Build 3 - Bullet Proof Tranny Etc.

We did the original Build 1 in 2007-2008 and finished in the late summer of 2008. We ran that setup for all of 2009 and at the end of the season started to get serious with our Build 2 which we campainged successfully in 2010 in our New England SCCA region taking top honors in SSM. However, at the last event in August we blew 2nd gear in the tranny. Inspite of missing the last few events, Brian still took the regional trophy with points.

So, the primary goal was to make a bullet proof tranny that would handle the Rotrex power and give us all the right gearing that we need for the setup. Turns out, the K-Series 2nd gear is notoriously weak and tends to break, as we found out. Apparently, all the drag race people found this out long ago, but it was (sad) new for us. We did a lot of research and decided on going with a 1-2 gear set from PPG (Pfitzner Performance Gearboxes) in Australia. They make all kinds of gears for various cars including full dogboxes. We did not really want to go that route due to cost and drivability. Turns out they make a 1-2 or 1-4 replacement set of gears for the K-Series which work with the normal synchros (more on that). Of course we need to match a final gear to the PPG gears and also worry about 3-6 gear spacing, this turned out to be an interesting, but fun, challange.

In addition to the Tranny work, we also need to work on a few othe things. Most importantly, after the tranny, was cooling. Inspite of our oversized custom radiator in build 2, the engine would spike over 220F at the end of a hard AutoX run on a hot day. We felt that was mainly a matter of getting proper airflow through the radiator so we need to work on some shrouding.

The rest of the stuff is minor, like different brake pads and a way to enable our Hondata K-Pro to log engine parameters during a run.

PPG Gears

OK, so the K-Series 2nd gear is weak and can't handle the abuse of 340WHP and constant AutoX second gear runs. Total transmission rebuild with custom gearing and (hopefully) bullet proof 1st and 2nd gearing. As we mentioned, we chose to go with a 1-2 gear set from PPG. Besides the ability of the gears to handle the high HP and abuse, we need to choose a final gear/gear ratio combination which is optimized for our event. In the Build 2, we used the stock ITR gearing and changed the Final Drive to a 4.052 from a 4.764. This gave us a 67 mph top in second, was a better match for the Rotrex power, and gave a reasonable cruise on the highway. But we were still hitting readline too often in 2nd in Autox. The PPG 1-2nd set matched up nicely with the original 4.764 final drive to give us a nice 73mph redline in second, but then 3-6 stock gears were then all to close and we lost our highway overdrive.

So what we did, is pick and choose gears from other honda transmissions to build a reasonable set of gears. Yes the K series transmission gears are all interchangable, with some caveats. The caveat is that some of the gears are designed for double or triple cone synchros, some for singe. Our ITR transmission uses triple cones in 1-2 and doubles in 2-6. A Civic Si transmission on the other hand uses single cones for 5 and 6. We went with the EP3 gears for 3-5 and the Civic Si gears for 6th to give us an overdrive. The EP3 3-5 are single cone however (you can't mix the synchros between single and double/triple cones as the gears have to be made to accept one or the other). So we give something up, but not a big deal for us. Below is a comparison of the gears we ran previously (stock ITR with 4.052 final) to the PPG/custom set.

The gear ratio chart shown below gives you a graphical display of the ratios. As you can see the gearing is well spaced out. The Red lines are the old gearing and the blue are the new PPG setup. As you can see, the lower gears are a bit taller in the PPG setup, which is what we want. (Thanks to MFactory racing for the nice online gear calculator).

If you were running the car in road racing or drag, you might choose different gearing, but for what we do, this is pretty close to perfect.

Transmissions aren't cheap, and neither are the parts. The PPG gearset alone is around 2 grand! So we ordered up all the parts and did the tranny rebuild, below is a pictorial on the build.

Of course this is all a lot of work, we just pray that there are no problems. When we first started it up we heard a terrible whining noise. Turns out the straight cut gears make a lot of noise in neutral, at least we hope that is all it is. Here is a video to see how straight cut gears sound.

More to come...