Primary & collector sizing --> Opinions needed!!
03-23-2005, 03:53 PM
#1
Racer
Thread Starter
Primary & collector sizing --> Opinions needed!!
I know I'm shotgunning questions today, but I've got a lot of ideas floating around in my head!
In selecting the right primary and collector sizing, the May issue of Popular Hot Rodding had a good writeup. I'd like to run this by those with experience in this arena and see what your thoughts might be in regards to sizing.
Motor is a 468 ci big block, AFR heads, solid roller cam, 10.7:1 CR --> should be in the vicinity of 650 hp or so.
Primary Sizing - Based on the article as it relates to primary header piping figured by exhaust head CFM, it appears that 2.125 would be the primary size of choice. Would you agree?
Collector Sizing - The article says that primary size X 1.75 = the correct collector size. If 2.125 were the right primary size, then the collector size 'should' be 3.7. Given a choice of 3.5 or 4.0 for the collector, which would you choose?
Thanks again!
Regards,
Bryan
In selecting the right primary and collector sizing, the May issue of Popular Hot Rodding had a good writeup. I'd like to run this by those with experience in this arena and see what your thoughts might be in regards to sizing.
Motor is a 468 ci big block, AFR heads, solid roller cam, 10.7:1 CR --> should be in the vicinity of 650 hp or so.
Primary Sizing - Based on the article as it relates to primary header piping figured by exhaust head CFM, it appears that 2.125 would be the primary size of choice. Would you agree?
Collector Sizing - The article says that primary size X 1.75 = the correct collector size. If 2.125 were the right primary size, then the collector size 'should' be 3.7. Given a choice of 3.5 or 4.0 for the collector, which would you choose?
Thanks again!
Regards,
Bryan
03-23-2005, 04:17 PM
#2
Race Director
Don't have the answer but is there a formula for a relationship between exhaust CFM and primary pipe size, what do your exhaust ports flow ?
03-23-2005, 04:53 PM
#3
Racer
Thread Starter
Originally Posted by MotorHead
Don't have the answer but is there a formula for a relationship between exhaust CFM and primary pipe size, what do your exhaust ports flow ?
In article I referenced was called "Exhaust Science Demystified". They actually had a chart with your head exhaust port CFM at full lift graphed against the exhaust primary I.D. in inches. So, you could just follow your flowbench # up the graph until you hit one of three lines (essentially stock motor, hot motor, full race) and that would give you what primary sized pipe you needed.
They didn't give a forumula (like they did w/ collector sizing or choosing a muffler); they just included that graph.
B.
03-23-2005, 05:57 PM
#4
Race Director
The Hooker Super Comp headers are the only one that has the size your refering too as a aftermarket over the counter header. The only problem is they are for competition and not very streetable. Great set of headers for a BB, but ground clearance is very minimal 
03-23-2005, 06:41 PM
#5
Melting Slicks
Member Since: Jun 2001
Location: Moro IL
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IF you go with the hooker supercomps with the sidepipes, you'll be pretty close to where you want, plus the primaries are very long so you have a broad torque curve with them. I went from 1 7/8" primaries to 2 1/8" figuring I was going to lose some low end torque but if anything I gained, I guess becouse the primaries are about 44" compared to about 30" with the standard long tubes.
Pat Kunz
Pat Kunz