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While reading Monstrbox's (David) The Monsterbox 4 Rotor build thread and seeing that he was going with straight cut gears It suddenly hit me that if we where to reduce the helix angle of our gears (manufacture new ones) we could make our transmissions stronger to hold more torque. I'm not too familiar with working on transmissions but maybe someone who has more knowledge on transmissions can help chime in. TLDR; reduced the helix angle of the gears in the transmission to reduce axial load thus making the transmission much stronger. This would also keep noise levels down and not cause a high pitched noise like straight cut gears that you see in race cars.
If I'm not mistaken, Liberty transmission already makes/ upgrades or factory transmissions to be stronger.
I think the member Blue TII, has an avatar of his blue FD with flames coming out the exhaust, has one of their transmissions. He is near 400HP if I'm not mistaken. Problem solved.
I'm sure he'll come in with more info or corrections to muy information. Sounds like a great option to me.
Option 2 that some are doing is the newer version of the T56, some of the 20B guys have done it already and someone makes the bell housing and flywheel to made it work. No idea on the solution used for the speed sensor or PPF.
You have to be making a LOT of power for the factory transmission to become a problem. Fortunately Mazda put a pretty hardy transmission in from the factory.
Anytime you talk about custom trans parts you start talking about a LOT of money. You also have to figure out if it's just cheaper to buy a few good used transmissions and swap if you break something - we're talking that level of money.
Some people have swapped to other transmissions, like the T56.
Regardless, it's a good idea, but someone would need to design the parts and find a shop to make them. There's a pretty decent amount of engineering involved as well.
I don't have the Liberty RX-7 transmission conversion, but there are several drag racers on this forum who do.
Liberty uses the stock gears and just cuts off the synchro equipment off them and replaces them with a quasi dog engagement ("Face Plating"). This just helps the transmission shift fast/easy at high rpm if you know how to use a manual transmission or really hard to shift if you don't know how to use a manual transmission.
These are the parts manufactured by Liberty Gears for the RX-7.
Albins makes helical synchro engaged internals for the RX-7 transmission (I assume for more favorable ratios) as well as straight cut dog engaged internals. I don't know if Albins revises the angle on their helical cut gears.
I suspect the RX-7 transmission case is just too weak/unsupported whether you have helical gears spreading the case and pushing the bearings front to back as well as spreading the shafts apart up and down or straight cut gears putting all the force into spreading the shafts apart up and down.
It is 3rd gear that strips on our transmissions first which is right in the middle of the shafts, so I think it is the shaft flexing that is the problem.
You could have a gear set made that did away with 3rd gear (and revised the ratios) and put in a shaft girdle to hold the two shafts together. 1-2-4-5 would be a pretty wacky shift pattern, but such strange things have been done.
AE86 guys make a 5th gear that is a ratio between 3rd and 4th for an 1-2-3-5-4 with ultra close ratios between 3-5-4.... Fun shift pattern.
Or you could just start with a stronger transmission out of a Viper, 370z, Supra or BMW.
You could have a gear set made that did away with 3rd gear (and revised the ratios) and put in a shaft girdle to hold the two shafts together. 1-2-4-5 would be a pretty wacky shift pattern, but such strange things have been done
I guess this is called a "cuff" as in handcuffs in transmission lingo.
Here is an Albins gear set with 5th gear replaced by a cuff. Imagine how much stronger it would be if 3rd were replaced with a cuff instead.
You have to be making a LOT of power for the factory transmission to become a problem. Fortunately Mazda put a pretty hardy transmission in from the factory.
Anytime you talk about custom trans parts you start talking about a LOT of money. You also have to figure out if it's just cheaper to buy a few good used transmissions and swap if you break something - we're talking that level of money.
Some people have swapped to other transmissions, like the T56.
Regardless, it's a good idea, but someone would need to design the parts and find a shop to make them. There's a pretty decent amount of engineering involved as well.
Dale
I know this has been asked a million times, but from your experience what would you say the torque limit is if the car is street driven with the occasional hard canyon runs.
Also my dilemma with with T56 and CD009 are the extensive modifications needed, I know this sounds ironic since what I suggested requires an extensive amount of modification. I just don't like how the T56 and CD009 require custom parts to mate the transmission to the block, and the fact for the T56 you need a auto rear end. I would also add in that the price for a T56 or CD009 swap might be equal to getting new gears made. I personally would rather rebuild my stock transmission with the gears I mentioned than do everything needed for the T56 and CD009.
I suspect the RX-7 transmission case is just too weak/unsupported whether you have helical gears spreading the case and pushing the bearings front to back as well as spreading the shafts apart up and down or straight cut gears putting all the force into spreading the shafts apart up and down.
It is 3rd gear that strips on our transmissions first which is right in the middle of the shafts, so I think it is the shaft flexing that is the problem.
Correct me if Im wrong, but wouldn't reducing the helix angle reduce the axial load thus reducing the load on the case itself.
Our cars are trying to dump the gears out the bottom of the case.
A 5th gear cuff or case plating will only marginally help the problem of spreading 3rd gear away from its counter gear and stripping it.
I know this has been asked a million times, but from your experience what would you say the torque limit is if the car is street driven with the occasional hard canyon runs.
One data point.
I was doing 420ftlbs on my super fast spooling EFR 7670 doing auto-x and kart track on Maxxis slicks and drag racing on MT ET Streets aired down to 12psi (still spinning all through 1st) and I was pretty merciless with that sprung 6 puck at times doing no lift shifts and such.
Probably wasn't going to last 180,000 miles like my 1st TII trans that I pushed 300ftlbs through for 40,0000 miles of abuse, but it was doing fine for the summer I was hammering on it.
One thing I can say is the box I'm building w/ the dog kit, is actually a liberty box with a sheared off 3rd. If you compare the shafts/gears, these gears are way thicker/wider and heavier and the shafts are thicker as well. I just wanna see what happens. There's so much theory that it would still blow the gears, but all I can see happening would be maybe the case would crack. I don't know what you call it, but the tooth interlock depth is so much greater than the stock gears, so seems like the shafts / case would need to flex much more for the gears to separate. We'll know soon enough haha
And like Dale was saying, it seems it does take a lot of power to break it. I put a lot of boost through the same transmission, over 25psi+ on 13b and 16psi regularly on R-compounds with 20b through the same transmission over years and never broke. Its so weird. But I never bang the clutch between shifts, never launch, and always roll the throttle. So kinda feel like shock is what does it. Or just wasn't making as much power as the guys that do break them. You know maybe something as simple as slave cylinder dampening, and transmission brace, maybe a more solid billet trans pan might make a stock trans hold up much higher levels.
Transmission gearset is epic. Do it. Been straight beating its *** in 3rd at 13+psi slamming the gears and no issues as of yet. I did have it pop out of gear between shifts from shifting so fast that 2nd gear slider rebounded itself back into second. Just needs some stronger detents installed
I will be getting my car back with OS-Giken gearset soon. Will give feedback. Intend to run mid 20s boost later on. With really hig power on slicks you can bust the gearcases but bolt in is a lot nicer. They are cheaper than Albins and have heard good things about them.
If I manage to break this I will sell the diff I've had built with cusco clutch centre and solid pinion spacer and buy one of the coupled gearbox diff from a corvette. Will require chopping out the tunnel, torque tube, new mounts, clutch etc so hopefully I don't split the gearcase.
10-01-17, 06:59 PM
Making a stronger stock gear box
