2000Firehawk

iTrader: (248)

Ok, Dynomax rates their mufflers with something called a PowerTech Index 'cold-flow' testing of 20.3 H2O (SCFM). They say that one of their mufflers flows 1100 scfm, & can handle 523 'free-loss' horsepower.
Can someone tell me what 2.5" , 2.75" , & 3" pipe would flow at this 20.3 H2O. Or give me an easy way to compare apples to pears ? <img src="images/icons/confused.gif" border="0">

What is 'free-loss' horsepower anyway.
<img src="gr_emb.gif" border="0">
What does the 'S' mean in SCFM ? <img src="graemlins/gr_cheers.gif" border="0" alt="[cheers]" />

And if this 2.5" inlet/outlet muffler can flow 1100scfm, & can handle 523 'free-loss' horsepower, then this would be a good muffler for an LS1 ?? I would think that 2.5" would 'choke' an LS1. <img src="images/icons/confused.gif" border="0">

Thanks,
Dave

gwj

I don't have an answer for you, but I do have a question. <img src="gr_stretch.gif" border="0"> Are you still running the SLP LM with the dynomax, or have I got the wrong person? I'm still running the dynomax, but have a Borla XR1 I'm gonna put in place of the "resonator" and see if I can ditch the dynomax. Just trying to see if I can tone it down a bit since I have more rpm on takeoff with the ST3500.

onfire

iTrader: (17)

1. I've used a flowbench before and 20.3"of h20 pressure drop is equal to 1.5" of mercury pressure drop and is one of the industry standards...along with 28" h20,etc....20.3 is common.
2. At 20.3" h20 a 2.50 pipe will flow around 564 cfm, 2.75 = 683 cfm, 3.00 = 812 cfm, 3.50 = 1106 cfm...so dual 2.50 = 1128 cfm = one 3.50 pipe.
3. I'm having a senior moment and can't remember s in cubic feet per minute.
4.If you cut the end cases off a Dynomax they might flow those crazy numbers but obviously if they have a pipe inlet/outlet less than 3.50 inches that muff can't flow +1000 cfm...flux capacitor???lol
5. Typical formula for "Free HP" is 2.2 cfm per hp at 20.3" of h2o...so if you want an exhaust system to support 400hp without any loss whatsoever = 400 x 2.2 = 880cfm capable system at 20.3" h2o.

Crazyquik

20.3" of H20 is common for testing intake parts (intakes, carbs, etc) and exhaust parts (mufflers, exhaust tubing, etc)

J.

LS1derfull

Dave, Dynomax flows at 20.3" because thats what carbs are flown at it, makes a good standard. Flow thru a straight piece of pipe will be more than a muffler of same size inlet/outlet.S in scfm must be for cold flow designation, 2.5" does sound small for inlet size, doesnt stock muffler have 3" inlet? <img src="images/icons/confused.gif" border="0">

2000Firehawk

iTrader: (248)

WoW, now you guys got me thinking hard now. <img src="graemlins/fluffy.gif" border="0" alt="[Fluffy]" />

gwj,
Yes I'm still working with that setup. I replaced the LM intermediate section with an intermediate piece from a 2OTL system. I also cut off the pass-side tailpipe , just have a 6" 'stub' at the 'y' of the LM that I use as a cutout. The end of this 6" piece acts like a sound reflector very, very well. So right now I'm running ALL the exhaust thru Dynomax 2.5" in/out #17295 & out the 2.5" drivers-side tailpipe. At the track SAME ET with 'cutout' opened or closed. MPH off by 1, so it is choking. Autotap showed this 'choking', by looking at the MAF flow, real 'choppy' up top. Need to put a 3" tailpipe in place of the LM 2.5" tailpipe on drivers-side. Quiet as a 'church' mouse with this setup. <img src="gr_stretch.gif" border="0">
I tryed an 18" Dynomax 'bullet' in place of the LM resonator once, NO change in sound control.
Still looking at some different 'angles'.
Read a 'paper' about exhaust, by David Vizard ? He says to go with the smallest, lightest, muffler, that will get the job done,(the sound level you want with no HP loss).
My goal is a light weight, highflow, quiet, single tailpipe system. <img src="graemlins/gr_cheers.gif" border="0" alt="[cheers]" />

Onfire,
That's what I thought too, how could a 2.5" in/out Dynomax muffler flow more than a 2.5" pipe ???? Thanks for all the good info, I need to call Dynomax now, to find out what the 'S' is ??

Dave

[ January 26, 2002: Message edited by: 2000Firehawk ]</p>

gwj

Hmmm. I don't think I'm losing anything with only the one outlet running through the Dynomax, and the sound at cruise is just right. But since the addition of the converter it's a little noisy pulling out from a stop.
I'm hoping the XR1 will smooth it out a tad w/o giving up too much in flow.
I was down in the garage today looking at the stock exhaust and I believe it's 2.75 or thereabouts where it was cut off "over the axle".

2000Firehawk

iTrader: (248)

Yes, the stock pipe size is 2.75", You will not lose flow with the XR1.

Just wondering, if so may people with flowbenches out there, has anyone done, any flow testing on mufflers. <img src="graemlins/burnout.gif" border="0" alt="[Burnout]" />

Also, because exhaust gases are hot <img src="graemlins/gr_devil.gif" border="0" alt="[devil]" /> , does heated gases flow different than 'cold' gas flow. Maybe thats how Dynomax can say that a 2.5" in/out muffler can support 523 'free-loss' HP <img src="graemlins/gr_cheers.gif" border="0" alt="[cheers]" />

[ January 26, 2002: Message edited by: 2000Firehawk ]</p>

cablebandit

iTrader: (37)

I dont know the principle but as the exhaust gas flows from the manifold to the muffler it cools and therefore needs less exhaust pipe diameter once it cools some.

LS1derfull

Yes flow changes from hot to cold and attention to temp. is important for comparison sake. DAVID VIZARD has many usefull books on related subjects. I believe one of them is HOW TO BUILD HP, it has different mufflers flow tested.Dynomax was the company with the ***** to start giving flow #s on there mufflers, because educating consumers only helped show their superiority!
You could probably call manuf. of muffler your interested in and ask flow at 20.3" to compare.

LS1derfull

Candlebit, is right about diameter needs. The concept behind step headers is as exh. charge cools, gas speed slows down and it needs progressively larger pipe to maintain velocity.
Interesting stuff, IMO.

Red2000SS

[quote]Originally posted by 2000Firehawk:
<strong>
What does the 'S' mean in SCFM ? <img src="graemlins/gr_cheers.gif" border="0" alt="[cheers]" />
</strong><hr></blockquote>

The 'S' is for "Standard", as in Standard Cubic Feet per Minute.

A Standard cubic foot of any gas is a cubic foot at *standard* conditions, which is 60°F and 1 atmosphere of pressure.

The amount of air or any compressible gas that will fit into 1 cubic foot of space is dependent on the pressure and temperature.