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Installing an MTI Racing Speed Shifter in a C5

Installing an MTI Racing C5/C6 6-speed super-stout transmission

Walt Thurn - August 01, 2011 09:00 AM

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The standard gearbox is dismantled, cleaned and rebuilt with the new Speed Shifter gears. First through sixth gears are replaced for road racing and first through fourth for drag applications.

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The MTI Racing technician is pointing to the Speed Shifter engagement selector. As long as power is applied the selected gear stays locked until power is released and the next gear is selected.

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This display board shows the stock factory gears on the right that are replaced by the new dog gears on the left. All of the new parts are lighter and stronger than the factory parts. However, with wider clearances the new gears are much noisier than the stock parts.

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The factory shift mechanism is larger and heavier than the replacement Speed Shifter parts. This reduces mass and heat in the transmission.

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The Speed Shifter second gear is shown on the bottom of the photo. Notice the reduced helix angle on the new gear teeth versus the factory unit on top. The new gear has fewer teeth, which makes it stronger but noisier than the GM part.

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The transmission has been rebuilt with the Speed Shifter components installed. It was painted black prior to installation into their development C6. This color helps the technicians to identify it as one of the modified transmissions.

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MTI Racing technician Louis Johnson removes the center exhaust from the silver development Corvette.

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A 24mm box end wrench and a 24mm impact are used to loosen and remove the lower rear shock tower bolt from the lower control arm.

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The ABS brake connector is disconnected and safely secured out of the way of the removal process.

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Using a 21mm open-ended wrench, the lower control arm ball joint nut is loosened, but not removed. The nut will remain in place until the ball joint is ready for removal. Louis lightly taps on the lower rear upright to loosen the ball joint that is attached to the lower control arm. Once the ball joint is loose, remove the nut and lower the control arm from the suspension upright.

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Drain the rear axle and transmission fluids prior to removal of both units. Be sure to capture all oil into a recyclable container.

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Support the transmission with a large floor jack before proceeding to the next step. Remove the four 18mm transmission mount bolts and the four 21mm cradle bolts. Once these nuts are removed the rear cradle can be lowered from the car. Once it is clear, remove it and set it aside in a safe out of the way location.

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Louis removes the two factory mufflers from the rear of the C6 Corvette. Many track day organizers require mufflers to reduce track noise.

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With the rear cradle removed from the car remove both rear axles from the rear end by prying them loose with a large flat screwdriver. Be careful to not rip the rubber axle boot. When the axles are removed from the differential, swing the axles forward as shown in the photo.

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Remove the five 15mm differential bolts that secure the unit to the transmission. Once the differential bolts are removed, move the unit to the rear of the car and slide it off the transmission main shaft. Set it aside for reinstallation.

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Louis lowers the Corvette and removes the MTI shifter assembly. This procedure can be done at the beginning of the removal or at this stage of the project. It is up to the technician.

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Remove all eight of the 13mm transmission bolts that are attached to the Corvette’s torque tube.

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Louis has attached two safety straps to the transmission prior to removal. MTI Racing technician Kevin Kirby assisted Louis when the transmission was removed from the car.

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Kevin carefully removes the shift rod from the hole in the torque tube as Louis removes the transmission from the Corvette. The old transmission will be rebuilt with all new parts and be used for a future project.

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The removal process was reversed and the new “black” MTI Racing Speed Shifter transmission is installed to the C6 development Corvette.

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Unless you live near an Autobahn in Germany, racing your Corvette on the street is almost impossible as well as illegal. This is one of the main reasons that track days have grown in popularity around the country.

These sanctioned events allow you to drive your car to the best of your ability in a safe environment. Certified instructors are usually on hand to provide you with instruction to keep you safe and maximize your track experience.

Reese Cox, owner of MTI Racing in Marietta, Georgia, is a former professional road racer. He still enjoys driving fast Corvettes and providing track day support to his customers. This includes providing driving instruction and mechanical support at a track day event. When he is at a track day, he tests various MTI Racing products on two Corvette C6 development cars. As his customers grow more experienced they want to go faster. Reece tests his new “go fast” products before making them available for sale. His most recent development project is the subject of this story.

 

Time is Speed

Sequential transmissions allow drivers to shift up or down without using the clutch. The transmission is electronically connected into the racecar’s ECM (electronic control module). This connection allows a momentary pause in the engine as the next gear is selected. Professional GT teams that switch to sequential gearboxes usually improve their lap times by two to three seconds. Unfortunately, they cost teams $20,000 to $30,000 each to purchase for their racecars.

Few weekend track day Corvette owners are willing to pay this high price to install them into their cars. Reese has been on the lookout for a less expensive alternative and finally he found one that he has been testing. He has named it the MTI Racing Speed Shifter transmission. On the outside it looks like a stock Tremec six-speed transmission. However, an internal modification to the gears and synchronizers converts it into a dog ring or Speed Shifter transmission. The standard Corvette six-speed gears and synchronizers are removed and replaced with non-synchronized heavy-duty gears and associated parts. This includes new first, second, third, fourth, fifth and sixth dog gears. For drag race applications only first through fourth gear sets are replaced.

Each dog gear features a unique back cut, which allows it to engage the shift slider and stay in that gear. The shift slider is much lighter and stronger than the factory unit. It also has additional clearance built into it to reduce friction. The downside is it is much noisier, which makes it unsuitable for street driving. Each gear features straighter teeth that are spaced further apart from each other than stock gears. This also increases transmission noise, but provides a more robust gear that will take heavier punishment.

The rotational forces of the reverse-cut dog gear keeps it locked into the shift slider. A quick release of the throttle removes that force from the dog gear and allows the driver to shift without using the clutch. Upshifts are easier than downshifts with this transmission. An accomplished driver can up and downshift with ease, however less experienced drivers should use the clutch for their downshifts.

 

Track Tested

MTI Racing has installed one of these transmissions into their development 788 rwhp black Z06 Corvette. This car set the production Corvette standing Texas mile with a speed of 206.08 mph. In addition, the Z06 has piled up quite a few racing laps at Road Atlanta. Lap times have improved nearly two seconds with this MTI Speed Shifter transmission at this twisty Georgia track.

Reese invited us to visit his shop while his crew installed a second dog box into their silver/black 660 rwhp 500 cubic inch LS small-block C6. Neither one of these Corvettes are ever driven on the street. They both feature gutted interiors and a full roll cage with fire suppression systems. The transmission project took seven hours to remove and replace both units. After the installation was completed we trailered the C6 to Road Atlanta and Reese quickly laid down some hot laps. Each Corvette is fitted with a data acquisition system and it was easy to chart lap time improvements with the Speed Shift dog ring transmission.

The results were amazing: shift times fell by .04 of a second. Reese was able to accelerate to the next corner more quickly and reach higher speeds faster. The data acquisition showed shift times of .07 on the stock transmission and .03 seconds on the Speed Shifter.

While .04 seconds might not seem like much, if you make 18 shifts per lap it pays off with every shift made. MTI Racing has monitored transmission temperatures during all of the track tests and no abnormal readings have been found. Upon disassembly and inspection, no wear has been found on any of the new parts.

If you are a serious track day C5 or C6 Corvette driver, we think you will be happy installing MTI Racing’s Speed Shifter Transmission. The track day Speed Shifter unit retails for $7,495, plus installation and a good working Corvette Tremec six-speed transmission to exchange; call for pricing on the drag race version.

At half the price and twice the fun, the Speed Shifter is hard to beat!

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