Really stupid question about dual exhaust pipe sizes

Good morning everyone. I was thinking the other day about dual exhaust tubing sizes and HP gain/loss. I've googled this a few times and mostly get people with race cars and open headers saying how the smaller the tubing size, the more restrictive it is. This is obviously true for high HP vehicles, but what about a vehicle with 250-400 HP? Would it be more beneficial to have 2" or 3" true dual exhaust, assuming routing it was not an issue?

I guess I'm REALLY asking this because I'm regretting going with 2.5" dual exhaust on my Tahoe (in sig). I have OBX stainless longtubes to true 2.5" pipes with knockoff Flowmaster mufflers (Xcelerator? I forgot). I'm wondering if stepping down to 2.25" would be a benefit or if I would lose power. I'm probably only making 300 +/- at the wheels, so I'm obviously not trying to break any records or win any races.

Most of me thinks that the larger exhaust, the merrier. However, another small part of me is thinking that some restriction would be a performance benefit. How? I have no idea.

Just a stupid random question of the day. LOL

Why are you disappointed? I've noticed a difference in performance with a stock or mild motor. I have a Yukon with 2.25" exhaust. 96-00 came stock with that size or maybe 2" don't remember. But the same years 3/4 ton got just about 3", off the manifolds to the muffler. With a healthy motor don't see how it would hurt it.

Why are you regretting it?
A flow restriction is just that, a restriction which means less airflow, less airflow means less power.

There is a good video on this kinda think on youtube and i cant find it.
but look at this one with a 600hp 454 on the dyno with 2.5 and 3" exhaust.

I just wished they would start dyno pulls down low in the rpms instead of 3000+.
Ive started pulls as low as 1600 rpms and it was a better representation of how the setup reacted under real world use of Daily Driving on the highway.

in my experience with exhaust i dont think its worth it for you to change from what you have. Dual 2.5" is 5" worth of exhaust.
we have made 950-1000rwhp on single 3.5" and 4" exhaust

If you just changed mufflers it would make a difference on flow.
Always considered FlowMaster mufflers to be a oxymoron since they dont flow all that well.

This is just something ive found on the interwebz. so take it with a grain of salt...

Having smaller pipes can produce back pressure and obviously the higher the rpms the more pressure it will produce. On my 77 blazer when I was working on the exhaust I had to run an errand and drove to pick up someone with open headers. Even with a 400 sbc I had no torque at low rpms.

I don't think changing from 2.5 to 2.25 is going to provide you with any benefit, I assume your real restriction was in the muffler. I would also be willing to bet that a good tune will allow you to recover all that you lost and then some.

The factory computer can overcome a lot more changes than a carb, but every time you change the flow characteristics of the engine you should have the VE table in the tune calibrated to account for it.

Also the factory programmed the PCM fairly conservatively. A good tune is generally the best bang for your buck improvement.

I had to re-read my original post. I have no clue why I said I wasn't happy with it. I apparently suck at multitasking. LOL

I AM happy with it, I was just wondering if it would be beneficial to step down .25" or so. I didn't ask this purely for my own vehicle, I've just always wondered it. It seems like on the hotrod forums there's always been a huge debate about this.

Honestly I don't think it is so simple as bigger is better or smaller gives better torque. I think everything has to be designed to work together.

Not quite the same comparison, but its close. bout 25 years ago I had an 83 Grand Prix. Was a decent car, had a mild 350, ran really strong. Had full length headers, and dual 2" exhaust with glass packs. (which I absolutely hate) I had a full 2 1/2" exhaust put on, and used flowmasters when they first came out. I think they were the 3 chambers. It sounded friggin awesome, and was a noticeable improvement all the way around. But if want to change the way it sounds, but bigger tips on it, this will give it a deep rumble, and get rid of any cackle....

RDF1 said:

Why are you regretting it?
A flow restriction is just that, a restriction which means less airflow, less airflow means less power.

There is a good video on this kinda think on youtube and i cant find it.
but look at this one with a 600hp 454 on the dyno with 2.5 and 3" exhaust.

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I just wished they would start dyno pulls down low in the rpms instead of 3000+.
Ive started pulls as low as 1600 rpms and it was a better representation of how the setup reacted under real world use of Daily Driving on the highway.

in my experience with exhaust i dont think its worth it for you to change from what you have. Dual 2.5" is 5" worth of exhaust.
we have made 950-1000rwhp on single 3.5" and 4" exhaust

If you just changed mufflers it would make a difference on flow.
Always considered FlowMaster mufflers to be a oxymoron since they dont flow all that well.

Click to expand...

we called them slowmasters. lol ditto on the dyno charts. they dont hit the button early because they already have, and they know the sheet will look like chainsaw blade until over 3000 rpm after they are on the cam and the biggass exhaust can get fast enough to clear reversion. its a direct indicator of a build not tuned.

RDF1 said:

This is just something ive found on the interwebz. so take it with a grain of salt...

You must be registered for see images attach

Click to expand...

lol. just pour the whole shaker down throat. length, bends, mandrel or acordian, seamless, temp, pressure, humidity, yada yada. let me guess, that chart from someone wanting to sell pretty exhaust out of a magazine?