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.

[KQQL IT]

Everything I've seen says bigger is better.

H or x pipes don't do anything for power just change the exhaust note.
And different engines will sound completely different with exact same mufflers.

https://youtu.be/kWFNY06vxxM?feature=shared

[Steeveedee]

Have you experienced any overheating or seen any degradation of your transmission fluid when towing things? If not, then your stock system is good enough, and not cooking the trans. One thing you will experience going to duals is loss of low end grunt.

[70STOVEBOLT]

According to most exhaust companies, an x-pipe is for high rpm power and an h-pipe is for low to midrange torque. Big block trucks had 2.5” dual exhaust from the factory with no crossover pipe I believe, but not sure what size on the small block trucks, but they were single exhaust only, no duals, I believe.

[1970cstblazer]

Originally Posted by KQQL IT

Everything I've seen says bigger is better.

H or x pipes don't do anything for power just change the exhaust note.
And different engines will sound completely different with exact same mufflers.

https://youtu.be/kWFNY06vxxM?feature=shared

Not necessarily. If you put a 3" dual system on a relatively stock truck, the low end grunt torque will suffer, albeit no restriction for ultimate horsepower production. These engines need to have some backpressure restriction for better torque production down low where most driving is done.

As for X pipes, there is dyno proof of power gains. This is an excerpt from a Corvette board:

The car dyno'ed was a SGC 368 with cams and the exhaust used was a new Triflo system with restrictor plates removed.

Before: 441.3 rwhp, 383.9 rwtq

After: 452.6 rwhp, 405.2 rwtq

Difference of 11.3 RWHP, 21.3 rwtq.

Big gain for just a piece of pipe!

The peak numbers do not tell the whole story however. The power and torque gain was throughout the entire power range.

For example at 4600 rpms the difference was 22.9 rwhp and 26.5 rwtq.

Cut and pasted directly from Flowmaster:

http://www.flowmastermufflers.com/?page_id=12583

13. Do I need to install an “H” pipe in my dual exhaust system?

Flowmaster® strongly recommends using a crossover tube, otherwise known as an “H” pipe or balance pipe on all true dual exhaust systems. The crossover pipe equalizes the exhaust pulses and allows the sounds waves to communicate between both banks of the engine. Not only does this usually improve torque in the low to mid rpm range, it also creates a deeper mellower tone both inside and outside of the vehicle and helps eliminate “back-rap” on deceleration.


14. Is an “X” pipe better than an “H” pipe?

Flowmaster has performed extensive testing and determined that the “H” and “X” pipes deliver no significant difference in performance, but do affect tone, the “X” pipe giving off a higher pitched tone. Flowmaster Scavenger “X” pipes however do increase torque through use of their patented
D-Port technology and retains the deep Flowmaster muffler tone desired by most performance enthusiasts.

However, some dyno tests have shown little to no HP gains, yet some have seen pretty dynamic gains. Another case of "your results may vary"....

[KQQL IT]

After they smashed the headers and showed little difference.
Im a firm believer go with what fits.
But recently my kid built a 3 in x pipe system and a 2-1/2 duals on 2 trucks same mufflers similar 6.0 LS motors.
3 in x pipes sounds like an exotic
And the 2-1/2 sounds like.. well you know.