Supercharged TR6

It’s now December 2005 and, forced by the Maine winter, the car is away until April of 2006. This year my sister Jo and her husband John have graciously allowed me to store the TR6 at their new home. Thanks guys.

The car has been gone only a week but I’m going through a bout of withdrawal. You know when you tinker with something evenings and nearly every weekend it hard to stop so suddenly. Oh well there are lots of other projects that will keep me busy for the winter. The biggest “honey do” project is already done! I also have a bunch of TBI projects to complete.

A short recap of how things are going can be summed in one word; WOW. It sure has been fun driving with all this new found power. It wasn’t that long ago that I had the feeling that this project would languish forever and never be quite right. That was until I added that big bypass valve and things really started to come together. Before the valve almost anytime I pushed the car hard the tubing between the blower and the throttle would blow off due to a huge pressure spike. It was very discouraging to have it happen on almost every run.

But now we are running boost whenever I get the hankering and I’m addicted! Running the supercharger is selectable from a little green dash mounted rocker switch. The switch is located where the choke knob once lived. For the moment I have a 0-15 psi boost gauge attached to the ash tray atop the dashboard. Alongside the boost are two trim pots that let me adjust the mixture and timing while driving. These two pots have been wonderful tuning aids but it won’t be too long and they can disappear. One winter project is to have anew dashboard ready to install come spring. The boost gauge will mounted where the useless dash light dimmer now sits.

Running without the supercharger’s electric clutch engaged is pretty much like driving a stock TR6. Maybe a tad more performance but not really noticeable. However when you hit the green switch, things really heat up! The first indication is the whirring sound of the blower. Not too loud at idle but as the tach goes up the sound goes up dramatically. Boost starts to show around 2800 rpm and peaks at red line at around 9.5 psi. Average boost is somewhere around 8psi. Unless you step on it no boost is developed at all but you still can hear the blower.

I’ve done some reading about quieting the blower and apparently because of the 2.75″ aluminum tubing the sound is amplified. Most factory installations baffle the air cleaner and “tune” the tubing. It’s taken awhile to get used to the sound but now it doesn’t bother me so this wall be a low priority issue.

Getting numbers from a G-tech accelerometer, 0-60 times are 5.13 seconds (stock TR6 is about 9.4), rear wheel horsepower is 173, and torque is 216 lbs. Not too shabby! Still some fine tuning needs to be done to the mixture and timing when under full boost and to lean things out a tad when cruising.

A problem that has persisted since converting to EFI has been the operation of the idle air control motor. This little stepper motor from a GM system is supposed to allow air into the intake to increase idle speed for warm up etc. It also follows the throttle opening action. Anyway it has never really functioned all that well. The settings are extremely critical and when incorrect cause “hunting” and a check engine light. Last year the idle air control circuit of the ECM burned up and had to be repaired by Electromotive at a cost of $150. The worst part it was over the 4th of July holiday. It still isn’t right and Electromotive has issued a firmware upgrade as well as a software update to solve the problem. I haven’t opted to install the updates as yet. The IAC motor is unplugged.

Adding boost has also presented an unexpected idle air control problem. Boost pressure forces the motor’s pintle off it’s seat raising the idle speed. After making a boosted run the idle speed would be up around 1200 rpm even with the motor disconnected. Blocking off the IAC ports has solved the problem for now. What needs to be done next season is to turn the valve around so boost tries to close it and try the Electromotive updates. The car is only used in warm weather so this is another minor problem but one that I want to resolve.

Aaron Cropley has been kind/daring enough to man the camera for a ride along video. It’s nothing fancy but crank up the sound and enjoy (it’s a big file at 20860K):

There is another video of interest that shows a quick under hood tour and video of a boost gauge taped to the steering column so it can be seen with the tachometer. I used this boost gauge clip to plot boost/rpm for tuning. The underhood tour has a blue hue that’s probably a reflection from the hood. This video will never win any awards either: