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Hi, im new.
I have an Alfa 75 1.8 carburation for rallying in spain.
My problem is in gearbox.
My gearbox has this setup:
- Semi-close ratio of 2.5 V6
- Pinion an crown of 1.6 i (9/41)
- LSD Bacchi Romano (disc) at 65 %
- Ceramic clutch with springs.

My problem is in the pinion and crown, i need 160 km/h approximately of top velocity. At present, with this setup, the top of velocity in a test bank is the 240 km/h.
1st - 70 km/h
2nd - 115 km/h
3rd - 160/170 km/h

For rallying is the worst, because my engine isnt big!!
I think that build the pinion and crown is cheaper than buy a close ratio of competition.

That advise me?

Thanks

What gear ratios do you have and how high do you rev?
It doesn't sound semi close or close at all for that matter.

With stock ratios and a 41/9 rear end you should have with 58 cm tires at 8k 64/107/134/178/236 km/h.

Only getting a shorter diff gear doesn't help much. Closer ratios would.

rev - 7.500 rpm approximately

The wheel are 15" and the tyre is 200/50/15 slick.

Because, doesn't help much getting a shorter diff gear??

Thanks

As I said, I really don't understand what you mean by semi close ratio. With the data you provided the fifth is longer than stock.
205/50R15 / 7500 rpm and 41/9 diff with stock 75 gears make:
61/102/128/170/226

There's only one stock diff longer than what you have. that's the Giulietta 1300 (43/9) which would give the following speeds:
58/98/122/162/215

It would help some but the two last gears would still be too long. At least here it's very hard finding these and I'd go for shorter gears instead. At least 4th and 5th.

Please, can you know witch pinion/crown are 150/160 km/h top speed with my ratio?

Thanks

If you now have 4.56 and 240 km/h then what you want is:
240/155*4.56 = about 7:1
Never heard of such but who knows

Alfa75_rallye: With factory gears you can only get shorter first three gears by taking them from AR 75 2.4TD.

Click on this link to see comparison of your gearbox and new with first three TD gears.

That's the shortest you'll get with factory parts.