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Old 04-08-2005, 03:26 AM   #1
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Question Exhaust pipes: 2", 2.5" or more?

Howdy folks!

Been thinking about some upgrades now that my engine is working properly again (blast those gaskets!) and since I still have the stock Y-pipe configuration... True dual exhaust it is!

But, I can order several diametres, which is best? Or does it make no real difference? Should I install a balancing pipe as well?

Thnx again!
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Very funny Scotty.
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Old 04-08-2005, 04:30 AM   #2
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It really isn't that simple. There are a lot of factors for an optimal exhaust. There are questions. What size engine. What RPM range will you be operating n? Other mods. If you are cammed you can check with them. With an exhaust, Bigger is not always better
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Old 04-08-2005, 05:38 AM   #3
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You're right, I'll try and fill in some holes:

- 1979 C3,
- Standard 350 GM Goodwrench engine,
- Stock cast iron manifolds,
- No cat (and not required either),
- Frame has the two holes needed for dual exhaust.
- RPM range: standard I guess.
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Very funny Scotty.
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Old 04-08-2005, 06:22 AM   #4
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When I upgraded my 1981 exhaust system with a mildly modified L81 350 engine, my exhaust guy said to go with 2.5 inch stainless and welded set up. If you already have the earlier C3 style 2 holes in the cross member your new set up will look even cleaner than mine. Be sure to get a "H" pipe as well to balance the system.

Enjoy!! ....... bug
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Old 04-08-2005, 06:35 AM   #5
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If it were mine (my 2 cents):
-2-1/2" dual exhaust (i think you may have to begin at 2" and enlarge to 2-1/2").
-forget about the balance pipe. If you really want to do this, let me send you some additional info for sizing, but I would skip it on this one.
-get quality mufflers for the rear of the car.
-consider small resonators just behind the crossmember if you want to change the sound further.

In other words, a factory style "hi-per" exhaust for SB C3s.

This should work well with the 350 and stock manifolds and sound great without wasting a lot of $$$, imo.

Keep us updated. . . S
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Old 04-09-2005, 10:05 PM   #6
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2 1/2", use glas packs from Summit, and always use an H-pipe.
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Old 04-09-2005, 10:31 PM   #7
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The Torch is right use an H- pipe or if you can make it work I would use an x-pipe. I've heard you get a little more torque over the h-pipe but i don't have numbers to back it up. as for the rest of your exhaust if you want to spend the extra money on mufflers and resonators go ahead but for me there is no sound more gratifying than the loud low rumble of of an engine without all that expensive ( well compared to the price of the same length tubing) sound deadening devises. However your neighbors may not like you as much anymore. unless they're like me.
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Old 04-11-2005, 03:26 AM   #8
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Allright, I have an appointment later today at a local exhausts shop. I'll discuss this with them, but I'm going for 2,5" and will start without the H-pipe.

If no H-pipe proves to be too loud or something else then I'll add an H pipe. Since I don't have headers I think any further investments won't have the maximum effect untill I do get headers.

Thanks for all the information!
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Very funny Scotty.
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Old 05-16-2005, 11:48 PM   #9
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My UTI buddy told me to go with dual madrel bent 3 inch pipes. Is he wrong? (383ci street) Also would it be bad to dump it right after the cats behind the trans x-member? (Like they do on Camaros and Novas) Also is it bad to hollow out the cats and have no mufflers? (Not enough backpressure) I've heard that you'll loose hp and possibly warp the valves this way.
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Old 05-17-2005, 06:46 AM   #10
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read these






the short answer is ANY BACK PRESSURE IS BAD!
what your trying to do with a correctly designed exhaust is to have the majority of the exhaust system act like extended collectors on the headers, in effect useing the inertia of the hot exhaust pulses from each cylinder to cause a cyclic low pressure wave to be timed to assist the next firing cylinders to scavage the cylinders

heres the info you need,



to adjust for your altitude

and if you want to get it perfect you should usr your DYNAMIC COMPRESSION RATIO VOLUME in the formula at the rpms for peak hp that your engine makes

most of the time that comes out close to the same as the static cylinder volume at the peak torque f.y.i.

you open the headers to have less back pressure correct!!

BACK PRESSURE IS BAD, BAD,BAD, the idea has gotten around that you need back pressure to build torque, FALSE!!!!!! that IDEA was prevalent because if you stick too large of an exhaust pipe on a low rpm engine it loses the ability to scavage the cylinders with the exhaust gas pulse in the exhaust with stock exhaust manifolds, some how the old wifes tale got around that you needed back pressure...FALSE.. what you need was EFFECTIVE CYLINDER SCAVAGEING which the smaller tail pipe dia. was provideing by acting like the collector on a set of headers! if you have headers , especially full length headers with a merge type collector OF THE CORRECT LENGTH,you can,t make the exhaust too large,THINK ABOUT IT! the first thing you do at the track is un-cork your headers....why? because YEARS OF TESTING PROVES, less BACK PRESSURE MAKES MORE HP WITH HEADERS!!!! now some one is saying yeah but thats at the track and your running the engine at 5000rpm-6500rpm , well true and a good point because we typically only run 1000rpm-3000rpm on the street what it shows clearly is the collector on a low rpm engine needs to be about 10ft long for max effect so you need an exhaust that works with a collector thats about 20" long at 6000rpm and one 10 feet long at idle, THATS WHERE THE IDEA OF TOO LARGE A EXHAUST comes from but as long as you follow these rules youll be fine, READ THIS,


btw Im writeing this like this to get you guys to think about it then we will look into the answers of how to get both ends of the rpm range covered and yes Im leaveing out some info on purpose

is exhaust back pressure killing performance ?
its a fast easy test that needs to be done and more than a few cars running older cats are having a restricted exhaust thats hurting your performance badly, and because the problem tends to build up slowly many people don,t notice the gradual power loss
first thing youll need to realize is that the TEST POINT needs to be after the header collector and in front of the CAT AND MUFFLERS. next thing you need to know is that to get a valid answer youll need to have a long connector hose so someone in the pass seat can CLOSELY WATCH the gauge as you accelerate under load (FLOOR THE CAR THRU THE FIRST 1-2 GEARS and watch the pressure surge. readings above 1psi mean somethings partly restricted, readings above 3psi are hurting your performance BADLY
the test kit is about $50.00

ITS NOT RARE TO LOOSE 20% or more of your hp to a restricted cat
your unlikely to lose much if any hp especially if you install an (H) pipe just before the reduction in tail pipe dia. and use a gradual reducer to change from 3' to 2.5" mostly because the exhaust gases have cooled a great deal by the time they reach that point in your exhaust system and with that heat loss a reduction in voluum and potential back pressure


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Old 05-17-2005, 01:34 PM   #11
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2.25 or 2.5 would be fine for that setup
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Old 05-17-2005, 03:55 PM   #12
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i would go for 3,5"
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