Big Block Exhaust - Impala Tech
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post #1 of 15 (permalink) Old 08-18-2012, 10:44 AM Thread Starter
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Big Block Exhaust

What I have is a 454 .060 over 1 3/4 Headman Headers. 450 to 475 hp. Thinking on running 2.5 inch exhaust x pipe and dynomax ultra flows. Should I go 3" and something different on mufflers ? Would like to hear different opinions. Also car will be be mainly a cruiser. Thanks
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post #2 of 15 (permalink) Old 08-18-2012, 04:44 PM
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Two and a half inches is as big as the factory ever went on any car ever built. Chrysler's 426 SC and the 440 had a two and a quarter inch exhaust as did the 454 Chevelle, Camaro with 375 horse 396 and the same for the Nova. I run that size exhaust through two series seventy pick-up truck mufflers on my 582 cube big block powered Impala. To get a free flowing exhaust on race day I just drop the pipe at the collector and reattach it with one bolt. Will a three inch exhaust make more measurable horsepower on a dyno? Yes it will but that isn't the reason people run a bigger three inch exhaust system. They just want to be heard! Same reason bikers do not run any mufflers on their Harley's and kids put baseball playing cards in the spokes of their Schwinn bicycles.

Big Dave
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post #3 of 15 (permalink) Old 08-19-2012, 10:22 AM Thread Starter
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Thanks Big Dave. I don't need loud and obnoxious. I think 2.5 " will sound good and give good performance.
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post #4 of 15 (permalink) Old 08-19-2012, 11:27 AM
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Just make sure you get mandrel bent tubing!

Two doors, four doors, wagons, and ragtops.
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post #5 of 15 (permalink) Old 08-19-2012, 04:21 PM Thread Starter
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Thanks Jason. I'll use mandel bent tubing. will exit under rear bumper.
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post #6 of 15 (permalink) Old 11-10-2013, 10:18 AM
 
 
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Could run 3" to the muffler and 2 1/2 tailpipes too. The further you get from the header the smaller pipe you can get away with. Adds to the sleeper image too if you run small tails imo.
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post #7 of 15 (permalink) Old 11-10-2013, 03:40 PM
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Quote:
Originally Posted by joel f View Post
Could run 3" to the muffler and 2 1/2 tailpipes too. The further you get from the header the smaller pipe you can get away with. Adds to the sleeper image too if you run small tails imo.
Joel, when I bought my 396 SS, it had that exact set up. I'd never seen an exhaust fitted that way before and thought it quite strange as it actually served to choke the exhaust as it exits into the smaller diameter at the rear.
I wasn't really happy with it, so I swapped it for a full 2.5" from the hooker headers to the rear bumper, with a balance pipe (X) in the middle.
Wow, what a difference, this thing is like chalk and cheese, has heaps of low end torque and pulls like a teenager.
I wouldn't recommend your suggestion.
Full 2.5" mandrel bent exhaust, with a balance pipe and flow through mufflers is the way to go.
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post #8 of 15 (permalink) Old 11-10-2013, 07:59 PM
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(Ducfat) Matt, was your new 2.5" exhaust mandrel bent while the older was not?

Just curious because Joel's theory is sound and proven and I'm sure you know that. (exhaust gas volume lessens as the gas cools further from the combustion chamber)
It's water under the bridge, but I'd more suspect that your 396 was hampered by too big of an exhaust pipe if it had 3" from manifold to muffler, rather than the 2.5" tails. JMO.

Kenny, I think your 2.5" pipes, x-pipe and Ultraflows will be a great combo and you won't regret it.

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post #9 of 15 (permalink) Old 11-15-2013, 01:52 PM Thread Starter
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Pypes

Bought the pipes stainless setup ,header back X-Pipe. This is nice stuff.
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post #10 of 15 (permalink) Old 11-16-2013, 05:16 AM
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Quote:
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Bought the pipes stainless setup ,header back X-Pipe. This is nice stuff.
Let us know how the install goes and post up some pics.
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post #11 of 15 (permalink) Old 11-22-2013, 12:57 PM
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I had the same set up on my 72 chevelle ss with 468bb and really liked the quality of the system. I used Pypes Race Pros and really liked the sound. I did however have the joints welded up instead of clamping them all together. This brought the system much closer to the underside of the car. It seemed as if I just clamped up the system it hung lower under the car... What mufflers did you go with?

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post #12 of 15 (permalink) Old 11-23-2013, 08:18 AM
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I have the 2.5 with x pipe exhaust from pypes on my 72 GTO. I also added on the electric cutouts for those times you just need a little bit more noise.
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post #13 of 15 (permalink) Old 02-14-2014, 08:08 AM
 
 
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I have always been told that with GM you dont need any x or crossover pipe and that there is really no gains and balancing is not needed. With Fords fireing setup its imperitive you have a x pipe though... Anyone?
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post #14 of 15 (permalink) Old 02-14-2014, 10:54 AM
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An X pipe or a H pipe effectively doubles the area of the exhaust pipe available to the exhaust gasses. Exhaust gases are a fluid and just like water it will seek the course of least resistance. As fluids expand and contract with heat the V component of the ideal gas law is directly proportional to heat (PV=nRT so with V=T there is a direct relationship if nothing else changes) the ratio seems direct enough such that Joel's theory sounds good, BUT ... Reality gets in the way.

The gas will not cool enough in the confines of the pipe to contract enough to fit in the smaller pipe. So what the gas is encountering is weir or small dam which forms a hydraulic jump. (to see a hydraulic jump go to your sink and turn on the tap. If your sink is empty you will see a circular set of rings where the water piles up caused by the shock of hitting a solid object such that it goes from moving at high speed coming out of the tap to slow speed spreading out across the pan of the sink). The turbulence this causes in the flow creates a greater resistance to moving the gas out than the reduced size does. To get an idea how long a tail pipe you would need to condense the gas just think of your moonshiners still. It has twenty feet of copper tubing a quarter inch in diameter so that the ratio of cross section to surface area is small and the length of tubing at ambient temperature can reduce the fluid from boiling at 212 to a liquid at 140 degrees over the length of the pipe. That small drop in Temperature (and the resulting drop in Volume) is what you are faced with when your exhaust gasses at the header are close to 650 degrees and you are trying to get it down to ambient.

Not even a school bus tail pipe could pull that off.

Big Dave
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post #15 of 15 (permalink) Old 11-11-2014, 02:48 PM Thread Starter
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exhaust pictures plus finished car

1405344201401406585824758.jpg5460556852.IMG_20140801_170611_906.jpgjpg0747.jpg1405344180615.jpg Not real good pictures but pypes exhaust with ultra flo mufflers 2 1/2 " Sounds good.
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Last edited by KennyG66; 11-11-2014 at 03:15 PM.
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