Zac,
If the input gearset has a lower reduction, (closer to unity) then all the
gears apart from the 1:1 direct coupled fourth will be taller. This means
that 1st, 2nd & 3rd close up but fifth gets wider. This is probably the
cheapest way to close up a gear set but it still has its problems. With a
1:1 fifth this makes a good way of changing ratio spread reasonably easily.
All 71B option 1:1 fifth boxes come with 22 drives 31 input sets so by
changing to a 21 -32 set you can lower too tall ratios to give a ratio set
in between option 1 and 2 etc. Eg option 2 with 22 31 gives 2.348,
1.601,1.296, 1.138,1. By changing the input to 21 drives 32 this gives
2.539,1.731,1.402, 1.231,1 (just like a taller option 1)
These are the common gearbox input ratios.
22:31
(The most common:- used in K 5 speed, 240Z 260Z, R30 & R31 Skyline, SR20,
FJ20, CA20.) these are all FS5C71B boxes. From my understanding the codes
mean F(rear wheel drive) S(overdrive) 5(five speeds) C(closer ratios)
71(Main housing type) B(extension shaft & housing type). These boxes have
typically 3.321, 2.077,1.308, 1, & 0.864 ratios. This is the most common
box used in Nissan vehicles.
21:32
(K 4 speed and other underpowered, commercial or heavier vehicles ( 720 or
Navara utes, 280C, 280Z, R31-CA Pintara etc) For smaller engined or
heavier bodied vehicles the above ratios were changed to 3.592, 2.057,
1.361, 1, 0.852 by using the 21:32 input set. These ratios allow you to get
of the line quicker with a heavy body that is under powered. This box is
then known as a FS5W71B box. The W being for wider ratios.
Most turbo boxes are the FS5C71B boxes with the naturally aspirated
versions having the FS5W71B boxes. If you go to an importer they will often
tell you a box is from a turbo or NA vehicle and often get it wrong. The
easy way is to put the box in first and turn the input shaft counting the
turns to produce one revolution of the output shaft. (3.3 turbo, 3.6 N/A).
The main difference with early 5C turbo boxes is the use of heavier section
countershaft (38mm diam) and gears. This means they change slower but can
handle heaps more grunt. The earlier boxes (240K, 260Z etc) up to about 85
usually had a 29mm diameter countershaft. All boxes from 87 on seem to have
the larger countershaft. 85 - 87 boxes can be a bit of a mixture of
countershaft types.
The best part of the FS5 (C or W ) 71B boxes is that once you have set up a
good set of ratios, you can change the box from vehicle to vehicle by
changing the bell housing. Eg an L series box to an RB 30, SR20, FJ20, CA
(16 - 18 - 20), Z (18-20-22-24) by changing the bell housing.
23:28
(early Z and fairlady boxes these are not interchangeable with the 71B
family boxes)
18:32
Nissan Vanette and other commercials (if fitted into 5C gear set this
gives, 4.190, 2.4, 1.650, 1, 0.865 ( a good cliff climbing gearset?)
There are other input sets around, it just means looking out for boxes in
bits and doing some counting
Cheers
Feral Errol
----------
From: Zac Campbell <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Subject: Re: Close ratio boxes
Date: Monday, June 26, 2000 10:13
Errol, will any of those effectively closen the ratios at all?
Then they could be combined with a different diff ratio?
zac
>Zac,
>The most common method of making a close ratio box is to have new gears
>cut, then machine the counter-shaft down and weld the new gears to the
>counter-shaft. There are a lot of people who can do this work but the
price
>works out at approximately $650/gear (ie $1950 for fist second and third
>gears) Thats why option boxes are so dear.
>Often you can change overall drive ratios by changing input shaft gears
and
>countershaft gears (ie 22 drives 31 used in most Nissan later 5 speed
boxes
>to a 240K 4 speed gear set with 21 drives 32) this used in a 240K 5 speed
>gives a very useful overdrive of 0.92, but first is useless and there is a
>big gap from second to third. So the first three gears need to be recut.
>There are a number of ratio options available using different input gears
>and countershaft gears. You can even have a stump puller 4.2 first if you
>want.
>Cheers
>Feral Errol
>
>----------
>From: Zac Campbell <[EMAIL PROTECTED]>
>To: Ozdat List <[EMAIL PROTECTED]>
>Subject: Close ratio boxes
>Date: Monday, June 26, 2000 10:02
>
>List, whats the possibility of building our own close-ratio boxes?
>I have heard of people sticking bluebird gears in an SR20 box to get a
>lower
>1st gear...
>
>zac
>
>
>
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