Really stupid question about dual exhaust pipe sizes

[Erik the Awful]

damn thats ugly . lol J/K, that was a lot of work and will make great midrange tq!
how many noticed your tri=y design?

We were doing an engine swap at the track because the bottom end was knocking. Come to find out it was the crank hitting the pan. Everybody stopped by to look at the headers, and all I heard about was the Frankenstein-looking welds and the angle cut bends. Meh. [shaking hands at the sky] SOME DAY THEY WILL RECOGNIZE MY GENIUS!

 

[Redneckgeriatric]

lol. yep, they never saw a factory race team road race exhaust. you know, you can still buy cones to DIY!! i applaud your want to understand how to build power.

 

[Redneckgeriatric]

That is no where near correct But you go on believing what ever you like

next time you ar n the dyno and experiencing reversion, take a 1x4 and lay it sideways across the end of the exhaust, or exhausts. watch lambda straighten up, and watch the dip and bumps in your tq straighten up. its called a popsickle. you can fine tune the popsickle by installing an eyebolt in the pie, or collector, whatever. i dont say stuff for my health, i say stuff to help. any tuner knows this trick, it proves reversion. a popsickle will not cure a restriction (which causes backpressure) it will cure reversion because it alters the reverse flow of FRESH AIR that is running backward up the pipe.

ever wonder what causes pops and crackles on decel?
peace

 

[David89gmc]

A basic rule of thumb for gasoline engines is: small pipes for low end, big pipes for high end. A crossover pipe is very important at all rpm, it actually helps push out the exhaust and smooths the exhaust flow.
Diesels don't follow this rule, they just need as little restriction as possible. That's why we see the huge exhaust pipes on diesels.

 

[CRF450R]

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

I did a cat delete full 3" dual exhaust manifolds back double H pipe single chamber thrush bottles 5" chrome tips on 90s it sounds good love it but not it's very quiet so I'm going to switch out to non chambered bottles.

 

[Spookers]

I have found that the smaller the pipe and/or less crossover the more crackles and more drone. 1 of my trucks has shortys 3" collectors that has been y-piped into a single 4" into a modified flowmaster 40 that's single 4 in dual 4 out(used to be 3in dual 2.5out which was a little too crackly/droney for my liking) it sounds awesome really rumbly and little to no drone just loud, I have capped 1 outlet before and that made it a lot quieter. Another truck I have has headers dual 3" x-pipe into a dual in and out 3" magnaflow straight through muffler which then exited behind the cab, that was really droney especially between 1700-2200rpm and ended up y-piping after the muffler to a single 4 into a mbrp straight through, 4" over the axle and out and that really made it a nice daily driver, cruised 65mph at 68-71dbz inside the cab (the dual 3 out the side was 80-85dbz). This guy I know runs dual 2.25, h-piped flowmaster at one point and borla mufflers with manifolds without cats which crackles at an idle, really obnoxious, drones the hell out of the cab, not my cup of tea but he likes it so to each their own.

 

[CRF450R]

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Now this was after I removed the bottles I've since put the bottles back on and it doesn't have that weird raspy rappy sound it had at higher rpms with the bottles now it's just a deep throaty tone I'll make a updated video tomorrow if anyone is interested.

 

[alpinecrick]

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 had the same experience:

1976 K10 SWB 400 factory SBC that was completely stock. 3.73 diffs. About 50k on the odometer and the 400 ci GM engines during that period were rated at 175-180 hp if I remember.

This was in the early 80's, and I installed a set of Cyclone AR1 headers that were advertised specifically for low to mid range RPM's. I drove it around the ranch and on the county roads several times with the open headers before I took it to town and had new exhaust with "turbo" mufflers installed. It had NO low end power from off idle with open headers. I was beginning to think I might have made a mistake.

With the exhaust system installed it improved the low end torque noticeably, didn't make a diff by midrange RPM's though. I put the headers on because I was ready to install a Rancho 2.5" lift with 12.50/33-15 tires--my first set of steel belted radials. With the factory locker diff and those tires that truck was a going sumbee in snow and mud........