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Old 05-12-2009, 10:38 PM
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single vs duel exhaust

Just wondering If I need to change my exhaust. Right now I have a 350sbc with shorty headers. 2.5 Primaries that come to a 3 collector then into a glass-pack the straight out. Would I be better with 2.5 all the way out? I have
no cat , and have limitless room under my "hot rod".
Thanks 811800

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Old 05-12-2009, 11:12 PM
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Hi,
2 1/2" all the way back w/mufflers would be good.
Rich
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Old 05-13-2009, 04:27 PM
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Quote:
Originally Posted by 811800
Just wondering If I need to change my exhaust. Right now I have a 350sbc with shorty headers. 2.5 Primaries that come to a 3 collector then into a glass-pack the straight out. Would I be better with 2.5 all the way out? I have
no cat , and have limitless room under my "hot rod".
Thanks 811800
This is in what and how is it used?

For unlimited space why shorties, they give up a lot of mid range torque against 3 foot tubes and are so-so up on top.

I have a problem with with the glass pack, there are glass packs and there are glass packs. The cheap ones are worse than reverse flow mufflers. The other problem with 3 inch mufflers are that most are made for smaller pipes and just use large end spuds leaving a sizable restriction between.

Bogie
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Old 05-13-2009, 05:55 PM
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Quote:
Originally Posted by 811800
2.5 Primaries that come to a 3 collector
Doesn't really matter I suppose, but the primary tubes are the ones that come from the ports. Likely they're 1-1/2" or 1-5/8".
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Old 05-13-2009, 11:04 PM
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Some glasspacks are remarkably restrictive. Which one do you have?

Its rare that a single glasspack (even the best) can support the flow required for anything more than about 250 hp.
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Old 05-13-2009, 11:07 PM
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I have to admit that my "hot rod" has a 350 crate, 600 holly vac secondaries,
5 speed 4.11 rear gears and 20 inch tires. That would be a nice hot rod if it were not in a 20,000 lb Thomas international bus It is my house it started its life as a church coach, now it is a rv. It also started its life with a 700+ lb mv404 international gas motor that you cant get parts for.
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Old 05-13-2009, 11:09 PM
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the reason I used the shorty headers is simple. They were free
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Old 05-14-2009, 01:12 PM
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Quote:
Originally Posted by 811800
That would be a nice hot rod if it were not in a 20,000 lb Thomas international bus
WHA..!?!

Cheesen'crackers, man! That it'll even pull it's own weight is a feat!

But seriously, your app is why some OEM 350 SBC engines came w/4-bolt mains, 1.72" x 1.5" valves (w/exhaust valve stems that measure 3/8") and a cam that's all-in by 4000 RPM.

IMHO, you are WAY into big block (or diesel) territory!
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Old 05-14-2009, 01:31 PM
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Alright you guys, while I'm not teaching English let's look at Duel versus Dual.

Duel is when we choose pistols, walk 20 paces, turn and fire at each other.

Dual is two of something.

Bogie
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Old 05-14-2009, 01:38 PM
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Quote:
Originally Posted by oldbogie
Duel is when we choose pistols, walk 20 paces, turn and fire at each other.
What if you backed two cars up to each other- connected the tailpipes w/radiator hose, fire them up, mat the accelerator pedals and had a "shoot-out?

First one to stall or burn his valves loses! lol
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Old 05-14-2009, 02:08 PM
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A single 3 is just a little smaller than dual 2-1/4's. So, I would guess a single 3 would would well to 300hp.

A dynomax bullet glass pack flows like a straight pipe. don't use glass packs with raised bumps in the tubes (very poor flow). Use the glass packs that use perforated tube, like the dynomax bullets.

if you want more quiet, then use a large case dynomax super turbo.

I like the way a V8 sounds with a free flowing single exhaust system. I had build a few single exhaust systems for datsun z car V8 conversions. My most recent build, I used block hugger headers, dual 2-1/2 pipe, then to a H-pipe, then 2 dynomax bullets (one on each side), then to a flowmaster Y-pipe (2-1/2 inch and 3 inch out), then to a single dynomax super turbo. I first built the systems without the bullets or H-pipe but the system made lots of exhaust droning. The car was almost undriveable. The bullets and H pipe fixed all of that. Used mandrel bent J-pipes from summit racing and made the system from scratch.

but, if you have the room, then use dual 2-1/2 with an X-pipe and dual dynomax super turbos.
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Old 05-14-2009, 02:10 PM
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Bogie -- It's funny
I noticed this duel as well. We've actually had quite a lot of dueling going on lately here at the engine forum. At, least so it seems to me. There have also been some duels going on over at the electrical forum, as well, but they have nothing to do with exhaust. Perhaps it all has to do with the duelity, er . . . . . duality, of a situation.



Pat
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Old 05-14-2009, 02:36 PM
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FWIW- I recall a Circle Track article (back when Smoky was still kicking and contributing to the mag) that outlined a back to back comparison on a limited "Hobby Stock"-type car that showed a net torque gain in the RPM range the car operated in, with a single 3" exhaust compared to a dual exhaust system (don't recall the exact size- was equal to more than a single 3" system, though).
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Old 05-14-2009, 02:50 PM
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dual 2-1/4 pipes with 0.062 wall has a cross section area of 7.089 square inches.

a single 3 inch pipe with 0.062 wall has a cross section of 6.48 square inches.
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Old 05-14-2009, 05:04 PM
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Quote:
Originally Posted by cobalt327
FWIW- I recall a Circle Track article (back when Smoky was still kicking and contributing to the mag) that outlined a back to back comparison on a limited "Hobby Stock"-type car that showed a net torque gain in the RPM range the car operated in, with a single 3" exhaust compared to a dual exhaust system (don't recall the exact size- was equal to more than a single 3" system, though).
The theory behind this is more esoteric than exhaust area, the thought of a large single pipe also includes the consideration that atmospheric pressure is less able to enter the pipe between exhaust pulses when all the pulses are in one pipe, therefore, there is less backpressure on the exhaust system.

You gotta give it up that Smokey was always thinking. In terms of tests, I've never seen and data, but then again, I've never gone looking for it either. I would think that if any thing was to be gained it would be a reduction in the inertia of in-rushing atmosphere that the next exhaust pulse would have to stop, reverse, and push the back out in addition to the simple pressure which exists at the end of the pipe that the exhaust has to push against. The only time I've used a single pipe is when customers desire it or rules require it to keep exhaust on the opposite side of the car from the fuel fill pipe.

Bogie
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