2.25 or 2.5 inch exhaust.

Edster · Sep 26, 2010

I'm wondering which would be best. 2.25 or 2.5. I"m runnin a 302 .030 over w/ D0OE heads that have had some mild porting done and have anywher between 10.5:1 to 11:1 compression w/ an Edelbrock perfoemer rpm power package. I think a 2.25 would suffice but also wonder if a 2.5 would be better or am I just wasting my money. Any thoughts?

Az Pete · Sep 26, 2010

My 289 is 10:1 with 2.25" exhaust with no problems. Been that for a long time.

Edster · Sep 26, 2010

AZ Pete, thanks for your service in the Air Force. I'm retired Navy myself. I reckon that a 2.5 was overkill anyway. I had the same engine in a Falcon with 2.25 and had no trouble either. I was just wonderin if I had anything to gain w/ a 2.5 inch.

Realmongo · Sep 26, 2010

Here is the chart that Magnaflow puts out for this:

MagnaFlow Performance Exhaust - FAQ, Frequently Asked Questions

2+2GT · Sep 26, 2010

That chart is surprisingly useless, they indicate a 289/302 should have 2" to 2-1/2" exhaust. If you look at the cross section area, that's about 3.14 square inches on a 2" pipe, and 4.9 square inches on a 2.5" pipe, a whopping big difference.

Realmongo · Sep 26, 2010

2+2GT said:
That chart is surprisingly useless, they indicate a 289/302 should have 2" to 2-1/2" exhaust. If you look at the cross section area, that's about 3.14 square inches on a 2" pipe, and 4.9 square inches on a 2.5" pipe, a whopping big difference.

Probably emphasizing a minimum and maximum for the the application.

2+2GT · Sep 26, 2010

Realmongo said:
Probably emphasizing a minimum and maximum for the the application.

Sure, but it's such a wide range as to be useless for deciding between stock 2" duals, or very non-stock 2.5".

It's also worth noting that the 67 GT500 428 dual-quad Shelby had 2" exhaust.

But then, even the BOSS 429 had only 2.25".

Something to watch out for is various fads for "bigger is better".

In my automotive life, I have seen fads for bigger

•rear tires. L60-15 was the ticket, and required High-Jackers to clear. Cornering was out of the question.

•coils. More powerful, of course, but large size with cooling fins was equally important.

•carburetors. If a 600 was good, 650 was better, and 750 double-pumpers guaranteed the jump to lightspeed.

•spark plug wires. Summa these things are starting to look like heater hoses.

•exhaust. I've seen pipes on Toyotas that would do a Peterbuilt proud.

There's a point of diminishing returns on size, for example, a 3-row radiator is maybe 50% better than a 2-row, but a 4-row is only about 10% better than a 3-row.

So, does a 302, even a really hot one, really require a coil four times as powerful as the one on Mickey Thompsons 427 Hemi Ford Thunderbolt?

Wicked65 · Sep 27, 2010

Id go with 2.5in. Reason being, if you have ever driven even a fairly stock 5.0 with stock exhaust, and then felt the difference with 2.5, or better yet a cat less x pipe, there is a fairly big difference. I guess the biggest thing with your car is the port work that has been done, and the higher compression, why make the exhaust the restriction?

horseballz · Sep 27, 2010

The 2.5" Magnaflow is such a great deal, when purchased through StangNet, that it seems to be a no brainer. From my searching, any other system, even a 2.25" that even comes close to the quality/features (including lifetime warranty) will cost as much if not more. To get the killer price, you need to follow the special pricing link on the Exhaust page, after you figure out which part number system you need/want. Unfortunately, Magnaflow doesn't make a 2.25" for our early Mustangs.
Just My $.02,
Gene

woodsnake · Sep 27, 2010

--------2.5------
The only way to go on a small block that has even just a better set of plug wires...

brianj5600 · Sep 27, 2010

I would do 2.5". Down the road you want N2O or a 347 with good heads on it and have to buy again if you go 2.25". I wish I had done 3" on mine.

tx65coupe · Sep 28, 2010

I have 2.5 inch exhaust on mine, but could have done just fine with 2.25.

Since that Magnaflow kit is such a good deal, I would probably just go with it. Does it have an H pipe?

I don't think 3 inch duals is needed on anything except maybe a really hot big block.

horseballz · Sep 28, 2010

Magnaflow has an "X" pipe.

tx65coupe · Sep 28, 2010

Oh. Its too bad it doesn't have an H pipe instead.

Vinyl66 · Sep 28, 2010

Undoubetedly 2.5". Do not crutch a V8 with any less.

brianj5600 · Sep 28, 2010

tx65coupe said:
I don't think 3 inch duals is needed on anything except maybe a really hot big block.

What about an 800hp 351w?

horseballz · Sep 28, 2010

tx65coupe,
You said:

"Oh. Its too bad it doesn't have an H pipe instead." Please explain. Is an "H" pipe better than an "X" pipe and why? From what I can tell it seems a topic of spirited debate with only minimal differences. I could be wrong. But if you click on the exhaust link near the top of the page, scroll down to the setup for your car and click the part number, it will link you to the Magnaflow site with an expandable pic that shows all the parts that appear to be quite well made with many good reviews throughout the internet.
Gene

blown65 · Sep 28, 2010

tx65coupe said:
I have 2.5 inch exhaust on mine, but could have done just fine with 2.25.

Since that Magnaflow kit is such a good deal, I would probably just go with it. Does it have an H pipe?

I don't think 3 inch duals is needed on anything except maybe a really hot big block.

There's gains on even my motor with 3" duals at its little 347 cu inch. 2 1/2 would be too small.

That magnaflow chart seems pretty good to me if you go by HP of the engine. I'm sure most 2 1/2 is more than sufficient on this site.

rbohm · Sep 28, 2010

personally i prefer 2.25" pipes on my mustang. as for H pipe vs X pipe, both have their advantages, i think the X pipe is a better choice.

65FBE2 · Sep 29, 2010

I had a 2" system with cherry bombs on a 289. I ran a best time of 12.83 with nothing more than a solid cam, 650 Holley and headers. The car ran within a tenth with open headers as it did with the full exhaust. Anything short of a full on rece motor does not need 2.5". This is the same as the guy who has a stock 289 with a 480 cfm autolite, bolts on a holley 600 and says wow what a different's that made! And it actually lost power and slowed down. Most of the power gains in a 2.5" system are in your head and not real. Just my 2 cents

2.25 or 2.5 inch exhaust.

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