wednesday 28th May 20:26
carsy said:
Like you say Derek, on the strip no difference but I think you will notice the IN gear acceleration being slower on the road.
I disagree. I think there is an illusion there as you are in the gear a little longer but you are accelerating to a higher speed. The numbers match on the strip so they are the same on the road. There may be times when you need to drop a gear that you may not have previously needed to. Just need to relearn the cars needs. Alexdaredevils said:
So you don't want my GKN now?
I don`t know what to do !can`t afford to keep paying labour to many times .. The problem with the GKN is the lack of parts . Its going to cost me £500 to get it refurbed .I could buy a second had one and chance it . If i bought a second hand working BTR at least it can be properly refurbished in the future . Or bite the bullet and buy a new one with brackets .
What about the speedo pick up whats involved ?
SILICONEKID345HP said:
Alexdaredevils said:
So you don't want my GKN now?
I don`t know what to do !can`t afford to keep paying labour to many times .. The problem with the GKN is the lack of parts . Its going to cost me £500 to get it refurbed .I could buy a second had one and chance it . If i bought a second hand working BTR at least it can be properly refurbished in the future . Or bite the bullet and buy a new one with brackets .
What about the speedo pick up whats involved ?
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