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Posted: Tue Sep 04, 2007 12:03 am Post subject: WHAT SIZE EXHAUST?
hey guys, I have a question of my own hopefully u guys can help me. Well here it goes, I'm in search of a exaust system for my elko, the motor that i have is a well built 383 that consist of new AFR 195 eliminator heads, probe forge pistons with 11.5:1 comp, solid roller engale cam with 242 duration, 1.6 roller rockers, 750 demon carb, with a single plane intake manifold, aslo have 1 5/8 dougs headers. As for the driv trian, is a well built 700R tranny with a 3000 vigilantie stall converter. So what size exaust system would you guys recommend? 2.5 w/ X pipe or 3" w/ X pipe. Also what type of mufflers do u recommend.
Necoa #: 6858
Location: 7(AL,GA,TN)
Joined: Feb 07, 2006
Posts: 937
Year: 1970
Model: El Camino
Posted: Tue Sep 04, 2007 8:53 pm Post subject: exhaust
From the Oct/07 Chevy Hi Perf, Kevin McClelland's Q&A . " Should you run 3-inch on your Chevelle? First, Flowmaster dosen't recommend using 3-inch systems on the street because of sound issues. The 2.5-inch system will support up to 450 hp with little or no power loss over open exhaust. You also have much better torque for street use with 2.5-inch tubing. With 3-inch you loose exhaust velocity and torque right where you drive on the street." Kevins words, not mine but I respect what he says. _________________ Jim
70 ElCamino 461 solid M20 331eaton
http://elcaminocentral.com/gallery-album_album346.html
From the Oct/07 Chevy Hi Perf, Kevin McClelland's Q&A . " Should you run 3-inch on your Chevelle? First, Flowmaster doesn't recommend using 3-inch systems on the street because of sound issues. The 2.5-inch system will support up to 450 hp with little or no power loss over open exhaust. You also have much better torque for street use with 2.5-inch tubing. With 3-inch you loose exhaust velocity and torque right where you drive on the street." Kevins words, not mine but I respect what he says.
Noise issues? 2 1/2" can create noise issues!!!
A good compromise is to run 3" to the mufflers then 2 1/2 from the mufflers back.
As for 2 1/2" supporting 450hp with little or no power loss, I'm not buying that, but there are many factors involved though and I think a general statement one way or the other could be wrong for any particular car.. I have 3" pipes about 2' long coming off the headers with cutouts on the end. then 2 1/2 branching off into the mufflers and out behind the rear wheels. I have not yet made back to back runs at the track with the exhaust open as opposed to closed. BUT, if smoke off the drag radials is any indication when playing around on some backroads tire smoke increases dramatically with the exhaust open. My big block has 350hp at the rear wheels so I'm damn close to 450HP at the flywheel. I would think a mild small block may not be as sensitive to exhaust changes but a stroked and roller cammed small block would have to be better with the bigger exhaust, but again, just another generalization.
So in short, if the only issue is too much noise then stick with the 2 1/2", otherwise what's it going to hurt to up it to 3"? _________________ Ol Paint and me
454/700R4/3.31 posi
8.30 @ 82.23 / 60ft @ 1.82
AND
14.5 mpg average on HRPT 2006
Necoa #: 6858
Location: 7(AL,GA,TN)
Joined: Feb 07, 2006
Posts: 937
Year: 1970
Model: El Camino
Posted: Wed Sep 05, 2007 7:54 pm Post subject: exhaust
I agree, James. This is something that would be case by case. The guy that asked Kevin the question described his car as a 70 Chevelle with a 350. No doubt a large displacement engine will benefit from the big pipes simply because it pumps more air. I do however like what he said about the exhaust velocity with the 2.5 system. There would seem to be a scavenging benifit like that of a smaller intake runner. A benefit for a street engine that would not apply with a race engine. _________________ Jim
70 ElCamino 461 solid M20 331eaton
http://elcaminocentral.com/gallery-album_album346.html
My personal choice is to run the 3" to the crossover or X pipe and 2 1/2 on back it makes putting the system in so much easier and does not hurt the power in any way on an engine of this type---thats what I have on my Monte Carlo SS with a 383, th700r4 and 3.73...I run 12.80s through the pipes on street radials....A 383 is a torque motor and seldom sees the plus side of 6000 and unless the head ports are huge you slow it down to go much higher.also after the crossover the flow is more of a continuous flow and less pulsing as with separate pipes all the way back....I have noticed no increase in mph or lowering of the ET with the headers open even----just my personal experience....oh I went with the flowmasters and they are pretty loud at full song but not too bad just cruising...........Dan _________________ I don't think I have ever had a car that was "FINISHED"........unless it was totaled.
I do however like what he said about the exhaust velocity with the 2.5 system. There would seem to be a scavenging benifit like that of a smaller intake runner. A benefit for a street engine that would not apply with a race engine.
Yep, and as old coot points out the hybrid of starting out with 3" and reducing to 2 1/2" is a very good option. I don't think it would matter if you reduced before the x-pipe or at the mufflers but it would still make for a good exhaust set up. _________________ Ol Paint and me
454/700R4/3.31 posi
8.30 @ 82.23 / 60ft @ 1.82
AND
14.5 mpg average on HRPT 2006
I'm not sure on a 5th gen but my 3rd gen is offset/offset. Lots of variables though unless you go with a complete aftermarket kit specifically for your application. _________________ Ol Paint and me
454/700R4/3.31 posi
8.30 @ 82.23 / 60ft @ 1.82
AND
14.5 mpg average on HRPT 2006
Necoa #: 10061
Location: 15(AZ,NM)
Joined: Aug 29, 2007
Posts: 6
Year: 1970
Model: El Camino
Posted: Wed Sep 12, 2007 5:43 am Post subject:
Your exhaust selection will depend a lot on how loud you want your car to be. Another thing to consider is emission testing. I am not familiar with the laws in your state but here in Arizona the pipes have to run to the rear of the bumper or in front of or in back of the rear tire. This is to make it easier for the monkeys at the emission testing station to hook up the sniffers to read your emissions. Also here in Arizona depending on the year of your El Camino, you are also subjected to under the hood inspection to make sure the factory emissions equipment is present.
With the setup you have I would not hesitate one bit to go with a full 3" exhaust with Flowmaster mufflers. Make sure you have the exhaust bends in the pipe mandrel bent. That is one of the biggest mistakes people make when getting exhaust work done. They go to a shop to have the exhaust done and the shop does not do mandrel bends. But again this will dictated by how loud you and your neighbors can live with. _________________ In the hot desert!
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