Exhaust size

At your power level, 2" is about right. It certainly wouldn't be worth the money to upgrade vs. power; I'd wait until the exhaust needs replacing and then go to 2 1/2".

It would be nice if somebody did some dyno time with cars of different hosepower levels to see what size tubing was best suited to a certain HP range.

For example:

2" 150-200Hp
2.5" 200-375Hp
3" 375-550Hp

Is anybody aware of such a chart, Or are my numbers a close enough guess?

I agree, it seems that everyone has their own opinions, and that's what they are-opinions. I think 2" is likely just fine for a mild small block street car, but I don't have any info proving otherwise and neither does anyone else, which is why the disagreements over which is best.

My exhaust mods are in my sig. I can tell you though that I had a 2' inch before, and it was choking the living crap out of my old 351..but then again, its a 351. The older 351 I had was also very stockish.

My new system sounds dam good. Its not super loud though, and inside its mild. I do not even have sound dampers. Its just a nicelow rumble. I have a lot of people tell me it sounds good. Is it worth redoing ? Well your pockets need to decide that one.

Through stock heads and tri-Ys, 2" isn't holding you back too much.

It wouldn't be a noticable increase to go bigger, and if you actually did get any gains, it would be towards the rpm level where your heads would crap out.

How about this... what were the stock exhaust applications out of the factory?

I had a 2 barrel 289 with the single exhaust which I think was 1 1/2 inches right? In addition, I think the stock setup was 190 flywheel HP correct?

What was the stock exhaust configuration for a dual exhaust 289 HiPo? Can you use these types of examples as a baseline?

Just curious...

2 inches is fine for your application. If you go bigger you might loose out on torque. No need to redo your exhaust unless it needs replacing.
Kevin

REPLIMOD #17 said:

Is anybody aware of such a chart, Or are my numbers a close enough guess?

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David Vizard did one back in the late 80s. He found that each horsepower needs 2.2 cfm.

19stang66 said:

I bought that Flowmaster american thunder system and have it almost installed. I take it this Wednesday to a muffler shop to have them fab up pieces to complete it. I used to have manifolds and 2 inch pipe with cheapo mufflers. Now I got tri-ys with 2.5" pipe and 40 series 2 chamber delta flows. I can't wait to hear how she sounds!

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this is the same thing I was hoping to do for my exhaust system. If you don't mind me asking, where did you order the system from and how much did the shop charge to weld it up? Thanks for any help.

The other thing to consider is that depending on what mufflers you are using, this will also change the chart around as well-

As a straight through 2.5" muffler will support more power then a chambered 2.5" muffler-

At Magnaflow, this is what we usually go by- this is for a N/A motor, no converters - with an X pipe

These are crank hp numbers- and would be an exhaust for a street driven car with light track duty, for a race car, I would go to a bigger exhuast sooner-

With forced induction, depending on power adder- you could also go to a bigger exhaust as well a little sooner-

0-225hp 2.25"
225hp- 550hp 2.5"
550hp- 900hp 3"

For a chambered exhaust- there are numbers I see some of our competitors use-

0-200hp 2.25"
200hp-475hp 2.5"
475hp-800hp 3"

Ha! Somebody else read the David Vizard article! One thing he points out is that the entire exhaust system will flow only as well as the most restrictive component. So, if you pop for headers and 2.5" pipes, but your muffler flows a cfm number equivalent to a 2" pipe, guess what? It acts like a 2" exhaust system. Unfortunately, few companies publish flow numbers in cfm. Of course, if all you want is the "right sound", ignore this.

stangkid88 said:

this is the same thing I was hoping to do for my exhaust system. If you don't mind me asking, where did you order the system from and how much did the shop charge to weld it up? Thanks for any help.

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I take her in tomorrow morning at 830! I bought kit from Summit Racing and the headers from CJ Pony Parts. I'll let you know tomorrow how much it cost for the shop to do welding, hopefully not a lot.

Stock K codes (HiPo's) used a 2" system from the manifolds back. That's what I still use on my K along with a pair of Flomaster 40's. Runs just fine and sounds very nice.