Teach me about exhaust

[Kalums]

Ok gents... I want to learn something new about exhaust. I've got a 1971 GMC K2500 with a 350/TH350 +NP205... After 6 months of chasing my tail I've finally figured out ultimately/finally why I can not get my engine to run "right". After taking off the intake manifold to swap it and the carb out I found I had a bent push rod on cylinder(s) 7 AND 8 (along with other carnage) *sighs* long story short me thinks my engine needs a complete teardown and rebuild. OR I still have that GM TBI crate motor, (no one bought it yet) may just swap that in... *thinks* hhmmm. Either way, I'm going to keep the stock RAM exhaust headers( provided they fit) ... But why is my current exhaust 2" from the manifold through the "y" pipe to the muffler and then 2.25 to the exit behind the driver's side rear wheel? Taking sound out of the equation, why do alot of after market set ups/ replacements run 2.5" from the manifolds back? If I'm interested in torque vs "go fast" should I keep the replacement as close to my current setup as possible? Why does my current setup have the "cross pipe" going directly under my transmission? Doesn't that effectively cook the fluid? What benefit is duals? What harm is duals? Sorry for all the questions and thank you in advance.

[1970cstblazer]

No harm at all with dual exhausts, but V6/V8 engines do respond better if there is a balance pipe to essentially connect the banks. The factory used mostly single systems because these were not intended to be race vehicles, and it was cheaper to run a single skinny pipe with that quiet, restrictive muffler. That type of system can add some low to mid range torque over a super free flowing system, but the top end really suffers with the single stock system.

[Kalums]

Originally Posted by 1970cstblazer

No harm at all with dual exhausts, but V6/V8 engines do respond better if there is a balance pipe to essentially connect the banks. The factory used mostly single systems because these were not intended to be race vehicles, and it was cheaper to run a single skinny pipe with that quiet, restrictive muffler. That type of system can add some low to mid range torque over a super free flowing system, but the top end really suffers with the single stock system.

I understand the "cheaper" part of the equation, a couple of bucks over thousands of vehicles ads up. Like I said I'm not really interested in Horse power or "go fast" at the top end (definitely not race vehicles here) I'm personally more interested in torque in the bottom to mid range ( I'd like to use this to tow a tailer, possibly a tractor, backhoe and or dozer buckets*grins*) If I did end up with duals, how does that work without a crossover (x-pipe)? I don't really see that as a possibility with the transfer case. Seems like I'd have to have the exhaust system pretty far away from the bottom of the truck/ hanging down pretty far.

[Wootdog]

I know you hear this analogy a lot but think of the engine as an air pump, the more air you can force through it intake and also exhaust wise, the more efficient it is. And that means more horsepower and or torque. It least that is how the exhaust companies explain it. i know they are out to make money. But it makes sense. As far as the pipe between the tubes, it balances out the exhaust notes and provides I believe less back pressure. Hope that helps. I am no expert by any means.
Wootdog.

[1970cstblazer]

Here is a factory exhaust diagram:



Here you can see the factory crossover pipe location. This is about the only spot one could be made to fit..





A competent exhaust shop should be able to make a dual system with a crossover in that location and manage to clear the driveshaft.