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2.5 Exhaust On A 330HP 327

 
Old 02-04-2019, 03:49 PM
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63 340HP
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Originally Posted by sidepipe seeker View Post
Almost NO horsepower gain using either an "X" pipe or "H" pipe vs NO crossover...
In my opinion the TV show "Engine Masters"...is the MOST informative and ACCURATE engine based show on TV!....Mark

https://www.dailymotion.com/video/x5s8nr8
Like most dyno tests, the video starts the test at 3500 rpm.

Where an H-pipe or X-pipe helps build torque is typically below 3000-3500 rpm, where the shared gas pulse momentum works as a gas extractor, and before the pipe pressure and surface friction losses exceed the momentum benefit.

This thread by AZDoug reveals an example of the benefit of coupled exhaust flows: https://www.corvetteforum.com/forums...-dyno-run.html

Peak torque and horsepower may not change but the average torque throughout the operating powerband for the typical street vehicle will benefit from a coupled exhaust (because it's not just oval track racers who want better fuel economy when cruising under a yellow flag at low rpm, or better low rpm torque exiting the pits and accelerating off a tight corner).
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Old 02-04-2019, 05:21 PM
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Originally Posted by 6T2Vette View Post
OK, my machinist just told me they used 5/8" long tube headers and the dyno people said I'd lose about 5.0% which would knock down my HP to about 315hp. Their recommendation is to go with 2.5" max, 2.25" min.
Bob
The switch from long tube headers to the 2.5" ramshorns impacts torque more at low rpm, because you lose the momentum effect of resonant flow in the head pipe tubes (an effect that is most beneficial at a head pipe exhaust velocity of about 240 feet per second). The peak torque and hp numbers occur at much higher exhaust velocity, where friction losses dominate, and the rough ramshorns drop peak power about 5% above 4000 rpm (in a 327/350), with most of that loss from inlet flange misalignment and collector restriction (and ramshorns are one of the best flowing iron exhaust manifolds that were mass produced).

Where the ramshorns do not impact power is downstream in the collected exhaust pipe at low rpm, where the collected exhaust momentum effect benefit peaks at about 120 feet/second velocity, with less benefit as the exhaust cools to a denser gas with more restriction as the pipe length grows. The need to reduce the exhaust system restriction as the exhaust gas cools is where an H-pipe or X-pipe helps, but only at lower rpm when the gas velocity is low enough to shed heat in the pipes before exiting into the atmosphere (and not much benefit at high rpm when the exhaust gas and pipes are hot all the way to the tips).

Exhaust gas velocity momentum tuning can fill in torque "holes" at lower rpm by targeting head pipe sizes and collector pipe size at the impacted low torque gas flows. In reality, however, we only have the choice of stock pipe sizes to match a header with the displacement and rpm of our engine, and most header systems optimize peak rpm through reduced flow restriction where the racer wants the boost (not at a much lower street cruising rpm).
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Old 02-05-2019, 10:05 PM
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I've decided on a custom made 2.5" system from collector to the oval 14" Dynomax SuperTurbo mufflers. Tail section will be 2.25". It will be made with mandrel bent pieces and tig welded rather than mig welded for cleaner looking joints. This will be done by the fab shop putting the car together. I found several shops that quoted me great pricing for a 2.5" exhaust. Unfortunately they would be made with 2.5" tubing that would be constricted at the bends. One offered to build it with mandrel cut pieces, but they would be mig welded rather than tig. I am looking forward to a great looking efficient exhaust system. I got some great advice and lots of food for thought..
Thank you all very much.
Bob
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Old 02-05-2019, 10:16 PM
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I would Highly recommend that your fabricator uses the "back purging " method during the pipe welding process...Mark

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Old 02-06-2019, 08:48 PM
  #45  
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Originally Posted by sidepipe seeker View Post
Almost NO horsepower gain using either an "X" pipe or "H" pipe vs NO crossover...
In my opinion the TV show "Engine Masters"...is the MOST informative and ACCURATE engine based show on TV!....Mark

https://www.dailymotion.com/video/x5s8nr8
I've tried watching that series, but, with the exception of the quiet mature guy that runs the dyno, those other two goobers annoy the hell outta me. The Hot Rod guy has what, a journalism degree or something? The other guy, I'm surprised he can tie his own shoes.

In your video these idiots just place the crossovers in a random position. Anyone who claims to posses even a modicum of knowledge of engine dynamics knows that it's nearly pointless (power-wise) to position a crossover that far back. The point of the crossover is to reduce the negative effects of the double-cylinder exhaust mass dump (cylinders 2&6 and 3&1) every firing cycle. Vizard, an actual engineer, recommends putting the crossover right at/behind the collectors. In a car, it's easy to put an H pipe at the correct position, but an X pipe, due to how much room that configuration requires, usually results in the X being put a couple/few feet behind the collectors (not an efficient placement).

IIRC, looking at the dyno configuration, it looks like the brake/framework is eating up the real estate where the crossover should go. At that point they should have at least mentioned that their test is only going to measure the effectiveness of crossovers installed in poor positions.

With those guys. it's too often hard to tell if I'm watching "Engine Masters" or "Roadkill".
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Old 02-08-2019, 02:05 AM
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Originally Posted by sidepipe seeker View Post
I would Highly recommend that your fabricator uses the "back purging " method during the pipe welding process...Mark
The tubing will be 2.5" aluminized steel. The tig process will involve cleaning the areas to be tig welded and resprayed after welding. It will all be back purged.
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Old 02-08-2019, 02:13 AM
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Originally Posted by Drothgeb View Post
Are you going with stainless or aluminized?
I was told today tubing will be aluminized steel. I was told a SS system would be much more expensive than using aluminized steel. I'd like to find out why?
Thinking about ceramic coating. If I do, should I start with Rams horn manifolds?
Bob

Last edited by 6T2Vette; 02-08-2019 at 02:28 AM.
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Old 02-08-2019, 01:30 PM
  #48  
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Originally Posted by 6T2Vette View Post
I was told today tubing will be aluminized steel. I was told a SS system would be much more expensive than using aluminized steel. I'd like to find out why?
Thinking about ceramic coating. If I do, should I start with Rams horn manifolds?
Bob
Bob go with headers and save the 5% HP lost your mechanic said the ramhorns would cost you. HP was your big push when building your new engine. 330 HP out of 330 Ci was the goal!
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Old 02-08-2019, 03:42 PM
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Originally Posted by 6T2Vette View Post
I was told today tubing will be aluminized steel. I was told a SS system would be much more expensive than using aluminized steel. I'd like to find out why?
Thinking about ceramic coating. If I do, should I start with Rams horn manifolds?
Bob
Stainless steel is more expensive to buy and more difficult to bend and weld (typical 304 SS).

I had my ported ramshorns jet hot coated, and they flow and look great (no loss of peak tq and hp at peak power rpm, but some low rpm torque loss compared to headers). The coating is the price of headers, so unless the desire is a stock appearance and the lower noise attenuation of iron manifolds, headers are more economical.
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Old 02-09-2019, 02:51 AM
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Originally Posted by 63 340HP View Post
Stainless steel is more expensive to buy and more difficult to bend and weld (typical 304 SS).

I had my ported ramshorns jet hot coated, and they flow and look great (no loss of peak tq and hp at peak power rpm, but some low rpm torque loss compared to headers). The coating is the price of headers, so unless the desire is a stock appearance and the lower noise attenuation of iron manifolds, headers are more economical.
The desire IS a stock appearance.
Bob



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Old 02-09-2019, 03:00 AM
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Originally Posted by RJ1 View Post
Bob go with headers and save the 5% HP lost your mechanic said the ramhorns would cost you. HP was your big push when building your new engine. 330 HP out of 330 Ci was the goal!
Yep, the goal was attained, perhaps under ideal conditions, but I seriously doubt I'll be able to feel a 5% difference.
Bob
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Old 02-09-2019, 07:19 PM
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Originally Posted by 6T2Vette View Post
Yep, the goal was attained, perhaps under ideal conditions, but I seriously doubt I'll be able to feel a 5% difference.
Bob
Agreed! What do you think rear wheel HP will be? Did you test rear wheel HP before rebuild?
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Old 02-10-2019, 02:50 AM
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Originally Posted by RJ1 View Post
Agreed! What do you think rear wheel HP will be? Did you test rear wheel HP before rebuild?
Dunno. 300HP~, but no less than 290. Avon tires I'm putting on it won't improve HP, but it'll sure as hell improve traction.
Bob
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Old 02-10-2019, 08:17 AM
  #54  
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Originally Posted by 6T2Vette View Post
Dunno. 300HP~, but no less than 290. Avon tires I'm putting on it won't improve HP, but it'll sure as hell improve traction.
Bob
The deduction to get rear wheel hp is usually 15-20%. So you are probably 270-280, which are still really good numbers.

Do you plan on running it on a chassis dyno? It would be interesting to see your results, considering you’ve had the engine on a dyno.
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Old 02-10-2019, 12:56 PM
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Originally Posted by Drothgeb View Post
The deduction to get rear wheel hp is usually 15-20%. So you are probably 270-280, which are still really good numbers.

Do you plan on running it on a chassis dyno? It would be interesting to see your results, considering you’ve had the engine on a dyno.
I wasn't going to, but I'm getting my curiosity piqued.
Bob
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