Does anyone know what the max exhaust CFM's of the Cummins HO is? It may not make a performance difference using the 40 or 51 inch mufflers other than sound preference...

 

Doug-
Looks like it's time for a complete muffler spreadsheet matrix too. <grin>.

 

I ran the exhaust flow calculation and came up with about 770 CFM. That number comes from a max RPM of 3200 and 900 for the exhaust gas temperature. If I ran the temp up to 1200 the number was around a 1000 CFM I believe.
From what I hear the stock muffler flows about 350 CFM.


Blownaway,
Thanks for the update. I would like to hear your tow report with the new exhaust.

MikeyB

 

I get 1600, using the Fleetguard/Nelson formula. I figure if we're talking about an after market high-flow muffler to reduce EGTs, then we're pushing things to the limit. So I plugged in 3200 rpm and 1200 degrees EGT, using the formula for a turbocharged aftercooled diesel of 361 cubic inches displacement.

At this upper extreem for CTD exhaust flow, the donaldson muff is right in the center of its intended operating range, loafing around at only 1 psi backpressure.

 

Doug,
What exhaust flow formula are you using?

I'm using cu.in. x rpm x 1.4 x exhaust temp (F) + 460 / 2 x 941760

MikeyB

 

we are using the same formula, only I used 1200 degrees EGT and a factor of 1.6 instead of 1.4. You probably meant to have a couple of parentheses in there; the formula as you typed it is not quite correct. I'm using:

CFM = [Displ x RPM x 1.6 x (1200+460)] / 2 x 941760


The way I interpreted the Nelson formula, 1.6 applies to turbocharged diesels with aftercoolers. That amounts to about a 15% increase in CFM, owing to the higher charge denstity of air as a consequence of the aftercooler.

 

Ok, I see, the formula I found only showed normally aspirated and turbocharged for efficiency. And for turbocharged only the value of 1.4 was listed.
Yeah, I left the parentheses out while I was typing...

Thanks

MikeyB

 

My trailer is going to be heavy! It is a 33.5 Fleetwood 5er loaded full of stuff, We have been living in it. I hooked up today and couldn't believe a 1 ton could sag like that

 

Blownaway,
I would like to hear you towing report with the Nelson.

MikeyB

 

Check out these 2 sites has Nelson mufflers brochure.

http://www.fleetguard.com/fleet/pdfs...s/LT32002B.pdf

http://www.fleetguard.com/fleet/pdfs...s/LT32002C.pdf

 

Left this one out! It has Cummins on it...

http://www.fleetguard.com/fleet/pdfs...s/LT32002D.pdf

 

I towed my trailer, I would estimate the weight at about 13,000-14,000 Lbs 33.5 Fiver very loaded down. My wife says she doesn't notice any difference while towing and I tend to agree, the funny thing is you can hear more noise coming from the cooling fan and engine than the exhaust, With the straight out stock tailpipe it does echo off of gaurdrails and other cars though. I am still very happy and more importantly so is she
It is still just my opinion, I am sure you are not going to find anything more quit than the stock muffler, which by the way looks like baffles down to about three inch on the inside.... That thing sucks!

 

Thats just what I am looking for but I want/need to keep the CAT on my truck so I was wondering about the Nelson 86514 as a way to increase some flow yet keep it quiet under cruise.

It has a 4" inlet with a 5" outlet that might make a nice CAT Back System. Looks like it has good flow vs db numbers.

Thoughts anyone for us that need to keep the CAT?

Great post and tons of good info.... Thanks!

 

If you have a cat and need to keep it, then why not just straight pipe it? With the turbo and a cat, it shouldn't be too loud and you can't get any less backpressure than no muffler at all .


-Muzzy

 

I was thinking about that Muzzy but I don't want to make any more noise.

Anyone straight pipe one with a CAT?