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HTSpec TSX Redeux: Part 2

  • Posted: 02-15-2014 11:34 PM
  • HTSpec TSX
Sometimes all the planning in the world can’t prepare you for circumstances of life. In planning to build the HTSpec TSX, we decided to go ahead and get the body pieces ordered and the Supercharger on the way from CT.

Then, we started getting a horrible sound from the drivetrain. We blogged about our investigative effort in determining the source of the noise a few weeks ago. After getting the car in the air, it became obvious that the trans needed to come out. It could be worse, though. Last year we attended an HPD event in which it became obvious that the car needed a Limited-Slip Differential to help put power down in the corners. With a supercharger increasing that power, an LSD is going to be more important than ever. The old "two birds" adage is always a good way to turn a frown upside-down.

In determining which LSD to use, we strove to find a good balance between performance, durability, and value. JDM brands and Quaife from the UK are known to be quite solid, but cost a considerable amount of money. We were definitely opposed to putting something in that didn’t have a known performance endorsement. We zeroed in on a helical MFactory LSD which we sourced from Synchrotech Transmissions.

Knowing we’d be doing a full rebuild, we also got a set of the Synchrotech carbon-lined synchros to smooth out our shifting, which had gotten a bit chunky of late. A full set of bearings was purchased as well. The only question that remained was: What was actually wrong inside the transaxle?

After getting the trans out of the car, we benched the Magnesium case and cracked it open to find that our ring gear looked like it just got done with 9 rounds with Iron Mike. Apparently this is a relatively common failure in performance Hondas, where if one side of the suspension is fully and abruptly compressed, the axle can bottom out and cause the gear teeth to mis-align. Crunch. See if you can spot the missing teeth...

Seeing this means that a complete tear-down is absolutely critical. Small bits of metal will find themselves in oil orifices and ports in the shafts and case, which need to be removed.

So here we were; transmission apart and in need of a new final drive. Many people would go ahead and change the final drive to a shorter set, providing faster acceleration. Knowing that we’d be boosting the car, and had no desire to have a higher RPM on the highway, and we were not tuning the gearing for any particular track, we opted not to go this route. The decision was made to simply replace the broken ring gear and compromised counter-shaft with a new one. And as luck would have it, we had received some incorrect final drives years ago when we had ordered DC5 ones, which happened to be very suitable replacements for what the TSX needed. Who knew the AWD CR-V final drive gears were the same as in the TSX? The only difference we noticed was a couple millimeters of mounting-offset on the ring gear, which proved to be no issue at all as we assembled the transaxle.

Our tranny exploded. It is really important to stay as clean and organized as possible here. We are not going to get into specifics and how-to's because the factory service manual has all the important information you need in it, and you should have one if you are looking to do anything remotely as complicated as this.

Here is the difference between the Synchrotech carbon synchros on the right and the standard ones on the left. Actually, our synchros are in pretty nice shape, but why wouldn't we change these out while we are in there? Check out Synchrotech's site for details on these bad boys. Spoiler alert: The HTSpec TSX shifts butter.

The issue we did run into, however, was that the main-shaft and differential both needed to be shimmed to eliminate thrust (play), and we didn’t have the shims we needed. With an 800-mile road-trip planned the following week, we had run out of time to get the perfect ones. However we were very close to having it spot on, and the decision was made that 7 days of downtime was going to have to be enough and the transaxle was reassembled.

It would be silly to have the transmission out of the car and not install a new clutch, even though the old one looked ok. Looking for a higher performance quotient, the stock flywheel was ditched in favor of a billet aluminum piece from AASCO Motorsports. We choose AASCO as our flywheel supplier because of the racing heritage they bring to their every-day products, and the uber-light weight. This flywheel weighs little more than 8 lbs! Some people ask “is there any reason not to get such a light flywheel?” We say; yes, in cases where you don’t want the maximum horsepower gain and fastest revving possible. Definitely more weight is a compromise in performance and not a benefit.

The clutch itself we elected to do a bit of an experiment to test a hypothesis. We figured that a rigid-hub disc, as we had in the past, was going to give the absolute best drivetrain response possible because sprung hub discs add excessive movement. Clutchnet is a supplier not only of clutches, but clutch components to some of the biggest brands in the industry. We ordered a custom package from them, using a heavy-duty pressure plate offering a 60% increase in clamping force, and a full-face organic disc. The special addition here is a rigid drive-plate in the disc, which removes the springs adding a direct, non-dampened drive and lighter weight. We’d used a clutch with this configuration in the past and absolutely loved how direct the power transmission was. We hoped this setup would not be too twitchy or sensitive as our goal with this car, not to be forgotten, is to retain a fair bit of refinement.

Modern Honda/Acrua drivetrains are held in place by a subframe that cradles the engine, transmission, and suspension. So to remove the transmission, a significant portion of the under-carriage must come out as well. This provides a lot of space for more “might-as-well” projects. While waiting for miscellaneous paraphernalia to come in for the trans re-assembly, we took the opportunity to give a good scrub to the engine, subframe, and anything else we could reach.

The exhaust manifold was replaced with a shiny, new header from CT Engineering. Known to provide a nice bump in power while being very reliable and CARB legal, this header was a great choice for our street-performance, no-hassle machine.

With the transmission going back into the car, and our Hybrid Racing shifter cable bushings cleaned, inspected, and re-attached; tension mounted as the car was to be started the day before our long journey. Any sort of a shake-down period is ideal, but ultimately when the light turns green you just have to trust in the knowledge that you made the right calls and no detrimental compromises.

A short test drive was taken and initial impressions were truly awesome…right up until 4500 rpm when the engine just would not rev any more. The worst part was there was a lack of a CEL to help lead us down the path of discovery. After poking around online, we learned that there is one common pitfall in rebuilding K-series transmissions which we had overlooked on our re-assembly. The countershaft speed sensor is a magnetic pickup that is very easily damaged.

Frustratingly, this discovery was made on a Sunday morning, and our trip was starting out early the following AM. We would pass about a dozen Honda and Acura dealers on the way, and thankfully had found a new sensor not too far off-route. Even more thankfully is that this sensor is not buried deep in the depths of the engine, and so with a trusty 10mm wrench it was changed just as rain started to fall.

Interesting factoid: When you reset the ECU on there is an idle-learn procedure that should be followed, and in order to clear the code that comes up from the speed sensor the car must be driven at highway speeds for a steady period. The light extinguishes itself.

We’ll blog a bit more about our impressions of our mods in an upcoming release. Suffice to say, our road-trip was excellent for us to get to learn the new nature of our GT. For now we will leave you with the knowledge that we were successful in upping the sportiness of Acura’s greatest model without causing detriment to that which makes it a “nice car” in the first place.

Many thanks go out to this experience being a great one:
  • Evan from 360 Imports in Vancouver, Washington. Without whom, we would not have had the tools or tutelage needed to get our build done in short time.
  • James and the crew from Synchrotech Transmissions, for proving to be another unparalleled phone-a-friend.
  • Vince and Jordan at AASCO Motorsports, for their quick turn around on an excellent product.
  • The parts guys at Dick Hannah Honda in both Cornelius, Oregon and Vancouver, Washington, for having good stocking levels and quick turn-around.
  • Mista Bone and a bunch of other friends on Facebook for giving us more tips where needed.


04-14-2014 12:48 PM at 12:48 PM
AASCO flywheel bolt pattern for clutch is the same as in OEM TSX ?
MrHeeltoe: We do offer an OEM replacement flywheel for the TSX, but the one we installed is an RSX-S one.
02-21-2014 07:32 PM at 7:32 PM
Excellent posts! These are very exciting and inspiring to read! I have been curious about the carbon synchros for some time now. Are there other benefits besides smoother shifting? As for not replacing the final drive I understand that reasoning completely. Did you consider doing the 2-5 gear swap from civic Si (or other appropriate trans)? Or would that not play nice with the future supercharger?
Can't wait to read your full impressions later!
MrHeeltoe: The synchros are stronger cross-sections as well, which I suspect will hold up better under-force and abuse. I did not have a particular issue with the gear spacing personally, and really did not have time to get into that given our time crunch.

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