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02-04-2010, 10:29 PM | #1 |
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3 inch exhaust too much?
The machine shop told me my engine sould be running about 10:1 compression with my 2.02 double hump heads .40 over 350 with a mild port job. They also told me a 3 inch exhaust with an H pipe will be the ideal exhaust set up for me.
I'm all for the H pipe but 3'' inch exhaust just seems like alittle much for the said engine you know not enough back pressure?
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02-04-2010, 10:36 PM | #2 |
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Re: 3 inch exhaust too much?
I would think so too. I would figure 2.5" would be sufficient with true duals. Dual 3" would be enough for a really "built" 350!
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2007 Sierra Denali 1995 Sierra 4x4 (426,000 miles and counting) 2002 Acura TL-S (how did THAT get here????) |
02-04-2010, 11:15 PM | #3 |
The Engine Whisperer
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Re: 3 inch exhaust too much?
+1 for 2.5in. You'll be happy with the torque gains of 2.5 over 3 also.
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02-04-2010, 11:23 PM | #4 |
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Re: 3 inch exhaust too much?
I'd use 2.5" with an x-pipe. I use a 3" mandrel bent with an x-pipe, but I have a pretty healthy 406 with a mechanical roller cam. You will be much happier with 2.5" Good luck
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02-04-2010, 11:53 PM | #5 |
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Re: 3 inch exhaust too much?
2.5inch
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69 c-10 BBC 462ci, forged crank, H-beam rods, 10.5-1 KB forged pistons, Dart Iron Eagle 308cc, Straub Cam, Comp Cams chrome moly full rollers, Weiand Team G, Prosystems 950, TH400/3500 Dalenzie stall, Currie 9+ Detroit Locker w/31spline axles.3.5/6in drop. My Build. |
02-05-2010, 12:21 AM | #6 |
motor exploder
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Re: 3 inch exhaust too much?
I agree on 2.5" at the most, with an H or X. I talked to one of the guys at Pypes a little while back when I was doing research for my exhaust and was told a 2.5" setup with an X will support a 500-525hp. I wouldn't go to 3" unless I was pushing 550hp or more, especially in a street driven cruiser. I have a friend with a '77 Cheyenne swb with a 450hp 454 and he switched from a set of 2.5" duals to a 3" setup and claimed he lost some torque, but that's just a seat of the pants observation from him.
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02-05-2010, 12:55 PM | #7 |
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Re: 3 inch exhaust too much?
Biggest.....myth.....EVER! Back pressure is a bad thing, and you never want it in your exhaust. I do agree that 2.5" is plenty for the motor in question, but you wouldn't lose any power with 3".....just be a little noisier.
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02-05-2010, 01:58 PM | #8 | |
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Re: 3 inch exhaust too much?
Quote:
2.5" is plenty for that combo, but 3" would be bada$$. It did on my 355. Flowmaster sells a universal exhaust kit that works well on our trucks. That is what I made mine with. I am actually selling mine and you can see pictures in the classified section.
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02-05-2010, 02:23 PM | #9 |
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Re: 3 inch exhaust too much?
2.5" for a small block, 3" for a big block.
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02-05-2010, 09:15 PM | #10 |
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Re: 3 inch exhaust too much?
When It comes to gettings exhaust done I may go with the 3 inch exhaust if it isn't going to hurt me.
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02-05-2010, 09:39 PM | #11 |
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Re: 3 inch exhaust too much?
from what i read a long time ago in a hot rod/or similar mag..... use what the ENGINE NEEDS to the muffler and after the muffler WHAT EVER YOU WANT...... a engine is a big air pump, ya just gotta figure out how big is needed to get all the air OUT thats been sucked IN.....
3" would def. sound good.. |
02-05-2010, 11:32 PM | #12 |
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Re: 3 inch exhaust too much?
Hmmm.. I must have too big of an exhaust for my 347ci motor..
BTW, bellow are a couple dynograph overlays showing a mild cam and bolt on 347ci 3rd gen motor (stock heads). The lower numbers are going through 3" exhaust to the cut out then necks down to the 2.5" exhaust to the mufflers. The higher numbers are with the cut outs open IE dual 3" straight open.. I have done several exhaust similar to this, some 3" all the way through, some necked down to try and quiet it down a little.. All of them showed gains in both TQ and HP under the curve with less restriction. I was proving a lot of people wrong back in 01 about back pressure. Even with stock cams, the gains were all over.. I think a well thought out set of headers make the biggest difference with exhaust scavenging.
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02-06-2010, 11:04 AM | #13 | |
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Re: 3 inch exhaust too much?
Quote:
I'm planning to do 3" from the collector through the mufflers w/some 2.5" tail-pipes for a slightly warmed over 350 (and I do mean slightly....) because eventually it will get a 408/AFR combo sitting on the stand & I want to spend my money wisely. I figure that's a good all around compromise.
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02-06-2010, 12:32 PM | #14 | |
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Re: 3 inch exhaust too much?
Quote:
I was waiting for someone to bring that up. If you have a set of super cheepie 1-1/2" long tube blackjack headers dumping into a 2-1/2" collector,, ,,, dumping that into a 3" exhaust pipe and muffler just doesn't make any sense to me. THINK the system all the way through. Good pieces here and there just don't get the job done.
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03-10-2010, 06:41 PM | #15 |
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Re: 3 inch exhaust too much?
My BBC has 1.625 headers w/ 3" collectors. The old exhaust system was 2.5" thru cherry bombs and out behind the tires. All of that was cut out and 3" thru flowmasters dumping in front of the rear axle made a helluva difference. Another bonus is that it isn't really that much louder.
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03-19-2010, 04:49 AM | #16 |
"THE GREEN GOBLIN"
Join Date: Mar 2008
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Re: 3 inch exhaust too much?
Im running a 3" exhaust setup my mechanic recomended for the motor he build for the truck. Others would disagree but I like it.
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Petey-pablo
"THE GREEN GOBLIN" 1972 Cheyenne 10 Short Fleet Side Front 2.5inch Spindles with 2inch Springs Rear 4inch drop Springs. 454BBC TH400,Posi 1971 Cheyenne 10 Long Fleet Side 454BBC TH350,Posi Sold Drive it like you stole it! Petey-pablo@sbcglobal.net |
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