I don't currently own a evo as I waiting on the 2010's but I do know the problem with 5th gear cruising. This is a concern for me as I do a lot of highway driving and don't want to hear the engine scream. I did some math and came up with a few possible gears. I know a company that is willing to set up tool/machine time to run a few prototypes. The stock 5th is .761 which is about 3236 RPMs @ 65 and 3982@80 mph. Here are a few I came up with

.575 gear 2445@65 and 3009@80 <----best but will be the hardest to make and get to fit inside the trans.
.620 gear 2636@65 and 3244@80
.700 gear 2976@65 and 3663@80 <---this gear being the most likely easiest to make.

This unfortunately isn't going to be an easy mod as it involves removal and dis assembly of the transmission. Let me know what you guys think.

 

I think that you would also want to modify 4th to be taller because there is already such a huge drop going from 4th to 5th. The drop would be even worse if you only modified fifth. Personally, it's not a big deal to me, but I think that people with broken transmissions may be interested in modifying the gearing at the same time they are fixing it.

 

My take, drive the speed limit or buy an MR. Once you start digging into the stock transmission, say bye bye warranty.

 

I'm interested in taller gears as well, but like LaXGSR mentioned it would have to involve more than just a new fifth gear. There's a been a discussion going on about taller gearing a few threads down:

https://www.evolutionm.net/forums/ev...93-octane.html

 

The evo X certainly is not "quiet" at 80mph, but I don't find the engine noise to be that punishing. I think a lot of the noise is from the tires, my exhaust (RRE), and wind. I'm not sure a taller 5th would really a do a lot to combat the noise.

Also, I've noticed that the instantaneous mileage calculated by the ECU doesn't always correlate linearly with RPM. In fact, I get my best mileage in 4th gear at around 3500rpm. Changing to 5th actually hurts me at those speeds! But perhaps those who cruise at 80mph in 5th would see increased mileage.

 

Once you hit 400+ crank HP you may as well just get a taller final drive and space them all out equally. I'm betting at 550+ crank HP you have to row the gears so quickly it's almost silly, I can't imagine what it would be like in 700+ crank HP car.

 

would the point of a new 5th gear be for a quieter car and better mpg?
i feel it would kinda go against the point of the car. its for performance isnt it?

 

+1000

If you want a can to cruise at high speed all day long this just isn't the car for you.

I did 80mph all the way from FL to VA two days ago and it wasn't bad at all. I'm going to do it again next week, VA to FL.

 

HKS has had one in car for some time now from what I heard , 10-12% over was what I was told .

 

Is putting a 6 speed manual in just out of the question? If your going to get 500+ hp and have to do a lot of work on the trany anyway...

 

I would change the FD gears personally
That way you get taller 1-5 gears. The EVO X gearbox is super short which is fine with stock power levels but way too short once you start making serious power. This would aid in 1/4 mile times from not having to shift to 5th and also help with cruising speeds. 4.4 FD gear would be pretty good. Allowing you a 124 MPH trap in 4th with 7800 RPM redline and give you 3500 rpm cruising at 80 mph.