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Close ratio gear boxes


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#1 DatZed

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Posted 24 September 2009 - 03:00 PM

Short of getting a gear set made has anyone done a close ratio conversion?
I have got rid of my option boxes becuase they are so fragile, what I am looking for is a conversion using a late model gear box that has a close or semi close ratio.
My mx-5 has a six speed that's really close, but these boxes have a really strange gearbox cross member setup. They are the same unit that is used in S15's and Altezza's, with the obvious bell housing change. The great advantage of these gearboxes is that they have a 1:1 fifth, unlike the t56 which is over driven 5th.
Anyway, has anyone done some sort of conversion in the past?

#2 NZeder

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Posted 25 September 2009 - 02:14 AM

It depends on your budget and if you want a Nissan box. In Oz there are few that make gearsets for the 71C boxes. SWMotorsport can sell a complete box with 1:1 5th etc but that is not cheap - cheaper than a hollinger but up there for sure.

I think at one point I found 2 manufactures in Oz that do gearsets for the 71C boxes + then there Quaife from the UK

#3 PZG302

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Posted 25 September 2009 - 03:00 AM

Dat2kman on here is able to get gear sets from Japan and has played with plenty of these boxes to work out the best setup and ratios, when he puts his head in here I'm sure he'll be able to help out.

#4 260Coupe

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Posted 25 September 2009 - 03:07 AM

Try Needhams if you are serious (Old gearbox Co.) they custome build alsorts of race gear boxes for all vehicles.
Ben offered to build me a close ratio box for around $2k

#5 DatZed

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Posted 25 September 2009 - 12:51 PM

I really don't want to get into straight cut gears as this car is a bit of a toy. I use it for Sunday's and the occasional sprint so I don't really want the noise that comes with a straight cut box.
The gearbox in my other Zed was done by PPG in Adelaide and while they offer a great product it's bloody noisy. Great for what it's designed for, just not really nice for the road. The other issue that I have with straight cut boxes is that most manufacturers will have to swap reverse and first to make a 1:1 fifth from an overdrive fifth gearbox, which again is fine for racing but shit for the street.
So I am really looking for a helical cut box that has decent ratio's like the option boxes. As previously stated the option boxes are too fragile and impossible to fix, so I got rid of mine.


#6 NZeder

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Posted 25 September 2009 - 01:07 PM

Talk to BenZed on this site then he can get some kits that replace the first 3 gears, are stronger than stock and give a close ratio however you still have a 1.1 4th and overdrive 5th. However the 5th gear can be replaced (mate had it done on this race car box) to a closer unit ie 0.9x vs 0.78 etc.

#7 dat2kman

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Posted 25 September 2009 - 03:42 PM

Use your L series bell housing to start with. It will need some machine work depending on bearing size you use for countershaft, and cluster face needs deepening by 120 thou (3mm), and topmost selector rod hole opened up to 16mm from 14mm.
If you are wanting the 71C cluster (rather than 71B) and are after strength and durability, look for a second hand box from something with a RB20 turbo RWD  car It will have the input drive/driven ratio of 1.409. Good wide thick gears, nice chunky synchro forks
You can either simply give the cluster assy to Albins in Bendigo/Ballarat Vic, and they will machine off the 1st/2nd/3rd gears from the bottom cluster shaft, and press fit/weld on their new outer gears to your existing many year old cluster shaft, they then provide all new 1/2/3rd main shaft gears, you will need to supply new dogs and synchros. ( cost, dunno, last I heard approx 2200??)
You will end up with a usable close ratio box and a 1:1 fourth BUT, fifth is a horrible 0.752, it'd be OK with a 4.375 or 4.1 diff for longish straights on some track ie Bathurst/ Phillip Island, but with the 0.75 changing from 4 to 5 will not give any acceleration.
Solution is to look at dismantling other RB late model type boxes to obtain a 0.83 fifth, they do exist. ( dunno about a 0.9 fifth though ???)
Other option is to look up/Google "Kameari" learn basic Japanese, ( or Ben Zed or I can get it for you!) ( after you have got pricing from Albins??)  supplying you a brand new countershaft with all gears intact and not welded on, and main shaft gears (Ex Japan) made to Nissan specs, ( not Option type), these are Helical cut gears with standard dogs and synchros, you then get your local gearbox and diff shop to re-assemble the box with these brand new items, and, it's a solid strong close ratio box, still with a .75 fifth though!
I got a hybrid Nismo Option 1/2 box here that goes into an old Datsun 120Y, it has full dog ring engagement and is helical cut, input ratio is 1.2:1.
I have also done the close ratio setup on four L series 71B boxes, and am doing a 71C box at the moment.
Only killer is the crazy Jap Yen to our Pacific Peso exchange rate!

#8 DatZed

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Posted 26 September 2009 - 03:01 AM

I have had a little bit of experience with the Albins product both good and bad. If I was going to get a gearbox made locally I would go back to PPG.
I am currently considering a TRD six speed from an SXE10 with a custom bell housing, will have to spend some time with the tape to work it out.
I'll keep you posted.

#9 Thomo260

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Posted 26 September 2009 - 02:44 PM

I know a bloke running an RX8 6 speed in his 79' Skyline. Box cost him $600 and to get the L series bell housing cut off and welded in place onto the Mazda box cost another $400. 5th gear is 1:1 with 6th overdrive.

#10 DevilZ

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Posted 01 October 2009 - 03:33 AM

I know a bloke running an RX8 6 speed in his 79' Skyline. Box cost him $600 and to get the L series bell housing cut off and welded in place onto the Mazda box cost another $400. 5th gear is 1:1 with 6th overdrive.


I'd be incredibly interested in having a 6 speed made up. Do you know who built your friends gearbox?

Does anyone know of any other 6 speed conversions out there or suggestions on whats the best 6 speed to have adapted?


#11 Thomo260

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Posted 01 October 2009 - 11:20 AM

Box was built by Jesse Robison's father. Jesse rallies a 260Z in the VRC/VCRS series ( ) and his father has a very trick little workshop setup. He just cut off both bell housings and rewelded L housing onto the RX8 box. I can try and get some contact numbers for you if you like.

#12 DatZed

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Posted 01 October 2009 - 03:39 PM

I will look at making custom bell housings for mx-5 gearboxes in the future. I have a source for them for $800, then just a bit of time with the mill and tig should do it. I am looking at doing the altezza or is200 gearboxes as well since they seem to be even cheaper. The length of the mx-5 box is an issue becuase the shifter would end up too far back. To the best of my knowledge all of the japanese six speeds getting around at the moment are variations on the aisin warner six speed with the exception of the supra, 3000gt and gtr. The S15 six speed is supposed to be weak, but that's easily fixed.
If you are serious about a six speed I can make a second bellhousing if you like.

#13 DevilZ

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Posted 02 October 2009 - 03:29 AM

Hi Thomo260. Numbers would be great if its not too much trouble. :)

DatZed. I'm not too clued up about MX-5 gearboxes. Do there ratio's come out right? I'm sitting on 300hp so i'm not sure if the gears will be too short? I'd really prefer to go down the lines of a tried and tested set-up. I don't want to run into too much trouble getting the box in and doing a lot of re-engineering of cross members etc....
Is the 6 speed from a GTR a easy/possible adaption? I hear the GTS-T 5 speeds are suppose to be a fairly simple conversion, so I'm wondering how the GTR box will go.  ???

#14 DatZed

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Posted 02 October 2009 - 03:41 AM

The thing to remember is that hp doesn't kill gearboxes torque does, as well as abuse...
The Rx-8, mx-5, altezza, is200 and s15 gearboxes are not really rated for large amounts of torque, so if you were running a turbo'd l28, perhaps they would become marginal if you were nasty to them.
The thing to remember about the gtr six speed is that it's got a transfer case strapped to the back of it, which could be an issue for your trans tunnel. The supra six speed is the same unit, getrag V160 but both gearboxes fetch well over $3k, plus making it fit.
The mx-5 unit should be the same as the rx-8 unit, I will have to check. How do you upload excel spreadsheets? I have a gear speed calculator that may be of some use to you for calculating gear ratio's.

#15 DevilZ

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Posted 02 October 2009 - 10:06 AM

The thing to remember is that hp doesn't kill gearboxes torque does, as well as abuse...
The Rx-8, mx-5, altezza, is200 and s15 gearboxes are not really rated for large amounts of torque, so if you were running a turbo'd l28, perhaps they would become marginal if you were nasty to them.
The thing to remember about the gtr six speed is that it's got a transfer case strapped to the back of it, which could be an issue for your trans tunnel. The supra six speed is the same unit, getrag V160 but both gearboxes fetch well over $3k, plus making it fit.
The mx-5 unit should be the same as the rx-8 unit, I will have to check. How do you upload excel spreadsheets? I have a gear speed calculator that may be of some use to you for calculating gear ratio's.


Ohhh yeah, I complete forgot GTR's are 4WD.
With the RX-8 and MX5 boxes i've heard some bad things about how fragile they are from a mazda specialist. I do put out a fair bit of torque being a stroker engine so i'm keen to find something strong. The Altezza box adaption could be a good option. Still I'd be keen to see someone run it first and if possible just pay for a complete conversion or be supplied with all the parts........I'm getting lazy now a days and dont feel like doing my own conversions






#16 dat2kman

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Posted 03 October 2009 - 04:35 AM

Look at a RB25 DET rear wheel drive skyline box, the bell would need to be cut off, and an L bell, or an adaptor plate used.
Some of the s13 s14 s15 sylvia guys are using the rb25 turbo box, with stock bell, but are using a 1 inch thick adaptor to mate the rb box to the sr motor, biggest problem I can see is they also need to use a machined boss to move the flywheel back off the crankshaft by the said 1 inch, in high rpm situation, get this wrong even by fractions of a thou misalignment and it's a didsater waiting to happen.
However, the current crop of sylvia drift guys dont really care, example, just look at the condition of their cars after they have been "hard at work" drifting.




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