3" versus 2.5" collectors on 1 3/4" primary headers
11-21-2012, 04:20 PM
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3" versus 2.5" collectors on 1 3/4" primary headers Will 2.5" collectors yield less or more scavenging effects than 3" collectors across the entire torque curve given 1 3/4" primaries, stock ls1 heads, cam in the 218-228 range and limiting rpms to 6300 or so?
I'm interested in reasonable theories not options based on what some other guy is running. I posted it here for a reason.
I'm interested in reasonable theories not options based on what some other guy is running. I posted it here for a reason.
11-26-2012, 10:13 AM
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Oh, stock cubes as well.
Here's my theory on the subject.
I'm looking at this as the piping system that this is. There are four 1-3/4 primaries each with 2.405 sq in. of area, 9.621 sq in in total going into the merge collector, which is the area as a 3.5 in pipe. The key here is not all these primaries are flowing at the same time. Arguably, when the two cylinders on one bank fire 90 degrees apart they are close enough to look like one big pulse at the collector. This would imply that the collector only needs to be the area of two primaries or 4.81 sq in equal to a 2.475 in pipe. It would also be noted that we still want to maximize pulsing though the collector as the two banks combine at the Y or X-pipe giving additional scavenging with an appropriate length secondary pipe. I would think that for this relatively mild setup, the 2.5 in collector is more appropriately sized. Now this is a lot theory and no real world experience of my own to back it up so please input your theories.
Here's my theory on the subject.
I'm looking at this as the piping system that this is. There are four 1-3/4 primaries each with 2.405 sq in. of area, 9.621 sq in in total going into the merge collector, which is the area as a 3.5 in pipe. The key here is not all these primaries are flowing at the same time. Arguably, when the two cylinders on one bank fire 90 degrees apart they are close enough to look like one big pulse at the collector. This would imply that the collector only needs to be the area of two primaries or 4.81 sq in equal to a 2.475 in pipe. It would also be noted that we still want to maximize pulsing though the collector as the two banks combine at the Y or X-pipe giving additional scavenging with an appropriate length secondary pipe. I would think that for this relatively mild setup, the 2.5 in collector is more appropriately sized. Now this is a lot theory and no real world experience of my own to back it up so please input your theories.
12-01-2012, 08:19 PM
#3
I wouldn't even mess with 3" and especially not a 2.5" collector! Set your merge collector to 2.75" choke diameter and then run a 3-1/2" collector and head pipes into an X....how does a 53RWHP/49RWTQ gain over a stock 2-1/4" dual exhaust with CAT's sound to you (especially with zero tuning!) For facts and data about this read on http://www.montecarloss.com/ls1monte.../August02.html
And by the way, these were a stepped 1-3/4" to 1-7/8" true equal length primary tube header on a stock LS1 with a puny 221° cam!
And by the way, these were a stepped 1-3/4" to 1-7/8" true equal length primary tube header on a stock LS1 with a puny 221° cam!
