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2.5 or 3" Exhaust system?

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1967rsss350

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Discussion starter · #1 ·
Hey guys,

I think I have decided on the Magnaflow system with the X pipe, due to some positive info on this site.

I am just wondering if it would make a difference for me to get the 2.5 or the 3" pipes...

I have somewhere around 400 HP

350
10-1 Comp
480 lift on Cam
Holley 750 Double Pumper
Pete Jackson timing gears.
411 rear end
MSD ignition
Headers

What do you think?

Nick
 
#6 ·
i agree, with your current combo, 2.5 is fine. however if you ever plan on stepping it up a bit, you may want to go 3" now, and avoid the cost of doing it twice. just another point of view
 
#7 ·
Where would the "break" horsepower be go from 2.5" to 3" in that exhaust system? If at 400 HP he put on the 3" system, the cost would be a loss in low end torque right?

Just trying for tap the "why" behind the answers everyone gave here...

Thanks,
Scott
 
#8 ·
imo, after about 450 true horsepower the 3" will be the ticket. and personally i feel if the 400 is real, the 3" won't hurt anything, the loss in low end torque would be negligible at best, if any at all. the only thing you'll save at the hp level is weight of a 2.5" system over a 3", which isn't much.
just my opinions :beers:
 
#9 ·
I would agree that at about the 450 HP range that the 3" inch exhaust system would be a better choice. Is max performance the goal, or just a great sounding and fun car to drive?

I just installed a new 3" system on my 550HP Chevelle and I can tell the differance. :D 3" pipes are VERY loud! Can you live with loud?

Hope that helps.
 
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Discussion starter · #10 ·
Hey Guys,

Thanks for all of the replys. This is mainly a fun street car that I will take to the track once in a while.

The car has never been dyno'd, but I have been told that it should be around 400 horse. If you need any more specs, I'll try & get them to you.

I am replacing the exhaust, because I only have cherry bombs attached to headers with turn downs & besides being incredible loud (which I sometimes like) it crackles sometimes or pops.

That being said, whenever possible, if I am replacing a part & I can replace it with something that will give me more power, that is always the best option for me! However, if the 3" will steal any low end torque .... I will probably go with the 2.5 ( I love that low end power!)

Nick
 
#11 ·
Okay, one last bit of help for you.

I had mentioned in an earlier post that I had just installed a new 3" system on my Chevelle. I used a Torque Tech kit with an X-pipe. It fit very well, better than the 2 1/2" Flowmaster kit that I took off the car.

Here is my recommendation: I would use a Torque Tech 2 1/2" system with an X-pipe and your favorite mufflers. I like Flowmasters myself. Alot of guys on the site here like the Magna Flows. Many types are available with the kit. Just a thought, check out the site:

http://www.torquetechexh.com/default.htm

To me, a great exhaust system completes a car and is as important as a great set of wheels or the paint job.

Good Luck :D
 
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#13 ·
I just put a 2.5" Flowmaster set up on a 67 SS 350 and am very happy with the sound and performance. I am at the same HP level you mentioned. The set up is pretty loud with the 40's and the 3" system is, I hear, even louder when stomping on the loud pedal... I think you'll like the sound of the 2.5" system. :thumbsup:
 
#14 ·
I also just put the 2.5 inch Flow system on my 68RS 327. I was surprised at how quiet it is inside the vehicle. Sounds nice at idle and when you get on it!
 
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#15 ·
Another approach(I read this in other posts on other sites) is to run 3" pipe to the mufflers and 2.5" out over the axle. The theory, as I understand it, is that most of the exhaust gas expansion is over with by the time it reaches the mufflers, so the 2.5" tailpipes can handle it; working like an expansion chamber.
 
#16 ·
gmranch said:
Another approach(I read this in other posts on other sites) is to run 3" pipe to the mufflers and 2.5" out over the axle. The theory, as I understand it, is that most of the exhaust gas expansion is over with by the time it reaches the mufflers, so the 2.5" tailpipes can handle it; working like an expansion chamber.
Click to expand...
Yeah, I'm a subscriber to this theory too, this is what I do with my 454. I run a 3" x-pipe, then I have a 3" to 2.5" long tapered reducer just before the mufflers.
 
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#18 ·
I have a 77 Suburban with a 91 update kit on it, bone stock 350 SBC with cast iron exhuast manifolds. When I got the truck the single muffler fell off on the freeway two weeks into owning it. The Muffler shop in the area that was open on Sat wanted an outragous amount to install 2.5 dual exhuast on my exiting 2" exhuast, so I went home a got an exsisting exhuast that was off my Camaro, but it was 3". I brought him a 2" reducer for headers and told him to put it on backwards and keep my collectors on this exhaust (this was going to be a temporary fix till I could get it to another muffler shop I usually deal with.) He said it would be loud and the truck would run bad and that he was not responsible for it. He charge me $100 to cut the pipes and weld on the reducer (like I said this was and expensive shop), fired up the truck and it sounded real good. The owner of the shop came out to see it, asked the his muffler guy what he did and could not believe it. Truck ran great and still has those mufflers on it. I put a different set on the Camaro.

Now a friend wanted to put a stock 350 with cast iron exhuast into his 6 cyl Nova and wanted to do a similar exhuast in his car. After the 350 was in we went to the local muffler shop in his area and told him we wanted 2.5" exhuast out of the manifolds to 2.5" header reducers run backwards with collectors to 3" pipe to 3" Mufflers back to collectors to 2.5" reducers and the 2.5" pipe run out the back of the car. With the collectors we could completely remove this exhuast if we had to to work on the tranny. The muffler guy said the same thing as the previous muffler guy at the other shop had said, that this exhuast would not work, he had done plenty of work for Magazine guys and this was not how it was done. We told him this is what we wanted so he did it. When it came off the rack, wow did it sound good. The muffler man could not believe it and said this would be an option for guys who want to run 3" but only 2.5" fits, and for guys with stock manifolds who want a little more rumble but don't want headers.

Both car and truck used dual 3 chamber 3" Flow Masters.
 
#19 ·
I would say if you plan on upgrading your engine in the future put the 3 inch system on but use somthing like a flowmaser 50 series. this way you wount make yourself def , get pulled over every time you drive it and obtain a comfortable balance of flow vrs back preasure. down the road you can always cut em outand with a few pieces of 3 inch pipe retrofit somthing like a full race muffer. or you could even go ahead and put some cut outs off the headder collectors if you plan on driving her to the track , playing then driving her home , so you dont have to remove your exhaust ect.
 
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#20 ·
I had 3" x-pipe going into 2.5" Flowmaster 50 series and the interior drone was deafening. I am trying Magnaflows as soon as I get the engine back in.
 
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