Questions on 2.5" vs 3" Exhaust - Page 3 - Chevelle Tech
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post #31 of 91 (permalink) Old Dec 5th, 18, 6:57 PM
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jerry
 
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Re: Questions on 2.5" vs 3" Exhaust

Quote:
Originally Posted by mr 4 speed View Post
Use a 3" inlet/outlet muffler with a tapered reducer for the 2.5" tailpipes.
This....I couldn't find any SS mufflers that had a 3" in and 2 1/2" out that had a staggered left/right which is needed for proper A body fitment.
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post #32 of 91 (permalink) Old Dec 5th, 18, 7:31 PM
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Re: Questions on 2.5" vs 3" Exhaust

Quote:
Originally Posted by cheveslakr View Post
This....I couldn't find any SS mufflers that had a 3" in and 2 1/2" out that had a staggered left/right which is needed for proper A body fitment.
Do you guy's have enough room to put a reducer out of the muffler?
I'd just reduce it to 2.5" before the muffler.
Then you could fit the long tapered reducer in no problem.

I had zero room to do that.
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post #33 of 91 (permalink) Old Dec 5th, 18, 10:07 PM
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Re: Questions on 2.5" vs 3" Exhaust

Here is what I had done to my Exhaust so it would be Quiet on the Street
and I could uncork the Cutouts at the Track for Performance Runs
HAD
HEADERS-Hookers # 2455-1HKR CeramicCoated OD#s 2 Tubes x 30 Long / Collectors 3.5 x 10 Long
http://www.jegs.com/i/Hooker-Headers...d=#moreDetails

Reducers 3.5 to 2.5 CeramicCoated = http://www.jegs.com/i/Hooker-Headers...10351/10002/-1

FlowMasterAmnThunder #17119 2.5 Mandrel Bent / Super 40 Series Mufflers
http://www.jegs.com/i/Flowmaster/389/17119/10002/-1

Did this to Exhaust :
1. Cutoff 3.5" to 2.5" Reducer and some 2.5" Piping to before H pipe
2. New Hooker 3.5 Flange Kit # 11435 $ 49.Cdn x 3 https://www.jegs.com/i/Hooker-Header...11435/10002/-1
3. Hooker # 11235 3.5 Header Extensions $ 83.us
.... https://www.jegs.com/i/Hooker-Header...11235/10002/-1
4. Vibrant # 129970 - 3.5 Steel Circles for Blockoffs on Cutouts $ 46.45 Cdn
5. Vibrant # 13073 S/S Pipe 3.5 Mandrel Bent 60* attached to Header Ext then to 2.5 Exhaust before H & Piping to Mufflers
.... https://www.jegs.com/i/Vibrant-Perfo...13073/10002/-1
6. Vibrant# 16635 AdapterFitting https://www.jegs.com/i/Vibrant-Perfo...16635/10002/-1 $7.us x 5
... Vibrant # 1194 02SensorFitting https://www.jegs.com/i/Vibrant-Perfo.../1194/10002/-1 $14.us x 2
... Russell # 624183 Hose End Fitting 90* https://www.jegs.com/i/Russell/799/624183/10002/-1 $24.us x 2
7. Have Extension to attach at the Track also so the Exhaust from them Exits past the Body of the car at the Doors






67 Chevelle Malibu SS Cdn
Born 283 / PG / A51
468/TH400 2,500 stall/ S60 3.70 Gs
Prev Best on M/T ET S/S #3454 street Tires/Dress 2018/05/20
60' = 1.664
1/8 = 7.532 et / 91 mph
1/4 = 11.814 et / 115 mph
NEW Best with 3,500+ Stall TC 2019/06/23
60' = 1.561
1/8 = 7.411 et / 90.18 mph
1/4 = ??.??? et / ??? mph


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post #34 of 91 (permalink) Old Dec 5th, 18, 10:25 PM
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Re: Questions on 2.5" vs 3" Exhaust

Quote:
Originally Posted by WHT/73 View Post
Do you guy's have enough room to put a reducer out of the muffler?
I'd just reduce it to 2.5" before the muffler.
Then you could fit the long tapered reducer in no problem.

I had zero room to do that.
The muffler outlet was over 3" long, cut that shorter and welded on a swedged reducer. Overall length was the same.
Not sure if every muffler shop can supply these fittings. I found a local high end fabricator who specialized in 304 SS pipes. He had a mandrel bender and swedged tool. I'd bet most large towns will have at least one of these type shops.
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post #35 of 91 (permalink) Old Dec 6th, 18, 4:13 PM
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Here’s what the reduced X looked like.
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73 nova,3515#(all steel)Pump gas!(91octane)406ci N/A, best 1/4,1.45 '60,[email protected],10.6 @ 122.38, short shifting,NO tuning!


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post #36 of 91 (permalink) Old Dec 6th, 18, 9:24 PM
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Re: Questions on 2.5" vs 3" Exhaust

Just a comment on the whole "exhaust" subject. To be clear, this is NOT directed at anyone in this thread...

In my opinion, people get WAY too hung up on stuff like 2.5" vs 3", and muffler "X" vs muffler "Y". A dual 2.5" system with a crossover of some type and a pair of large body performance mufflers (AP xlerator, Dynomax Turbos, magnaflow, etc) will work well for 90% of the applications on this forum (250 to 550 hp SBCs/BBCs).

While there are probably a few ponies to be found in experimenting with different configurations, there are much better places to spend your time and money. Unless you are sure the rest of your combo is 99% optimized, pick something as described above that fits well, and has the sound you desire and move on. Most out-of-the-box headers are so far from optimal anyway (primary tubes too big, collectors WAY too big, etc), so why strive for perfection on the rest of the system?

I have the same opinion when it comes to choosing between different dual-plane intakes, or one carburetor vs another (assuming similar CFM), but that is a whole 'nother can of worms.

Again, JMO.
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post #37 of 91 (permalink) Old Dec 7th, 18, 5:12 AM
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Re: Questions on 2.5" vs 3" Exhaust

Only input I will give to this thread is, with the 469" motor, I ran Hedman 68198 (1.75 x 3" ) headers into 3" pipes with 3" X-pipe installed , through Pypes 3" in/out 18" Race Pro mufflers. I did have 3" tails, but I do think 2.5" tails would have worked fine. Exhaust volume was very manageable cruising around and sounded great at WOT. Probably could've ran 2.5" head pipes with little to no compromise. I think the big issue is whether you run a straight thru design muffler or baffled.
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post #38 of 91 (permalink) Old Dec 7th, 18, 7:07 AM
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Re: Questions on 2.5" vs 3" Exhaust

OP, you confused yet?

BTW, I run Magnaflow 12578 mufflers, with 2.5" tails swedged up to fit the 3" outlets. Too much discussion over nothing in a few posts. 2.5" tails and 3" mufflers get swedged together, no reducers. Thats what the pro installers did on mine. In fact, I dont know if 3" swedged down, or 2.5" swedged up, or BOTH!

So I go back to , I;d use 3" headpipes and 2.5" tails. 3" muffs will be slightly louder than 2.5" muffs. You choose.
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post #39 of 91 (permalink) Old Dec 7th, 18, 10:09 AM
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Re: Questions on 2.5" vs 3" Exhaust

As i have posted, i have a .030 over l88 short block and recently purchased a top end 215 heads, strip dominator intake with the matching cam of my guy a the shop. My truck has 3 inch collector tubes. My guy said the run the primary part off the collectors the same size. I have 3 inch chambered mufflers to try and see how they work. Truck currently has 3 inch flow masters. If i put on tail pipes that is where i might go down to 2 and one half inch pipes to help go over the rear axle. Anyone know anything about the chambered mufflers. I fully expect this truck to run 10.0 in the 1/4 mile too
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post #40 of 91 (permalink) Old Dec 7th, 18, 11:25 AM
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Re: Questions on 2.5" vs 3" Exhaust

Quote:
Originally Posted by 427L88 View Post
OP, you confused yet?

BTW, I run Magnaflow 12578 mufflers, with 2.5" tails swedged up to fit the 3" outlets. Too much discussion over nothing in a few posts. 2.5" tails and 3" mufflers get swedged together, no reducers. Thats what the pro installers did on mine. In fact, I dont know if 3" swedged down, or 2.5" swedged up, or BOTH!

So I go back to , I;d use 3" headpipes and 2.5" tails. 3" muffs will be slightly louder than 2.5" muffs. You choose.
Very close to setup I ran, except mufflers were 18" instead of 22" and had 3" tails. Your car has ran 116-117 mph (is that correct??), my 469" motor was running about the same, tells me not much HP difference in 3" tails vs 2.5" tails. Obviously not apples to apples, but hey what is.

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post #41 of 91 (permalink) Old Dec 7th, 18, 11:27 AM
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Re: Questions on 2.5" vs 3" Exhaust

Quote:
Originally Posted by RickyHill View Post
As i have posted, i have a .030 over l88 short block and recently purchased a top end 215 heads, strip dominator intake with the matching cam of my guy a the shop. My truck has 3 inch collector tubes. My guy said the run the primary part off the collectors the same size. I have 3 inch chambered mufflers to try and see how they work. Truck currently has 3 inch flow masters. If i put on tail pipes that is where i might go down to 2 and one half inch pipes to help go over the rear axle. Anyone know anything about the chambered mufflers. I fully expect this truck to run 10.0 in the 1/4 mile too

This is a whole other topic. Chambered mufflers is one thing, expecting a truck to run 10.0 in the 1/4 is quite another. What kind of truck? Are you going to run 5.13 gears? Spray it with a lot of N2O?

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post #42 of 91 (permalink) Old Dec 7th, 18, 1:21 PM
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Re: Questions on 2.5" vs 3" Exhaust

Chambered mufflers CAN rob a ton of HP depending on size and # of baffles. "it depends on the bends". Wait! I said that b4 in this thread!~ No issue with straight thrus on that. Tryin' to squeeze 600hp out of a 427, they better be 2 chambered Race flows imho.

PS, that system I put up was designed for a full on 427 OR a bigger cube 650+ monster. 3.5" collectors thru 3.5" X 3" X pipe back to Magnaflow 12578 #" straight thru muffs.

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post #43 of 91 (permalink) Old Dec 7th, 18, 2:10 PM
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Re: Questions on 2.5" vs 3" Exhaust

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Originally Posted by GRN69CHV View Post
This is a whole other topic. Chambered mufflers is one thing, expecting a truck to run 10.0 in the 1/4 is quite another. What kind of truck? Are you going to run 5.13 gears? Spray it with a lot of N2O?
My S10 has run low low 9 seconds already with one of my old 360 motors. I bought this kit of mrnova that Struab keeps thinking i am. Its some old magazine engine. 427 that ran 10.7 in the quater mile with more then 3600 lbs weight. Mrnova had it running 10.4 in a nova. I think my s10 is 500 lbs lighter. The us only motor. My frame is boxed and i have 12 1/2 by 29 inch tires. It has California tack spings with traction bar not the California tack bars. I took the roll bar out for the street. Only 4.10 from the 4.88 the 360 runs. I think my mufflers came from classic chambered exhaust. They are 3 inch ones. Guess we will see. I did a post a while back asking about head bolts for some heads. Mrnova said these heads were better then the aluminum i think they were procomp heads. So we will see in the summer.
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post #44 of 91 (permalink) Old Dec 7th, 18, 5:51 PM
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Re: Questions on 2.5" vs 3" Exhaust

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Originally Posted by RickyHill View Post
My S10 has run low low 9 seconds already with one of my old 360 motors. I bought this kit of mrnova that Struab keeps thinking i am. Its some old magazine engine. 427 that ran 10.7 in the quater mile with more then 3600 lbs weight. Mrnova had it running 10.4 in a nova. I think my s10 is 500 lbs lighter. The us only motor. My frame is boxed and i have 12 1/2 by 29 inch tires. It has California tack spings with traction bar not the California tack bars. I took the roll bar out for the street. Only 4.10 from the 4.88 the 360 runs. I think my mufflers came from classic chambered exhaust. They are 3 inch ones. Guess we will see. I did a post a while back asking about head bolts for some heads. Mrnova said these heads were better then the aluminum i think they were procomp heads. So we will see in the summer.

Should've known you were talking S10. Is that even considered a truck????

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post #45 of 91 (permalink) Old Dec 8th, 18, 5:55 AM Thread Starter
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Re: Questions on 2.5" vs 3" Exhaust

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Originally Posted by 427L88 View Post
OP, you confused yet?
LOL....yeah Gene, seems like we're all over the map on this one, but it makes for some interesting discussion.

I guess I should come clean as to why I'm considering a 2.5" vs the 3" exhaust on the 496. I mentioned earlier that it was due to "space limitations" and what I meant by that is, I plan on installing an air ride system on the Impala and slamming it on the ground. So the exhaust has to be tucked up tight to the floor pans and not hung down below the frame. Like everything else in life, there's always a compromise to get what you want. And in my case, maybe giving up some performance to achieve the slammed look maybe the case in my situation.


This is what I'm considering......Shorty headers (el' cheapo's from Ebay) 1.75" primaries with 3" collectors. 3" spintech oval tubing piped back to the rearend (no mufflers). reduce down to 2.5" to route over the rear axle and tuck in a 2.5" straight thru exhaust resonator (glass pack) and dump exhaust down at the rear bumper. I'll probably add an H or X pipe in there if there's clearance, and I'm also considering some electric exhaust cutouts to help the 496 breath a little easier when the youngster with the 5.0 coyote wants a little bit of the old school hot rod, lol .
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