gearbox strength
 

how strong are the fd3s gearboxes? how much wheel power can they put down?

the gearbox can hold in excess of 500WHP but they are quite fragile when it comes to hard launches at that horsepower level.

I sheared all the teeth off 3rd gear after repeated 500+rwhp/20+psi pulls..... was decimating every car I raced, but had to limp the car home from NC to NJ. Not fun. This was my original trans that had been rebuilt twice.

Been running a JDM box since and it seems to be holding up fine. I'm not running as much boost on it, and not doing it nearly as repetitively either. I have an OS Giken forged unit about to be installed :D

Its a very strong gearbox, depending on how much power is in front of it and how much rubber and gear are behind it.

In comparison I'm guessing the auto gearbox is about 2/3 the strength of the manual? 330rwhp max?

The auto gearbox is good for holding a door open or anchoring a small personal watercraft.

Dale

:lol:

Not a whole lot of testing has been done to improve its limits. I wonder how much a good tranny cooler and good ATF would help, as heat is typically the main killer on A/T's.

That's kind of what mine is doing now!

Hahaha. I've read a bunch of times that the stock tranny can hold around 420rwhp. After that you will have problems.

I also just shredded the 3rd gear in my original Tranny with high miles and close to 500 hp, hopefully my series 7 jdm low miles Tranny doesn't break.

used to build autos many years ago, there is alot more factors than just heat and oil. these autos simply aren't designed for the type of abused a modded FD can provide.

i'm sure they can be beefed up with billet clutch cages and larger roller bearings in conjunction with some valve body mods to tighten up shifting but it's still a mushy power slurping dog of a tranny in the end. we're talking thousands of $ to still retain that 20-25% drivetrain loss.

hmm ok thanks for the feed back....
reason im asking is, i am looking for a reliable and tough gearbox to adapt to a mazda 2.0 4cyl to convert it to rwd. looking to put down 400whp in a approx 650kg chassis and in the future over 500whp. the car is being built for time attack/circuit racing. which brings another question, how much stress can it endure during constant upshifts and downshifts....? and what are common problems with them?
anyone has pictures? or comparisons to other boxes?
http://img692.imageshack.us/img692/2293/img6375k.jpg

out of curiosity - what kind of car is this that will only weigh 650kg?

I feel like I'm in crazy town when I visit RX7club.com because something like this happens every week on this forum.

lol im sorry. its a mazda at least, im trying to get info on the rx7 box to hook it up to a mazda engine....i know its not rotary but at least its still kinda in the family ? lol

96fd3s - hmmm im just avg arnd 300lbs or so taken from gutting it and exchanging for the lighter stuff going in it'll probably go over that with the cage....its a mazda bd 323.... 840kg kerb weight....im hoping to come out arnd the kerb weight when done...basically all im keeping that's heavy steel is the shell and cage, trying to reduce weight everywhere else...the flooring is being redone into a frame and aluminium sheeting, doors being done in fibreglass,etc.....

hope y'all dont mind me posting this on here.....let me know if its a problem, im just looking for a lil help with the box...

3rd gear is the weak link at even 350 rwhp. I've lost 3 running no more than that power and have lots of friends running equal power or a little more who've also lost 3rd gear more than once. The JDM trans is marginally better with a few tiny upgrades but none of the those upgrades will prevent the gears from separating which is what causes a trans to pop under load.

Not a good trans for road racing but they are cheap and plentiful and if you keep the power at or below 350 they'll last a decent amount of time.

I think it's just one of the those scenarios when everything is right (heat, worn gears, dirty old oil, possibly synthetic oil that's not allowing proper spacing etc...) for the gears to separate and boom you have bits and pieces all over the place and your day is done. I also believe that heat as always could be a part of the problem so frequent gear oil changes and possibly a trans cooler (I may add one this winter) is a smart move for anyone road racing the FD.

I elect you as mayor of this town!

thanks fritz, i appreciate the input.....350whp is edging it for my build, i dont want to have to worry too much at that hp level. if im looking at 400+ then im going to be worrying about if it breaks and when,etc. finding a tough rwd box is difficult.....350z is real tough but expensive and not as easy to find, the toyota alteza beams is also tough but expensive......

hmmmmm......crap !! not looking good so far.....

Hmm, garbage bag full of clothes as jack stand, crazy town indeed.

lol, maybe you missed the jackstand behind the bag. :P

lol......bag of rags

IMHO, when 3rd gear breaks in this transmission it's due to tooth breakage. Whether this is caused by gear separation or tooth design doesn't matter much. Even at 500hp, it's only when shock load is present that these let go. Time attack and road course driving are about smoothness and speed.

I believe this is a pretty good transmission, especially considering how weight-aggressive the FD's design is. They are not expensive and pretty light. They shift smoothly when driven hard (if anything the shifting is clunky when you're on the street easing through the gears). So if the ratios are what you want and you are really out to trim weight this is not a bad option.

But all said you have the choice of many transmissions. For a little more weight you can get a 5- or 6- speed from a heavier, higher torque car. There will be many more spares, cheaper drop-in gearset options, etc.

In my experience the 3rd gear doesn't let go because of a hard hit or improper up or down shift. It's the top side at around 6,500 to 7,500 RPMs and BOOM. My last trans was super quiet and a joy to shift so I think the gears and bearings were tip top it just couldn't handle the heat combined with torque/power and possibly the HW synth oil gets whipped up into a lather causing more issues with gears separating which is the only thing that makes sense to me. My car wasn't making more than 350 when it let go not nearly enough power to break a gear tooth off under acceleration. Also if that happened I think I could still drive the car. My last trans had a bad 5th and when I was done with it half the teeth were missing talk about a trans that was noisy and hard to deal with lol. It hated to go into 3rd and 4th and loved 2nd which on occasion I'd find at the most inopportune times :)

:rofl: