Backpressure on V6 S10?

While surfing another group (alt.trucks.Chevy) I came across a conversation about poor performance on a '82 S10. One issue came up about how the aftermarket dual exhaust might be flowing with not enough backpressure for
the exhaust valves to operate correctly and causing the (or some of) the performance issues.
Here are some snips:
By the way, one reader suggested to me in email that the aftermarket dual exhaust (already on the truck when I bought it) could be causing my performance problems. Apparently this V6 likes a certain amount of backpressure on the exhaust valves in order to operate well, and my dual exhaust (and lack of cats) could be providing too wide of a pathway, thus lower pressure. I think I may pursue this and try reverting to a factory exhaust system. Thank you, Rich!
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Do yourself a favor and ignore Riches advice. The less backpressure your engine has the better it will run. Bob -------
What size are the pipes? Rich is partially right. That truck probably came stock with a 2 1/4 single pipe. Its not that it needs back pressure, but that it needs flow. A pipe that is too large will kill the flow-the velocity of the exhaust going through it.(its hard to explain) It might be worth while to research it a little.
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If we were talking about headers Rich could be right.... but we aren't talking about headers. If it has dual 6" pipes all the way back from the converter or even from the manifolds it isn't going to lose power because of it. Bob
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Oh, BTW, forgot to mention that I do not have catalytic converters. The truck would have come factory with one, but I've never seen it. Two 2" pipes all the way from the manifolds to the rear bumper.
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As I am considering new exhaust for my '88 S10 Blazer, I wanted to know what you guys thought.
TIA, Joe
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Just ask anybody who rides a Harley and has replaced their exhaust. A free-flowing pipe is great for bottom end torque but not so good at the top. Why? Because without the proper amount of back pressure the burning combustion gasses inside the chamber have a tendency to expand out into the exhaust manifold/pipe decreasing the amount of power transfered to the piston and burn your exhaust valves. Even guys who like to use drag pipes (straight pipes with no muffler) sometimes use a restriction cone in the pipe where it connects to the exhaust outlet.
This is why it is so important that when you change your exhaust you also need to pay attention to air-fuel mixture, timing and intake restriction. Bigger is not always better - it all depends on what you want to achieve as far as performance, driveability, fuel economy, etc.
Cheers - Jonathan
--
Jonathan A. Race
Lieutenant, EMS Supervisor
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I may be confused, but I read something about this somewhere, and maybe somebody can clarify for me...
It has to do with tuning an exhaust system to work with a particular engine.
When the engine is running, the exhaust gases flow through the pipes in pulses caused by the release of exhaust from each cylinder. These pulses act similar to sound waves and help to keep the exhaust gasses flowing properly by creating low pressure points between each high pressure pulse. If I'm remembering right, the low pressure areas help to draw the exhaust out of the cylinder and down the pipe. If the pipes are too large, the high pressure/low pressure pulses aren't generated properly. I think this was due to the lack of enough exhaust gas being released from each cylinder to create a large enough high pressure pulse to fill the pipe.
Somebody please post and let me know if I'm off base... I wish I could remember where/when I was reading about this.
-NW

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Clearly this is why 'people' put coffee can size tips on their exhaust -- they are very concerned with keeping the backpressure just where it should be :)
I still don't get the allure of a pimped out Honda Civic, let alone a Honda Civic. Crazy kids.
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...

improve my 19mpg mixed. I'm going to need to replace pretty much my entire exhaust, so I figure I should spend the extra and do it right. I plan on keeping the truck as it is in good shape.
It's a 88 Blazer S-10 V6 4.3 4x4 TBI automatic. I would like to replace my stock exhaust manifolds, put on some headers, new y pipe, cat all the way back.
As the speedo only goes up to 89 (enough to time travel mind you) and I don't need to go uber-fast, I assume I would be happy with good low end.
All that being said:
1. Is it just a guessing game as to what is TOO much of an increase in exhaust size, or is there a percentage that I could go by. Some other method? 2. How does new headers play into that, if at all. 3. Do I need to get a high-flow cat converter, or will a stock replacement be okay? 4. What kind of exhaust/muffler would give a good sound on a S-10?
Again, I just want a every day driver with a bit more pep that it does now.
Thanks in advance, Joe
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IMO, unless you are going to improve the breathing capability(intake, heads, cam etc.) you will get little, if any benefit from straying from a stock system. The general pays some pretty smart people to figure out what will work best with a stock engine. It's just me, but I don't like the sound of a louder than stock 4 or 6 cyl. If you want more power and good sound, drop a 350 in it(it ain't that hard). H
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Jonathan Race wrote:

As a Harley rider, the *exact* opposite is true. You loose low end torque and power with open exhaust. You gain top end to replace it.
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Actually, backpressure is never good. Scavenging is the word you are thinking of.
GMC Gremlin

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4-stroke engines do not need back-pressure in the exhaust to function correctly, end of conversation..............PERIOD
--
Mad Dog

"Joe Webster" < snipped-for-privacy@cawfeemilk.com> wrote in message
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We're not talking about 4 cyl., I was saying 6 cyl.
-Joe
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He said "4 stroke", not 4 cylinder. H
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Oh :) I see now
*moves along*
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Not quite the end of the conversation. Removing the back pressure will cause the engine to run lean which can cause loss of power and burned exhaust valves. Computer controlled injection systems will usually compensate for this by adding more fuel to the mix. Carburetors often need to be rejetted to accomplish the same thing. In my experience, you usually end up with a little more power and a little less fuel economy. H
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Ok, all things being equal...... 4-stroke engines do not need back -pressure to function correctly. Primary pipe length and diameter as well as Collector length and diameter will effect the torque curve and horsepower potential of the engine but back-pressure is not required and will only hinder the performance of any 4-stroke engine.
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Mad Dog

"Hairy" < snipped-for-privacy@hotmail.com> wrote in message
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