The 'Stealth' Z - Part 9

by Steve 'Stealth' Webb

The 'Stealth Z' Part IX

      To answer the first question; No, I didn't get the 'Stealth' out to the import races on April 5th, so I don't have any quarter mile time or horsepower figures for the latest setup. We'll get to the new/new engine in a minute.

      I spent the last month or so dialing in the Haltec F5 additional injector controller. I installed it on 'The Grape' (the '77 280Z). The difference in horsepower and response was nothing short of dramatic. With everything the same, just installing the F5 produced over 1 PSI more boost. The enrichment is actually set to activate while I'm still in vacuum, as this really seems to helps boost response and horsepower down low.

      The F5 only has controls for boost onset and richness, while the Greddy Rebic III and the HKS AIC also have 'RPM onset' controls. The F5 is an excellent unit for the money, but the RPM feature would allow even finer adjustment ability.

      The 'super H' compressor wheel arrived several weeks ago, and I can't wait to install it. The difference in size and diameter is amazing.

      Now to the 'Stealth'. I wasn't planning to build my 'Killer Motor' until sometime late summer or fall, but current circumstances dictated otherwise. The overall goal is to have a very dependable unit with prodigous power output potential. As I found from experience, I was continuously bouncing off of the rev limiter @ 7,000 RPM. Wanting to up the power by at least 25% to 50%, I expect the situation to be even worse. Knowing this, I plan for the upper usable rpm to be 7,400 RPM, redline set at 7,500 RPM and the motor balanced to 8,000 RPM.

      Graph 1 gives some insight to my ideas. Power currently drops off past 6,000 RPM while using the '17C' turbo. The Eclipse running the '20G' (although a 4 valve motor with 8psi more boost) shows the greater amount of air it can flow, so with a little VE (Volumetric Efficiency) improvement and my '20G', hopefully I can get close to that. I know this sounds like comparing apples and oranges with 6 cyl vs. 4 cyl, but with turbos, (generally speaking) it takes a certain amount of air to make a certain amount of horsepower, regardless of cylinder count.

      Starting from the top, I will be using the P90 (turbo) head and installing larger stainless valves. Upgraded valve springs and lightweight retainers will be a necessity due to the RPM expectations. It will also receive a mild 'street' port and polish. I plan to use the stock cam at this time, but with the addition of an adjustable cam sprocket.

      The lower-end will receive either JE or Arias forged pistons, oversized a 'bit', on stock shot-peened rods. To keep reliability, the crankshaft will retain stock stroke and will keep the full counterweights. The crank will be doweled for the flywheel though.

      The exhaust manifold will be ported and tapped for pressure gauges to measure backpressure. The stock manifold works so well I hope to keep it, but the pressure ratio (intake vs. exhaust) will decide how long I hold on to it.

      The intake manifold will remain the same for a while. To make the high-end hp that I plan to eventually produce, I believe the manifold will need a larger plenum and shorter runners. A little dyno time will tell. As expected, all work will be done @ Alamo Autosports in Arlington.

Go To Begining