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

[Ken Ames <ameskg@xxxxxxxxx>]

Er, wouldn't that be less dense/more volume when hot, and more dense/less volume
when cooler?  : )


Ken


Quoting 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!). 
> 
> -----------
> 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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> 


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