Exhaust questions.

[79Fairmontphillis]

So I have a 1979 Fairmont 2 door box top with the I6 I recently did some engine work. Bored .030 over decked the block .20 of an inch and polished and ported the head. Other than that everything is stock.

My question is should I get a bigger exhaust or should I stay with the stock exhaust? Would it make any difference performance wise? It is my daily driver.

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[xctasy]

Anything that reduces back pressure without losing mixture motion in the combustion chamber and gas speed from the first 40 inches from the exhaust port will improve performance. Peak power isn't hurt at all with backpressure reductions, but everyday driving torque is always enhanced if the pipes and engine spec and tune are optimised to improve gas speed as well as reducing backpressure.

Performance consultants run programs to calculate optimum exhaust sizes for cam, port and engine configurations. It is analogus with painting the outside of a header and pipe system with a line of enamel paint, , and cutting off the active section of the collector where the paint burns off.


So yes, it is worth it if done right. Peak power and torque go up, fuel economy at steady and transient car speeds go down.


Ford Australia found this with the 225 HP 5.0 in 1997; it was modified to make 268 hp in the "30th Anniversary" Falcon GT, and they reduced back pressure by more than 50%, but got improved economy as well.


Same with running the altered Football exhaust in the 1980 to 193 3.3 liter Fords. Although they lost the gains made in some years, the use of a honey combe ceramic primary cat and big ass header pipe with a small tail pipe and secondary cat raised power significantly for 1981 (94.5 hp verses 85 hp for the 1978-1979 cars) and

94.5 hp was the rated amount for a 1980 B-code manual, but it varied from 87 to 94.5 nominal 1980 thru to 1983, with any number of ratings between 87 and 94.5.

Torque was the same or up to 6 lb-ft more, at less rpm, depending on year.

In addition, Ford at some stage had to detox the engine for manual gearboxes, while some areas didn't have that option. Even when Ford retarded and played with the camshaft, the result was still more power and more torque with this exhaust in an era where there was now a mandatory air pump, and secondary AIR in CA models. The 1980 B code model had 9.5 hp extra over the 1979. Then it varied according to other changes in 1981, 1982, and 1983, but always more than 85 hp by 3 to 7 hospower. Rated torque was often up despite the variances.

http://fordsix.com//viewtopic.php?f=...573043#p573043

A twin 1.875 to 2" internal diameter exhaust pipe like the 1985 Ford 5.0 4-bbls ran with a big replacment secondary cat, and a primary cat like the 1980 to 1983's will dampen air speed peaks, and help power and torque. The 4.25" football catalyst exhaust would help.

If you want to use a tubing header exhaust, you could gain some more torque and power, but you loose the ability to run AIR and A/C, so if your hot and bothered in an emissions state, you'd hate the choice.