FE Power Forums
FE Power Forums => Non-FE Discussion Forum => Topic started by: Qikbbstang on May 16, 2016, 01:08:33 PM
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Despite it being a Rat it made good power - not a whimpy motor to take advantage of large pipes
Freiburger's Scientific Analysis by screaming through mufflers was priceless
https://www.youtube.com/watch?v=_PVXvHkr-Vs
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Needed to lean that thing out before making the blanket statement on power and torque. I've tested a muffler or two over the years....and have been surprised how close you can get at times.
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They should have tuned the mixture on the 2 1/2" combo. And no mixture results on the 3". All that trouble building exhaust and they fall short.
There was a chassis dyno test online with a Pontiac years ago that showed that exhaust flowing through a 3" pipe had sufficiently cooled and compressed by the time it hit the muffler that running 3" over the axle had no advantages over 2 1/2". But, much easier to bend the smaller tubing.
Didja know Finnegan started his own channel?
https://www.youtube.com/channel/UC1IdPylqngGiuHFLJqHbG_g
Click on Videos
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Needed to lean that thing out before making the blanket statement on power and torque. I've tested a muffler or two over the years....and have been surprised how close you can get at times.
They did mention the difference between dyno and real driving, to their credit. The idea that bigger tubing robs off idle torque is valid, despite all the sarcasm.
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On two occasions of running 2.5-in pipes through approximately stock under-chassis routing and tailpipe exit locations (in an 80 El Camino and a 67 Cyclone) the fit was VERY tight, especially going over the axle tubes and out the back. I imagine with 3-in tube it would be a first-class exercise in frustration. But Freiburger's zip-tie philosophy is not in the least bounded by such old-fashioned constraints.
As someone who messed with more than his fair share of thrashed muscle cars back in the day, I can't think of many -- if any at all -- that had pipes bigger than two and a quarter inch diameter. But they weren't making 600 hp either, most realistically only about half to two thirds that amount.
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I have never seen a larger intermediate or tail pipe lose power or torque. I have seen it happen at a certain point in the curve with too much primary pipe (header tube) or too short of a collector with open headers, but not after the collector with a full exhaust. In fact, many of the techniques, X pipe, H pipe, and termination boxes, try to fool the exhaust into thinking it has escaped/dissipate the pulses, creating essentially a "huge or infinite ID". (I am no engineer, so if I murdered that last part, correct away)
In fact, even the lowest compression, laziest V-8s seems to make at worst no gains, or improve, with "too big" full exhaust if the headers are sized right. In my experience, cost and body fitment drive the exhaust size. My technique is to use headers that match the build, then run a mandrel bent exhaust the same size as collector. Additionally, muffler design is important too, and modern absorption muffler like Hooker Maxflo, Magnaflow and the like, tease a bit more out of it as well.
That test doesn't surprise me, but does surprise how much of a difference. FWIW, my 8.5:1 270H 396 woke up going from 2.25 to 3 inch, but it's hard to say if it liked the ID or the bends as I went from 80s crush bent to modern mandrel bending too. Admittedly, I didn't build that much exhaust for the tired 396, I did it in prep for the 445, but it worked out better everywhere even with the old engine, and that's a 4400lb truck with 33 inch tall tires and 3.50s, not a high RPM screamer