[Skip Fix]

I'd go 3" myself, at least through the mufflers maybe a 2.5 tailpipe but for me easier to keep it all the same.

[grandville455]

Originally Posted by Skip Fix

I'd go 3" myself, at least through the mufflers maybe a 2.5 tailpipe but for me easier to keep it all the same.

X2!

[ta man]

I have 3 inch into cone reducers into 2.5 Ultraflows into 2.5 inch tailpipes...good so far for mid 118's at the strip...

[Speargun]

I read a thread several years ago that basically said to go 3" - 3.5" to the muffler then 2.5" out the back. The premise was that by the time the gasses reached the mufflers, they had cooled (and contracted) enough that the smaller pipes were big enough to keep it flowing out the back without loosing velocity or causing back pressure.

I'll see if I can search for the thread tomorrow unless someone else here gets it first.

[RamAirIV28]

any article half a page long does not due the subject justice. I'll bet the other half of the page was an add for a header or exuast vendor.....

first thing, exuaste systems are not and should not be rated by HP but by flow, so there is your first sign somebody's pushing up roses

second thing, sever authors who have written up on exuaste system development, those of any credible worth have written articles 10-20 pages long or longer and cover the system from the valve to the tail pipe

and to give the subject its due there was a book written and then edited several times called the scientific design of intake and exuast systems, written by a couple of PHD's by the name of Morrison and another guy, 250 pages long and available on amazon.com for about 24 bucks. anybody worth their credibility quotes this book. its an excellent read.

Funny thing is the article in the latest HPP that states that a RA4 and factory log are only like 9 hp diference in comparison. just for the record that is a ridiculous way to measure flow. flow is measured in cfm not hp.

just my 2 cents worth but I was introduced to much written by David Vizard and any of his books will get you where you want to go befor you chum out hard currency on a system

[zeebo]

what is a good way to measure flow in an exhaust system? some type of air flow meter? a DP gauge to measure back pressure? that would be a good starting point i believe.

[leeklm]

Originally Posted by zeebo

what is a good way to measure flow in an exhaust system? some type of air flow meter? a DP gauge to measure back pressure? that would be a good starting point i believe.

Easy to make a pressure meter. Just mount a couple of clear plastic or glass tubes (about 18" long" on a piece of plywood, about 6-8" apart. Connect the bottom of the tubes with a U shaped piece of tubing. The end result looks like a large straw in the shape of a U. Now, add some water with dye (so you can see it) so the U is about 1/4 to 1/3 full. Connect a piece of tubing to one end of the U, and connect that to a piece of brass tuning as a "probe". To complete, add some reference lines by each tube so it looks like a thermometer.

You can now insert the probe in front of a muffler or cat, measure the pressure change from the atmosphere. I did this once by first measuring in front of the Cat, then in-between the cat and muffler to see the change in back pressure.

You should be able to google this and get much more detailed info regarding the measurements in Hg, etc. and what it all means...

[jonmachota78]

I havent seen the cam LSA mentioned yet. Engines with Wider lsa cams Can tolerate more back pressure. Tighter lsa's respond better to freer flowing exhaust.

[grandville455]

My road paver is 112 LSA