The 'Stealth' Z - Part 5

by Steve 'Stealth' Webb

More dyno graphs... Picking up from last month, we found a peak increase of 60 ft/lbs of torque and 44 HP in the mid range. This was done with an increase of about 1 psi in the lower rpm range and some tuning on the DFI. On the road this difference was immediately noticeable as I was sideways in 2nd gear at least 3 times in the first 5 minutes of driving!

That week I was invited to the Mitsubishi Owners Club (connected with the Alamo Autosports in San Antonio) drag race in Temple Texas. I wasnít use to the extra torque and ended up sideways all the way through first, second and the start of third! Definitely not the way to post fast º mile times! Granted this was on smaller 245/45/17 street tires versus the 275/40/17 BFG R1ís I usually run. The run back from the track (a good 2 ‡ hours) was probably the most fun though. As 5th gear is now a STRONG passing gear even at 2000 rpm (60 mph)! Now I know how Ronnie feels.

Back on the dyno, even after lots of tuning the top end was still dropping off. I finally put a pressure gauge on the fuel rail and found that past 4800 rpm, the pressure dropped from 60 psi to around 30 psi. Time to modify again. Now onto the graphs:

The first graph is a comparison of my very first run (basically how Iíve had the car for the last 2 years), and currently after the above tuning and a second session of dyno tuning 3 weeks later. This second session of tuning, in conjunction with the first, resulted in a dramatic increase in torque and horsepower starting at 1600 rpm and peaking at a 91 ft/lb and 58 HP gain at 3600 rpm! This was accomplished by raising the boost with a VBC (variable boost controller, which is a bleed type boost control), to 7 psi initial and boost creeping to 12 psi by 4800 rpm. A fair amount of DFI experimentation went into this as well. Working from this info, I definitely plan to invest in a Profect electronic boost controller as soon as the x-mas season is over, and quit messing around with the VBC. The top end fuel starvation was finally fixed by putting another FI pump (an extra 280ZX pump) in series with my high pressure pump. This was not my original intention, as I still plan to install my beloved ësurge tankí when time permits.

Graph 1 - 34Kb

First run compared to current configuration. Huge increase in midrange with a little more top end to boot. And yes, "077" is the 77th run made with the car.

The second graph is my latest run compared to Ronnieís from last month (his impressive torque peak was a good goal). Itís amazing what a bit of tuning and a couple more psi will do. I still havenít driven this latest version on the street, but I canít wait. In Ronnieís ëdefenseí, he found a faulty wastegate actuator that was allowing the boost to drop off at higher rpmís. He has also installed another turbo engine in his car (a good turbo block and his first non-ëjunkyardí engine) and is designing a different fuel enrichment system utilizing a second ëZí FI brain and 6 more injectors!

Graph 2 - 32Kb

Current configuration compared to Ronnie's run from the last month. Ronnie is working on a new fuel management system which he feels will net him some big increases from this run.
On the following page is a picture of the dyno itself with some kind of strange looking American built sports car on it. I think it called a Viper GTS Coupe or something... Just for fun I included the dyno graphs made during that series of runs. Sorry, but Iím not about to embarrass myself and compare the ëStealthí to that monster! 400 ft/lb of torque at the wheels at 1800 rpm! Kindaí gives me a new respect for some American machinery.

Many people have inquired as to what the Dynojet really looked like. Well, here is is with a sports car on it similar in basic shape to the Z... Ok, maybe not... 29KB


Dyno Graph! - 10Kb

Hoping to break the 400 HP level, Brice and I worked hard during the last series of runs in search of power. We managed over 400 ft/lb of torque, but an estimated 384 horsepower was the best we could do (this is all on 93 octane pump gas). I think the limiting factor is partially in the turbo and partially in the intake and exhaust system. The intake upgrade is half built and will be installed next and dynoíed. The special exhaust tubing is on order and will be installed soon along with a carbon fiber muffler. I am making a point to document things in a step by step manner to provide the most useful and meaningful information possible.

A very good friend convinced me to follow my search for horsepower utilizing a totally stock L28 block. With that in mind, I am going to proceed along that line and add and modify as many external components as possible in search of power. Stay tuned...

[Again, thanks to Brice Yingling of Alamo Autosports
for his expertise and use of his Dynojet chassis dyno]

Go To Part Six
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