One issue I have with my 2003 WRX is the gearing. Or more specifically 2nd gear’s huge dropoff (from 3.454 to 1.947) with a 2.0 liter that makes peak torque around 4,000 RPM. While I was pretty happy with this 5MT gearing on my 2009 WRX (EJ255) it is annoying as hell on an EJ207 with equal length headers and a VF-series turbo.

I have changed my driving style to accommodate this as much as possible. I know I need to rev 1st gear out past 5,000 RPMs for at least decent acceleration in second gear. So I have to rev out 1st gear? Woe as me. 😆

However, there is a daily driving scenario where I am going too slow for second gear and too fast to just slip it into first gear. This usually happens on a slow right hand turn that I can’t plow through, and someone barrelling down the road behind me, so I need to make a choice. Try to rev match it into first or slug it out in second.

Neither choice is great, so I generally opt to keep my speed up whenever possible. If I have passengers in the car I usually avoid putting it into first and hope my bearings won’t hate me when they grow up.

In the long term I want to rectify this via gearing. The perfect candidate would be a 6MT from a 2004 or 2005 STi. I always felt like that car was over geared for the EJ257 and it needed another 1k of powerband to compliment the transmission. Which is most of the reason I went with an EJ207 this time around.

That said, 6MTs are heavy and expensive for the complete swap. Obviously, if one showed up via the car parts fairy (also known as FedEx and UPS trucks) it would find it’s way into my Subaru within the hour. Project +Lightness be damned. 🙂

However, I want to compare my 5MT options, let’s start with what I have now. As you can see below, 2nd gear can take me from 20 MPH to nearly 80 MPH! Any throttle input below 3,000 RPM in second gear is basically a no man’s land of power. Just sit tight and wait for reinforcements.

2003 WRX 5MT
3.454 / 1.947 / 1.366 / 0.972 / 0.738 – FD 3.90

Now an easy fix would be to grab an FXT 5MT (or JDM WRX 5MT) since they can be had cheap and comes with a 4.444 FD. The advantage of a shorter final drive is increased wheel torque at the expense of top speed per gear. Cruising RPM speed will be higher as well but considering I am driving a gear lower than I normally would on an EJ25X this should work out fine.

200X FXT 5MT
3.454 / 1.947 / 1.366 / 0.972 / 0.738 – FD 4.444

Now this doesn’t change the wide-ratio between 1st and 2nd, but it should help improve the dead zone in 2nd gear around 20 MPH (~2,300 RPM). At 30 MPH would put me at 3,500 RPM vs 3,000 RPM with 3.90 FD. Since I hit full boost at around 3,800-4,000 RPM that should make a big improvement in response on the street.

There are 5MTs with shorter 2nd gear ratios (2.062, 2.333, etc..) but as far as I can tell, none with the 4.444 FD and 3.454 1st gear. I don’t want to build my own custom setup either due to the costs.

However there is the close ratio RA 5MT. These are hard to come by, but they do pop up from time to time, so let’s check it out.

RA 5MT
3.454 / 2.333 / 1.75 / 1.354 / 0.972 – FD 3.90

The interesting thing here is that in 2nd gear at 20 MPH I will be at 2,400 RPM and at 30 MPH I will be at 3,700 RPM!. Oh mi gusta! Even in 3rd gear at 30 MPH I would be at 2,700 RPM.

One other benefit of the RA 5MT is the center differential. Some come with a DCCD center diffs although open front diffs. Add in an R180 to the rear and you’ve got most the grip of an STi without the weight penalty. Personally I would like a helical front diff and a clutch rear diff and a open center if one of my diffs had to be open.

The big drawback besides whatever these cost on the internets, is that at 80 MPH I will be cruising at a brisk 4,100 RPM. A full 1,000 RPM more than the stock setup. The FXT setup is about half that.

There are other 5MTs out there in JDMLAND with varying combinations of gear ratios, diffs and availability, but I haven’t had time to parse them all.

5MT_Comparo.gif


As I was typing this post up, I noticed Engineering Explained posted a video on this topic. He explains things better than I do.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s