Re: [Amc-list] scavenging in a stock exhaust system?

[Frank Swygert <farna@xxxxxxx>]

I don't know about scavenging, but the little 196 OHV DOES like to have it's airways opened up! When I built my 170 hp 196 OHV, I used a 2" exhaust with turbo muffler all the way out. I don't think any larger will help at all, there's just not much volume being pushed out! Exhaust gas is densest when hottest right out of the manifold, so that's where the larger pipe should be. The 1-7/8 head pipe should be larger, then a slightly smaller tail pipe can be used behind the muffler as the gasses have cooled and become less dense. Since the head pipe was good on mine and would have been harder to make, I just cut it right in front of the original muffler and slipped the 1-7/8" pipe inside a 2" pipe and had it welded on. The 1-7/8" pipe is a nice fit inside a 2". The engine sure did seem to like the freer exhaust! Between that and opening up the snorkel on the breather to 4" (from 2" -- quadruple the open area), I figure I gained nearly 15 hp. That along with another 20 from a cam 
 change and I was estimating 170 (started with a 135 hp 2V engine). Someone ran the figures on DeskTop Dyno and came up with around 170 also. Not precise, but at least my guesstimate was as good as the software's, so it should have been in the 160-175 hp range (at peak -- which was around 3000-3500, the 135 rating was at 3800, and the engine wouldn't turn that much pulling the car on a level -- wouldn't turn more than 3200!). 

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Date: Thu, 30 Oct 2008 10:19:28 -0700
From: Tom Jennings <tomj@xxxxxxx>

OK, the exhaust in my American is pretty much 100% iron oxide now, so it 
get's a new poop chute next month.

Though it's a typical 3-into-1 iron manifold (two cyls per exhaust port) 
it seems less restrictive and less angular than the later six (OK the 
exh ports in the head run nearly 90 degrees...)

Question: is there any likely scavenging benefit possible from running 
something like 48" of skinny pipe (like 1.75") down from the manifold, 
then dump into larger 2" - 2.25") from muffler to tailpipe? Keep in mind 
this is a small engine that spends most of it's time 2000 - 2800 rpm 
(hence the 48" number).

Or should I just run "as large as I can get" (say 2.25") from end to end 
with a good muffler? I'll mailorder one from Summit or somewhere.

-- 
Frank Swygert
Publisher, "American Motors Cars" 
Magazine (AMC)
For all AMC enthusiasts
http://farna.home.att.net/AMC.html
(free download available!)


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