Ideas for V6 power gains by Lee Brown <firstname.lastname@example.org>
A number of people have asked various questions about what they can do to improve the performance of their V6 powered Fiero's. The following was excerpted from "FIERO KITS-ALL FIRED UP!" by Herb Adams. Herb Adams has raced a variety of Fieros over the years, and currently sells some of the best suspension upgrade/racing parts for Fieros. The article was published in the September 1991 issue of Kit Car.
Even the fuel-injected V6 Fiero provides only average acceleration and top speed, so many Fiero owners want to know what they can do to increase their engine's power level. As part of the racing program, I conducted a series of power development tests to determine ways to improve the output of a Fiero V6 engine. Racing applications were at the IMSA Firestone Firehawk Events, which allow open exhausts, so most of the testing was done in this manner. The performance improvements, then, should be proportional to those found on a car with a street-legal exhaust.
Before I made any changes, the stock V6 engine was dyno-tested "as installed" with the factory's exhaust, air inlet, and electronics management systems. The Fiero V6 engine produced a peak-corrected horsepower of 110 at 4500 rpm, significantly lower than the advertised 125hp. The difference might be accounted for by differences in dynos, but the important thing for the evaluation was to establish a good baseline.
Blueprinting an engine refers to the practice of bringing all the internal specs and tolerances up to those published in the MVMA book. The process is simple, but time-consuming because the engine must be removed from the car and completely disassembled. My race team machined the block to provide .005-inches of piston fit and to produce the minimum deck height allowed. We also decked the heads to provide minimum chamber size. The bearings were fit to .0020 / .0025-inch, and all the rotating parts were precision balanced. Head porting is not allowed, but a precision valve job was done to ensure the best possible airflow through the heads. Our dyno testing showed that the blueprinting work increased peak output 3 horsepower at 4500 rpm and 17 horsepower at 5500 rpm. Less friction and better breathing help at higher engine speeds, so if you are interested in using more rpm, it would be worth the effort. Note that the test on the blueprinted engine was done with the stock intake and exhaust systems.
Open exhaust tests showed a six horsepower gain from 4500-5500 rpm. This system replaced the stock muffler and converter with a six-foot long, two-inch diameter straight pipe. Such a system is too noisy for the street, but it does show potential with an improved street-legal system. The open exhaust test was run with the stock exhaust manifolds and with the stock air inlet system.
The next stage of engine development involved a high-lift camshaft. Most stock engines will see a power increase with more valve lift. We needed to keep the idle equally smooth and the emission levels the same as the stock engine, so we didn't increase valve timing. With a higher lift cam, the valves are opened faster as well as farther, but the opening and closing point are the same as stock. A high-lift cam increased the power level by 15 horsepower at 5000 rpm and 14 horsepower at 5500 rpm.
The level of increase might be less on a car with a street legal exhaust, but the effects should still be rewarding. Installing a new camshaft in a Fiero with the V6 engine requires removing the engine, so some owners might want to switch to 1.60 rocker arms instead. The performance improvement will be slightly less, but the installation is easier.
Inspection of the Fiero exhaust manifolds showed some manufacturing related problems that severely restricted flow of exhaust gases. The manufacturer left excess metal inside the manifolds. After these edges were ground away, power increased eight horsepower at 5000 and 5500 rpm. You can eliminate these edges on your Fiero exhaust manifold with a small die grinder.
WHAT YOU SHOULD LEAVE ALONE
In searching for more power, my race crew tested the Fiero V6 engine on the dyno without the stock air cleaner and inlet system, we were surprised to find that this produced no change in power. Apparently, the Pontiac engineers did a good job on these parts because they work well, even though they look restrictive.
Another alteration that made little or no difference was cam timing. Advancing or retarding both the stock and high-lift cam resulted in power level changes of only one horsepower, more at some rpm’s and less at others. This shows that both cams are optimized at their normal position.
Testing various PROM (Programmable Read-Only Memory) computer chips in the electronic engine management system also showed that the Pontiac engineers did their job well. Different PROMS with various fuel/air ratios and timing curves showed no power improvement. We did choose a PROM with less full throttle enrichment at high rpm to help our fuel economy during the endurance races. This change gave us about five minutes more racing on a tank of fuel, so we used it for many events. The last race was run at night. The weather was cool so the air was dense. After about an hour of racing, we burned a piston from being too lean. We weren't too happy, but it showed again that the factory electronic engineers usually know what's best for the average customer.
Owners of Fiero-based kit cars can make a number of performance improvements with a relatively small investment of time and money. Using any or all the above modifications will substantially improve speed and handling. Like most things, though, the results will be proportional to how much effort and money you choose to invest.
Lee Brown – Taken off of the Internet