Lower ratio 5th gear

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snakeknuckles
Posts: 44
Joined: Wed Jan 16, 2013 7:47 am
Your car is a: Fiat 1982
Location: Maryland

Re: Lower ratio 5th gear

Postby snakeknuckles » Fri Mar 10, 2017 2:16 pm

So on paper here it is (please check my math):
Ratios :
trans : 1-3.667, 2-2.1, 3-1.361, 4-1, 5-.881
rear wheel w3.90: 1-14.30, 2-8.19, 3-5.31, 4-3.9, 5-3.44
rear wheel w 3.56: 1-13.05, 2-7.48, 3-4.85, 4-3.56, 5-3.136

for 15" tire: od=22.5", 60 mph = 896rpm(wheel) = 3082 rpm(engine) w 3.90, 2804 rpm w 3.56

and w .78 fifth gear and 3.56 rear: 60 mph=2483 rpm, and 140mph =5804 rpm

With all that said, I will let you know how she performs with the 3.56 rear. I might wait for the dust to settle on my credit card before getting the new trans...

ps. do I have too much time on my hands?

djape1977
Posts: 986
Joined: Sat Apr 21, 2012 6:08 pm
Your car is a: 1970 fiat 124bc
Location: Belgrade, Serbia, eastern Europe

Re: Lower ratio 5th gear

Postby djape1977 » Fri Mar 10, 2017 8:14 pm

my 2 cents

fiat is not a lazy american v8
it's perfectly normal for it to be driven at constant 4-5k rpm

being a drop top, 124 spider is inherently noisy at high speed. by installing a tall ratio rear end you're robbing it of it's best part - short bursts of acceleration and nimble handling on curvy roads. whatever you do to it, it's never going to be a silent high speed cruiser.

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RRoller123
Posts: 6913
Joined: Sun Nov 13, 2011 2:04 pm
Your car is a: 1980 FI SPIDER 2000
Location: PLYMOUTH, MA USA
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Re: Lower ratio 5th gear

Postby RRoller123 » Sat Mar 11, 2017 8:42 am

I get that, but we don't use 5th for short bursts of acceleration on curvy roads. That is for 4th.
'80 FI Spider 2000 (rolling "resto")
'74 X1/9 (many years ago)
'79 X1/9 (fewer years ago)
'86 Jaguar XJ6 (2nd Hobby Car)
2011 Chevy Malibu (daily driver)
2010 Chevy Silverado 2500HD Ext Cab 4WD/SB
2015 Keystone Montana High Country 343RL

snakeknuckles
Posts: 44
Joined: Wed Jan 16, 2013 7:47 am
Your car is a: Fiat 1982
Location: Maryland

Re: Lower ratio 5th gear

Postby snakeknuckles » Sat Mar 11, 2017 7:32 pm

... or 3rd

snakeknuckles
Posts: 44
Joined: Wed Jan 16, 2013 7:47 am
Your car is a: Fiat 1982
Location: Maryland

Re: Lower ratio 5th gear

Postby snakeknuckles » Thu Mar 16, 2017 11:50 am

So it took me about 6 hr to complete the swap... The diff I got from Bayless seems to be in excellent condition and has the 43/12 ring and pinion. I just drove it around town and so far I am pleased. no perceivable loss in acceleration from stop, cruising 65mph shows 3000 rpm. Just have to relcalibrate speedo now...

djape1977
Posts: 986
Joined: Sat Apr 21, 2012 6:08 pm
Your car is a: 1970 fiat 124bc
Location: Belgrade, Serbia, eastern Europe

Re: Lower ratio 5th gear

Postby djape1977 » Fri Mar 17, 2017 6:04 am

then you must have 300hp engine if there is no loss in acceleration. :mrgreen:

snakeknuckles
Posts: 44
Joined: Wed Jan 16, 2013 7:47 am
Your car is a: Fiat 1982
Location: Maryland

Re: Lower ratio 5th gear

Postby snakeknuckles » Mon Mar 20, 2017 6:08 pm

Serbian water must be intoxicating...

djape1977
Posts: 986
Joined: Sat Apr 21, 2012 6:08 pm
Your car is a: 1970 fiat 124bc
Location: Belgrade, Serbia, eastern Europe

Re: Lower ratio 5th gear

Postby djape1977 » Mon Mar 20, 2017 7:35 pm

if you're willing to talk about water, how is your water supply? tested for lead recently???

snakeknuckles
Posts: 44
Joined: Wed Jan 16, 2013 7:47 am
Your car is a: Fiat 1982
Location: Maryland

Re: Lower ratio 5th gear

Postby snakeknuckles » Wed Mar 22, 2017 9:32 am

Whoa... Sorry to drift off topic. I was looking for a polite way to say you are wrong about the performance of a 2l 120hp motor that red lines in the mid 5ks... Don't get me wrong, the 3.56 rear does not make a major change in drivability, but I think it helps. I still haven't put a ton of miles on the car since the switch, but I do think the lower gears are much more useful in town now and the 3000 rpm/65mph cruising is much nicer than 3300. I still plan on some day going for the .78 5th gear as well.
ps. I am waiting for a speedo adapter (Clark Bros aa 10888) which should correct speedo.-I hope I can make that work

pdx124
Posts: 16
Joined: Tue Nov 24, 2015 12:49 am
Your car is a: 1980 pininfarina 2000 fi

Re: Lower ratio 5th gear

Postby pdx124 » Fri Apr 21, 2017 5:01 am

ANother option is to put in a 131 gearbox. I think they have a lower OD ratio.

fiatfactory
Posts: 479
Joined: Sun Jun 13, 2010 11:22 pm
Your car is a: 1970 128

Re: Lower ratio 5th gear

Postby fiatfactory » Fri Apr 21, 2017 11:25 am

Boosted engines love tall final drives, they have plenty of torque down low... it's not the amount of Hp the engine has, it's the torque curve it develops that makes the difference in this case.

SteveC
2014 500 Pop (Daughters daily drive)
2007 Punto Sport 1.9 Turbo Diesel
1982 131 SuperBrava 2litre
1982 Fiat Ritmo
1978 124 Spyder
1978 X19 serie speciale 2000 DOHC
(and a bunch of other Fiats but not enough characters for them all in this signature line)


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