Just a quick question. Besides bragging saying I have a 3" exhaust. At what point is it a good idea to go with 3" verse going with a 2.5" exhaust. From header and all he way to the tip?
I have been using 3" from the header to the muffler, then 2.5" tail pipes. It fits significantly better that way and there is no loss of performance. Thanks Brent
I have Torque Tech 3" all the way back on my 70 Stage 1 with M/T Repro headers and Walker Super Turbo mufflers. The tail pipes fit well with no rubbing any place. It runs as fast capped as it does uncapped up so I stopped bothering with uncapping it when making a run. On the street, 2.5" is likely sufficient up to a point unless you spend a lot of time above 5000 RPM. I have Torque Tech 2.5" on my 71 350 car and they fit well. If you put 3" from the collector to mufflers and then 2.5" out of the mufflers, you probably would be good to go. Exhaust gases cool as they go and require less volume the farther they go.
All depends on your combo and what you plan to do with it. Street? Track? A 3" system weighs a measurable amount more than a 2.5" one. I have shorty headers with 3" down pipes, into a 2.5" "X," UltraFlo mufflers and tailpipes. Shifting at 5,200 - we have very similar cams - I can't imagine losing anything vs a 3" system.
I like the 3” then 2.5” from the mufflers back idea, less chance of droning, if that’s a concern to you.
I have MT headers with a full 3" X Pipe exhaust into N25. I use Magnaflow 14264 mufflers. It is tight in some places behind the muffler, but it doesn't rub anywhere. The Magnaflows are just like the Walker 17749 mufflers they replaced. The system is amazingly quiet at cruise with no drone, but it screams when you get on it.
Engine Masters did a comparison a long time ago, it should still be on YouTube. They gained about 15hp w/3” over 2.5 on a 500+hp engine. The power gain seemed to diverge around the 400hp mark, that’s about where I would start considering it depending on what you’re doing with it. Cruiser I would wait til at least 500hp, a bracket/track car, I would switch after 400. The 3” to the crossover or muffler would be the best compromise and would probably only kill power by single digits until 550hp in my estimation. I ran a supercharged 4v ford 4.6l into the 550hp mark with 2.5” until the muffler and stock 2.25” tailpipes. I was surely giving up power, by the lack of drone and sleeper look surprised a lot of people and flew under the police notice.
Those are the Wheelz tips, so they are quite a bit bigger than stock N25 tips. Being they hook up to the 3" pipe, they taper quite a bit, so as you extend them out, you run out of room pretty quick. I found the best option was to have the bottom of the tip contact the bottom of the bumper opening. I put a section of door edge molding onto the lower edge of the opening. That way, they extend a healthy amount so they look good, and there is enough room on top that they don't rattle.
The hotter the gasses are the more volume they take up so a diameter big enough is helpful. With a full lenght Exh system by the time the Exh gasses get to the outlet side of the muffler they have cooled enough that even for a 600 hp motor 2.5" tail pipes are ok.
I have been running full 3” systems for 25 years. All have great results in the cars. I also like to run the cars at the track exactly how I drive them. I don’t run open headers or anything like that. With the right system,you don’t need to. I now have two cars that I will be switching to a full 3.5” system. The 3.5” tails are a little more challenging to tuck up and disappear,compared to the 3” tails,so I did some frame modifications to gain me some room. The area where the tail crosses over to the outside and is squeezed between the tail and the tire is very tight and I run bigger tires with deep backspacing. On the 3” tails,I had to ovalize that section of pipe,but the frame was also stock,not modified. You don’t see any of the system from the side of the car. You see the header collector,then it all disappears. It is easier to do this with an H-pipe vs an X-pipe. An X-pipe just requires more work. Cut,rotate,re-weld,but it can be done.
