Gear Ratio Discussion

[IDon'tKnow]

I'm quite confident that I'm not the first person to notice or complain that the gearing for the AW11 is pretty short.

The short gearing serves it's purpose with a factory or lightly modified 4AGE, but what about for those making big numbers? (I can't imaging that having a 300hp MK1 is very satisfying when you're mechanically restricted to a top speed of... what 120mph(?).)

Also, I personally would prefer that I not have to keep the tach at 4k+ just to keep up with interstate traffic.

I've looked around at transmission options for the 4A and seen a few things. It seems though that even with the 6 speed swaps that top gear is still fairly short.

I think I've only ever seen final drive kits that lower gearing. Anyone here ever considered raising the final drive ratio on a 6 speed (1-5 would remain close to the original 5 speed) or even just the 5?

I've considered just throwing on a larger diameter rear wheel but would rather not fool with such shinanigans.

Thanks in advance for your thoughts guys.

[dirocyn]

I've pondered it in every car I ever owned, never have actually attempted it yet.

The kits for lowering the gearing are for people hunting faster quarter-mile and half-mile times.

[mr2_jake]

I agree. I have contemplated the 6 speed swap. I was told by some redneck guy that he swapped the internals out for those of a Tercel 5 speed? Something like that.. But I wouldn't try it. I'm not sure of the ratios, but I would look into BT/ST 5 speeds, or possibly GZE transmissions. It's not for beginners, but FWD transmissions can be converted to run in MR2...

[dirocyn]

We have C50 transmissions in the 85-86 models, and C52's in the 87-89. C50s were also used in Corollas, C52 in the Corolla GTS and the Geo Prizm. But they all have the same 0.815 5th gear ratio. Our transmission is the same, or very nearly the same, as a FWD transmission--so others might fit, esp. with some modification.

With gear ratio, smaller number = taller gear. The C transmission doesn't have a 5th gear with a smaller number than 0.725, but that's quite a bit taller than you've got. In some transmissions that's a 5th gear, in others it's a 6th. It's probably the same gear. I bet that gear fits right on in place of the 5th you've got. If it doesn't, there's a good chance a machinist can make fit into a C52 transmission.

Here's a list of C transmissions/applications. Toyota C transmission - Wikipedia, the free encyclopedia

If you can get it to work, I might try it too.

[IDon'tKnow]

That is an interesting possibility; just throwing the .725 into the c50 I've got. Probably the least expensive solution at least.

Using the .725 5th gear in a C50 would give 72.4mph @ 3,000rpm; 4k would be 96.5mph. At least that's what this calculator gives me. I'm not sure I trust it. It says that the C50 is geared to top out at 150+mph.

I think I'd prefer to punch these numbers myself. I'll look around for the equation in a few minutes.

Theoretically I think the ideal transmission choice for a powerful daily driver AW11 would be a C60 on the C50 or C52 bell housing with a C50 ring and pinion, 1st, & 2nd gear (would look like this).

First and Second gear would be more wheel spin friendly although 2nd wouldn't be best for exiting corners slower than 40mph. Third, Fourth, & Fifth would be nice and short for roll on acceleration and keeping the engine at the peak of the power band all the way into the 6th gear upshift; the 2/3, 3/4, & 4/5 upshift would each only drop the RPM's by 1500.

I assume the only way to find out if this is a viable option would be to pull them both apart and give it a try.

[IDon'tKnow]

I haven't been able to find the equation I'm looking for. Anyone have any leads?

Also, I think that the C60 with just the C50 ring and pinion might be a bit easier to sort out and better anyway.

[Kerry Phillips]

I totally agree about DROPPING the RPM's. The 6 speed final gear ratio is almost identical, the only advantage is less RPM drop while changing the middle gears.

My career silvertop project, I am using a Geo/Corolla tranny, 1994 with the 7age engine. The differential is 15% Taller (lower rpm). Fortunately, first gear is 15% lower so overall first gear ratio remains uneffected, while gears 2-15 are 15% higher.

THe 10-15% better MPG would be sweet.

SUpposedly one can "easily" mix and match internal gears and differentials amung the C series trannys.

IMHO settle for the 15% (improvement) upgrade the C50 to a stronger C52 and call it a done deal.

BTW legend has it that the silvertop engine is more efficient, I am hoping for 40-42mpg. With the improved suspension, my car should be fast, fun and CHEAP to operate! 42 MPG in a fun to drive daily driver!! WOO WOO
Kerry

[espguitarist33]

WOAH really the ST is that good???? i was thinkin i'd get like 35 max (3sfe(?) i think 90s corolla afm was recomended to me and i know that gets pretty good mpg)
or are you saying wiht the geo transmission it should be about there

[IDon'tKnow]

Well from what I understand, having done a bit of reading on the net, the C60 bolts right up to the C52 bell housing; I assume the same for the C50. Once it's bolted up your need to modify the selector shaft housing and use the C52/50 selector shaft in the C60 housing. That's not exactly an easy job but it's not rocket science either.

In my opinion, using the C50 ring and pinion to give a 3.722 final drive as opposed to the 4.529 would give you the best of both worlds: 3.722 final drive with .725 ratio in top gear and you'd still have the benefit of less RPM drop on upshifts.

[IDon'tKnow]

Kerry, I don't think that a 15% rise in gear ratio will give 15% better gas mileage. Correct me if I'm wrong, but I don't think that it's a parallel relationship.

To figure it out you would need to know what the specific fuel consumption (lb/hr/hp) is for a 4AGE20V and then calculate the lbs. per minute fuel flow required at two RPM points; cruise speed with the shorter gear and then again with the taller gear.

I punched some numbers not specific to the 20V and came up with a drop of 7.5% in fuel consumption for a drop in cruise engine speed of 800rpms: 3800rpms to 3000rpms. So you might expect to see an improvement in fuel economy from 34mpg to about 36mpg.

[espguitarist33]

40 sounded rediculous( evne though it got me excited)...otherwise...they'd have to like freakin sell these again with the ST though..as an economy vehicle

[IDon'tKnow]

It's definitely possible but it would not be in the interest of someone who wants to enjoy the MR2 as a sports car.