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WagonCrazy
12-10-2017, 09:37 PM
Also pondering this question, and wanted some real world experience so went to youtube and found this video that compares 2 systems on an engine via a dyno, tracking and analyzing the results.


https://www.youtube.com/watch?v=_PVXvHkr-Vs

So with my Nomad engine being a bone stock LS1 (about 340 horsepower) and the desire for quieter (3 chamber mufflers), I'm wondering if I need to bother with a 3 inch system?
Either diameter size would fit (with the thru frame AME cross members I have welded into my frame).

Let's hear it guys, what's your real world experience with 2 1/2 or 3 inch exhaust?

Rick_L
12-11-2017, 06:32 AM
I built a hybrid 3" to 2-1/2" system. 3" from the collectors to the mufflers, a 3" muffler with 3" to 2-1/2" adapters welded to it, and 2-1/2" beyond that. Flowmaster 2-1/2" mandrel bent tailpipes, modified to suit.

chevynut
12-11-2017, 09:12 AM
I went with 3.5” pipes from the header collectors to the cutouts and 3” to the x-pipe and beyond that. But that’s with a 502 that pumps a lot more air than an ls1 at any RPM. Unless you’re planning a bigger engine or supercharging I’d stick with the smaller pipes. I think 3” is typically recommended over around 500 hp.

markm
12-11-2017, 09:22 AM
I have owned numerous street strip cars over the past 40 some years both SBC and BBC and found little if any difference in et open headers or muffled when equipped with a good 2.5 system. Have ran strip only SBC car with exhaust because it really did not hurt performance.

NickP
12-11-2017, 09:53 AM
Also pondering this question, and wanted some real world experience so went to youtube and found this video that compares 2 systems on an engine via a dyno, tracking and analyzing the results.


https://www.youtube.com/watch?v=_PVXvHkr-Vs

So with my Nomad engine being a bone stock LS1 (about 340 horsepower) and the desire for quieter (3 chamber mufflers), I'm wondering if I need to bother with a 3 inch system?
Either diameter size would fit (with the thru frame AME cross members I have welded into my frame).

Let's hear it guys, what's your real world experience with 2 1/2 or 3 inch exhaust?

Bone stock, 2-1/2". I see no need for anything larger. If space allows, either an X or crossover should tone it down also. I'm not a fan of the pictured mufflers though but have found Borla to be the quieter of selections out there. Traveling any distance with that constant drone is un-nerving at best.

Bitchin'57
12-11-2017, 01:56 PM
I agree, at your horsepower level, a 2-1/2" system is fine.

enigma57
12-15-2017, 06:49 PM
Some years ago, David Vizard conducted tests to determine what it would take to build a full length muffled exhaust system for a race car that made the same power throughout the engine's operating range as with open headers.

He determined that the key to doing this is to build a system that will flow 2.2 cfm per HP generated (measured at flywheel).

Exhaust sizing......

Vizard's rules of thumb: A pipe will flow 115cfm per square inch of cross-sectional area (measured as ID). You need 2.2 cfm of flow capacity per horsepower.


350 HP X 2.2 = 770 cfm


770 divided by 115 = 6.695 sq. in. CSA = 2.91" ID (round to 3" OD) single pipe or dual pipes 2.06" ID (round to 2-1/4" OD)


Bear in mind that this is based upon flow through straight pipe. There will be some degree of friction loss at each piping offset or bend. The more offsets or bends, the more friction loss and the tighter the bends, the more friction loss. So use mandrel bends and build your system with as few offsets or bends as possible and make any bends you must use with as long a radius as you can fit in the space available.

Regarding mufflers, the 2.2 cfm per HP generated rule of thumb applies there, as well. I like the Dynaflow Super Turbo mufflers (quieter and flow better than Flowmaster in tests of same size mufflers). The older listings for the Super Turbo mufflers actually had a HP capacity based upon 2.2 cfm listed beneath the mufflers on their website (may still be there).

Now that does not mean that a size smaller system will not work with the same displacement and max RPMs at redline (think of the engine as an air pump). It just means that a smaller size system will begin to be restrictive and choke flow (rob a bit of power) before redline RPMs are reached.

Anyway...... If you are building a system for a 350 HP engine, 2-1/2" OD duals should be all that you need (in theory, 2-1/4" OD would 'just' do it, but in the real world, 2-1/2" should make up for friction losses at offsets and bends). Just make sure your mufflers do not restrict flow volume. One school of thought holds that it would be fine to downsize your tailpipe from muffler exit to point of discharge at rear of vehicle for reasons I won't go into here. On the other hand, I have run larger systems than absolutely necessary on several cars I have built and it has never been a problem. Ran 2-1/4" OD single exhaust system on 1600cc (98 cu. in.) Toyota engine and 2-1/2" OD single exhaust system on 170 cu. in. slant 6 many moons ago.

Add a full sized crossover (balance) pipe connecting left and right bank and you should be good to go. Either an 'H'-type or 'X'-type balance pipe will do just fine. 'X'-type only has a small advantage over 'H'-type in those instances where center of 'X'-type can be placed at exact point (length) that correctly tuned header collector extensions would terminate if car was running open headers on the track at RPM where max VE is achieved (usually a couple hundred RPMs past peak torque).

2-1/2" duals with mandrel bends should flow sufficiently to support over 400 HP so long as mufflers also flow 2.2 cfm (or better) per HP at peak.

Hope this gives you some ideas,

Harry

WagonCrazy
12-16-2017, 10:11 AM
I'm going with 2 1/2 diameter. Still pondering the materials though. (Stainless or mild steel). We're still debating pros and cons on that on the other thread I started here in the Exhaust forum.
Thanks for your advice guys.

Rustaddict
12-16-2017, 05:39 PM
I'm going with 2 1/2 diameter. Still pondering the materials though. (Stainless or mild steel). We're still debating pros and cons on that on the other thread I started here in the Exhaust forum.
Thanks for your advice guys.

What kind of mufflers are you going with ?

Rick_L
12-16-2017, 05:53 PM
Key question here is does a muffler with 3" inlet and outlet flow better than one with 2-1/2" inlet and outlet? It certainly won't flow less. The muffler is the deciding factor here.

It's also why I think a Flowmaster at least has the chance of being less restrictive due to its large case. Just a gut feel other than its reputation.

Rustaddict
12-16-2017, 08:28 PM
I agree. Rumor has it that many mufflers with 3 inch or bigger inlets and outlets still only have 2 1/2" or less OD on the piping on the inside.

WagonCrazy
12-20-2017, 09:33 AM
I'll post some links to the mufflers I'm considering very soon.

WagonCrazy
03-25-2018, 07:16 PM
Went with 2 1/2 inch exhaust system. Aluminized pipe and bends, magnaflow mufflers, v band clamps, chrome tips. Parts ordered from Summit Racing...about $700 total.
Pics coming soon (the photo loader on this site doesn't seem to be working at the moment)

WagonCrazy
03-25-2018, 07:32 PM
8554

8555

8556

8557

8558

WagonCrazy
03-25-2018, 07:38 PM
Some of my Mig welding skills on display here. I'm a practically blind hobby welder at best. 110v Lincoln 135 with argon mix bottle.

8559

8560

55 Tony
03-26-2018, 06:15 AM
Some of my Mig welding skills on display here. I'm a practically blind hobby welder at best. 110v Lincoln 135 with argon mix bottle.


I've done a lot worse. After a long time of crappy Mig welds I found it worked better with flux core wire. Now I save the mig for really light stuff and do better with a stick and a buzz box. Looks like you cheated and did many small welds instead of moving, I should try that with my POS welder.

chevynut
03-26-2018, 10:22 PM
Paul, why aren't you using your TIG welder for that? I think it would work a lot better for that kind of work. Here's my v-bands in stainless......

8584

And here's mild steel on the headers and O2 bungs with TIG:

8585

WagonCrazy
03-27-2018, 08:13 AM
Paul, why aren't you using your TIG welder for that?

Ummm...because I don't own a TIG welder. Only the little Lincoln Mig. So using what I have and sacrificing on the look. This whole exhaust system gets jet hot coated at some point anyway...

55 Rescue Dog
03-27-2018, 08:59 AM
It looks like you might be welding outside. Any breeze at all will plays havoc with a weld, and it looks like on some of the tacks it didn't have shielding gas on it. It looks like it will work fine though.

chevynut
03-27-2018, 09:18 AM
Ummm...because I don't own a TIG welder. Only the little Lincoln Mig. So using what I have and sacrificing on the look. This whole exhaust system gets jet hot coated at some point anyway...

Sorry I thought you said you owned a TIG. :)

markm
03-27-2018, 09:19 AM
It looks like you might be welding outside. Any breeze at all will plays havoc with a weld, and it looks like on some of the tacks it didn't have shielding gas on it. It looks like it will work fine though.

That was my best guess too, however. since I was not 100% I was afraid of stating my opinion and giving the troll a reason to bad mouth me.

chevynut
03-27-2018, 09:29 AM
That was my best guess too, however. since I was not 100% I was afraid of stating my opinion and giving the troll a reason to bad mouth me.

Says the troll who has never even demonstrated that he knows how to turn a welder on. He probably still uses a stick welder....from the 60's. :D

55 Rescue Dog
03-28-2018, 05:42 PM
Says the troll who has never even demonstrated that he knows how to turn a welder on. He probably still uses a stick welder....from the 60's. :D
Can a TIG welder be used for underwater welding, or something like bridge building? Some of the best welding I've ever seen was done with either a stick or a torch. I never even heard of what a TIG welder was, when I was in the Navy when ouur ship was in the yard for repairs/rebuilding.
https://en.wikipedia.org/wiki/Shielded_metal_arc_welding

markm
03-29-2018, 04:50 PM
Actually my stick welder was upgraded in the mid 80s, got my first mig about then also, have since bought two more. I now have a 90 amp 110v, 140amp 220v and 225amp 220v models.