Technical discussions specific to 1964-1967, 1968-1970, and 1971-1973 Classic Mustang. Discuss all tech related to in-line six cylinder and V8 powered Vintage Mustangs here.
Im sure this has been talked about many times but here it goes. Looking at dual exhaust on my factory single exhaust A code 66. First Q is headers. I want more horsepower of course, but dont want to lose too much torque. Are long tube headers better or worse than a pair of Tri-Ys? And what is the best size of exhaust tubing?. A guy at work said 3 inch, but to me thats a bit overkill as the 289 will be lightly modified at best. My first idea is to get a pair of long tube headers, with 2, 2.25 or 2.5 inch pipes and Magnaflow mufflers exiting out the rear valance ala GT-style.
My setup is a 289 built to road race, ceramic coated Try-Ys, X pipe and 2 1/2" pipes. If your engine is mildly built I'd go with 2 1/4" pipe.
As far as 3" pipe, way to big for a street 289. Before I rebuilt the car I changed the exhaust from 2 1/4" to 3" (at a friends recomendation) and lost all the torque down low. I don't ask him for advice anymore
Boy that was a bad pun... Anyway, back to the advice. Silverblue offers good advice I reckon, so I wont repeat that. And as he mentioned, there is way too much BS information around regarding exhaust systems.
For a mild 289 such as yours, a street driven car, you need all the torque the engine can make. Torque makes the car nice to drive at lower RPMs where you will be driving on the street (mostly hehehe)
Do remember to use a crossover pipe after your headers, now sometimes called an X pipe too (due to the shape) That will make the "note" sound better and increase torque. Use quality mufflers, do not use glass packed straight through "hot dog" mufflers. If you have time and the money, use header wrap or ceramic coating to keep the heat in the exhaust system, it makes the headers more efficient and reduces under hood temperature (lower temps helps increase power too) If you do the header wrap, paint it with the heat proof paint to make it last longer.
I agree that Tri Ys should produce more torque, it really dpeands on how good both the headers are, and longer, narrower header tubes will make torque at lower RPMs.
The exhaust will make a huge difference to your ride, putting a big smile on your dial.
Oh, just in case you are wondering, my exhaust is twin 2 1/2" and I am still hunting a good set of headers. (Hooker I think)
cheers n beers, Mick.
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Time and Money, our two main weapons in the fight for the perfect stang. nb I dont have enough of either
Toy: 70 Coupe, 351Clevo, 11.7:1cr 2v closed chamber ported heads, twin GRA propane/LPG converters and 900cfm twin mixers, twin 2 1/2" exhaust system, RightHandDrive conversion, 15" wheels, stock power disks and steering. A work in progress.
I totally agree with these two guys. As for my set-up, I have a mildly modified 289. I run Hedman headers down to an H-pipe (yea, X-pipes are better for power, but H-pipes are better for sound, which I wanted). Then I go to the 2-chamber Flow's out to my tips which go through my GT valance. I went with the 2.5" piping. It sounds really mean at idle, especially with my cam loping.
Remember, when Carrol Shelby was building the Mustang GT 350, he tested all the different header types available, long tube, shorty, whatever, but then he chose the TRI-Y style as the best overall header for the 289 & Mustang combination. That says a lot in my opinion.
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66 Coupe, CandyApple Red, original 289 engine, bench seat, and manual drum/drum brakes. Tri-Y headers with Flowmaster mufflers.
66 Coupe, Tangier Orange, originally a 6cyl, converted to V8 suspension, with 1985 5.0L HO engine and 57 Fairlane 9 inch rear with 3.56 gears, 17 inch Bullitt rims.
header and exhaust Q 
exhausting & its a hot topic 
