The input about my question on headers has been informative.  Distilling it down, and after talking to Jerry Christenson as well as Gord McMillan in Calgary who has built a lot of blown Y-blocks, I have the following conclusions:

For my application, which will use up to 10 or 12 psi at the blower outlet at 6000 rpm, I can expect to get about 6 psi in the intake manifold because I am using high output impellers and high flow components all through the ducts, bonnet, carbs, and heads.

Given the above, the concensus is that the 2-inch primary header pipes I considered would increase high-end horsepower, but at the sacrifice of low and mid-end performance.

Because I am building a car for the street, Jerry Christenson and Gord McMillan both recommend that 1-5/8 headers and 2-1/2 inch extensions (collectors) 2-1/2 inch exhaust pipes will give the best low and mid-end performance for street use with a small sacrifice of high-end horsepower.  This is also consistent with the comment from Frank/Rebop.

If I were building to race, I would follow Ted Eaton's advice that bigger is better and go with at least a 2-inch or 2.5 inch primary and bigger extensions.  Note that Ted cautioned me that his experince was for high end performance for racing, not a street machine.

In the final analysis, I think I will experiment with tri-Y headers, probably from Stan's Headers in WA, to get some scavenging effects while feeding into a 2-1/2 inch collector.  I am in Montana, so WA is not too far to take the car, if Stan's needs to custom fit things.  Anybody out there running tri-Y's on a Y-block?  How do they work?

In all the tests I have ever seen regarding 4 into one versus tri Y, they seem to work equally well below 3000-3500. After that point, individuals seem to be better. Caveat, I have never seen this on a blown Y-Block.

    In a somewhat direct comparision, Hoosier Hurricanes engine is similar to mine except more cam, and ported heads. Mine are very close to stock, as is the cam. the major difference is John's fenderwell headers versus cast iron manifolds. He is at least 100 hp stronger than I am. The Hurricane has gone 119 mph, I've gone 106. You can check with Hoosier, but I believe his headers are 1 3/4 and 32" primaries.

Frank/Rebop

Bristol, In ( by Elkhart) 

My headers are off the shelf fenderwells from JC Whitney, no longer available.  They are 1 5/8 by 23" primaries, 4 into 1, with a 3" collector about 6" long dumping into a 3 12" collector about 18" long.  I haven't tried anything else, so I have no comparison.  I believe they are the old Sanderson stocker headers from the '60s.  Another difference between Frank's and my car is that his is a stick and mine an automatic.  At 119 mph the horsepower calculates to around 485.

John in Selma, IN

John - "The Hoosier Hurricane"

Well, I got the fenderwell part right!

Frank/Rebop

Bristol, In ( by Elkhart) 

Frank:

Don't feel bad!  I didn't know the dimensions until yesterday when I went out and measured them.  I had just bought them and blindly bolted them on.

John

John - "The Hoosier Hurricane"

Some internet research found some "Block Hugger" headers by Pacesetter for 1955-1970 Ford Fairlane cars.  They are advertised as mandrel-bent 1-5/8 mild steel 16-gauge pipe with 3/8 flanges.  Has anyone had any experience with these?  The picture is probably not application specific, but looks suspiciously like a F-100 header, not a car header.  I need headers for a 57 Ford Fairlane 500 with rack and pinion steering and plan to equip it with a top loader tranny.

Also, they can be purchased with a metallic-ceramic finish.  Does anyone know if the metallic-ceramic finishes stand up to the exhaust temperatures provided with a blower?

The Pacesetter header add is at www.car-stuff.com/store/?N=10359+4294963821+1616+11920+9125

My impression after perusing their ads for 3 point seat belts & oxygen sensors for early Fords, is that whomever is doing the ads, has no idea what they are talking about. So best be careful..

Paul

Well maybe I'm just stupid but I call it "old" but I don't guess I understand "boost". The only experience I have with "boost" is my Banks turbo on my '92 Ford 7.3 diesel pickup. It cruises a 5 psi and under a load it is at 11 - 12 psi. If the wastegate sticks it will peg the needle at 15 psi. I think any powerstroke is at 14 psi. I realize that it is diesel vs gas and detonation is a way of life with a diesel. I remember when Ford first came out with turbo's in '94 it made about 4 -6 psi and it was almost like not even having a turbo. I think tractor pullers have like 200 psi through up to 4 turbos. How in the world can they make that much boost if 6 psi is too much for a Y-block? Is turbo boost different than supercharger boost? I think old airplane motors had like 75 psi and they used 115/145 octane fuel. I know the experts on here, and I mean that, you guys are experts, can explain this to me ...

Doing Fords for 45 years. '56 Customline Victoria

E.J. in Havana FL

It's all in how the engine is designed.  An engine running 200psi has been built for it.  Everything from the block, crank, rods, pistons, heads, etc is beefed up to handle the power.  Most of the Y-blocks running around have cast pistons.  With cast pistons about 6psi is the most it should take.  Cast pistons are fragile.  One episode of detonation and something is probably coming appart.  The Y can take a lot more if it is built for it.  The same is true for most other engines.

Turbocharger and supercharger boost is the same.  A turbo system is a little more dynamic.  Since it's not belt driven, the boost pressure is not a function of engine rpm.

Lawrenceville, GA

The boost typically added to a Y-block by a supercharger or turbo ultimately is not the issue, unless someone is going above 11-12 psi, measured at the supercharger outlet.  The issue is horsepower.  Your answer hits the nail on the head.  As you increase boost, horsepower increases.  If you add too much horsepower to an engine that is not made for it, you will break something.  Elsewhere in this forum are some pictures by Ted Eaton of sbf engines that were built up to more horsepower than they can take.

My earlier comments about boost were made to provide some idea about how much air I need to run through the engine as one factor to consider in selecting headers.

I may have mentioned somewhere above that if you measure boost from the supercharger I plan to use, at about 6200 rpm it will show 11 to 12 psi at the blower outlet.  If you measure the same pressure in the intake manifold, after various losses through the carbs, etc., you will see no more than 6 psi, maybe less.  That is because of friction loss in the system.  Typically, boost has traditionally been measured at the blower outlet, but measuring manifold pressure is a better indicator of what may be reaching the valves, where even more friction loss occurs as air flows through the head to the cylinder.  I am not sure where you are measuring the tubo boost on the Powerstroke, but it is likely somewhere near where the air enters the head, thus 15 psi of boost on your diesel is probably equivalent to the 6-psi I would read in a Y-block manifold when the supercharger is putting out 11-12 psi at its outlet.  If so, the diesel turbo is adding a lot more boost than I plan to add to a gas Y-block for street driving.

Getting back to the header issue, everyone seems to agree that going to more than 1-5/8 inch primary pipes on the header will cost low and mid-range power on a street car, even with the supercharger.  I accept this, but I am not sure I understand exactly why this happens.  Can anyone explain this?