How much power are 2.5" duals good for?
How much power are 2.5" duals good for? I see a mix of 2.5" duals and 3" duals on here. Seems like 2.5" duals is a pretty hefty flow area, bigger than a single 3" exhaust. Dual 3", with an area greater than a 4", seems like overkill on anything but the highest power motor combination.
I'm just cam only with nitrous.
Your thoughts? (the search here sucks.)
I'm just cam only with nitrous.
Your thoughts? (the search here sucks.)
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This was taken from the sticky up top
Originally Posted by jrp
Hey guys I just got done reading a good article in the May 2005 issue of Popular Hot Rodding Magazine. The article was written by David Vizard who seems to be one of the most accredited and respected people in the automotive performance world. In the article he stated that CFM is a great way to help develop a zero loss exhaust system. For zero loss a exhaust must flow 2.2 CFM per horsepower(This means less than 1% of total power produced by the engine is lost due to back pressure.). From reading the article I think that a lot of people that see gains when going from a 2.5” exhaust system to a 3” dual system see them because the muffler on the 2.5” system didn’t flow enough for their application. David stated that per square inch of exhaust tubing there is 115 CFM of flow. So plugging some numbers into the good ole TI-89….. ((3.14 * radius^2)*115[*2 for a dual exhaust system])/2.2 = Max hp supported with zero loss
A 2.75” (stock) single system is good for a 310hp engine with zero loss…
A 3” Single system is good for a 370hp engine with zero loss…
A 3.5” Single system is good for a 503hp engine with zero loss…
A 4” Single system is good for a 657hp engine with zero loss…
A 2.25” dual system is good for a 457hp engine with zero loss…
A 2.5” dual system is good for a 513hp engine with zero loss…
A 3” dual system is good for a 812hp engine with zero loss…
Now these numbers are assuming that everything else is set up perfectly. The muffler must flow as much as the open pipe or more to get zero loss at the listed hp levels. He also states that using a muffler with a larger inlet/outlet diameter than your exhaust pipe is a great way to get more out of a smaller diameter system since the muffler flow will be able to match the straight pipe flow. Now there are many other things to consider when designing an exhaust system but I figured this would give a great foundation to build on.
Just a side note that he stated that I thought was neat... “Just as fish don’t feel the weight of water, we don’t readily appreciate the weight of air. Just to set the record straight, a cube of air 100 feet square will weigh 38 tons!”
Hopefully I’ll get some more understanding of flow in a closed space in my fluid dynamics class next semester.
- OldSchoolSS
A 2.75” (stock) single system is good for a 310hp engine with zero loss…
A 3” Single system is good for a 370hp engine with zero loss…
A 3.5” Single system is good for a 503hp engine with zero loss…
A 4” Single system is good for a 657hp engine with zero loss…
A 2.25” dual system is good for a 457hp engine with zero loss…
A 2.5” dual system is good for a 513hp engine with zero loss…
A 3” dual system is good for a 812hp engine with zero loss…
Now these numbers are assuming that everything else is set up perfectly. The muffler must flow as much as the open pipe or more to get zero loss at the listed hp levels. He also states that using a muffler with a larger inlet/outlet diameter than your exhaust pipe is a great way to get more out of a smaller diameter system since the muffler flow will be able to match the straight pipe flow. Now there are many other things to consider when designing an exhaust system but I figured this would give a great foundation to build on.
Just a side note that he stated that I thought was neat... “Just as fish don’t feel the weight of water, we don’t readily appreciate the weight of air. Just to set the record straight, a cube of air 100 feet square will weigh 38 tons!”
Hopefully I’ll get some more understanding of flow in a closed space in my fluid dynamics class next semester.
- OldSchoolSS
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what would be the minimum horsepower recommended to run true duals. I have heard some people say that on a stock car, if you run true duals you might end up loosing horsepower. True?
Just as a quick note, those numbers are flywheel numbers and a perfectly flowing exhaust system with no restrictions or major bends. Factor in the drive train loss, muffler selection, future mods and power adders you may quickly outgrow a 2.5 inch system. Knowing how I like to mod and really dislike doing a job twice, I couldn't see any reason to not give up the .5 inch ground clearance when fabbing up a system and would go straight to a 3 inch exhaust.
Galen
Galen
A different characteristic you want to incorporate, is rpm. As the rpms Move up, volumetric efficiency goes down. Obviously it's not a linear Graph, but where you spend most of your time is key. As an open tracker who lives at high rpms, sure yea you need to cross reference volumetric efficiency with bolton potential. Alternatively as a street driver who spends time at low to missed rpms, it's not as Important. Nevertheless I concur it's obviously a good idea to shoot for an established rwhp goal and choose accordingly.
