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Five speed to suit L-series with lower revving fifth.
http://www.ozdat.com.au/forum/viewtopic.php?f=29&t=12466		 Page 1 of 1
Author:  green200b [ Thu Apr 10, 2008 7:48 pm ]
Post subject:  Five speed to suit L-series with lower revving fifth.
Hi all, I own a Datsun 200B fitted with an L20B and a five speed which I believe to be out of a Bluebird. Fifth gear is more like a gear 4.5, and it's revving at over 3,000rpm at 100km/h. This is a bit higher than I'd like it to be revving, so I was wondering if anyone could suggest a five speed that will mate up to my motor and allow it to rev a bit lower?

My old ED wagon revved at about 2,100 at 100km/h in fifth gear, and my current RX-7 revs at just over 3,000rpm, having said that it is a rotary. Just some comparisons.

I had a series 3 Bluebird once, and it seemed to rev a bit lower at 100km/h in fifth. I still have the five speed, so if I swapped the bell housings over, would that be any better? Does anyone know if there is a difference between the ratios in both boxes?

All help or suggestions appreciated :)
Author:  bad510 [ Thu Apr 10, 2008 8:23 pm ]
Post subject: 
My L18 powered 510 used a 5speed stanza box with an r180 diff, cant remember the diff ratio, but it would rev at 3200rpm at 100kph.

I was going to try and find something a bit better suited to freeway driving as i travel an hour a day to and from work costing me a fortune in fuel, my L18 blew up before i had a chance to do much research , a few people told me that a 260z 5speed would be a good match.

As for the bluebird boxes im not to sure.
Author:  nick [ Thu Apr 10, 2008 9:09 pm ]
Post subject: 
easier to change diff ratio...?
Author:  Cowboy1600 [ Thu Apr 10, 2008 9:37 pm ]
Post subject: 
nick wrote:
easier to change diff ratio...?
Probably. That said, a diff change lowers the ratios in all gears, but there may be a box with similar or identical 1-4 and a biggr overdrive on 5th. Maybe :)
Author:  Boyracer [ Fri Apr 11, 2008 12:44 am ]
Post subject: 
There's a few pages out there that will tell you the Gear ratios of all the various boxes, the info I have thus far says...Live with it.

The 240K box I believe has the same ratios as the early Bluebirds, 5th —> 0.864. The 260Z is the steel synchro box, but is better only in the spread in the first four gears and only marginally at that, 5th —> 0.864
Then you move onto the R31's and the such, 5th —> 0.838, slightly better, maybe enough to make it worth while. 2nd Gear is shorter (slower) and the rest are the same.

These engines were designed to rev. 4spd box with 1:1 top gear and to overtake someone you'd knock it back to third and feed it to it. Of course that's with a 3.9:1 diff ratio. Sounds like you might have something a bit shorter in there.
Author:  nick [ Fri Apr 11, 2008 2:42 am ]
Post subject: 
had a look in a folder of mine tonight and found written down:

1982 onwards 280zx has 0.752 fifth.


I cant guarantee its correct but try searching for this perhaps if a diff change is out and let us know how you go. :wink:
Author:  Waz [ Fri Apr 11, 2008 8:48 am ]
Post subject: 
ca18 is good.
Author:  sbthomo [ Fri Apr 11, 2008 9:31 am ]
Post subject: 
Check the ratio's in this table. http://zhome.com/ZCMnL/tech/GearRatios.html
For a dato that does a fair amount of highway work I have found the R180 3.545 diff works best with any g/box combo. Think from memory 100kph in a 4 speed with 1:1 4th was 3000rpm so in 5th would be around 2800 ish.
Author:  SR20Datsun [ Fri Apr 11, 2008 9:45 am ]
Post subject: 
Nice gearbox is the R30 skyline alloy box.
5th gear is a true overdrive so great for cruising.
Don't know the ratios off the top of my head though.
Author:  green200b [ Fri Apr 11, 2008 1:11 pm ]
Post subject: 
Thanks for all of the replies!

I had considered changing my diff ratio, but I thought I would see if there was a better gearbox to use first. How about a 720 five speed? The website that sbthomo suggested I look at said that they had a longer fifth.

Or would I be better doing a gearbox rebuild and putting different ratios in?
Author:  bluebird68 [ Sat Apr 12, 2008 5:44 am ]
Post subject: 
As the bluebird 5 speed ratio's are .864 overdrive , it's not the gearbox that is the problem. Getting your gearbox rebuilt with a custom gearset from ALBINS in ballarat will cost $2000. Changing the diff ratio to something like 3.5 would be cheaper as long as you can find one to suit.
Author:  Boyracer [ Sat Apr 12, 2008 1:33 pm ]
Post subject: 
Less than a minute with google http://www.gracieland.org/cars/techtalk/gearing2.html :roll:

The 720 has a taller 5th, but then they also have a different cluster ratio, you'd need to find out what that gear ratio with the cluster ratio from your box would be. I think the 720 has a shorter cluster set, so could be by the time you throw the 5th gear set in there you'll end up with a stupid o/drive and the car will stuggle to push it up a decent grade in 5th. Also the websote only lists the post '80 720 Boxes, the earlier boxes would have a different ratio I think as the diesels and petrols had different diff ratios.
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