3” dual exhaust

fmorelli

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http://www.exhaustvideos.com/faq/how-to-calculate-muffler-size-pipe-diameter/
I come across this information a lot. which sums up around 2.2cfm per HP often.
This is all over the map:
Hotrod Magazine: http://www.hotrod.com/articles/what-exhaust-pipes-work-best/
Summit Racing: youtu.be/wa4rYZVo8fw?t=133
Dynomax: http://www.dynomax.com/downloads/product-catalog/2015_dynomax_techsection_secure.pdf
Flowmaster: https://www.flowmastermufflers.com/faq/ (Here are some guidelines for exhaust tubing size vs power that can be used for street applications: Street V8 applications – dual exhaust 2” tubing200 hp – 250 hp 2.25” tubing 250 hp – 375 hp 2.5” tubing 350 hp – 500 hp *3” tubing 500 hp – 600 hp)

As I understand it, exhaust design is a factor, and rocket science (though less so with turbo cars.)

But that said, I'm wondering about all these guys around here are running 500-750whp cars with their exhaust systems? Wouldn't mind seeing some posts from people that say what their dyno sheet says, and what their exhaust configuration is ...

Filippo
 
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langsbr

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I think Payam has said he ran the stock exhaust to 700 whp or a bit more and didn't see a difference with a different one until over 800.
 
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Rcboosted2007

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Ive run a high of 698 on mmps through my dual 2.5s no cats. But how much am i loosing out by. And everyone else for that mater. Will turbo spool faster. Id like a true no loss system to hit the market
 
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langsbr

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This thread is basically the same as a previous one. I had thought of dropping the exhaust to see if there was any gain and was pretty much lambasted by @dyezak about how is a waste power wise and is been done by plenty of people and that if there was a gain it would've been done already.
 

langsbr

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Basically the stock exhaust is not a restriction at all below 800+ whp. No gains from removing or replacing it.
 

Rcboosted2007

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9DD3E64B-99C3-486E-90D9-A76670051771.png
 

langsbr

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I'm not a millenial so I'm not up with the lingo on what Bruh means. I am not disagreeing with you regarding the stock exhaust - simply check out my posts in this thread on the same topic:

https://bmw.spoolstreet.com/threads/stock-exhaust-system-capacity-with-upgraded-dps.2368/#post-25283

There is also a post on another forum that I can't find that Payam said he measured no difference in backpressure with stock exhaust vs no exhaust (if I recall correctly) on 700+ HP.
 

Rcboosted2007

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Are you pre 1980? Its just a funny clip of a person fainting.Ive seen these
Kinds of post, but im talking logs, turbo spool/response by rpm range. how much are we really missing out on you know.and most cars now are far passed 600hp crank and wheel.
 

fmorelli

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There is also a post on another forum that I can't find that Payam said he measured no difference in backpressure with stock exhaust vs no exhaust (if I recall correctly) on 700+ HP.
I'd like to see more on this. Honestly I find this really hard to believe as possible. I don't know how the E90 exhaust is, but my E89 N54 exhaust, especially the passenger side pipe, was a complete kinked up joke.

Filippo
 

colinod

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I had a twin 3" catback made. No mufflers, twin 3." High flow cats. Sorry no dyno data. Yes you can make 700 whp with a stock catback. Doesnt mean you should or that you wouldnt make any more HP with a freer flowing exhaust.
 

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dyezak

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My apologies @langsbr for making you feel lambasted, that wasn't the intent. But the whole exhaust thing is an item that has been visited and revisited countless times over the 11y history of the e9x platform. And the fact is that you can free up lost horsepower....but for the cost/benefit you get with an exhaust, there are far more beneficial places to spend your money if you are under 500-600hp. If you are doing it just for horsepower, dollar for dollar, it doesn't make sense at this level

Think of it this way, any decent exhaust is going to be $1000-2000 (a dual 3" will most certainly be the upper end of that spectrum). What are you gaining for that $$?? If you get a 5% increase in power you would be on the high end of what people have recorded with back to back dyno measurements on this platform. So a 400hp car will net roughly 20hp increase, a 500hp car will net a 25hp increase.

Nobody argues the HP is there. But at the level of 400hp, you can bet that the person is a stock turbo car without inlets and outlets. That stock turbo car can net far more than a 20hp increase with inlets, outlets, and a tune to take advantage of that.

A 500hp car is going to be a stg1-2 aftermarket turbo. At that point you'll net more (for cheaper) with just a boost increase, ignition upgrade and a tune to maximize that.

The fact is that power (at these levels) is so cheap that it isn't financially smart to chase horsepower in the exhaust.

Once you are in the 6-700hp range things change. You are either a single turbo conversion, or some of the more wild twin turbo upgrades with all the supporting mods. You are pushing your factory engine pretty hard at this level. Do you really want to increase stresses on the engine by increasing the boost or other previously "cheaper" alternatives? At this point grabbing 30-40hp via relieving stress and reducing backpressure for that same $1000-2000 is actually smarter than any other alternative that you have left at your disposal.

All this is just talking about HP here. If you are desiring a different sound, or a different look, or a weight reduction then that changes the calculus.
 
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