Part III: Zex Perimeter Plate Nitrous System tuning and dyno results
In Major League Baseball, the idea of stepping up to the plate is a big commitment. Once you enter the batter’s box, you’re at the mercy of the pitcher with thousands of fans’ eyes fixed on you. A lot can go wrong, but when all goes right, the payoff is incredible.
When we installed the new Zex Perimeter Plate Nitrous system, the analogy went a little deeper than first considered. Everyone in the office was curious to see what could be done with it. Some were banking on modest gains; others had hopes for a tremendous power increase.
In our first installment, we plumbed the Zex LS Series Perimeter Plate Nitrous System on a ’99 Trans Am with a T56. The car already had a handful of bolt-ons and a diminutive-by-today’s-standards T1 cam (221/221-degrees duration with 0.558/0.558-inch lift on a 112-degree LSA). We then wired the Zex system, and upgraded the fuel pump to a Racetronix in-tank, 255-lph pump and hotwire kit. We were ready to hit the dyno.
The chassis dyno is an indispensible...
The chassis dyno is an indispensible tool for tuning. We strapped this ’99 Trans Am to our in-house Dynojet and plugged the wideband into the rear O2 sensor for the most accurate air/fuel ratio readings.
As we stepped up to the plate, all eyes were on us to make a good number. Unfortunately, things weren’t going according to plan. With the T/A strapped to the Dynojet, we soon learned from the wideband A/F meter that the engine was running a 15:1 air/fuel ratio—very lean, even for naturally aspirated. We immediately corrected it to 13:1, made a pull, and achieved the horsepower number we were looking for. However, something was still off. We knew we needed a tuner to dial-in the car correctly, but with deadlines looming, we pushed on.
Unfortunately, the perfect storm had amassed in the FAST 90mm intake manifold. A fuel puddle had accumulated in the back of the manifold, which is common and clears out quickly and harmlessly in a properly running engine. A telltale sign that it’s there is the motor idling high for a few seconds. In our case, however, the ignition system was not up to 100-percent, and we later found out that our spark plug wires were backing off the plugs. The wires were just worn and not “clicking” into place correctly.
When you combine the circumstances of a weak ignition system, fuel in the intake, and the fact that we didn’t run the engine long enough prior to the next pull to evacuate the excess fuel in the intake, it resulted in a nitrous backfire into the intake manifold, which broke it.
Our baseline pull at 26-degrees...
Our baseline pull at 26-degrees timing with no nitrous netted 346 rwhp and 361 lb-ft of torque, but we needed to add fuel before spraying anything. Greg richened the air/fuel from 13.80 to 13.21, ideal for a normally aspirated setup, and the engine produced 351 rwhp and 354 lb-ft of torque.
Bruised, but not beaten, we dusted ourselves off and went back to the drawing board—Nitrous Safety 101. We determined where we went wrong and made corrections. First, we replaced the plug wires. Second, we converted the car to run an LS2 intake—we didn’t have a spare FAST intake lying around. Third, we installed a replacement MAF—ours was no longer reading. Finally, we performed a compression check and confirmed the engine to be in great shape.
Thankfully, Greg Lovell from AntiVenom in Seffner, Florida, was able to come to our Tech Center and help us start from scratch with the T/A’s tuning using HP Tuners VCM Suite. He reduced timing and adjusted our fuel curve until he had a safe tune that still made power. Greg answered a few questions about nitrous systems and tuning to help give you a better idea of where to begin with your Pontiac.
HPP: What do you think everyone should do before installing nitrous on a higher mileage car?
GL: You should do a compression test and make sure there is good even pressure in all cylinders. This means the rings are fine and the engine’s top end is healthy. Make sure the intake is sealed correctly and the ignition system is working properly because it could create a whole list of problems if it’s not. Finally, and most importantly, make sure your fuel system is up to snuff. Delivering the proper amount of fuel is paramount with any engine modification, and keeping up with the fuel demands to compensate for 100 or more horsepower of nitrous is a must.
[1] Nitrous backfires can...
[1] Nitrous backfires can be unfriendly to the newer composite intakes. This was caused by a fuel puddle in the intake, which we didn’t clear out by letting the engine run long enough before our next pull. To prevent this sort of thing from happening to you, never spray below 3,000 rpm, and never make back-to-back pulls without letting the engine settle back down to a regular idle.
[2] Zex only includes eight...
[2] Zex only includes eight sets of nitrous and fuel jets, so we got a bag of extra Zex-specific jets from Sam at Coastal Dyno in Tampa just in case. We ended up using a 0.030 fuel jet in place of the supplied 0.028 jet for our 100-shot. This left the mixture safer and allowed us to run a tune that didn’t sacrifice naturally aspirated performance.
[3] Greg looks for knock retard...
[3] Greg looks for knock retard from our pulls and doesn’t find any.
[4] Greg explores a high-octane...
[4] Greg explores a high-octane timing table. It shows the total timing on the big end; the color differences indicate changes from the factory timing.
[5] This graph shows a commanded...
[5] This graph shows a commanded air/fuel relative to coolant temperature with a multiplication factor of 14.7. This is a great feature of the factory LS1 ECU.