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Old 11-20-2012, 01:34 PM   #1
Scooby Guru
Member#: 261612
Join Date: Oct 2010
Location: Minneapolis, MN
2002 WRX - 750WHP
9.5s @ 150mph

Default 08+ WRX 5 Speed Short Shifter Comparison (Stock, SPT, Kartboy)

08+ WRX 5 Speed Short Shifter Comparison (Stock, SPT, Kartboy)

I was curious to try some different shifters, and I managed to get the stock, SPT, and Kartboy all together at the same time, so I decided to take some photos and measurements for anyone who is curious. I didn't see much like this online, so I hope they are interesting/useful to someone.

The first thing that I would like to point out is that these photos and measurements are for the 2008-2013 WRX / 2006-2009 Legacy GT / 2006-2008 Forester XT. Other models may have different dimensions. I also wanted to clarify that the SPT shifter is the OEM factory short shifter. It is often called the "STI Short Shifter" and is sold via SPT. I am calling it the SPT shifter to avoid confusion with the 6 Speed STI transmission. As confirmed by Tom at Kartboy, the shifter itself is what creates the shorter throws with the SPT setup. The linkages are exactly like stock. They are only sold as a package because that is how Subaru receives them.

Before going any further I'll give a quick rundown on how a short shifter works. It is not a difficult concept, but some people may not be fully aware. Some people think of a short shifter as being physically shorter. Others think of it as having shorter shifts. In most aftermarket shifters both of these things are true. Skip this part if you already understand what a short shifter does.

There are two aspects that can be changed in regard to shifter throw. The first is the overall height of the shifter. This reduces the amount you have to move your hand in order to shift into gear, simply by placing your hand closer to the linkage. I will be referring to this as the "top" (distance between linkage connection and the top of the shifter). This obviously will also decrease the overall height of the shifter.

The second change is to increase the distance between the pivot ball and the linkage connection (I will refer to this as the "bottom"). This changes the length of the throw by reducing the leverage (and actually will marginally increase the overall height of the shifter if nothing else is changed). Either of these things can be done independently, but they are most often done at the same time to provide the best results.

If you understand this concept you may realize that a very short top section, and very long bottom section would result in the shortest throws (taken to the extreme, your hand would simply be holding onto the linkage to shift). This is true, but there are other constraints that must be considered. Reducing the overall height too much will be hard to reach and uncomfortable. Increasing the length of the bottom section can only be done so far within the given limits of the linkages going to the tranny. And doing either of these too much will reduce leverage and result in notchy, hard shifts.
With that out of the way, I'll start with some overall photos of the shifters side by side:

You can see that the stock and SPT shifters have the same overall height, but the position of the linkage connection on the SPT shifter is higher up, which creates the shorter shifts. The SPT and Kartboy shifters have similar distances between the pivot point and the linkage connection, but the overall height is much shorter on the Kartboy.

Next are some photos of the top and bottom sections (table of measurements below):




The pictures aren't perfect, but here are the measurements I took:

Shifter	Bottom	Top	Ratio	Reduction
Stock	2.44"	8.50"	3.48	-
SPT	3.00"	8.00"	2.67	23% 
Kartboy	3.00"	7.00"	2.33	33%
The "Bottom" measurement is from the middle of the ball to the middle of the hole for the linkage connection. The "Top" measurement is from the middle of the hole for the linkage connection to the top of the threads. The distance to the bottom of the threads could also matter, depending on what knob you have (more on this later), but I didn't use this for the calculations. The measurements should be accurate to within 1/16" (and then converted to decimal) as long as my eyes weren't deceiving me.

After taking the measurements I calculated a ratio of top vs. bottom length. This can be seen to represent how long the throw will be. Because the linkage connection point has to move the same distance for all of the shifters (this is fixed by the transmission's internal design), you can simply use the ratio as a multiplier. Based on the ratio I also calculated the % reduction in throw (both %'s are in relation to the stock shifter).

First looking at the Stock vs SPT knob. The first photos showed that the overall height is nearly the same between the two (possibly off by about 1/16"). The measurements show that the difference is that the SPT shifter has a bottom section that is about 1/2" longer, and the top is 1/2" shorter (to maintain the same overall height). Doing the math, this says it will be a 23% reduction in throw (with no change in overall shifter height).

The Kartboy lever has a bottom section that is identical in length to the SPT. The top section of the Kartboy is 1" shorter than the SPT (and therefore it is 1" shorter overall). Because of the reduced overall height, the ratio changes, and therefore for the throw is shorter. Based on these measurements/calculations the throw is 33% shorter than stock (an additional 10% shorter than the SPT).

In case the ratios and percentages are not meaningful, I also converted them to physical distances:

Shifter	Linkage	Ratio	Shifter	Reduction
Stock	0.55"	3.48	1.91"	-
SPT	0.55"	2.67	1.47"	23% 
Kartboy	0.55"	2.33	1.28"	33%
To do this I estimated that the shifter linkage has to move 0.55". This is just an estimate, but it should be fairly close. This will be the same no matter what shifter you have (dictated by the transmission's internal design). Using 0.55" as the fixed distance, you can multiply by the ratio to find out how far the top of the shifter has to move. You can see that the stock shifter is close to 2", the SPT is about 1.5", and the Kartboy is close to 1.25".

I also wanted to mention that your choice in knobs can affect this as well. Here is an example.

Knob Comparison:

Due to how different knobs thread on (and bottom out) the effective "top" length can be changed. As you can see in this photo, when the the shorter Kartboy lever is paired with the taller stock knob it is basically the same height as the SPT shifter when paired with a round ball shift knob. Keep this in mind when comparing shifter setups with someone who has a different knob than you do.

What conclusions do I draw from this?

First is that 3" from the middle of the pivot ball to the middle of the linkage connection is likely the upper limit to how long you would want that section. You can go a little higher if you bend the bracket in the shifter area, but the shifts start to get very notchy beyond this length. The adjustable shifters (COBB/MODE) can definitely be extended longer than that, but you will get notchy shifts. I think SPT and Kartboy use this length because it's significantly shorter than stock, but still feels very good.

While I was a bit surprised that the lower section was the same length on the SPT vs. the Kartboy, I was not surprised that the Kartboy was shorter overall. The SPT is a really nice option for someone who does not want to reduce the overall height of the shifter, but for someone that wants the shifts to be a bit shorter and more crisp, the Kartboy is great. I think either can be a good option depending on your preference.

Unfortunately I didn't have any other shifters to measure. I have owned the MODE (ie. COBB) double adjustable shifter in the past. It was great quality, but I found that it could make the throws much shorter than I needed. You should be able to set it up identically to a Kartboy if you wanted, but I don't think you can make it as long as stock.

From my experience with both, I wouldn't hesitate to recommend either, depending on what you want. The COBB is more flexible so you can dial it in exactly how you want (but you can actually set it up to feel pretty bad too). Versus the Kartboy that is just plug and play. No adjustments, but it's really nice out of the box.

On a semi-related note, the shifter bushings also make a huge difference. Doing a short shifter a long will make the shifts shorter, but they'll still be very sloppy. The bushings really change the feel of the shifts. For the small price you pay, they make a huge difference in how it feels to dive. I would recommend them to anyone.

Last edited by xluben; 11-21-2012 at 12:07 PM.
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