From racer@wasatch.comMon Jun 5 12:21:35 1995
Date: Tue, 30 May 95 08:45 MDT
From: Lee Brown <racer@wasatch.com>
To: fieros@cabana.ncsa.uiuc.edu
Subject: Ideas for V6 power gains
A number of readers of this list have ask 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 (see Peter's Fiero WEB page
for address and phone number). The article was published in the September
1991 issue of Kit Car. If you would like (and I find the time) I'll enter
the remainder of the article that covers tires, suspension and handling. (A
quick tease, Herb Adams on Fiero tires: The stock rear fenders have room for
Goodyear ZRS 255/50x16 tires on 16x9 wheels, although 255/50x16 on 16x8
wheels will also provide improvement.)
===============================================================
ENGINE ENERGIZERS
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 of 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. As indicated by the power curves and the dyno data sheet, 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 air flow through the heads. Out 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're 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 to 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 attached sketch
shows where 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.
FLANGE __x_________x__ Grinding off excess metal
|_______________| in the exhaust manifold
| | can result in a significant
| | power gain. (Problem is at
| \ points marked with x's)
\ \
__________________\xx xx\_______________________
-------------------------> Flow of exhaust Gases
______________________________________________________
COLLECTOR
FIERO V6 DYNO DATA CORRECTED HORSEPOWER
(Approximated from chart) 3500 4000 4500 5000 5500 RPM's
Ported Exhaust manifolds 109 124 135 143 139 HP
Installed High-lift cam 103 117 126 135 132 HP
Blueprinted Engine w/Open Exhaust 99 112 120 119 118 HP
Blueprinted Engine w/Stock Exhaust 96 108 113 113 111 HP
Pure Stock Engine w/Stock Exhaust 94 107 110 107 94 HP
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, and 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 rpms 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 of 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 | lee.brown@sltrib.com | "He ran out of talent half way |
| lee.brown@graphcon.com | through the corner"...from ??? |
| racer@wasatch.com | |
| Stock Cars: For people who think race cars have fenders! |
