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Old 08-06-2011, 11:17 PM
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SBC header tube size?

I'm looking for the proper header tube size. The motor is a 350, with a hot street cam, possibly a thumper. Using Edelbrock RPM heads from a top end kit (pt. #60899), an air gap RPM manifold, 9:1 comp, probably a 750/800 carb. I want everything to flow as best as possible. My question is: the motor is in a '66 pickup and headers are slim pickens. Would 1 1/2 dia be sufficient? The choices from Summit are Flowtech 1 1/2" tubes or Doug Thorleys 1 5/8" tube. The heads have an 1 1/2" square port with a approx 1/4" radius in the corners. The Doug T's are 3x as much as the Others. Any suggestions on where to look for larger tubes without hitting the $600 mark?

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Old 08-07-2011, 12:24 AM
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Summit has these also:http://www.summitracing.com/parts/HOK-2452HKR/ which are 1 5/8" primaries for extra $$ they are available in ceramic. The more common 1 1/2" primary headers help low end torque which you would want on a street driven truck which may help MPG also.The Hookers would be a good match for the heads you chose.
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Old 08-10-2011, 06:08 PM
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SBC Headers

OK, I'm looking for 1.75" tube, full length, coated. I've been all over online and the phone. What I'm now looking for is some help from some experienced truck engine swappers and SBC power nuts. This is a 66 GMC w/ a 350/350 auto trans. I'm looking for someone who knows what other application of headers would work on my truck. A while ago, I was told Chevelles but never got any specifics. I'm going to run Edelbrock Performer RPM heads, manifold, etc, and I just want everything to breath and flow. The 1.625" tubes cover about 15 % of the 1.5" square exhaust ports. That just doesn't seem like the plan. Any help please!!!
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Old 08-10-2011, 06:14 PM
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To big of a tube will kill your low end on a street motor and will only help at 6000 rpm and up. How much time will your street motor see above 6000? How much will it see at 1800-4000. Buy your headers based on these facts.
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Old 08-10-2011, 09:54 PM
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Larry,you have to take into account two factors first your truck is no lightweight and second it has the aerodynamics of a brick,so what does it take to get it moving? TORQUE! To make it launch and get rolling it gets right back to torque output,getting overly large primaries decreases low end torque.The Hookers will work well with the RPM heads and to promote even more torque and horsepower you should run an X-tube in the exhaust system.I had a '65 C-10 with a stout 350 and 700R4 with 4:11's,biggest problem was getting it to hook up it could smoke the hides something fierce (not much weight on the back of a pickup) so use some of the bucks you save on the headers and put it into the suspension so it will hook up.
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Old 08-11-2011, 03:06 PM
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Ok guys. Thanks for the info. I copied and pasted a Q & A from another post on this site. Please read the reply to this guy's question. I hear what you're saying about low end torque, but the stuffing plate seems like it would be a somewhat compromise, something in the middle of 2 different answers, flow and low end. I just can't see covering good ports with smaller pipes. This will be a street motor, but I'd like to get Edelbrocks quoted 410 horse with this top end kit.
Originally Posted by 406chevycaprice
ok i'm looking to get a set of dart iron eagle heads 200cc runner 2.02/1.60 64cc .now what i have now is D port 1 5/8 primary tubes .i tryed to get a bigger primary like 1 3/4 but nobody make's a header like that for my car .
what i'm asking is with a 1 5/8 primary tube is this going to be a problem when i go to bolt up the header to the heads with a small primary tube .

thank's rob



There's a couple things going on one is simply header flow capacity, a high revving engine or a large displacement engine needs more capacity than a slower turning of smaller displacement engine. The combination of fast and big gets to be additive. In your case you're starting with a 406, so at least bigger applies.

"""""Next is one of gas flows inside pipes. Here the basic rule is that the header primary pipe needs to be as big as or slightly larger than the port. The reason being is that if the header and flange are smaller or overhang the port, the fitments bump is seen by the flow as a large obstruction. If you can't buy the correct size header for the engine and chassis off the shelf, the best option is a custom made set. This could come from a commercial maker that will bend sizes to order, or you can obtain kits of flanges and tubes with which to "roll" your own.

The lesser but still reasonably effective option is to use a "stuffing" plate between the head's ports and the header. This would be about 1/2 inch thick aluminum. It would be machined to provide a smooth transition from the port size and shape to the header size and shape.""""""""

Bogie
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