New 5th gear for the R154 - how about a taller overdrive?

[Doward]

Yep. I've had the prototype sitting here for about a week now. I'll be finishing up the 13" front brakes this weekend (finally!)

My original idea was to go to a T56. Then I started playing with the idea of just replacing the 5th gear.

Benefits? Well, no custom work needed - just swap the 5th gear! Lower highway rpm = better gas mileage.

*EDIT* @ 70mph

Stock is a 0.753. ~2800 rpm on a stock 3.91 rear equipped Turbo model. You 3.73 guys are running around 2650 rpm.

You 4.30 guys? Damn near 3100rpm!

The 5th gear I've put together here is a 0.66 overdriven gear.

The results?

3.73s = ~2350 rpm from ~2650
3.91s= ~2450 rpm from ~2800
4.30s= ~2700 rpm from ~3100

These calcs are all on stock 225/50/16 tires. What kind of real-world difference will they make? We'll find out when I throw the fresh r154 in Jeff's Supra.

I think Jeff is liking being local to me

Cons? The new 5th gear is physically smaller than stock - so naturally, it is slightly weaker. My solution to that? I'm going to cryo treat it.

And YES - I'm working on rear brakes, guys!! No plans for doing a GB just yet - I have to contact a moderator first.

Or if one wants to chime in here, that'll work too.

So what do you guys think? Any interest in a new taller 5th gear?

 

[IwantMKIII]

Cons? The new 5th gear is physically smaller than stock - so naturally, it is slightly weaker. My solution to that? I'm going to cryo treat it.

VERY nice :icon_bigg always depends on price of course :biglaugh: I love my 3.91 but cruising RPM's suck on the highway


However, one thing. You're solution is cryo treating to the smaller size. While i understand the concept behind this, last i heard there isn't much evidence at all to support its true effectiveness. I could be wrong here, but input would be nice as I usually have a very good memory with these things but still occasionally doubt myself as it has been a long time since i've heard it.

 

[GC89]

Im interested pending testing. My only worry would be 2350 being too low and wanting to bog and actually decreasing mileage. What rear end does jeff have? Would you be doing a few lengthy cruises for mileage testing and then again after the swap?
Thanks again John for the continuous innovation and products you bring to the community.

 

[IwantMKIII]

^i feel like this would only be an issue for the 373's on steep inclines like 6% grade or higher. The 7m's have some good torque, especially in combination with weight (for momentum). Plus its not hard to downshift every once in a while in order to save major gas mileage

 

[Moy]

I'm definitely interested in hearing the results of this. I have a 4.30 LSD rear end right now and it really sucks cruising on the highway because I've seen the needle on my gas gauge go down...

This might be a better solution for me than to mess around with swapping in the 3.91 LSD I have sitting in my garage right now.

 

[Doward]

Considering you'd be spinning LESS rpm than the 3.91 stock, while still having the acceleration of the 4.30s....

Think on that one

Jeff's got the '92 (7MBoost) so he's sporting the 3.73s I have the 3.91s in my '88

 

[hvyman]

^a diff is easier to swap then dropping a tranny and pulling it apart putting it back then back into the car.


interested but in no hurry.

 

[GC89]

^i feel like this would only be an issue for the 373's on steep inclines like 6% grade or higher. The 7m's have some good torque, especially in combination with weight (for momentum). Plus its not hard to downshift every once in a while in order to save major gas mileage

3.73s here, I love em just wondering if it would be a bit much. I know someone who went from 4:10s to 3:73 in a 7M mkII and got worse mileage from downshifting all the time:dunno: I get better mileage than my 87 did with 91s but im still in for test results

 

[IwantMKIII]

^probably more depends on driving style then anything

 

[Doward]

Yep. I built it specifically for my cross-country trip to Wyoming this summer My goal is to push 30+ MPG from the Supra on the highway

 

[IJ.]

Should easily be doable Dow I was getting 28>29 USmpg with the Auto.

 

[Guyana00]

I was always interested in regearing an entire R154 long down the line.

I like this idea, but 4th gear should be worked with as well. Reason I say this is when you're on the roads and not on the highways. I can usually be in 5th cruising from about 70km/h. With this gearing I would have to stay in 4th because shifting to 5th with this ratio will bog.

Playing with fourth means messing with 3rd as well, for me. That's why I wanted to do something custom in an R154.

I do like the idea and want to see how this works out.

I'm watching tv right now and can't remember another point I had to make.

I hope this works out good for you, what kind of cost was involved for you doing this? Where did you get the gear, any more info you have to reveal?

 

[Doward]

I can only ask how you 'know' it will bog? The automatic uses a 0.70 4th gear (vs 0.753 in the r154) and I don't recall hearing about any bogging there

Nah, not giving away any secrets just yet - I'm just looking to see if there is interest.

I will say this much - I am NOT mass producing these. I learned that lesson with the front brake sets. I'll probably only build 5-10 and no more until down the line.

 

[IJ.]

Ummmm 4th isn't actually a gear so NFI how you're going to "play" with it.....

 

[sancho886]

Very Interested :icon_bigg

 

[Doward]

Ummmm 4th isn't actually a gear so NFI how you're going to "play" with it.....

Hush with your logic

 

[IJ.]

<kicking dirt and shuffling feet> awww shucks Mister I was only trying to help

 

[Doward]

<kicking dirt and shuffling feet> awww shucks Mister I was only trying to help

ROFLMAO!

Going to be very fun when I toss this r154 into Jeff's car. He's going to get to do a back to back comparison of a good condition but well worn r154 vs a tightly blueprinted fresh r154.

 

[IJ.]

1 2 3 4 7

 

[Cz.]

I would be interested in one.
Are the rpm numbers you posted in the at 60mph? I haven't driven my supra for a while so I can't remember what it should be at.