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Xnke

L-series 6-speed Transmission Conversions

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Not sure if I need to post this in For Sale or the Vendors forum, so here it is in the Vendors Forum.

 

I can convert the bellhousings on the S15 6-speed manual transmission, AKA Nissan FS6R92 or Aisin Automotive "Model AZ6", to fit the L-series or KA series engines, and use standard L/KA clutch assemblies. This transmission works out to be 31.5" long from the end of the tailshaft to the front face of the bellhousing after the bellhousing is converted, and the transmission mount is 23" from the front face of the bellhousing after the conversion. You will need a different, larger, slip yoke to fit this transmission. Stock transmission is 1" diameter, 24 spline, and the S15 transmission is a 1.088" diameter, 24 spline. (unless I just counted the splines wrong again, I may have to update this post.)

 

This transmission gets a bad rap as being a weak box...which simply isn't the case. At sustained torque levels of 350+ft-lbs, OR heavy shock loading due to a grabby solid hub clutch and sticky tires, this transmission in unmodified condition can snap the circlip that retains the 4th countershaft gear, allowing it to crash into the reverse gear assembly. This generally tears the box up pretty bad. This can be limited by having the circlip modification performed by a qualified transmission shop, which I am not and I am still looking for a reputable shop with some experience with these transmissions to recommend.

 

That said, for any engine that puts down LESS than 300ft-lbs, you're within the safe zone and this box is a viable option for you. They are readily available from importers and due to the "weaksauce gearbox" rap they are going for a little less money than most other options for a 6-speed behind an L-series engine. The gear ratios are listed below:

 

3.6

2.2

1.5

1.3

1.0

0.76

 

This is a nice close ratio box, and is suitable for road racing as a 5-speed by ignoring 1st gear and using it as a dogleg-first gearbox. This means you leave the starting line in 2nd gear, and shift up into 3rd, using 3-4-5-6 in the standard 4-speed pattern to obtain a close approximation of the Nissan Competition close ratio gearbox. If you desire a closer ratio, then there are a 0.892, 0.869, and a 0.862 6th gearsets available. The 0.862 gearset is available via NISMO.

 

To do this conversion, I need the front case from your S15 SR20 6-speed transmission, the front case from your L-series or KA24 transmission, and 375$. I will return to you a modified S15 6-speed front case, ready to be bolted back up to the transmission and fitted behind the engine. This transmission is not terribly easy to remove just the front case from, but it can be done safely as long as you're cautious. I don't mind providing telephone support for the dissassembly process if needed.

 

If you require a mechanical speedometer drive, make sure your S15 transmission is machined for one. NOT ALL OF THEM ARE. The ones that are suitable will have a removable aluminum plug bolted into the usual location for the speedometer drive and the tailshaft will be machined for two circlips and a ball bearing. The tailshaft can be examined through the speedometer drive hole and you can see if the machine work was done or not. I do not have the facilities to re-harden the shaft after machining, so I can not currently convert the non-speedometer drive versions. This transmission does NOT have a drive cog inside on the tailshaft...so it's not just a bolt-it-in-and-go solution. I can machine your 5-speed speedo drive cog to fit, if you send it with your bellhousing. The cost for this is 45$, which includes machining your speedo cog, the ball bearing, and the two circlips to re-install it onto the tailshaft of the transmission. NISMO charges A LOT more for these parts, but the speedo drive cog, ball bearing, and circlips are available from them as well. I am not sure what the current price is.

 

If you are not comfortable dissasembling the transmission, then ship the entire transmission plus your bellhousing and speedometer cog, and I can do the bellhousing conversion for 430$, and the speedometer drive for 45$. It is totally understandable if you don't want to try to break one of these boxes down, as they are VERY tricky to reassemble properly. Very easy to lock them up when it comes time to put the bellhousing on...and then it all has to come apart to get it unlocked.

 

I can be reached by telephone or by PM here on HybridZ, PM me for the phone number please, I won't be posting it on the internet.

 

Here are a few shots of the process; for those who are curious. Pardon the clutter, my shop is now a 12x16 machine shop due to leasing issues. It's a wreck right now from all the parts and concurrent projects running trying to get my Z ready to go to Branson Z fest.

 

Here's a few shots of the process.

 

Cutting the SR20 flange off the front case:

 

IMAG0538_zps9e325f68.jpg

 

Getting the L24 flange bolted to the block, getting ready to align the welding jig:

 

IMAG0535_zps75512804.jpg

 

No photos of the welding jig; I spent a lot of time to work out this conversion and I'd rather not just hand it out in a single photo.

 

Starting to weld the two bellhousing sections together along the outside:

 

IMAG0539_zpsd74e60c8.jpg

 

Finished bellhousing, ready to be scrubbed down and reassembled onto the transmission: (Yes Alex, that's your bellhousing!

 

IMAG0540_zpsa8c697c4.jpg

 

Any questions, just ask. Everyone knows that 4 speeds is good, but 5 speeds is better...so 6 speeds must be best!

Edited by Xnke

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Just for reference on the gear ratios in this box, I will direct you to the Nissan Competition Option boxes as to what the traditional options are...as I said, it's a close ratio box. For example, here's the Nissan Option transmission list:

 

This is the S15 6-speed: 1st: 3.626, 2nd: 2.200, 3rd: 1.541, 4th: 1.213, 5th: 1.000, 6th 0.767

 

This is the S15 5-speed: 3.321, 2nd: 1.902, 3rd: 1.308, 4th: 1.000, 5th: 0.838

 

This is the S14 5-speed: 1st: 3.321, 2nd: 1.902, 3rd: 1.308, 4th: 1.000, 5th: 0.754

 

These are the FS5C71-B "Option" transmissions:

 

32010-N3130 Gearbox ratios: 1st: 2.906, 2nd: 1.902, 3rd: 1.308, 4th: 1.000, 5th: 0.864

 

32010-N3030 Gearbox ratios: 1st: 3.321, 2nd: 2.077, 3rd: 1.308, 4th: 1.000, 5th: 0.864

 

And the F5C71-B "Option" boxes:

 

32010-N3220 Gearbox ratios: 1st: 2.818, 2nd: 1.973, 3rd: 1.470, 4th: 1.292, 5th: 1.000

 

32010-N3221 Gearbox ratios: 1st: 2.348, 2nd: 1.601, 3rd: 1.296, 4th: 1.138, 5th: 1.000

 

32010-N3222 Gearbox ratios: 1st: 2.192, 2nd: 1.601, 3rd: 1.470, 4th: 1.138, 5th: 1.000

 

32010-N3201 Gearbox ratios: 1st: 3.321, 2nd: 2.270, 3rd: 1.601, 4th: 1.240, 5th: 1.000

 

OS Giken sells the following close ratio gearset for the FS5W71C transmission:

 

1st: 2.596, 2nd: 1.765, 3rd: 1.250, 4th: 1.000, 5th: 0.833

 

These gearbox ratios are all setup for competition use...thus I likened the gear ratios to the Nissan COMPETITION boxes. They're generally run with 3.90 or lower ratios in the rear, and the guys running 4.11 or 4.375 gears can use these VERY effectively for high-RPM, and thus high-horsepower usage. I'm not the one installing your rear end gears, so I don't get a say in that matter. In my opinion, the 6 speed would be GREAT with a 2.73 rear end...but I'm also running a supercharged engine with plenty of low-end grunt. The guy with the moderately cammed L16 in a 710 wagon might enjoy a 3.545 or 3.70 rear gear with these ratios, since it is low enough to keep the engine on the cam, but has a tall enough OD to return decent highway mileage.

 

For those out there who are using their cars for road race or other usage where a tight ratio box is desired, or if you have a big cam with a narrower power band, then this box is a much cheaper alternative to the Nissan Option boxes. The POINT of a close-ratio box is to keep the RPM's in a narrow power band, or in the OEM's case, the car is geared such that the close ratio box keeps the car in a nice, tightly-controlled RPM range that they can minimize fuel consumption and emissions without sacrificing much in ultimate power...instead of having to work a much wider range for the optimization and giving up power over a wider band.

 

For reference...the last time I saw a Nissan Option gearbox change hands the price paid for a used good transmission was 1400$. The new, never installed gearbox was 3200$. I'm sure the price varies wildly depending on condition and demand.

 

*EDIT* Edited listings above to reflect proper transmission codes, thanks Alan!

Edited by Xnke

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Just for reference on the gear ratios in this box, I will direct you to the Nissan Competition Option boxes as to what the traditional options are...as I said, it's a close ratio box. For example, here's the Nissan Option transmission list:

 

 

These are all for the FS5W71B "Option" transmissions:

 

32010-N3130 Gearbox ratios: 1st: 2.906, 2nd: 1.902, 3rd: 1.308, 4th: 1.000, 5th: 0.864

 

32010-N3030 Gearbox ratios: 1st: 3.321, 2nd: 2.077, 3rd: 1.308, 4th: 1.000, 5th: 0.864

 

32010-N3220 Gearbox ratios: 1st: 2.818, 2nd: 1.973, 3rd: 1.470, 4th: 1.292, 5th: 1.000

 

32010-N3221 Gearbox ratios: 1st: 2.348, 2nd: 1.601, 3rd: 1.296, 4th: 1.138, 5th: 1.000

 

32010-N3222 Gearbox ratios: 1st: 2.192, 2nd: 1.601, 3rd: 1.470, 4th: 1.138, 5th: 1.000

 

32010-N3201 Gearbox ratios: 1st: 3.321, 2nd: 2.270, 3rd: 1.601, 4th: 1.240, 5th: 1.000

 

Purely for accuracy's sake:

 

All those 1:1 5th gear 'Direct Drive' ( ie, not 'Overdrive' ) 'boxes are actually F5C71-B type code, and the N3130 and N3030 are FS5C71-B type code ( not FS5W71-B ). 

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What is a good source for the S15 boxes? I did some Google searches and didn't see many options.

 

Any of the JDM importers can get them for you, a lot of the S15 engines coming over have them attached and the buyer isn't wanting to deal with the headache of getting them installed. I am not 100% on which of the US-market versions of the Aisin AZ6 transmission that this swap is possible on, but this same gearbox comes installed in the Mazda MX-5 Miata from 1999-2007, the RX-8, and the Scion FR-S/Subaru BR-Z. I have not done any conversions on those bellhousings; however the internal components are the same, only the gear ratios change slightly. All have a closer overdrive than the S15 box; coming in between 0.833 and 0.896.

 

 

Purely for accuracy's sake:

 

All those 1:1 5th gear 'Direct Drive' ( ie, not 'Overdrive' ) 'boxes are actually F5C71-B type code, and the N3130 and N3030 are FS5C71-B type code ( not FS5W71-B ). 

 

 

Thanks Alan, I was curious about the difference in type as I believe those boxes have Porsche-type steel synchros, as opposed to the warner type brass ones installed in the FS5W71-B.  Am I off the mark here?

 

I will update my post to reflect the correct nomenclature.

Edited by Xnke

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