Theoretical Calculations: B16B v K24A2

Since the car is in Cincinnati and I can’t really do anything from Chicago, I have been doing some analytics to compare my current setup to what we’d like to do. I wanted to see the comparison in power from the B16B to the K24A2, as well as evaluate my transmission options for the best setup for autocross.

Here is a dyno comparison between my B16B and an average K24A2. As you can see, the difference is dramatic. The car really is a blast to drive in its current state, but the K24 will be a gamechanger for taking the car to the next level of where it needs to be.

B16B v K24 Dyno

Here is a comparison of acceleration forces between the B16B and the K24A2 with EP3 5-speed. You can see that first gear and second gear have the most dramatic differences, but the K24 setup is quicker in every single gear.

B16B G Force

K24 G Force

Choosing the K24 wasn’t really the difficult decision to make, choosing the transmission was… From talking with a few people and reading the forums, most people were going with the 06+ Civic Si Transmission with LSD. This seemed like the go-to answer for my setup, all until I actually analyzed the ratios…

Here is my current gearing in the B16B. My second gear tops out at about 65 mpg, which is pretty ideal for autocross.

B16B Gearing

Here is the K24 with Z3 transmission. This gearing is ridiculously short… 2nd gear tops out at about 53mph, which would cost me time on the course from having to shift more frequently. In talking with another SMF driver from Florida, he was launching in 2nd and running his car in 3rd when he had this setup.

K24-Z3 Gearing

After speaking some more with one of my buddies on Honda-Tech, he advised me to look into either the EP3 5-speed or a 4.065 Final Drive for the Z3 transmission.

The EP3 transmission, with a bumped up 8000rpm redline, will hit just shy of 65mph in 2nd.

K24-EP3 Gearing

Here is the Z3 transmission with the longer final drive, 4.065. 2nd gear tops out around 63 mph in this configuration.

K24-Z3 4.0 FD Gearing

The drawback of the EP3 transmission is that it does not come with a factory LSD, and has slightly slower acceleration in 2-5 than the Z3 w/ 4.065 FD. But it is about $700 cheaper, which frees up the budget for an MFactory clutch-type LSD, which will be better than the OEM helical in the Z3. While it’s not quite as sexy as having the 6-speed, I can’t deny the $/benefit of the EP3 transmission.

When all is said and done, I will end up going with the EP3 transmission and MFactory clutch-type LSD.

Calculations were all derived using information from Fast Car Physics by Chuck Edmondson

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