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ideal ratio
gaz_gaz - 3/1/13 at 04:05 PM

What's the ideal diff ratio in your opinions for a boosted BEC.

I dont mean out of what's available. I mean ideal, if you could have anything!
Decided to stop faffing around looking for over priced items and make a crownwheel and pinion.

[Edited on 3/1/13 by gaz_gaz]

sdh2903 - 3/1/13 at 05:36 PM

Would depend on what Bike engine as they have different final drive ratios iirc. I would imagine a 3.14 would prob be a good all rounder if you were after an available one.

coozer - 3/1/13 at 05:49 PM

Around 3/1 or a bit higher, maybe 2.8/1 if you want a mega top end...

wylliezx9r - 3/1/13 at 06:04 PM

quote:
Originally posted by gaz_gaz
What's the ideal diff ratio in your opinions for a boosted BEC.

I dont mean out of what's available. I mean ideal, if you could have anything!
Decided to stop faffing around looking for over priced items and make a crownwheel and pinion.

[Edited on 3/1/13 by gaz_gaz]


If your going to make them, do me 4.4 for a sierra 7" diff and make it for cheaper than the £500 + VAT that quaife charge. Pretty please

SPYDER - 3/1/13 at 07:55 PM

Hi there! What engine? What tyre size? And what intended use? There's little point in gearing up for a mega top end speed
for use on circuits where it will be unachievable.

gaz_gaz - 3/1/13 at 08:12 PM

i've spoken to people with turbo BEC who are hitting the rev limiter in 6th before the end of the straight on Brands Hatch Indy circuit with a 3.14 ratio diff
I currently hit the limiter in my non turbo car before the end of the straight so with an extra 80 or so bhp it certainly won't be a problem,
I had my car at Snetterton 300, Nurburgring and Spa last year and it was terrible,


using some software i use at work these are the predicted calculations for some ratios. looks fairly accurate to me and the 3.62 is spot on

3.62



3.14



2.8

jossey - 3/1/13 at 08:18 PM

3.62 would not be a fun drive though.

It would have you changing gear a lot.

gaz_gaz - 3/1/13 at 08:22 PM

3.62 isn't an option really.
no where near enough top speed with the car na, it'd be as good as useless when turbo'd

jossey - 3/1/13 at 08:27 PM

3/1 would be a good aim.

gaz_gaz - 3/1/13 at 08:28 PM

how about a 2.9... i like the look of this.


SPYDER - 3/1/13 at 09:06 PM

What ratio are you using at the moment? If other people with similar turbo'ed cars are finding a 3.14 to be too short then the 2.9 could be a solution. But isn't it preferable to be on the rev limiter for a couple of seconds at the end of the straight rather than never getting there at all. Going from 3.14 to 2.9 is quite a big step. The 2.9 gives a higher speed in 5th than the 3.14 does in 6th! There's more than a whole gear ratio difference. Would 3.0 be a better compromise as previously suggested?
Do you think you will realistically use the 150mph potential of a 2.9?