3" vs 2.5" Exhaust?

[Lex]

What is the determining criteria for choosing 3" or 2.5" exhaust pipes?

[DynoDon]

Generally it has to do with horsepower levels. When you start approaching the 500 horse level you will see the biggest gains. Some folks will say it has to do with cubic inches, but that is not the case as much as power levels. Power and powerbands are really determined by the Header design and the exhaust will mostly only hinder the efforts of the headers, they can't really make it any better, unless the header design is really poor. So more exhaust flow is usually better. A 3" system on a 250 HP motor won't gain anything, but it probably won't hurt it either.
The new Mustang 5.0 comes from the factory with a 2.75" exhaust. I did a set up in all 3" for a well known Mustang car builder and they reported back a 23HP gain over stock. Now I'm sure some of that came from the fact that our mufflers flow much better than the stock Ford ones, but it certainly was a noticeable increase with the 3"

[Lex]

Thanks for the advice Don. I have a 78 TA. I just ordered the Tri-Y headers from Ron Watt. I found Ron on this site as well. My motor is around 500HP so I'm going to run Pypes 3" exhaust with the crossover and Pypes race pro mufflers.

[wmhjr]

Before you order the Pypes stuff, you might want to take a look at Ram Air Restorations products. I can tell you from first hand experience that the oval X-pipe, along with the actual X-Pipe design, will give you great performance with more ground clearance. 3" round is problematic on some cars and the oval design is wonderful.

[Lex]

Thanks. I will check into that. Any preferance on mufflers?

[wmhjr]

I'm real happy with the Spintech mufflers I got at the same place, but everyone has very different tastes there. Plus, sound varies so much depending on the engine build.

[Scarelane]

My 347 stroker has 453hp on the dyno and I went with 2.5" exhaust.

[Lex]

Before you order the Pypes stuff, you might want to take a look at Ram Air Restorations products. I can tell you from first hand experience that the oval X-pipe, along with the actual X-Pipe design, will give you great performance with more ground clearance. 3" round is problematic on some cars and the oval design is wonderful.

I went to the Ram Air Restoration site but it is down right now. I went to Spintech to check out there stuff but they seem to be very $$pricey$$. I do need an oval design though because the Tri-Y headers I'm getting have oval collectors.

[1red68]

Where are you going to dump the exh? are you going out the side or out the back?
I have not been under a T/A in a long time but my first thought is 3" pipe is a tight fit and 2.5 would be more user friendly......

[Lex]

Where are you going to dump the exh? are you going out the side or out the back?
I have not been under a T/A in a long time but my first thought is 3" pipe is a tight fit and 2.5 would be more user friendly......

I would like to go out the back with the split tips but I need to speak with Ram Air Restorations about it. It looks like I will have room to do it though. The tips should sit right outside the monoleaf and inside the panel right in the back corner.

[critter]

Jim Hand did a lot of exhaust testing on his wagon back in the day. His informed opinion was that a 2.5 inch system with a free flowing muffler was good to 500 horsepower. After that you need to step up. My motor is roughly 400hp. I went from a 3 inch system to a 2.5 inch for ground clearance and could tell zero difference at the dragstrip or on the street.

[Lex]

Here are some pictures.

[Nemesis RR]

Jim Hand did a lot of exhaust testing on his wagon back in the day. His informed opinion was that a 2.5 inch system with a free flowing muffler was good to 500 horsepower. After that you need to step up. My motor is roughly 400hp. I went from a 3 inch system to a 2.5 inch for ground clearance and could tell zero difference at the dragstrip or on the street.

Is that horsepower rated at the crank or at the wheels?

[wmhjr]

Jim Hand did a lot of exhaust testing on his wagon back in the day. His informed opinion was that a 2.5 inch system with a free flowing muffler was good to 500 horsepower. After that you need to step up. My motor is roughly 400hp. I went from a 3 inch system to a 2.5 inch for ground clearance and could tell zero difference at the dragstrip or on the street.

I have huge respect for Jim Hand though his material is a bit dated at this point. I found he's pretty spot on in general theory and application, but there are a lot of options and tricks available today that weren't commonly available back when most of his research and publication was done. Things like the different designs of the X-Pipes which help scavenging, newer roller cam profiles, etc. That being said, another option made more convenient with the oval pipe is 3" oval to/through the mufflers, and then 2 1/2" through the tailpipes (where the exhaust gas has cooled quite a bit so volumne is far less critical).

[wmhjr]

I went to the Ram Air Restoration site but it is down right now. I went to Spintech to check out there stuff but they seem to be very $$pricey$$. I do need an oval design though because the Tri-Y headers I'm getting have oval collectors.

Interesting. The Ram Air site is up right now - don't know what happened. Anyway, the Spintech mufflers I got were part of the entire setup. Pricing was not separate. I'm very happy with the quality and the sound. For the collectors, you just need transitions to whatever you want. If you really wanted for some reason, you could go from oval to round.

[Lex]

Interesting. The Ram Air site is up right now - don't know what happened. Anyway, the Spintech mufflers I got were part of the entire setup. Pricing was not separate. I'm very happy with the quality and the sound. For the collectors, you just need transitions to whatever you want. If you really wanted for some reason, you could go from oval to round.

Hi. I just visited the Ram Air site. I really like the 3" oval x-pipe design. The pricing is what it is so I just have to deal with it. I'll probably just go with the 3" oval exhaust system with the spintech mufflers. And I like what you said bout using 2.5" tail pipes and tips.

I don't want to change the subject but I see your profile picture of Ronald Reagan and I really miss having him as president. He was the best!

[66ls2]

I used the ram air restorations 3 " oval on my 66 chevelle for ground clearance and I can say there product is great saved me alot of ground clearance and the customer service was great. I used 3" oval to dynomax super turbo mufflers(supplied by me) to 3" round tailpipes straight out the back. I used to have a 2 1/4 exhaust dyno @ 360 rwhp 3" exhaust dyno @380 rwhp same dyno same tuner. If I used there spintechs it would flow a little better but I wanted to keep the noise down.

[Lex]

I used the ram air restorations 3 " oval on my 66 chevelle for ground clearance and I can say there product is great saved me alot of ground clearance and the customer service was great. I used 3" oval to dynomax super turbo mufflers(supplied by me) to 3" round tailpipes straight out the back. I used to have a 2 1/4 exhaust dyno @ 360 rwhp 3" exhaust dyno @380 rwhp same dyno same tuner. If I used there spintechs it would flow a little better but I wanted to keep the noise down.

Wow! Thats a big improvement on the rwhp. Are the spintech mufflers really that loud? I don't mind loud but not to the point where my eardrums rattle out of my head.

[wmhjr]

Are the spintech mufflers really that loud? I don't mind loud but not to the point where my eardrums rattle out of my head.

That's a really difficult question to answer. I have the "short" spintech mufflers (I'll post a pic below - I ceramic coated me entire exhaust so they don't come looking like that). Anyway, I really don't think they're really loud at all. You can definitely hear them, but I think they're pretty reasonable and I really like the sound. But remember, sound varies so much as a result of the engine build. I'm running 11:1 compression on a pretty decent sized long stroke motor.

[Lex]

Wow! Thats a beautifull setup! It's so damn clean under there. My brother used to hav a 67 GTO. His wife totaled it though. Wasn't her fault she was rearended. I loved that car too. Where do you get the ceramic coating supplies? I just got a price for oval x-pipe and mufflers not including tail pipes. It's alot of money but im sure its worth it.