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BenseBuilt modified J-series Transmission

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14 April 2017
South Carolina
After talking with some of you about details of the J-series frankenstien transmission setups I can build, many of you are surprised and shocked that this is even possible, so I figured I'd make my own post about this, rather than scattering replies here and there on various threads containing my transmission work.

I've been modifying Honda trans since 2005. I got crazy into it and ran all these awesome Frankenstein gearing setups. I did lots of work with D-series trans (parts were cheap, easy to experiment with), but I've also done work with B-series, F-series, H-series, and K-series trans. In 2007 I reached a point where I realized that in order to do the things I wanted to do with Honda trans, that I'd need to go to school and pursue a bachelor's degree in mechanical engineering. And that's what I did. (Didn't graduate, had to step away halfway through my senior year due to financial/health complications -- none the less, I'm typing this right now while wearing my university class ring... for whatever that's worth).

Fast forward to 2016 -- After taking a transmission hiatus while in school, I began working nightshift job in a datacenter. Restricted internet, and being bored out of my mind lead to me beginning the work/research of hoarding tons of information pertaining to all Honda transmissions. I reverse engineered tons of Honda transmissions from pirated OEM literature such as factory service manuals, and pirated overseas Honda OEM parts catalog software. After doing so I compiled everything into organized tables in a spreadsheet that I setup. I programmed gearing calculations such as tables that told me which mph the gears would end, the RPM drop percentage, mph drop percentage and other various parameters that I use to give me insight into what the gearing setup is like. Every gear ratio is calculated from the exact gear teeth counts that I have personally confirmed, and then is calculated with globally defined tire size, redline, and cruise speed.

Anyway, sorry to get sidetracked rambling about all that (I got excited lol) -- in 2017 I picked up a J32A2 CL Type S J-series 6-speed transmission from a junkyard and started tackling J-series. The first thing I noticed was that the gearing was atrocious. I referred to my spreadsheet and I purchased 6 additional transmissions, as well as over $3000 in OEM parts from Honda Europe + Honda Japan. I reversed engineered an overseas transmission so specifically, that I programmed formulas into excel that would calculate possible whole number quotients given the gear ratio in decimal form. This allowed me to calculate what the gear teeth count was for each specific gear. After I received the transmission from UK, I opened it up, counted the teeth, and checked the very few measurements that I was not able to determine using OEM factory service manual + parts catalog. I wound up being 100% correct in ALL of my gear tooth count estimations. All of the other measurements and fitments were 100% exactly what I thought they would be. I confirmed EVERYTHING.


Gears taken from whole transmissions I purchased.

Over $3000 worth of brand new OEM gears purchased from USA Honda, USA Acura, UK Honda, Honda Japan.

Testing and confirming everything... but mostly ballin out with all these awesome gears and my Clemson Tigers National Champions hat lol

To start, the J-series FWD transmission needed a better final drive. So I figured that out. I found some additional OEM final drives that can be used in the trans that nobody else seemed to know about. I also found out that some other j-series tuners were spending tons of money to get custom 4.11 final drives made. I told them that they were wasting their time, and that I already had one. They didn't believe me and I got banned from the facebook group lol!

Final drive ring gears. From top to bottom; 3.286, 3.550, 3.90, 4.11

One of my many, stupid responses to the J-series facebook group haters that banned me for saying I was lying. Me pretending to wave around my OEM 4.111 final drive countershaft as if it were a light saber like Obi-Wan lol

After I figured out the final drives, I then began to figure out a way to optimize the 1-6 gearing so that it was closer-ratio. Upon researching this and testing out options, I also came to realize that Honda 'upgraded' the J-series trans by giving it a larger diameter mainshaft. We first saw this in the US in the 2011-2014 Acura TL SH-AWD 6MT trans. Additionally, Honda also used this design in the 2017+ FK8 Civic Type R K20C transmission, as well as the 2018+ Accord Sport 2.0T 6MT transmission. The FWD J-series mainshaft is 42mm in diameter for the 3rd gear needle bearing race. The larger diameter, 'big-shaft' AWD J-series and the K20C trans is 48mm in diameter for the 3rd gear needle bearing race. Furthermore, the 'big-shaft' AWD/K20C trans has larger synchros, synchro hubs/sleeves for 3/4/5/6 gears.

OEM Mainshafts. From left to right; F22 (basically same size/diameter as B-series), K20, J-series small-shaft, J-series big shaft.

However, even after finding an OEM final drive upgrade, and stronger OEM mainshaft with larger, stronger, more durable 3/4/5/6 synchros -- I still was not content. So I also figured out a way to make the 1-6 gearing closer ratio than even what is found in the FK8 type R trans. Using OEM Honda/Acura gears taken from six different OEM transmissions, I was able to devise a close-ratio OEM Frankenstein gearing combination that would work with the 'big-shaft' J-series setup. I have personally tested and confirmed fitment of all of these parts.

Final Presentation!

Everything unassembled

Gear Ratios
There are two different mainshafts that can be used. Mainshaft #1 has a shorter first gear, which is less ideal, however it has a taller 2nd gear which makes the 2nd -> 3rd shift closer (less RPM drop). This would be more ideal for road racing where rolling starts / 1st gear isn't utilized. Mainshaft #2 has a slightly taller 1st gear but shorter 2nd gear. This provides a closer 1st -> 2nd shift, however it widens the gap between 2nd and 3rd. This would be more suitable for those that care a lot about the 1st -> 2nd shift. After testing out and running several gearing setups in my various Hondas, my preference is to use the mainshaft with the taller 2nd gear.

There are also a few options for 6th gear. (0.848, 0.734, 0.686). I prefer the shorter, 0.848 sixth gear, as I prefer my 5th -> 6th shift to be very close (most aftermarket close-ratio performance gears are setup this way). However some may want the 0.734, and some may want 6th to be a long overdrive gear.

BenseBuilt preferred 1-6 configuration (Mainshaft #1 , short 6th gear)
1st = 3.933
2nd = 2.037
3rd = 1.529
4th = 1.190
5th = 0.976
6th = 0.848

Mainshaft #2
1st - 3.625
2nd - 2.115

Available final drives

How does it compare to the NSX 6speed?
This configuration most closely mimics the gearing of stock OEM NSX 6speed trans; 3.842 final drive, mainshaft #2 . This configuration with 245/40/17 tires and 8000rpm redline, results in 1-6 gears ending at the following mph
[43, 73, 100, 129, 157, 180]
alternative 0.734 sixth gear ends at 208.

NSX 6speed trans with stock 4.062 final drive, with 245/40/17 tires and 8000rpm redline.
[47, 74, 101, 129, 158, 202]

BenseBuilt J trans, 3.842 final drive, mainshaft #2 , 0.734 sixth (green) vs NSX 6speed with OEM 4.062 final (blue)

How does it compare to the NSX 6speed with OS Giken 4.40 final?
Just use 4.11 final.
BenseBuilt gearing, mainshaft #2 , 4.11 final drive -- 245/40/17 tires, 8000rpm redline. Gears end at following mph.
[40, 68, 94, 120, 146, 169]
alternative 0.734 sixth gear ends at 195.

NSX 6speed trans with OS Giken 4.40 final drive. 245/40/17 tires, 8000rpm redline.
[43, 68, 94, 119, 146, 186]

BenseBuilt J trans, 4.11 final drive, mainshaft #2 , 0.734 sixth (green) vs NSX 6speed with OS Giken 4.40 final (blue)

One last plot...
BenseBuilt J trans, 4.11 final drive, mainshaft #1 , 0.848 sixth (green) vs NSX 6speed with OS Giken 4.40 final (blue)

LSD options:

OEM Acura CL-S, 2004-2008 Acura TL.
MFactory Helical
Cusco Clutch/Plate
HPD (Honda Performance Division) Clutch/Plate -- (I speculate that HPD is just selling the Cusco LSD)

The cost of these transmission setups is dependent upon which LSD is desired. MFactory helical is about $900, and the Cusco / HPD plate is over $1500.

I can build one of these transmissions for about $4000 using OEM LSD. This is with all new synchros + ISB + core trans, new seals, new input shaft bearing, new 3-4 synchro hub/sleeve, new 5-6 synchro hub/sleeve, new 5-6 fork. Even the most expensive configuration, with all new bearings, seals, synchros, synchro hubs/sleeves, forks (if necessary), Cusco / Honda HPD clutch LSD, and with J-series/K20C dual-mass lightweight flywheel / 'performance' clutch disc / 'performance' pressure plate kit -- and it still costs less than what NSX 6speed trans are selling for.


Some of the other discussion / posts that I've made can be found in this thread: (It's page 15 for me using the forum default for 'Number of Posts to Show Per Page')

Please note, I do not have an NSX. Nor do I know anyone that's local to me that has one. I've only seen them in person a few times.

I have a 2001 Accord Sedan EX 4cyl 5MT, with a JDM H23A, with hybrid-geared F23/H23A1 trans. I came across a 2003 CL Type S 6MT in a junkyard last year, and picked up the entire swap. The transmission setup that I have developed uses the same mounts, shifter mechanism, axles, flywheel, clutch, pressure plate, shift cables, etc that are used on stock Honda/Acura with J-series V6 6MT.

The reason that I am on this forum is because I was researching details pertaining to the NSX transmissions during the time when I was looking at specific NSX transmission parts / gears to see if any of them could be used in the J-series transmission. During the time that I was buying all those OEM gears from Honda to test fit for my close ratio gearing options, some of the gears were from the NSX transmission. -- To be specific, I was looking at the 5speed JDM type R 4th gear of 1.033 to see if I could use it as a 5th gear in J-series (more about this in a minute).

I am posting this because I have seen various threads on here where others have found ways to use J-series engines/trans in their NSX. If you are wondering what all is required to get my J-series transmission working in your NSX, unfortunately, I'm not able to be of much help. My suggestion is to see what others have done to get the J-series trans working. -- What I can tell you is that earlier J-series transmissions have the same bell housing bolt pattern as C-series engines. I do not think that the splines on the J-series input shaft will allow you to run the C-series twin-clutch setup. You will most likely want to run J-series flywheel/clutch/pressure plate. Beyond that, you will need to figure out a way to get the shifter mechanism to work. (If only I had access to an NSX....)

Some will be disappointed that you're not able to run the c-series twin disc. Please note that the J-series pressure plate is 'dual-diaphragm'. It's a different clutch spring design. Honda engineers deemed this dual-diaphragm design to be adequate for the J-series V6, as well as the turbo K20C. And since these engines produce more torque than C-series it's a non-issue. Makes me curious if the clutch slave cylinder has a different bore diameter than c-series. Perhaps one of you can look at your c-series slave cylinder. The bore diameter is usually cast or stamped on the slave cylinder housing.

After I received the JDM NSX Type R 4th gearset that I ordered, I test fitted it on J-series shafts. I confirmed that they will not work in J-series. The NSX trans has a smaller C.D. than the J-series trans.
C.D. is 'center distance' -- it is the distance between the centre axis of the mainshaft and the centre axis of the countershaft. It is a measurement that automotive engineers use that represents the strength of the trans and the loads that it is capable of. The greater the distance, the larger the gears can be, the larger the teeth can be. Thus, the greater amount of mechanical shear and normal stress can withstand before failure.

Here's a link to FF transaxles that Aisin-AI offers. Take notice that the only design measurement that they provide is the C.D.

So, not only is my modified J-series transmission cheaper, more available, easier to get parts for, has more gearing options -- it is also a stronger design than the NSX 6speed trans.
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Glad to see you took the time to put all this into a thread.
Hopefully one of the J swapped guys will try it out, or even a C owner who can get the clutch/flywheel, transmission mount, shifter cables and drive shafts to work.
This could very well allow 5 speed owners to upgrade to 6 speed fully customized to their driving style with a very reasonable cost.
+1. Great to see your passion for these transmissions. If I had a Manual Transmission in need of repair or replacement I would seriously considering benefitting from your skills. Being a guinea pig that could potentially extend the lifespan of our cars (due to current and future parts shortage) would be honorable.

Sent from my Pixel using Tapatalk
Your solution is a potential game changer for those of us in the market for a rare and extremely expensive NSX 6-speed transmission. I wish someone like SOS would step in to fab the mount, shift cable and clutch mods that would be required to do this.
well Chris is a gamer...maybe he and the op could come to some kind of business arrangement.
well Chris is a gamer...maybe he and the op could come to some kind of business arrangement.

The Science of Speed 6-speed J kit...if they can get RPS to build them a NSX "sport" clutch, surely they could spec out a J clutch setup?
I just gotta say one thing....

Clemson 44
Alabama 16

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Who's going to do this?

A particular scene from the 1989 Chevy Chase film, Fletch Lives comes to mind. Reverend Jimmy Lee Farnsworth (as portrayed by R. Lee Ermey, 'Gunnery Sergeant Hartman' from Full Metal Jacket) makes a call to the church congregation, asking "Who's gonna be the next one to get the call? Who's going to be the next one that gets SAVED?!"

It comically amuses me while I'm trying to think of the best way to ask which one of you is going to be the first to work with me on getting one of these setup in an NSX.

For those interested, the particular quote begins at the 0:46 mark in this video:

The more people that reach out to me, asking me about this, the more excited, and more anxious I get to get one of these setup in an NSX.
Any advice on what could be keeping me locked out of reverse? Ive tried everything to coax it into reverse, but nothing. Does not even try to engage the synchro. Every other gear works great. Used it last night and it worked great. no reverse this morning.
Hey [MENTION=33689]Bense[/MENTION], I bought a fifth gearset from you back in 2009! I think we met at a Honda-tech meet in Charlotte. Anyways, glad to see you're still at the transmission thing - I never finished my hybrid d-series build unfortunately.
[MENTION=18814]crxguy52[/MENTION] I think I remember you. If you're who I think you are. I remember talking with someone online a few months prior to a Honda-Tech meet, who then, overheard me talking with my friend about transmissions at that meet and then came and asked me who I was and introduced themselves.

Coincidentally, in fall 2015, shortly after I moved to Charlotte, I remembered that meet (2005 or so?) and tried to figure out where in Charlotte it was.
Then about a year or two later, (spring 2017) I was walking through a park that I had been to a handful of times. I was looking at my phone while walking, then when I looked up, it dawned upon me that I was standing in the exact parking lot we had the meet in, Freedom park.

The reason it hadn't been apparent to me before was because all the trees, etc had grown so much since my recollection. It was somewhat of a 'coming of age' moment.

Which fifth gear did I sell you?
[MENTION=33689]Bense[/MENTION] that sounds right, small world! Time flies doesn't it?

I was planning a d-series ZC\Si\HF hybrid transmission, you sold me a HF fifth gear set. I never got around to finishing the project, though. I've got an NSX now, if you're ever in the Raleigh area I'd be happy to show you around the car.
Wow look at all those parts. Those were bought with...my money.

I believe its been THREE years now Bense, I fronted you 1000$ as a friend because you needed rent money and I was going to buy the H23 you blew up, now stop stalling, I see youve made money, and its been nearly 6 months since we started the 50$ a month YOU agreed to and have refused to pay, blocked my phone number, and ignore any emails or paypal money requests. Want to tell everyone on here why you refuse to pay me back?? Or at least give me some of those gears I can sell myself?
Wow look at all those parts. Those were bought with...my money.

I believe its been THREE years now Bense, I fronted you 1000$ as a friend because you needed rent money and I was going to buy the H23 you blew up, now stop stalling, I see youve made money, and its been nearly 6 months since we started the 50$ a month YOU agreed to and have refused to pay, blocked my phone number, and ignore any emails or paypal money requests. Want to tell everyone on here why you refuse to pay me back?? Or at least give me some of those gears I can sell myself?

Loan or gift?
Definitely a loan, or rather, that was for a purchase for an engine. That was not a 1000$ present, its something he needs to pay back, its been 3 years, thats not cool Bense.

PS. Nice post, is that Bill Hader?
Minor post edit / revised.
Bringing this thread back up. [MENTION=33689]Bense[/MENTION] is it possible for you to sell a "kit" of a fully assembled mainshaft, countershaft and final drive/LSD? I'm looking at the economics of this and it might be possible to market this to either 5-speed owners who want to upgrade to a 6-speed or automatic owners who want to do the same in a way that makes financial sense versus just buying a real NSX 6-speed. Maybe [MENTION=6927]nsxmugen[/MENTION] can chime in as to the costs below, but it looks like:

Junkyard Trans + Harness (from CL Type S or 03-07 Accord 6-speed): $500
Custom Driveshafts (Driveshaft Shop): $1,300
Left and Rear Mounts (nsxmugen): $250
Custom Shift Cables and Brackets (nsxmugen): $250
Custom Clutch (Spec Clutch maybe?): $1,500
TOTAL = $3,800

So, for about $3,800, you can get a working 6-speed in your NSX. Considering that you can get a used real NSX 6-speed for about $5,000, that leaves $1,200 in room for what you are offering. Do you think you can offer the gearsets for less than $1,200? Ideally, it could be a drop-in kit. The customer puts your gear stacks into his own junkyard transmission end ends up with effectively the same transmission as a real NSX 6-speed. If you can get the total walkaway cost of the conversion lower than $5,000, I think you would have a long line of customers willing to pull the trigger.
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