Exhaust theory
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Teching In
Joined: Dec 2009
Posts: 33
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From: Bonham Tx
Exhaust theory Growing up around SBC engines I read alot of the Smokey Yunik's genius testing with the motor top to bottom. One that caught my attention was always the exhaust research. This stuff applies to all motors in general not just SBC. So in this I wonder why so many people running 1 7/8" long tubes. Most exhaust head ports on LS1 head RARELY exceed 1 3/4" so why wold there be any reason to run larger primaries? I understand it could be an advantage with forced induction or nitrous but why would this be necessary for N/A apllications? On the Pat G 500hp recipe he even used 1 3/4" headers with 3" daul into a 4" merge. In theory if the 3" daul was "nececity" then it was HAVE to run into a 6" single pipe or it would become a point increasing backpressure. At what point to backpressure help and hurt hp. Just trying to pick yor brain....
Because dyno tests have shown that 1 7/8" headers gain over 1 3/4" headers, with no other changes.
Theory is nice, but sometimes real-world numbers are more important.
Plus, backpressure never helps horsepower. That's where scavenging, primary and collector sizing, etc gets interesting.
Theory is nice, but sometimes real-world numbers are more important.
Plus, backpressure never helps horsepower. That's where scavenging, primary and collector sizing, etc gets interesting.
TECH Junkie
Joined: Dec 2005
Posts: 3,092
Likes: 11
"Because dyno tests have shown that 1 7/8" headers gain over 1 3/4" headers, with no other changes."
Exhaust theory could make for an interesting discussion. In the above case could it be the 1 7/8" headers were covering up or band aiding another problem? Maybe the 1 3/4" headers were over scavenging during the overlap period? The larger diameter primary pipe would cut down on the speed of the exhaust gases and therefore cut down on scavenging during the overlap period. The real problem may have been the wrong valve timing events because of the wrong camshaft for that engine combination. Just some food for thought.
Exhaust theory could make for an interesting discussion. In the above case could it be the 1 7/8" headers were covering up or band aiding another problem? Maybe the 1 3/4" headers were over scavenging during the overlap period? The larger diameter primary pipe would cut down on the speed of the exhaust gases and therefore cut down on scavenging during the overlap period. The real problem may have been the wrong valve timing events because of the wrong camshaft for that engine combination. Just some food for thought.
"Because dyno tests have shown that 1 7/8" headers gain over 1 3/4" headers, with no other changes."
Exhaust theory could make for an interesting discussion. In the above case could it be the 1 7/8" headers were covering up or band aiding another problem? Maybe the 1 3/4" headers were over scavenging during the overlap period? The larger diameter primary pipe would cut down on the speed of the exhaust gases and therefore cut down on scavenging during the overlap period. The real problem may have been the wrong valve timing events because of the wrong camshaft for that engine combination. Just some food for thought.
Exhaust theory could make for an interesting discussion. In the above case could it be the 1 7/8" headers were covering up or band aiding another problem? Maybe the 1 3/4" headers were over scavenging during the overlap period? The larger diameter primary pipe would cut down on the speed of the exhaust gases and therefore cut down on scavenging during the overlap period. The real problem may have been the wrong valve timing events because of the wrong camshaft for that engine combination. Just some food for thought.
