Bill's Isuzuperformance; Dyno Testing and Comparison of Headers for 90-91 1.6 liter DOHC Isuzu and Geo Storm Cars

Background

Discussion about exhaust headers for the 1990-93 Geo Storm, Isuzu Impulse, Isuzu Stylus, and Asuna Sunfire has been almost as spirited and heated as discussion of cat back exhaust systems for those same cars, possibly more so. Debate over design, build and material quality, fit, finish, price, and just about any other aspect possible.
We decided to dyno test and compare exhaust headers for the 1990-91 1.6 liter DOHC engine along with our dyno testing and comparison of cat back exhaust systems for 1990-93 Isuzu and Storm cars.
As discussed before, we came to an agreement with Mustang Muscle Performance and Dyno Service in High Ridge, Missouri, to use their DynoJet Dynamometer to measure performance.

The headers to be tested were the stock manifold and down pipe, the Paceseter header, and the Stan's Headers brand header, all paired with the best performing exhaust system from our previous testing, the Stan's Headers cat back exhaust system. The vehicle used in the testing was a 1991 Isuzu Stylus XS 1.6 liter DOHC, with a fresh engine rebuild to stock specification with all OEM Isuzu parts ordered directly from Isuzu, a Mueller Fabricators aluminum flywheel, a Unorthodox Racing underdrive pulley, and a Isuzuperformance cold air intake system.

Dyno testing involves parking the vehicle with the drive wheels and tires on the rollers of the dynamometer and then straping the car down to the ground so that it will stay on those rollers while the drive wheels and tires spin them.
An inductive electrical current sensor is placed around one of the ignition wires so that the machine can measure information on power produced at each specific engine speed.
The settings of the machine are adjusted to match the gear ratios of transmission of the vehicle by correcting engine speed and roller speed to match.
Once the machinery is ready, the vehicle is accelerated through first, second, and third gears, to fourth gear, and the engine speed is held at 2,000 RPM by the opperator. The opperator then hits a button to begin the measurement and presses the accelerator pedal to the floor. Engine power is measured by the machinery at wide open throttle from or just above 2,000 RPM, all the way just short of the rev limiter, or 7,600 RPM in this case.
The machinery measures the air temperature, humidity, and barometric pressure, so that it can correct the results for the atmospheric conditions. This correects the results to SAE, which is what we have used in all of our comparisons.
In order to avoid any possible impropriety, as we are the exclusive distributor of one of the products being tested, all of the testing was conducted by Daryl, the owner of Mustang Muscle, or Matt, his son. They both have many years experience running dynamometers and had no intrest in what the results of the testing were.

For our comparison, we sellected the best results obtained from each session with the exhaust in each configuration. We must stress that we are comparing the best results obtained from each product to the best results obtained from the other products in the comparison. Results for comparison were chosen specifically so that each product's best performance was being compared to every other product's best performance. We do have copies of the results we did not use if anyone wishes to verify that we did in fact compare the best results to the best results in all cases.

Baseline Numbers

As mentioned before, our baseline numbers were taken of the 1991 Isuzu Stylus XS with stock exhaust manifold, stock down pipe, stock catalytic converter, and the Stan's Headers brand cat back exhaust system.
The original equipment manifold and down pipe is of Tri-Y design. This means that the four cylinders gather in pairs to two and then those two gather into one at a final collector. The primary passages through the manifold would appear to be between six and seven inches long and 1 1/4 inches wide. The secondaries are 15 inches long and 1 1/2 inches in diameter and merge in the collector pipe to a single 2 inch pipe. The collector pipe is attached to the B pipe in front of the catalytic converter by a spring loaded ball in socket type joint.
The O2 sensor installs in the manifold in a openning cut between where the primaries merge into two at the secondaries. This allows the sensor to sample exhaust gas from each of the four cylinders.

Performance On The Dyno

Baseline performance was measured at a peak horsepower of 105.2 and a peak torque of 102.0 ft-lb.

The Pacesetter Header

Our first product to test was the Pacesetter brand header part number 70-1011 for the 1990-91 Geo Storm GSi, Isuzu Impulse XS, and Isuzu Stylus XS, with 1.6 liter DOHC engine. Pacesetter has decided to design this header to fit both the 1.6 liter DOHC engine as well as the taller 1.8 liter DOHC engine of the 1992-93 model cars. Some problems with this will be discussed later. The header was ordered through Pacesetter's Midwest distributor and was drop shipped from the manufacturer, directly to us. Delivery took over three weeks, but not nearly as long as the cat back exhaust system.




Packaging

The Pacesetter header arrived loose, in a large box. There was no wrapping, no padding, and no packaging. The box was quite a bit larger than the parts themselves, and the parts had quite obviously banged around against themselves quite a bit in shipment.



The Product


The Pacesetter header consists of two pieces, a upper piece which bolts to the head of the engine and consists of four pipes collecting to one under the engine, and a collector pipe that goes between the upper piece under the engine, and the original equipment B in front of the catalytic converter. There was no hardware or gaskets included with this header.

The upper piece is a 4 into 1 (4-1) design header, meaning that all four primary pipes are brought together at one point, or one collector. The upper piece consists of a 3/8 inch thick, flame cut header flange with 1.4 inch diameter primary pipes. The primary pipes for cylinders 2 and 3 turn down closest to the engine while the primary pipes for cylinders 1 and 4 turn in and then down on the outside of the primary pipes for cylinders 2 and 3. The primary pipes for cylinders 2 and 3 are 23 inches in length, while the primary pipes for cylinders 1 and 4 are 29 inches in length. All four primary pipes merge at a single collector which connects to the collector pipe with a pipe clamp (not included).

The inside of the collector is very sloppily welded, with large globs of weld, and very poorly contoured which undoubtedly causes a great deal of exhaust turbulence.

The EGR fitting consists of a 1/4 inch thick flame cut flange attached to the end of a pipe, welded to the number three primary pipe. There is no brace or bracket to steady or reinforce the EGR pipe.

The O2 sensor fitting is welded to the number one primary pipe. That fitting is quite deep and holds the sensor well back from the exhaust gas flow through the primary pipe. In addition, the end of the fitting is drilled to only 7/16 inch while the head of the O2 sensor is 9/16 inch in diameter. This leaves the O2 sensor completely shrouded and isolated from the exhaust flow that it is supposed to be measuring. It is doubtable that the sensor receives sufficient exhaust gas flow to accurately measure the air/fuel mixture of the engine, even on the one cylinder that it is sampling from.
The collector pipe is 2 inch in diameter, with the end expanded to slide over the collector, and the other end terminates in a 1/4 inch thick, slotted two bolt flange with a flat end, which is to be attached to the original equipment B pipe in front of the catalytic converter. That B pipe is reused with this header.

The pipe is 2 inch in diameter and has been painted black. As there is no attempt to pad or protect the paint finish in shipment, the header and pipe arrive chipped up, with surface rust showing through wherever the paint finish has been scratched or marred.
The pipe itself measures .062 inches in thickness, which makes this 16 gauge pipe.

The parts are clearly marked as "Made In MEXICO". Pacesetter offers their headers with "Armor Coat" ceramic coating by Jethot, which consists of a single coat of the low temp aluminum coating rated to 1,200 degrees. The low temp coating has been noted by some customers to discolor from being overheated because the exhaust gas temperature of the Isuzu engines is in excess of 1,500 degrees. Flaking and bubbling of the coating and rust out from the underside has also been reported.



Warranty

There was no warranty information with this product. However, it is assumed to have the same warranty as the Pacesetter exhaust system, which came with a rather long winded warranty paper, indicating a three year limited warranty, repair or replacement at Pacesetter's option in the first year, and replaced upon payment of a prorated fee by the customer in the second and third years (they will sell the customer another exhaust system to replace the failed unit).
The warranty specifically excludes burnout, blow out, surface rust, rust through, paint, plating, or any of the hardware. The most conspicuous part is that they exclude rust, blow out, or burn out, the very reasons a header would fail, therefore, they have eliminated any possible cause of header failure from their warranty coverage.



Installation

There are no written instructions, but installing a header is fairly straight forward. Remove the original collector pipe and manifold and then bolt the new pieces in place.
We have found that removing the radiator and unbolting the power steering pump to slide it to the side, allows a lot of work space on the front of the engine and makes the job a whole lot easier as far as clearance to manuver a header into place.

Installing the Pacesetter header on the test vehicle was an absolute nightmare.

• The header included no gaskets and an exhaust gasket had to be purchased from the dealership parts department.
• We knew before trying to install this header that the bolt holes cut into the header flange were not lined up correctly because we test fitted it to an engine on an engine stand. We had to pull all but two of the exhaust studs out of that engine to get the header onto that engine, so we knew right away that we would have to grind the holes so they would line up with the studs. We were also lucky to have a spare head and access to a machine shop with a die grinder so we could grind the holes and repeatedly test fit the header to a head to get those holes to line up. The average customer without this type of facility might very well find themselves driving back and forth from a machine shop many times to have those holes ground and reground until the header slid onto the exhaust studs in the head of their engine. It took a little under an hour of labor with an air powered die grinder and a carbide bit to grind those holes enough that the header would fit over the exhaust studs on the engine.
  
  
• There were no nuts or bolts to attach the EGR pipe to the EGR fitting of the header. The manifold has threaded holes and uses metric bolts. The Pacesetter header has slotted holes with no threads. Two 5/16 inch bolts and nuts had to be purchased to attach the pie to the header.
• The O2 sensor would not fit into the sensor fitting on the header because the end of the sensor was bottoming out in the fitting before the threads would even meet. The fitting had to be drilled out so that the sensor could be attached to the header.
There was not EGR fitting gasket and one had to be purchased from the dealership parts department.
• The EGR fitting was positioned incorrectly and would not allow the EGR pipe support bracket above the transmission to be reattached. This pretty obviously put the EGR pipe in a strained position where it would likely break, or break the unsupported fitting away from the header.
• There was no 2 inch U type exhaust clamp to attach the upper header assembly to the collector pipe, and one had to be purchased to put it together.
• The collector pipe would not fit between the upper assembly and the B pipe because it was one inch too long. Correcting this required the use of a chop saw, to shorten the end of the pipe that is expanded to slip over the end of the upper assembly. It might be recommended that a customer make sure they have access to a pipe expander or a muffler shop with a pipe expander so that after cutting most of the expanded end off of that pipe, they can expand the rest of the pipe enough to slide over the end of the upper assembly.
• The collector pipe was then found to be bent incorrectly, with a 15 degree error in the angle of the slip joint to slide onto the end of the upper assembly when the two bolt flange was bolted onto the B pipe. This was corrected again with the chop saw by cutting the middle of the collector pipe and using a exhaust pipe union repair section and two 2 inch U type exhaust clamps to rotate the positon of the pipe and then clamp the two pieces back together.
  
  
• When the collector pipe was attached to the OEM B pipe, it would not seal, and there was no gasket provided with the header. A donut type gasket had to be purchased from an auto parts store to put the header on the car, and even then the OEM shoulder bolts and tension springs would not hold the joint tight enough to keep it from leaking, and two additional fine thread metric bolts had to be putchased to attach the two pipes together with enough seal to eliminate most of the leak.

Needless to say, if there were instructions with the Pacesetter header, they would need to indicate that a die grinder and a chop saw are required for installation of the product on the car.



Cost

The Pacesetter Header Itself:
Jobber Wholesale Cost: $123.47
Manufacturer's Retail Price: $138.99
Manufacturer's List Price: $159.95


The Additional Parts Required For Installation:
One Exhaust Gasket: $13.50
One EGR Pipe Gasket: $6.98
Two 5/16 Nuts and Bolts, Four Flat Washers, and Two Lock Washers: $.84
Three 2 inch U Type Exhaust Clamps: $3.27
One 2 inch Exhaust Pipe Union: $1.49
One Ball In Socket Joint Donut Gasket: 15.00
Teo Fine Thread Metric Bolts For Ball Joint: $2.50
One Hour Labor Die Grinding On Flange: ?
Labor Expanding Collecor Pipe Inlet After Cutting: ?


Total Expected Cost With Parts Required For Installation:
Retail + Parts: $182.57 Excluding Tax, Excluding Machine Labor Costs




Driving Around With It On The Car

The formerly deep exhaust tone of the performance exhaust with the stock manifold and down pipe was turned harsh and annoying by changing from the stock manifold and down pipe to the Pacesetter header. The exhasut note was more buzzy and unpleasant.
There was a noticable increase in vibration through the steering wheel and the unibody frame of the car with the Pacesetter header, probably due to the lack of any sort of woven flex joint between the header and the catalytic converter, which would dampen engine vibration and keep that vibration isolated from the rest of the car.

The paint on the Pacesetter header began burning immediately once the car was started, emitting heavy smoke. With the hood closed, the smoke came out the edges of the hood thick enough that the car looked like it had overheated and blown the radiator cap. The stench of the burning paint was uncomfortable, even inside the car, and all of the paint around the upper half of the upper assembly was turned to grey ash by the time the car was driven the four or five miles from our location to Muscle Mustang for dyno testing.

With the Pacesetter header, the car felt like it really lacked in power below 3,000 RPM, with some gain at mid range, and the noise seemed to make the car appear faster at higher RPM, but the dyno would tell a different story.



Performance on the Dyno

The performance of the Pacesetter header meassured at a peak horsepower of 102.6 and a peak torque of 104.1. This is a loss of 2.6 peak HP.
We were rather surprised that the header posted a net peak loss of 2.6 horsepower against the stock manifold and down pipe. More surprising still was that the loss of power by the Pacesetter header got worse after the peak and lost a consistent five or more horsepower everywhere above 7,000 RPM.
The Pacesetter header showed an average loss of 1.0 HP and .6 ft-lb of torque from 2,200 RPM all the way through 7,600 RPM. This represents a huge loss in power output using this header.
The power appears to follow very close or just a hair above the performance of the stock manifold and down pipe until 4,400 RPM, where power trails off drastically by comparison, through the entire rest of the RPM range. That loss grows from a 1 HP loss at 5,600 RPM, 2 HP loss at 6,000 RPM, 3 HP loss at 6,700 RPM, 4 HP loss at 6,800 RPM, 5 HP loss at 7,100 RPM, maxing out to an almost 5 1/2 HP loss at maximum engine speed.

It is rather common knoledge that 4 into 1 headers tune for a single, sharp peak in power at a single point in the engine RPM range. It is also common for manufacturers to tune headers, by selecting a combination of pipe diameter and length, to produce most of their power gain high in the RPM range, so that their product will result in an increase in peak horsepower. Because 4 into 1 headers produce very sharp peaks and manufacturers usually tune for high RPM power, it is generally assumed that 4 into 1 headers produce most of their power at engine redline, sacrificing mid and low range power, well above the area that would enhance driveability and acceleration through lower engine speeds to get to that peak horsepower and high RPM power gain.
Pacesetter appears to have attempted to get around this problem by intentionally selecting long lengths for their 4 into 1 header, in an attempt to pick up mid and low range power. The results as indicated by the dyno, show that they did not accomplish this, and that their low and midrange power remains very close to the stock performance level, while they loose huge amounts of power everywhere past the point the tach needle goes vertical.
The dyno graph shows several other interesting things. Earlier, in the product description, it was mentioned that the 4 into 1 header with 1.4 inch diameter primary pipes, two being 23 inches in length while the other two are 29 inches in length. This means that two of the cylinders are tuned to make peak power at one engine speed, while the other two are tuned to make peak power at a totally different engine speed. Using the primary pipe measurements and engine displacement with the header pipe length software at the Automotive Programs by Bowling and Grippo Website, a little manipulation with the "maximum engine speed" field, which is actually the desired point for peak power output, the peak power points of the two pairs of runners of the Pacesetter header can be determined. The inner two primary pipes are tuned for peak piwer at 4,100 RPM while the outer two primaries are tuned for peak power at 3,200 RPM. Looking at the graph shows low to mid range power of the Pacesetter header almost identical to the stock manifold and down pipe, except for two anomalous little spikes in power, right at 3,300 and 3,900 RPM, with immediate drop offs back to the stock performance directly on each side of those little spikes, which, of course, are the points that the two different pairs of primary runners are tuned to. It is interesting that the Bowling and Grippo program was able to predict where those spikes would occur, within only 200 RPM by using only the pipe diameter and length along with the engine displacement to calculate.
The improper tuning of the primary pipes causes a splitting of the power into two, seperate spikes, and had those primary pipes been made all the same length, the header might very well have produced performance curve with a larger peak and less drop on each side of that peak, for at least some noticable gain in low to midrange power before dropping off at higher engine speeds.
The problem with these two little spikes and the understanding that two cylinders are being tuned to make power at a different point in the RPM range than the two cylinders they are nest to, is that this causes the engine to run out of balance, with higher stresses and different cylinder pressures in the various cylinders depending on where in the RPM range the engine is opperating. And during normal engine opperation, the engine speed passes these two points in almost every gear. This causes stress to the pistons, rods, and crank shaft because two cylinders are always fighting the other two cylinders, and they are never working together.
This is a serious reliability consideration drawing concern to the life of the various bearings and seals of the engine and how running the engine out of balance will shorten the life expectancy of those and other parts.

The Stan's Headers Brand Header

This is the exhaust header we have manufactured for the Isuzu cars.




Packaging

Although we did not ship this product to ourselves for testing, we do go to a great deal more effort to keep the Stan's system from being damaged in shipment. The box is sized to match the product. Each piece is wrapped in either bubble wrap or corrugated card board. The insides of the box walls and ends are lined with additional layers of currugated cardboard as the product is being placed into the box, and any extra space is taken up with more cardboard or packing material to keep the pieces packed tightly and prevent any damage from pieces hitting each other or from the pieces breaking out the sides of the box itself.



The Product


The Stan's Headers brand header consists of two pieces, an upper piece which bolts to the head of the engine and consists of four pipes which pair off to two pipes which collect together under the engine, and a collector pipe which connects between the upper assembly and bolts directly to the front of the catalytic converter. Hardware included is one .040 inch thick dead soft copper exhaust gasket, one .040 inch thick dead soft copper EGR fitting gasket, one four bolt catalytic converter gasket, two 5/15 inch bolts and nuts, four flat washers, and two lock washers for the to connect the EGR pipe to the header, and two 3/8 inch bolts and nuts, four flat washers, and two lock washers to connect the upper assembly to the collector pipe.

The upper assembly is a Tri-Y design header, meaning that the four primary pipes are brought together in pairs to two larger pipes, and that pair of secondary pipes is then brought together again at the final collector. The upper assembly consists of a 3/8 inch thick, water jet cut flange with 1 1/2 inch diameter primary pipes. The primary pipes are 10 5/8 inches long. The secondary pipes are 2 inches in diameter and are 10 1/2 inches long. The secondary pipes merge at the final collector, which is 2 1/2 inches in outlet diameter, and the header terminates in a ball in socket connection where it attached to the collector pipe.

The EGR fitting consists of a 1/4 inch thick waterjet cut flange welded to the end of a pipe that is welded to the number four primary pipe. The EGR fitting is braced with a 3/4 inch wide, 1/8 inch thick, welded bracket between the fitting pipe and the header flange below the number four primary pipe.

The front O2 sensor fitting is at the collector position where the number 2 and 3 primary pipes merge to their secondary pipe. The O2 fitting is shallow, exposing the end of the sensor to the full flow of the exhaust gasses from the number 2 and 3 cylinders.

The collector pipe is 2 1/2 inch in diameter and begins at the ball in socket joint, passing beneath the engine and through a woven, stainless steel flexible joint, terminating at a four bolt flange that bolts to the front of the catalytic converter.

The hangers to secure the collector pipe beneath the car are just in front of the flexible joint.

There is a second O2 sensor just behind the ball in socket joint at the beginning of the collector pipe. This fitting is positioned after the final collector so that it can sample from all four cylinders. This fitting is also shallow, exposing the end of the sensor to the full flow of the exhaust for accurate metering of air/fuel ratio.
The pipe itself measures .082 inches thick, making it 14 gauge. This pipe is 33%, or one third thicker than the pipe used on the Pacesetter header, adding greatly to the durability and expected lifespan of the Stan's product over the Pacesetter product.
We don't put any stickers on the Stan's Headers products, but they are made in Auburn, Washington, USA.
The Stan's Headers brand header is available in ceramic coated finish. The ceramic coating is Techline brand Insulcoat 2,400 degree coating inside and out with Cermakrome, 1,400 degree, aluminum colored coating as a finish coat on the outside, applied in multiple coats over a grit blasted preparation of the header to ensure good adhesion. The pieces receive four exterior coats and three interior coats to protect the pipe against oxidation and keep the exhaust heat from radiating off of the pipe.



Warranty

We have no specified warranty on the headers, as we have been selling them for five or six years now and keep getting reports back from customers indicating that the pieces still look like new.



Installation

Again, there are no written instructions, but installing a header is fairly straight forward. Remove the original collector pipe and manifold and then bolt the new pieces in place.
We have found that removing the radiator and unbolting the power steering pump to slide it to the side, allows a lot of work space on the front of the engine and makes the job a whole lot easier as far as clearance to manuver a header into place.


We had no problems installing the Stan's Headers brand header. Everything went together as if it were original equipment pieces, the header fitting the engine, the EGR pipe lining up correctly, nothing needing cutting or modification, going on extremely smoothly.
No rattles and no leaks.
We do recommend the use of K&W or similar spray on copper gasket sealer, to help seat the copper gaskets. A little spray on each side is all that is needed.



Cost

Plain Steel Header: $399.00
Ceramic Coated Header: $499.00




Driving Around With It On The Car

The Stan's Headers brand header did increase the exhaust sound volume some but not tremendously. The sound tone was basically unchanged, remaining deep in tone without harshness, though slightly louder than with the stock manifold and down pipe.
There was no difference in the vibration of the steering wheel or the unibody of the car between the stock manifold and down pipe and the Stan's brand header, as was found with the Pacesetter header, which is likely due to the woven flexible joint of the Stan's brand header.



Performance on the Dyno

We tested the Stan's Headers brand header using the rear O2 sensor fitting that samples from all four cylinders and then tested it again using the front O2 sensor fitting to compare the performance of the two.
The front fitting posted the higher horsepower of the two, measuring a peak horsepower of 109.1 and a peak torque of 103.4 ft-lb. This is a peak power gain of 3.9 HP and 1.4 ft-lbs of torque.
The rear O2 sensor fitting posted the higher torque of the two, trading a little upper end power for a little lower end power, measuring a peak horsepower of 108.2 and a torque of 104.4 ft-lb. This is a peak power gain of 3.0 and 2.4 ft-lbs of torque.
We included both curves on the graph because there was some difference between the two.
The Stan's header produced a more consistent and even power gain across the entire RPM range compared to the Pacesetter product, and the Stan's product excelled in both low, middle, and high range power. Neither the stock manifold and down pipe, nor the Pacesetter header, came even close to the Stan's brand header above 4,200 RPM, where the Stan's product picked up 3-4 peak horsepower over the stock manifold and down pipe and 6-7 HP over the pacesetter product. This disparity grows even wider above the peak, where the Stan's brand header out performs stock by 4-6 HP and outperforms the Pacesetter by 7-12 HP for the last 1,000 RPM before redline.
The Stan's brand header averaged a 1.9 HP gain over the stock manifold and down pipe across the entire RPM range. The Stan's brand header also resulted in a gain of 3.9 peak HP over stock, and produced a maximum gain of 6.6 HP and 4.6 ft-lbs of torque over stock at 7,600 RPM.
The Stan's brand header averaged a 2.9 HP gain over the Pacesetter header across the entire RPM range. The Stan's brand header also resulted in a gain of 6.5 peak HP over Pacesetter, and produced a maximum gain of 12.0 HP and 8.3 ft-lbs of torque over Pacesetter at 7,600 RPM.

To many, it seems a mystery as to how Tri-Y headers work. The Tri-Y header, with it's paired primary pipes and two secondary pipes, tunes for two peak gains, spread across a wider area than the 4 into 1 header. This is done by carefully selecting the lengths of the primary and secondary pipes and making sure those lengths are equal. The primary pipes of the Stan's brand header are 10 5/8 inches long, while the secondary pipes are 10 1/2 inches long. Using the software at the Automotive Programs by Bowling and Grippo Website, entering the primary pipe diameter, length, and engine displacement indicates the the tuning of the primary pipes for a peak power improvement at 7,600 RPM, or maximum engine speed. Using the same program with the length of the primaries plus the secondaires and the diameter of the primaries and engine displacement indicates the tuning of the secondary pipes for peak power at 3,900 RPM. Looking at the dyno charts, it is easy to see that the Stan's brand header shows two distinct areas of power improvement, the first centered around 4,100 RPM and the second just before maximum engine speed, and both peaks in improvement over the stock performance level show a smooth transition between those peaks from the first to the second, without ever falling to the level of the stock manifold and down pipe in between. This is reason that the Tri-Y header yields smooth and consistent power over 4 into 1 headers, and why Tri-Y consistenly out perform 4 into 1 headers when tested side by side.
The Stan's brand header produced 6.5 more peak horsepower gain than the Pacesetter header.
It would be nice to be able to say that the Stan's brand header produced a peak power gain of however many times larger than the Pacesetter header, but the Pacesetter header lost peak power, so that is not possible.
It is, however, possible to say that the Stan's Headers brand header resulted in over six percent more peak power than the Pacesetter header.

Conclusions

• The Stan's Headers brand header outperformed the Pacesetter header across the entire board.
• Comparing the two on the basis of dollars spent per peak horsepower gained, the Stan's header cost $103 per horsepower, but the Pacesetter header lost power, so there is no gain to compare.
• Fit and quality between the Pacesetter and Stan's brand header is drastically different, illustrating the old addage, you get what you pay for.
• The quality difference will save the user even more over the long run because the Stan's system will easily outlast the Pacesetter system.
• There is a serious concern of running the engine out of balance with the Pacesetter header that may cause problems with the engine seals and bearings.
• Any concerns of a Tri-Y header sacrificing peak power output or loosing power anywhere in the RPM band compared to a 4 into 1 header would seem to be somewhat less than valid, as the Tri-Y header outperformed the 4 into 1 header across the board, and only the 4 into 1 header actually lost power.
• Similar concerns of collector pipe diameter size relating to low and midrange torque output (similar to concerns of exhaust pipe diameter relating to the same performance), would also be shown to fall flat given the results of the testing.
• Pacesetter uses this same header for the 1.8 liter DOHC Isuzu engine in the 1992-93 Geo Storm GSi, 1992-93 Isuzu Impulse XS, Isuzu Stylus RS, and Asuna Sunfire. We expect performance on that engine would be similar to what was measured in our testing of that product on the 1.6 liter DOHC engine. In addition, the Pacesetter header design for the 1990-93 Isuzu 1.6 liter SOHC engine used in the Geo Storm Base model cars and the Isuzu Stylus S, shares the same 4 into 1 design with long primary pipes of uneven length with the inner pair being several inches shorter than the outer two. We expect, based on the testing above, that comparison of the Pacesetter headers for those cars with the Stan's Headers brand headers for those cars, would reach similar results. The Pacesetter header showing mid and high RPM losses with the same anomalous spikes in two narrow spots, while the Stan's brand header showing performance gain across the baord with significant gain above the middle of the RPM band.

The Final Word

Question:

What is the difference between the Pacesetter header and the Stan's brand header?
Answer:
6.5 Peak Horsepower and 12.0 Horsepower and 8.3 ft-lbs of Torque at 7,600 RPM.

Daryl and Matt at Mustang Muscle Performance and Dyno Service have stated that they are more than happy to discuss their testing and equipment with anyone who has any questions, and they are more than happy to help if you want to dyno test your own car at their facility. They can be reached at:

Mustang Muscle Performance and Dyno Service
1506 Gravois
High Ridge, MO 63049
TEL: (636) 677-9987
FAX: (636) 677-3632
Website: www.mustangmuscleonline.com