The 'Stealth' Z - Part 6

by Steve 'Stealth' Webb

Only one graph this month, and itís not even from my car. This graph is of two different 300ZXTTís and shows the rather dramatic difference that couple of PSI increase has on horsepower. We have had many people question if you really get 90+ hp increase with the intake/exhaust/chip combo on the late modes 300ís. While neither of these cars are totally stock, this shows the difference of running 15psi vs. the stock 9.5 - 10.0psi. The car running the higher boost is actually making an estimated 410+ flywheel hp with just the three bolt-onís.

BRYAN.007         67.3F 29.41-0.51 in.Hg.   500 ft. CF=1.00 RPM/MPH=52

   Max POWER = 341.4   Max TORQUE = 385.3

   Same AS RUN 4



JAN.001           46.2F 29.36-0.24 in.Hg.   500 ft. CF=0.87 RPM/MPH=51

   Max POWER = 255.5 Max TORQUE = 254.5






About 2 days after my last article, I again put the ëStealthí on the dyno. After numerous runs carefully enriching the fuel map in very small degrees, I decided to do an experiment. I first took the whole map and richened it by 10%. Power fell off over most of the graph. Next I decided to lean it out some. Starting with the same baseline, I went the way of caution and leaned the whole map by 5%. Power and torque came up a bit. I then went to 10% (total), and power and torque increased with a peak of 30 ft/lb over the previous best published readings!! Holy hidden horsepower Batman!

Even with this leaned map, the retard amount remained the same. With the sensitivity adjusted to minimum, and no detonation audible, we had a suspicion that with the increased output of the engine, the knock sensor was starting to ëfalseí on engine noise. John at J&S (manufacturer of the unit) was very helpful and stated there would be no problem in reprogramming the unit to reduce the sensitivity a bit. Currently I am eagerly awaiting the reprogrammed unit.

The only ëbadí news is that I promised my girlfriend Julie that I would quit playing with my car on the dyno as she feels that the car had more than enough power even before I started messing with it, and to concentrate on getting the d**n thing painted. After you read the following adventure, you might agree:

My first ëtest driveí since this last tuning session occurred around the end of December. It was a late Saturday night and I was warming up the car to put it back inside. I decided to run the car up and down the parking lot just to blow the gunk out (good excuse right?). On the first run, I found first gear to be almost worthless as it would smoke the tires and bounce off the rev limiter before I could even put the throttle halfway to the floor. Easing into second gear would spin the tires as soon as boost came up, which was rather funºit never pulled like this before! On the way back towards the building during the second pass, I decided to get into it a little past º throttle in second again. This time the acceleration was even more intense as the rear end drifted out to the right. I countersteered and lifted right away as I was suddenly moving 50+ MPH and drifting towards one of the few cars left parked in the lot. As I lifted, the rear caught traction and swung quickly to the left (I was rather surprised as I have had this car sideways a LOT and it has never swung so violently before). I counter-steered again as I was heading towards the other of the few cars in the parking lot!?. In a widening pendulum effect, I went again to the right. And finally on the next swing to the left, I waited until I was aligned with the center of the lot and nailed the brakes. After a lengthy slide to a halt, I let out a rather juvenile holler, and cautiously pulled up to the shop door as about a half dozen friends looked on in disbelief, "Dude, that was the coolest thing I have seen all year!". I donít know about the ëcoolí part, but it definitely was an experience. A brief look over the car revealed part of the cause of my ëexperienceí a left rear tire with probably about 3psi of air in it between the low profile of the tire and the light weight of the car, it was hard to notice upon first glance. Time to put the car up for the night...

In recounting my tale over the phone to longtime turbo guru Corky Bell, he laughed for a moment then proceeded to give some advice, I cringed a bit as I knew I had fallen short in his eyes, "Steve, Iím a lot older than you are, and have been driving a lot longer", oh boy here it comes, I thought, "there is one thing I know, you donít want to die in a parking lot. You want to go out in something much more spectacular, but not a parking lot". After saying goodbye, I stood there a moment in shock, slow in the realization of his statement. Itís good to know I wasnít he only one.

I was fortunate enough, through some contacts in the San Antonio Alamo Motorsports, to get some flow numbers for the mitsu turbo I am using. The stock TD06-17C-8CM2 that is on the car now flows 550 CFM @15psi. The upgrade TD06H-20G-14CM2 that I want to use flows 650 CFM at the same psi. I canít wait to upgrade to this unit as we just had a 2.0L Mitsubishi Eclipse Turbo produce 413 hp at the wheels with a hybrid TD05/06-20G turbo at 24psi with some 116 octane race gas mixed in (remember, that converts to over 500HP from a ërelativelyí stock 4 cyl)!! This was a daily driver, although running at a more conservative 20 psi on the street. It kind of pissed me off at first, having a 4 cyl car best me by 100hp, but when I put that same compressor section on my Z with 6 cylindersºhmmºBut Julie, just one more dyno run, pretty please???

Iím afraid I was remiss in some thank-youís the last couple of articles. I forgot to thank my very good friend and coworker Larry for LOTS of help tuning the car as well as machining some very trick stuff for the car including our killer strut tower brace (which now sports a mirror polish thanks to Larry). And thanks to Herve Oulette for a lot of good advice over the years and helping me out of a ëjamí more than once.

I try to mention everyone involved in my endeavor as without the support and involvement of friends, club members and loved ones, there would be no point in it at all. Itís the interaction and appreciation of peers that makes things worthwhile, whether its cars, computers or stamp collecting. I hate to say it but ëMadí Mike was right (that hurts to admit), but "itís not the cars it is the people".

Well, Iím about dyno graphed out, so Iím sure everyone else is. With power at a ëmore than adequateí level right now Iím going to concentrate on finishing the car for a bit. Next month weíll look at gauges, wiring and possibly some sound insulation. And maybe a little more engine work...

Go To Part Seven
Go To Begining