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MUSTANG 2.8
Supertune by John Christy
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We're going to have to face it: the days of big gains in middle range performance through dyno-tuning are disappearing. They're goin along with the disappearance of 98-100 octane fuel and the appearance of such things as exhaust gas recirculation, VSAD distributor retards and camshafts ground for exhaust leak-back.
That is not to say that dyno-tuning no longer works. It does work and it's worth the doing if only for the sake of response and driveability on the '74 cars. Of course, with the exception of the losses due to lowered quality fuel it still works worthwile improvements in both power and response on the earlier cars.
Our current lesson in the realities of the era of fuel-abusing ecological extremism is the new Mustang II equipped with the 2.8-liter V-6 engine. At first blush one would tend to think that since the 2.6-liter engine, as seen in the 2600 Capri of '73, responded so well to dyno-tuning the larger version would be that much better. It just simply isn't so, even though the new engine has more displacement and a more sophisticated cylinder head design. However, as is the case with a number of other manufacturers, the size increase is an attempt, only partially successful, to offset the power-robbing effects of the strigent '74 emissions requirements and the add-on controls found necessary to meet them. Where the '73 2600 would rev freely to 6500 rpm and pull its peak power at 5500 rpm, the new 2800 just flat runs out of breath at anything over 500 rpm and the power peaks out at 4500 revs, even after tuning. The 2800 does make more rear-wheel horsepower both stock and tuned than does the 2600 but it's power of the tractor variety, coming in fairly early and running out much too soon to suit the four-speed gearbox. Truth to tell, it's much better suited to the automatic, especially in stock form.
Our dyno car was the same Mach I version that we used in our 30-day test (MT-December'73). We were thus thoroughly aware of its good points, its shortcomings and the overall "feel" of the car when we got to the Geraghty Auto and Marine dynomometer with it. Our expectations were ambivalent in that the 2600 we had done before had responded so well to the treatment. But that one had also been a bit of a screamer in stock tune, so much so that we'd suspected we had a ringer. This one, on the other hand, had exhibited that shortness of breath above 4500 mentioned aboce. It was also covered with such a mass of emissions control plumbing that the under-hood area looked more like a can of fishing worms than an engine compartment.
After probing down into this mas of rubber plumbing and finding the necessary attachment points for the diagnostic equipment we put the car on the rollers. the first check was to make sure that it was up to specification. It was, surprisingly enough, after the hard use to which it had been put earlier. An emission check for hydrocarbons and carbon monoxide was then made and it was found to be as squeaky clean as the law of the land requires and then some. The readings at idle were 1.3 percent CO and a mere 200 parts per million in HC. At cruise under partial load, the equivalent of 35 to 40 mph on the street, the reading dropped to 1.0 percent CO and 180 ppm in HC. The primary power system (accelerator pump) kicked the CO up to 3.0 percent, dropping back to 2-+ percent when the secondary throttle kicked in.
With that out of the way a power run was made and, as mentined, the engine was surprisingly strong in terms of plain, torque-related horsepower. It started out with 24 horses at the rear wheels at 2000 rpm. The power built quickly to 38 hp at only 2500 revs and at 3500 it was putting 60 horses down on the rollers. At 4000 revs there was 64 hp and that was the end of any more gains thanks to an overly hot plug range. The Autolite AG-42 plugs started to give up and the power dropped to 52 at 4500 and then went away to the point where we didn't bother to record the reading.
The diagnosis from all the data gathered indicated that while it was only a touch lean on the primary side or cruise, it went dead lean when the secondary throttle opened to allow a new rush of air. This just made the hot plugs worse and effectively shut things down at 4000 rpm. In the ignition department things looked better. The 2800 doesn't have a vacuum retard so there was no unsolvable problem on that score. In fact the only thing that might cause a loss in performance was a slightly slow mechanical advance curve, with a total of 35 degress (crank) coming in at 4500 rpm. Coupled with the six degrees of vacuum advance it was more than sufficient in amount. Since the vacuum advance was only six degress it didn't need to be limited as has been the case with some other cars and since it utilized mild venturi vacuum instead of the strong manifold vacuum there was no surge. The only change needed was a quicker mechanical curve to bring in the peak at 3300 rpm. This the only change required in the igntion was a lighter secondary spring which was done.
This last item is simply done with the distributor off the engine and placed on a Sun strobe machine. The trick is geting the igniter out of the engine and getting it back in again. The blasted thing is buried way at the back of the engine and nestled down next to a heavy plate. The only way it can be loosened is with a special crow-foot ignition wrench which any decent gas station or garage should have but which is a bit rare in the home mechanic's toobox. Nonetheless the job is one of those knuckle-barking, profanity-invoking bears. It isn't complicated - just annoying. The replacement isn't quite so bad but it's best to bump the rotor into an easily marked positon before removal, so that the distributor can be reinserted within a reasonable area of right timing.
The other painful job is concerned with the plugs on the right side of the engine from the driver's view or left when facing the engine. The first or front pair are not difficult, just annoying but the rearmost one is a swine, hidden down behind the battery. It can be removed with a ratchet and socket but be prepared to swear a lot. The other side is, as if to make up for it all, a snap - just reachin in with the socket and do it, no problem. This was all learned in the replacent of those hot Autolite AG-42 plugs with AG-32 items which is what it should have had in the beginning since the 42s were practically cremated.
The air/fuel reading incdicated that the carburation was almost on in the primary circuit, needing only a touch of richening, less in fact than a normal jet step. The secondary circuit, however, was leaning out to the point where plugs would fry in a few thousand miles and quite possibly valves would go in a few thousand more if the car were driven much in the scondary or high-cruise range. It was quite likely this factor as well as the high heat range that had brought the original plugs to the verge of demise. As a consequence the primary power was richened a mere touch with a jet from an earlier kit and the secondary system was enriched by enough to prevent the high lean-out. It might seem that this would be counterproductive for economy and on the dynamometer where the operation is full load, full throttle, it is. However, on the road, in a real-world situation the effect is that less throttle is required to make the car do what it did originally on nearly full throttle, particularly in the areas of climbing hills and part throttle acceleration in traffic. With the slight enrichment of the primary circuit and the improved igniton curve more time is spent in low-cruise or primary operation with the scondary throttle closed than before and booting the gas pedal through the firewall is not longer necessary to make traffic pases.
On the dynamometer the improvement wasn't spectacular but it was significant and a somewhat different picture emerged from the first runs. There was a gain of five at 3000 revs. At 3500 rpm the gain was only three. But a 4000 rpm where it had peaked before with 64 rear wheel hp it now showed 71 and at 4500 revs, 76 hp showed where only 52 horse had lived before. At 4750 it was still making 68 hp and at 5000 rpm it was still pulling 64. Very obviously the camshaft for the 2800 was different from the one in the 2600 since that is the item that controls where peak power occurs. It gives one to think that if one wanted to cheat a bit, the cam could be retarded by a degree or two, sacrificing some of the tractor-like low end torque an gaining maybe a thousand extra usable revs. This is purely conjecture since we haven't tried it but things like that havce worked elsewhere and we might just make some future experiments along those lines. If it works we'll let you know.
In any event, while the numbers shown on the dynamometer weren't all that specatcular, performance on the road, as indicated above, was significant. The response was such that shifts both up and down could be made much more neatly and with more precision. Acceleration in traffic was better with less throttle and full pedal was not need to maintain speed on freeway hills. Although the dyno runs were followed by 220-odd miles of hard driving on that tank of fuel, the same on which the dynamomter runs were made, the mileage was higher by one mile per gallon than was the previous tankful which had been used over much the same sort of driving terrain. While this doesn't constitue a test per se it is indicative since part of that tank was used in the fuel-consuming dyno-tuning process and in harder driving than normal to test the results.
In any event a kit is planned for the Mustang II 2800 in the near future and while the installation won't exactly make your Mustang give you nosebleeds it will make it more driveable, responsive and, if you drive it right, just could give yuo a little more distance per tank of gas. To check the availability, write Geraghty Dyno-Tuned Products, 3223 N. Verdugo Rd., Los Angeles, CA 90029. And if you do install it, please do it right; it's more important than ever on '74 cars.
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