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Old 01-25-2020, 09:12 PM
JUDGE3 JUDGE3 is offline
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Default question for exhaust guru

72 firebird

Wilhite built 455 (472) engine round port e heads butler ported.
my exhaust plan:
oversized round port exhaust manifolds to 2 1/2" downpipes, x crossover, 2 1/2" pipe to flowmaster 40's.

my question is, if I use 2 1/4" tailpipe after the flowmasters will I see a significant power loss vs using 2 1/2" tailpipes?

I will be using exhaust splitters. I ask because there's not much room over the axle and to the splitters on 70-81 firebirds.

already have the exhaust manifolds, didn't want mini starter header hassles anymore. and after a quieter exhaust to.

open to recommendation here. I know Jim/Tom hand are experts. read about the wagon and testing for years. good stuff.

  #2  
Old 01-27-2020, 11:17 AM
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Formulajones Formulajones is offline
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The general rule, in theory, is that as exhaust gasses cool while they travel through the system, the pipe size becomes less important.

It's been tested many times over, and this very scenario tested by the Hands as well and has shown pretty interesting results.

I've built a couple of cars in this fashion specifically to lower the exhaust tone. I can say for sure the slightly smaller tail pipes do in fact change the exhaust attitude and tones it down.

If all out performance is a concern, electric cut outs are always a flip of the switch away, and tons of fun.

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Old 01-27-2020, 07:37 PM
JUDGE3 JUDGE3 is offline
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thanks for the reply, I am more into performance for sure. the electric cut out would definitely be fun. loved that comment from famed Pete McCarthy in good ol' HPP magazine...……"me, if I don't have enough power to shred the tread off a recap, i'm just not happy" couldn't agree more.

wouldn't it be hard to tune for best closed cut out performance and open cut out performance?

  #4  
Old 01-27-2020, 09:01 PM
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Formulajones Formulajones is offline
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Yeah, sometimes it requires a little carb tweaking. I tend to have things a little on the fat side anyway, especially at 5,000 feet elevation, so the engines are pretty safe when I open the cutouts.

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Old 01-27-2020, 09:49 PM
tolerico tolerico is offline
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Stay away from Flowmaster mufflers... maybe get a nice Dynomax or MagnaFlow straight thru style instead.

2.5" pipe from manifolds to the end is ideal for your engine.

And I prefer SpinTech mufflers - they'll make whatever size you want

  #6  
Old 01-27-2020, 11:47 PM
tom s tom s is offline
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I have done 2 cars with Hushpowers mufflers and like them better than super turbos and WAY better than 2 chamber Flomasters.Stil a good muscle car sound but not over the top.Tom

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