Over-drive question Options

[BrettKoster]

Here is a question that has come across my mind while driving on the highway with my Celica. I have a 1995 Celica GT Manual and when I drive over 65 my rpms seem to be high, above 3000 and when I reach 80 I am at 4000 (5th gear of course, the highest gear I have). When I drive another Celica GT that is an automatic, I am driving at 3000rpm at 80mph. I would assume that is because there is an over-drive feature in automatics, but is it possible to have that feature in a manual Celica as well either by default and I am some how missing it? Or if it isn't in there by default can I have it installed on a manual (that doesn't require a whole new transmission?)?

Otherwise what can I do to bring the rpm's down when I am at a high speed?

Thanks in advance for any help given

[mkernz22]

The manual is just like that because of the gearing ratio's and there's no over drive on the manual

[BrettKoster]

So is there an aftermarket modification I can install that will allow me to reduce the rpms? Maybe by adjusting the gear ratio? Thoughts

[delusionz]

5th gear in a manual is OD in an auto.

both are called overdrive gears because their ratio is less than 1 gearbox (about .9) rotation for every 1 wheel rotation.

I'm not sure if USDM S54 and A154 have different ratios to the JDM S54 and A154 boxes, But it seems to me 1st and 4th gears in the A154 share the same ratios as the S54's 1st and 5th gears. its just the auto's 2 & 3 which are longer gears than the manuals 2,3,4.

It seems the Automatic doesn't rev as high because the torque convertor wheel is lazy inside the slushy box, but if you manage to watch the speed/revs by putting your foot to the floor with 4th gear selected (OD ON, MANU ON) you'll notice its the same as the manual's 5th gear.

I wouldn't argue if you came back and said the automatic revved a couple hundred RPM lower, but no less than 200rpm lower its really negligible. you might be saving some gas revving lower, but your slushy box car is rated 200kgs heavier an equivalent manual car.

[delusionz]

Anyways, Your easiest option is a bigger rolling diameter wheel/tyre, and then use a speedo corrector so you can see the difference you've made (it is however unrecommended to go above or under 3% of factory spec)

Then the other option is by transfering an E153 gearset into your S54, or by just adapting the whole E153 gearbox to be used by your 5S-FE.

For the 7A-FE you have the option of longer gears from the 1.6 supercharge motor Toyota Levin GT-Z.

Hope this helps

[delusionz]

Going the gearbox modification route may require custom clutch,flywheel and drive shaft combinations,

Best research this, czwalga is doing something similar within his big project so search his threads.

I think in the end you'll find theres more trouble than its worth

[celica-s]

if you are revving higher on every gear as compared to an auto, your clutch could be slipping, or maybe you need engine tuning.