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Discussion Starter #1
I'm anxious to replace my exhaust just because it's getting so loud. I currently have standard manifolds, 2" pipes, H pipe, and big ol' loud glasspacks. I've been planning on 2.25" pipes, an X pipe, hi-po manifolds, and nice, quiet Flowmasters (well, quieter than what I have now!). Then I read (in a recent Mustang&Fords) that a 2" pipe is best for low end torq. Something about backpressure...

I estimate I have between 250 and 270 horsepower, and the car is a daily driver. In other words, no racing and no need for tremendous high RPM power.

So, should my new exhaust stay at 2", or should I go up to 2.25", or even 2.5"? What are the pros and cons of larger piping? Yes, I want a cool sound; but mostly I want my engine to breath and perform.

Thanks!
 

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I just had my 65 dualed out. Have tri-y's, 2" tube, H-pipe with Dynomax mufflers. There was an article in Mustang monthly a while back that tested all kinds of mufflers on the '65. The Dynomax were about the quietest ones and I really like the sound. Look for the article. I think the mufflers were number 17762. I strongly recommend them.
 

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Discussion Starter #3
Yeah, I've kind of narrowed down the mufflers I'm interested in... my questions concern the pipe diameter. 2", 2.25", 2.5" or what? Is 2" better for street driving? And if so, then why is everyone getting 2.25" and 2.5"? I know everyone wants to be first off the line, right? I doubt a larger pipe would be very popular if it slowed us down. Any opinions?
 

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I think 2" is plenty especially with the hi-po manifolds. Those should be you major concern regarding exhaust. I would highly doubt anything is going to better performance wise unless you reduce that bottle neck. Go with some nice headers on your car and feel the car pick up dramatically. If you want something that isn't loud, then I'd probably look at something else over Flowmasters. Though I like my Flowmasters, they aren't for everyone. My current setup is overkill, but I did notice a huge increase in power once installed. I have 2.5" exhaust, H-Pipe, Flowmaster 40's, and Heddman Headers. I think headers will give you the biggest gains and the nicest sound.
 

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Discussion Starter #5
I'm mainly leaning towards hi-po manifolds for ease of fit. I had a '65 years ago with full-length headers. There's nothing to duplicate that sound! But getting to the starter can be a real headache. Hi-po manifolds flow ALMOST as well, and there's no problem with fit.

I think Flowmasters will be quiet enough for me; especially with sound deadener throughout the car. I do want SOME noise - I'm not completely an old fart yet!
 

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I vote for 2.25"
My reasons: My '71 has 2".... too small
My '67 ..2" ..too small
My '68 ...2.5"... too big.
 

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Why not get shorty headers? No ground clearance problems. No starter problems. Better flow then manifolds. IMHO they are the best compromise. A word of advice though Hedman Shorties part # 88400 do NOT fit with the orignal z-bar linkage even though their literature says they do.
 

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I have an article at home on this topic. The size of the pipe should be determined by the size of the motor, HP rating and usable RPM. For duel exhaust motor with around 300 CI that is production over 250 and less than 300 HP then 2.25 inch pipe diameter should be fine. If you were going with headers, I would recommend 1.5-inch primary tubes. If you go with the 2-inch pipes, then your exhausts gases will maintain a higher velocity at lower RPMs but will be a constraint at higher RPM. Plus the 2-inch will be easier to install. In other words, how to you plan to use the car. For example, if you have an intake and cam designed to work above 3,000 RPM but your heads and exhaust flow best at 2,000 RPM, then your motor will always under perform at all RPMs. Enough of the theory, if you have a mild cam and under 3.00:1 rear gear, go for the 2 inch else if the duration on your cam is close to 220 or more at .050 and/or runner a lower gear (higher number IE 3.50:1) then go for the 2.25. Hope this helps more than confuses.
 

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Holley Street Avenger recommendation is 2.25" for 289-5.0L hot street engine. I think thats what you want, right? You may want to check the Edelbrock Performer recommendation as well but I doubt its any different.
 
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