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Open Header vs. freer flowing exhaust vs. stock, affect on power delivery

4K views 11 replies 3 participants last post by  XCNuse 
#1 ·
I hold the belief that no matter what the less back pressure an engine has the more power it will make. Many others oppose this idea and we should hash this out. Please do not post unless you have a dyno comparison to prove your point otherwise we are just all arguing without any proof.

i would like to reference this post showing multiple dynos ,on an old Honda which can be debated, between open 4-2-1 header vs. stock exhaust vs. 4-2-1 + stock exhaust. Seems power is always to be gained with a reduction in exhaust back-pressure. Has anyone done a dyno of open header on a Mazda 3? Or even comparison on dyno between different exhaust systems and setups?
 
#2 ·
Stock vs Cosworth intake, MSDS header, SRI, 2.5" exhaust

Loss in torque, gain in power. Exactly as expected.
2 dyno runs within 10 minutes of each other.

Please look at the charts thoroughly before making an argument about my car making 161hp and the other not even close. Look closer at what you're reading please.



 
#4 ·
I hold the belief that no matter what the less back pressure an engine has the more power it will make. Many others oppose this idea and we should hash this out. Please do not post unless you have a dyno comparison to prove your point otherwise we are just all arguing without any proof.

i would like to reference this post showing multiple dynos ,on an old Honda which can be debated, between open 4-2-1 header vs. stock exhaust vs. 4-2-1 + stock exhaust. Seems power is always to be gained with a reduction in exhaust back-pressure. Has anyone done a dyno of open header on a Mazda 3? Or even comparison on dyno between different exhaust systems and setups?
Based upon your insistence on pushing this issue I'll try one more time:
You use the term "power" as a universal term, however, things aren't that simple in the real world. The thing is, there is mid range power (torque), and their is high end power (horse power), and changing manifolds and such will affect both. Typically the factory intake and exhaust are tuned for mid range torque (at the expense of top end horse power), the kind of power used in every day driving. Also typically, aftermarket intakes and exhausts will improve power at WOT at redline (at the expense of mid range torque).


I trust you understand you cannot always drive around with your engine up near redline and as such, a modified engine will have LESS mid range torque (power available for normal driving), and be slower than a stock factory engine.
 
#5 · (Edited)
I agree changes to the intake manifold will change torque and horsepower delivery.

The real question is whether exhaust has the same correlation. Dyno graphs with just exhaust upgrades show more torque and horsepower across the entire rev range. How would someone explain the draxas vs stock exhaust comparison done in the below thread as the only change was the exhaust system.
http://www.mazda3forums.com/353-modifications-faqs-how-tos/244300-na-power-stage-2-basic-bolt-ons-intake-exhaust-timing.html
Snipped Dyno(attached) from above link by thebeansoldier
 

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#6 · (Edited)
I agree changes to the intake manifold will change torque and horsepower delivery.

The real question is whether exhaust has the same correlation. Dyno graphs with just exhaust upgrades show more torque and horsepower across the entire rev range. How would someone explain the draxas vs stock exhaust comparison done in the below thread as the only change was the exhaust system.
http://www.mazda3forums.com/353-mod...e-2-basic-bolt-ons-intake-exhaust-timing.html
Snipped Dyno(attached) from above link by thebeansoldier
I have to tell you, I've seen lots of dyno graphs, and that one looks pretty funny (and completely inconsistent with other graphs in the same thread); I'm thinking it was fudged or something else was going on with the engine or the weather.
 
#8 ·
I've changed jobs since I worked with engines on a regular basis and don't have any available (working for manufacturers means when you leave, all your research stays with them).
 
#10 ·
If Bean's dyno charts were real; why would the torque/power crossover be happening where it is?

I'll give you a hint. They aren't real.

Chances are you won't find any dyno runs of an exhaust swap. Why? Because it doesn't make that much of a difference.
Seeing as though my car "fully bolted" only saw a difference in +/-5tq/hp between completely stock.

Argue any case you want, but the fact of the matter is, the resources you're seeking do not exist, and don't exist for a reason. 1 because nobody would pay to do it because it's stupid when it would cost as much as some people are paying for an exhaust, 2 because everyone knows what it already does; loses torque, gains top end.
 
#12 ·
This should help. An interesting subject however is AFRs.

Bear in mind, this isn't again comparable because this is a V8 pumping over 600hp, so yes, it's going to require a larger exhaust, but do note, exactly what they note about the torque in the low RPMs (which is where you are while driving around town)

 
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