Michael:
Your intuition is correct. On an otherwise stock car, the gain
may be 3-5 HP, but on a modified engine the gain could be 10 or more.
This is why you often see "Gains UP TO 20 hp" on speed part ads. Usually
these numbers are wildly inflated because the engine the part was added
to had everything else modified, and the stock part being replaced with
the custom part was the bottle neck, so the gains are atypical. Makes
good advertising copy but most users will not see numbers that large.
In your case, if everything else is souped up and the muffler is
stock, then I would expect to see a very healthy gain if you put a
decent muffler in there. One caveat; The carburetor calibration (i.e.
the needle size) will probably change dramatically when you change the
muffler. If you do not recalibrate the carbs, your gains may be very
modest. So plan on reading your spark plugs (or use a color tune) and
adjust your mixture as needed. If your cam is stock, you can probably
use the "lift the slide" method, but if it is modified too I suspect you
will not be able to get the mixture correct.
I have a 270 degree cam, and I cannot get the "lift the slide"
test to work. No matter what I do the car stumbles as if the mixture is
lean, but when I read the plugs the color is purrrr-fect, and the car
runs and idles very nicely. Has anyone out there gotten the lift the
slide mixture method to work with a 270 degree or greater cam and a
raised compression ratio? Let me know if you did anything special....
Cheers,
Vance
-----Original Message-----
From: owner-6pack@autox.team.net [mailto:owner-6pack@autox.team.net] On
Behalf Of samuelsma@aol.com
Sent: April 26, 2006 12:38 PM
To: 6pack@autox.team.net
Subject: Exhaust
Listers:
The last couple of days with posts about exhaust systems have got me
wondering: Does the benefit of a free-flow exhaust system increase if
the upstream components are modified? To be specific, my '76 has K&N
air filters, "bowl work," 9.5:1 compression, headers, and a lightened
flywheel. The exhaust system looks stock to me. I like the sound of
the stock system. Should I change the muffler because free flow will be
even more important in my situation? Can I change the muffler only,
without installing a completely new system?
Thanks.
Michael
CF 57044U
|