manual tranzilla

[Earthworm]

I did a calculation as to what would happen if I added a 6th gear to the 5spd WRX tranny. Here's what I found out:



Basically, slapping a 0.631 gear would give near exact cruising RPM we're used to with the 4EAT.

[SVXer95]

Originally posted by Earthworm
I did a calculation as to what would happen if I added a 6th gear to the 5spd WRX tranny. Here's what I found out:



Basically, slapping a 0.631 gear would give near exact cruising RPM we're used to with the 4EAT.

Would it fit? How big of a jump would be if that took place of fifth? Could there be a compromise btw the .738 and .631?

I want a five speed, but I drive on the highway a lot. I am very interested in the possibilities of this.

[Nemesis Destiny]

That's awesome, Earthworm. I wonder where one might acquire said gear, or similar? Most likely it will need to be made custom.

So far, the 'master plan' is looking something like: Japanese RA 1-5 gears (similar ratios to the 5 spd, hopefully) in a WRX 6speed casing with custom 6th with a ratio of ~.631

How did you arrive at your calculations?

Seems this thread wasn't a waste of digits afterall... looks like there is some interest.

[Earthworm]

My calculations are all based on the RPM's at 60mph in top gear.

Here's an interesting bit of info you may be interested in:

I've been to the Reading meet the last 2 years. Last year with the 4eat and this year with the 5spd. I tracked my mileage both times. Last year my best mileage was 35mpg (1 Imp Gal = 4.546L). This year my best mileage was 34.5mpg with the average for the trip somewhere around 33 and it never dropped below 30. I also had one more person with me this year.

35MPG (Imp) = 29MPG (US)

[svxsubaru1]

What about changing the final drive ratio on the 6spd. You could always put the highest gears subaru made into the rear end and have a costom front diff made to match, maybe 3.545. I think this would be the best becasue then the gears would be spread out alittle more. Maybe you could even hit 60MPH in second.

[SVXer95]

Originally posted by Earthworm
My calculations are all based on the RPM's at 60mph in top gear.

Here's an interesting bit of info you may be interested in:

I've been to the Reading meet the last 2 years. Last year with the 4eat and this year with the 5spd. I tracked my mileage both times. Last year my best mileage was 35mpg (1 Imp Gal = 4.546L). This year my best mileage was 34.5mpg with the average for the trip somewhere around 33 and it never dropped below 30. I also had one more person with me this year.

35MPG (Imp) = 29MPG (US)

So, for the most part, there is no difference in fuel economy. Even with the engine at higher revs there is only about a .5 mpg difference.

[Nemesis Destiny]

there is no difference in fuel economy. Even with the engine at higher revs there is only about a .5 mpg difference.

That is assuming he went (about) the same speed and a similar route both times. More hilly terrain and other factors would affect this, but those numbers are very promising.

Maybe I won't be missing too much with 'only' a five speed. It would be cool to have bragging rights on a six speed though.

[Earthworm]

Originally posted by Nemesis Destiny
That is assuming he went (about) the same speed and a similar route both times. More hilly terrain and other factors would affect this, but those numbers are very promising.

It was basically the same trip. Highway speeds were around 75mph/120kph.

Maybe you could even hit 60MPH in second.

Actually I already can. In fact for me the rev limiter kicks in at about 68mph/110kph in 2nd gear.

What I'll do when I get home is change the gearing in that file to match the 6 spd STi tranny then throw in the 3.545 final drive to see what we get.

[FlagstaffSVX]

I've had this idea for years now and was just thinking about it today on the highway infact... ironic that I find this thread now.

I mean, in the mind it SEEMS simple enough, right? Take a 4.44 5MT and just slap in a .65 gear or so. Who cares what the differences between 4th and 5th are since you'd only use it for crusing.