Muffler size ?

FUNFER2 · #1 (**permalink**) 02-22-2009, 08:34 PM

I'm researching side pipes & mufflers. I have questions regarding muffler selection. By best friend Chad is a professional mechanic with his own shop, has a Mustang chassis dyno and we race sprint cars together.

He believes the 3" from Classic Chambered is too small for a engine that KC will be building for me. It will be a Pond aluminum and Edelbrock stage 2 heads alum. heads., with apx. 630-650 HP. The only 3.5" muffler I've seen is the Howe, but the problem is excessive noise. I do like the cobra fairy loud but, I don't want to piss off neighbors, getting nasty looks from other drivers, and MY wife, not wanting to ride in it. lol

We figure the 3" may restrict the flow, with this much HP & TQ.
So, how do I determine the needed size muffler with HP/TQ ratings ?

Rick Parker · #2 (**permalink**) 02-23-2009, 12:39 AM

If the neighbors peek out he curtains when it's running, then their just about right. Otherwise they are too small.

Ant · #3 (**permalink**) 02-23-2009, 01:37 AM

FUNFER2,

I am going through the same decision for my KC Yates 373 SBF which has similar hp to your engine, peaks on the dyno at around 7000rpm. I have a real nice merge collector which necks down to 3" and then back up to 3.5" I was intending on 3" perf tube stainless packed mufflers, which should be big enough I guess the only way is to find out on the dyno buts thats a hassle!

Apparently grouping several 4-5 small perforated tubes inside the main perf tube quietens them down significantly, so 3.5" main tube should work good but it may mean going to a 4.5" muffler case,to get a reasonable amount of stainless packing and space.

Quote:

Originally Posted by FUNFER2

I'm researching side pipes & mufflers. I have questions regarding muffler selection. By best friend Chad is a professional mechanic with his own shop, has a Mustang chassis dyno and we race sprint cars together.

He believes the 3" from Classic Chambered is too small for a engine that KC will be building for me. It will be a Pond aluminum and Edelbrock stage 2 heads alum. heads., with apx. 630-650 HP. The only 3.5" muffler I've seen is the Howe, but the problem is excessive noise. I do like the cobra fairy loud but, I don't want to piss off neighbors, getting nasty looks from other drivers, and MY wife, not wanting to ride in it. lol

We figure the 3" may restrict the flow, with this much HP & TQ.
So, how do I determine the needed size muffler with HP/TQ ratings ?

2KWIK4U · #4 (**permalink**) 02-23-2009, 04:21 AM

Kevin
I have the 3.5" Howe's with a 496 c.i. KC, 650ish and don't thinks it's overly loud, but do have the outlets turned down slightly.

Here's the scoop
KC Engine dyno: 649 hp, 668 trq

Stock LS exhaust
2" headers
1.75" J-pipes
3" collectors
LS mufflers ?size
3" outlets
Chassis dyno: 427 rwhp, 415 rwtrq

Exhaust #1
2" headers
2" j-pipes
3.5" collectors
4" x 24" Lobek Auger Mufflers, don't remember auger size
3.5" outlets
Chassis Dyno: 506 rwhp, 535 rwtrq

Current Exhaust
2" headers
2" j-pipes
3.5" x 3" x 3.5" Merge Collectors
4" x 24" Howe Racing Mufflers (3.5" I.D.)
3.5" outlets
Chassis Dyno: 519 rwhp, 541 rwtrq

Brad W.

PS: Added photo to gallery that shows the current setup

2KWIK4U · #5 (**permalink**) 02-23-2009, 05:03 AM

BTW
John Ross has an LS with a 482 KC and Howe's, but had the mufflers turned around backwards with the outlets straight out and it's way louder than mine. By far the loudest Cobra I've ever heard.

Brad

FUNFER2 · #6 (**permalink**) 02-23-2009, 09:06 AM

Brad, please email me your number, I would appreciate talking with you.
And, I'll PM/email you my number.

FUNFER2 · #7 (**permalink**) 02-23-2009, 09:12 AM

A.J- what brand of collector do you have ?

imagine2frolic · #8 (**permalink**) 02-23-2009, 09:43 AM

One 3" mandrel bent pipe is good for 500hp according to IMCO EXHAUST out of Texas.They are one of the largest manufacturers of exhaust.....i2f

FUNFER2 · #9 (**permalink**) 02-23-2009, 09:48 AM

I'll be over 600 hp. I"ll try and find their website.

392cobra · #10 (**permalink**) 02-23-2009, 10:01 AM

As far as ability of an exhaust system to flow enough air for a given amount of horsepower without causing significant back pressure, this is from one of David Vizard's books:

1. For avoiding significant restriction from back pressure, the pipe should flow at least 2.2CFM per horsepower produced.

2. A straight pipe will flow ~115CFM per square inch of area (using inside diameter of the pipe)

Here is some info on Primary tubing size...
http://victorylibrary.com/mopar/header-tech-c.htm

392cobra · #11 (**permalink**) 02-23-2009, 10:05 AM

Exhaust Size Calculator

http://www.mk5cortinaestate.co.uk/calculator5.php

FUNFER2 · #12 (**permalink**) 02-23-2009, 10:43 AM

Very interesting. It's incredible, that increasing the diameter as little as
1/8" can make that much of a difference.

Thank you for the links !

Ant · #13 (**permalink**) 02-23-2009, 02:52 PM

Quote:

Originally Posted by FUNFER2

A.J- what brand of collector do you have ?

www.spdexhaust.com
Chris Hill whose workmanship/Tig welding in my opinion is without doubt the best I have seen, very helpful and good to communicate with!
I use the std Merge which has a V Band clamp in the middle of the transition.

My primaries are 1-7/8" stepped to 2" then to the collector. I am not convinced that I need to go bigger than a 3" muffler, as too big may slow the air flow down, and considering the merge goes down to 3" so there maybe no advantage in going bigger further down stream!!!

FUNFER2 · #14 (**permalink**) 02-23-2009, 03:30 PM

I think with big blocks, 3.5" may help or, not at all ?

Although, I've seen a few dyno sheets that show with 2" primaries, 3" collectors and 3.5" mufflers, really help out so, I'm sure I'll go that route.

Now I have to make up my mind, on either mild steel and have them ceramic coated or stainless. I have a industrial buffer machine that I could polish them myself but, that will take a lot of time. If I could find a business and buy the pipes already polished, that would save a lot of time but, even that would be expensive. The advantage to SS is, longevity versus the ceramic lasting only a hand full of years, before you can't polish them out anymore, like what's happened to mine.

Thank you for the site link.

Ant · #15 (**permalink**) 02-24-2009, 02:07 AM

Kevin,

I think with 3.5" OD that gives a good amount of size, and you are probably right your Big block has substantial horsepower and may benefit from large mufflers. My understanding was with race cars they went big in the whole system depending on the rpms used!

Mild steel is good when ceramic coated and the advantage of cooler areas surrounding the where the exhaust goes, my pipes rusted bad after the dyno run but are now coated so should be ok for a few years - might see me out who knows!

undy · #16 (**permalink**) 02-24-2009, 03:22 AM

Kev, 3" is all you need.

Dave

Rare Iron · #17 (**permalink**) 02-24-2009, 05:41 AM

Read this from Ron Nichols - it's down in the thread a little on the first page: Howe Racing Mufflers

Personally, I don't think many Cobra owners would install mufflers with a 4.5" body diameter. According to Dynomax & their flow criteria, a straight-through Ultra Flow muffler with a 3" core will flow over 2200 CFM, which translates into over 1800 loss-free horsepower with a dual exhaust. Here's their formula:

How to determine necessary exhaust flow:
* Engine HP x 2.2 = loss free airflow capacity needed for a muffler used in a single system.
* For a dual system divide the single system number by 2 to determine the loss free airflow capacity needed for each muffler.

EXAMPLE:
* 300 HP x 2.2 = 660 SCFM single or 330 SCFM dual.