[d1hardcore69]

I'm the newbie on the block, so go easy... I am building my 1992 Toyota MR2 (I'm also on MR2OC.com and TwoBrutal.co.uk), I have torn apart the transmission because I am either going to replace it with a better version or stronger more reliable gears in this one. The transmission is Toyota's S53, minor variations but same as S51-S54. I'm looking at keeping the transmission as a five speed gear box but since I have this one taken apart, I though about going back to class to CNC some new gears. As it's know, the gears are cast iron, I'm looking for something at least as strong but lighter. My understanding is, typical power lose from flywheel to the wheels is 15%, I'd like to try to minimize this or be able to put more power through without stripping teeth. I was thinking dog gears. The gear ratio's are as follows...

A 5-Speed Manual Transmission.

Ratios:are not fin

First Gear: 3.285
Second Gear: 2.041
Third Gear: 1.322
Fourth Gear: 1.028
Fifth Gear: 0.820
Reverse Gear: 3.153
Final Drive: 3.944:1

Applications:

Toyota Camry
Toyota Celica

What I'd ideally want...

First Gear: 2.041
Second Gear: 1.322
Third Gear: 0.918
Fourth Gear: 0.731
Fifth Gear: ???
Reverse Gear: 3.153
Final Drive: 3.944:1

I'm only going into my second semester of CNC, 3rd out of machining, I have not clue as too where to start.

[d1hardcore69]

[packrat]

Don't think CNC'ed gears will work too well. Good gears are hobbed in a gear hobber. They have an involute profile that can't be cut any other way. Cut or milled gears are fine at slow low load but a car transmission is not that type of load. Milled gears will also create a lot of noise and heat.

[mactec54]

d1hardcore69
As it's know, the gears are cast iron

There is no way the gears are cast iron, They are a special alloy steel (something like 4130) machined case hardened, Lapped & some parts are ground, cast iron I hope you were just joking

[RICHARD ZASTROW]

Really good gears are pre-ground hobbed from 9xxx series steel. The gear teeth should be corner rounded/chamferred to the same specs as the originals or they may not engage/mesh properly. Then case hardened to keep the core of the gears tough, not brittle then finish ground.

Cast iron gears would self destruct shortly if under any sort of stress.

My advice would be to look into the performance after market.

Dick Z

[mactec54]

RICHARD ZASTROW
9xxx series steel

The 9xxx series steel is not a good choice for gears, it has to much silicon

It is almost never used for gears almost any steel up to the 8xxx series is steels that is used for gears, just depends on were they are being used

The link below shows some high performance gears made from EN36c one of the most common used for case hardened gears, you will see the change over the years in the different steels used for gears by this company as to what they use today for there high performance gears, EN36c is still the normal for regular gears

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[dmalicky]

Nice car. Even for an experienced engineer and journeyman machinist, it would be very challenging to save weight, lower friction _and_ increase strength/reliability from a gearbox that Toyota designed and built. Is this box known to be unreliable? If so, I'd find the tricks MR2 owners have already figured out to upgrade it... I imagine the turbo's box would be the easiest solution.

For your ideal gear ratios, why do you want them so steep? Those would be ratios for better mpg, not better acceleration.

For more power at the wheels, look to intake, exhaust, camshaft, valves, ports, and compression ratio. Or add a turbo/intercooler. There are many good opportunities there and I imagine lots of forum posts.

[RICHARD ZASTROW]

mactec54 We just finished building a CNC gear hobber for a shop that builds racing transmissions. All the gears and spline shafts are made of 9310.

Another one is producing gears for helicopter transmissions, also spec is 9310.

One equivalent chart lists 9310/En36. 9310 is a NiCrMo steel.

We often use 8620 for case harden apps. Costs less than 9310.

Dick Z

[mactec54]

RICHARD ZASTROW

The 9310 is not the normal 9xxx series steel it was a modifided 9 series steel to compete with the EN36c it is a little better than the EN36c for gears because you can get a slightly higher core strengh, I have used both, There are better materials than this for making high performace gears, the 9310 & EN36c is just a general purpose premium carburing steel

[RICHARD ZASTROW]

mactec54 In my world 9310 is a 9xxx series steel. If you want to spend a bit more of dihardcore69's money, why not try some of the Farrium alloys?LOL QuesTek Innovations LLC | Materials by Design®

Dick Z

[d1hardcore69]

Interesting choices. Yes, better MPG but also a higher top speed. With the power I am placing to the ground, most owners who have done the v-6 swap I have done, don't typically even use first gear. In the case above, I actually dropped all the gears from 2 too 1, 3 too 2, 4 too 3, and grabbed 4th the gear from Toyota's E153 transmission, and 5th as the cruising and top speed gear. with 5th being around .55 : 1, I could reach around 200MPH! Ultimately, I was hoping that while I a, in class and can utilize the equipment, that I could build a bullet proof transmission.

Yes, most people just do the turbo transmission swap (E153), but again, first gear is pretty useless and that's a shame and the added benefit of the possible MPG sounds super.

Cast Iron was my idea of a Chine's cheese reference lol, seriously not that retarded, wouldn't have spent as much time, money, blood sweat, and tears in this project as I have.

[packrat]

Wouldn't make more sense to change the ring and pinion gears? To a better ratio.

[dmalicky]

I'm unclear why to design it for 200 mph. That would require about 400 HP and well designed/tested aerodynamics to avoid aero instability. And a big track.

[d1hardcore69]

I'm shooting for a very reliable 600HP and there are many places to obtain the said desired speed. Like I said, while I am still in class and have the materials and equipment openly available to me

[RICHARD ZASTROW]

Do you have gear making, including gear grinding available? If so have your gears hobbed from your choice of material, hardened then ground. My neighbor makes gears for the NASCAR folks. Fairly pricey but good gears.

From my experience, you will need exceptionally good gears or they will self destruct at high stress extremes.

Good luck, Dick Z

[dmalicky]

For 600 HP (500+ ft-lb torque), the non-turbo MR2 box would be very high risk. The stock turbo engine only had 200 ft-lb, vs 145 ft-lb for the NA. For this relatively small increase, Toyota calculated that the turbo needed an upgraded box. That upgrade likely represents lots of factors, all designed for higher torque: case stiffness, gear width, shaft sizes, syncros, bearings, diff... For example, the E153 case is likely heavier with thicker webbing to keep the shafts from separating under higher gear forces.

I did a 914-6 conversion a long time ago. For that car, engine size was limited by the trans and there was no easy upgrade. For the MR2, based on the posts below, I'd say the existence of the E153 is a gift!
Other MR2 Turbo (E153) Gearbox in a Stratos
E153 transmission - Toyota Nation Forum : Toyota Car and Truck Forums

Keep in mind that even with the entire MR2 turbo driveline, reliability will be a relative concept at 500+ ft-lb torque. CVs, wheel bearings, suspension arms/bushings, motor mounts... likely none of those were designed for the loads induced from that torque.