2.5 vs 2.25 diameter exhaust

Discussion on fuel delivery & intake/exhaust tech & mods.
Numbah1
Posts: 75
Joined: Sun Jan 27, 2019 9:45 pm

2.5 vs 2.25 diameter exhaust

Post by Numbah1 »

Im just curious if anyone has proof that going to 2.5 *before the resonator* gives more than 5whp lol i find it weird that solo asked if i was super charged and b.c im not doesnt recommend 3" exhaust but the 2.5 was better, which i believe but i haven't found the a comparison. I also thought thought there was a kooks system that pairs with the stock mufflers, further making the argument that 2.25 - as long as the resonator and possibly pup cats are gone - are ok for even mild cams atleast. Thoughts?
s/c'd cav
Posts: 1382
Joined: Mon May 30, 2016 3:12 am
Location: PHOENIX AZ

Re: 2.5 vs 2.25 diameter exhaust

Post by s/c'd cav »

if you never race it , 99% street driven 2 1/4 is plenty

the larger the tubing the higher up peak hp will be , kooks and arh both go from 3" into 2 1/2" , into the stock , this also help some with exhaust velocity
Numbah1
Posts: 75
Joined: Sun Jan 27, 2019 9:45 pm

Re: 2.5 vs 2.25 diameter exhaust

Post by Numbah1 »

I race my car, want to lower my ET by something noticable for the work though. Have jba long tubes and catted connections pipes, then went into a 2.25 x pipe and stock back with qtp cutouts. Thinking about going 2.5" xpipe back. There doesnt seem to be alot of difference based on the FB pages dyno posts.
s/c'd cav
Posts: 1382
Joined: Mon May 30, 2016 3:12 am
Location: PHOENIX AZ

Re: 2.5 vs 2.25 diameter exhaust

Post by s/c'd cav »

how much power is the car making at the wheels , what size converter , what do you run at the track , was the cam set up for low to mid power , mid to high , or high ? when you race is it just the occasional night ? every weekend ?

2 1/4 is good around 500 , if all bends are mandrel , crush will lower it some , yes it can keep the car a little slower at the track , street manners will be better , from there the larger you go the more the tables tip to better track times

i know alot of people making over 800 wheel using the kooks/arh set up , through 2 1/2 mufflers , and running into the 9s

i used to drive my 327 4sp elco 90 minutes to the track , and knock big block powered cars on slicks and open exhaust , turn around and drive home , no loading/unloading , wrenching tweaking , and having more fun and wins
Numbah1
Posts: 75
Joined: Sun Jan 27, 2019 9:45 pm

Re: 2.5 vs 2.25 diameter exhaust

Post by Numbah1 »

Its a stock cam, thats why im wondering if ill gain anything. I have otr cai, rod mod manifold, headers, x pipe, cutouts and i just want it right b4 i remote tune. After all that, i dont want to leave 5hp out, 4 and its ok haha

Would it pick up another 5 going 2.5 after the header connection pipes?
s/c'd cav
Posts: 1382
Joined: Mon May 30, 2016 3:12 am
Location: PHOENIX AZ

Re: 2.5 vs 2.25 diameter exhaust

Post by s/c'd cav »

id worry/plan about spending money else where , 5hp is well with in a dynos error factor
CapriceX2
Posts: 85
Joined: Sat Jun 22, 2019 10:06 am

Re: 2.5 vs 2.25 diameter exhaust

Post by CapriceX2 »

I’ve read a lot of Vizard’s articles and he indicates that 2.25” pipes are good for up to about 415 HP without being a restriction. 2.5” should be good for up to 514 HP. I’d guess that 2.25” pipes are probably going to be a little small for you, but no idea if going bigger will get you 5+ HP.
CapriceX2
2011 Caprice 9C3 - TSP 220R W/ DOD delete, 10.8:1 Compression, Custom Stainless Exhaust
1995 Caprice Classic Wagon
1996 K2500 6.5L diesel
Willigaf
Posts: 71
Joined: Wed Aug 12, 2020 9:29 am

Re: 2.5 vs 2.25 diameter exhaust

Post by Willigaf »

I was skeptical after reading this thread and my friend reminded me about a vid I'd seen on youtube. I was ready to leave the exhaust alone. Engine masters on the motor trend channel had done this a while ago and no, their 514 making like 650+ on the engine dyno doesn't really compare...

But all other things the same, they dynoed with 2.5 inch exhaust and then gained like 15 crank with 3 inch.

I AM trying to make about 615-620 at the crank, so if I can find a 3 inch cat back for a friendly price I'll probably grab it.
User avatar
kevink
Posts: 480
Joined: Sun Aug 09, 2015 12:55 pm

Re: 2.5 vs 2.25 diameter exhaust

Post by kevink »

At 600, you're definitely going to want a full 3" mandrel bent system. Do you need it? NO. Will you make more power with it? Yes, most likely.
2011 9C3: 11.48 @118.
s/c'd cav
Posts: 1382
Joined: Mon May 30, 2016 3:12 am
Location: PHOENIX AZ

Re: 2.5 vs 2.25 diameter exhaust

Post by s/c'd cav »

Willigaf wrote: Wed Aug 26, 2020 7:49 am I was skeptical after reading this thread and my friend reminded me about a vid I'd seen on youtube. I was ready to leave the exhaust alone. Engine masters on the motor trend channel had done this a while ago and no, their 514 making like 650+ on the engine dyno doesn't really compare...

But all other things the same, they dynoed with 2.5 inch exhaust and then gained like 15 crank with 3 inch.

I AM trying to make about 615-620 at the crank, so if I can find a 3 inch cat back for a friendly price I'll probably grab it.
that 15hp at the crank , is with in the error factor at the wheels

but as i said before , a track only car will benefit from it , more than a street car will
Post Reply