header size for small block

[Dwight]

I have a 354 cubic inch 5.0 / 302 motor in my Cobra. I'm doing research on header size "again". I used an auto math web site to calculate my header size. It says I need 1 3/8" for 354 ci at 6500 rpm. But I was reading a article on master motor builders and the Ford small blocks (347 - 360 ci) used 1 3/4" or 1 7/8" headers. I have 1 5/8" headers and I'm going to replace my Lone Star side pipes with a pair of Classic Cobrapack mufflers. But now I'm confused about the header size.
Does anyone have a link to a header calculator site or know what size headers I need with a 354 ci motor at 6000 - 6500 rpm?


I'm always looking for something to change

Dwight

[blykins]

If a calculator is estimating 1-3/8" header pipes, then you need to find another calculator....

For a 351 sized engine, I would go with a 1-5/8"-1-3/4" size header....and I would probably lean more towards the smaller size.

However, if you ever have plans to stroke the engine, it may be worth your while to go big now.

[Jerry Clayton]

that engine is already stroked

I always try to use a tube size at least 1/8 larger than the exhaust valve size--many times. this then taking into consideration the tubing thickness, will generally give an ID header size equal to OD valve size-----
Also I use a sparkplug with a piece of tubing welded over it to similate socket and extension for clearance around plugs. try to keep the tube straight for a few inches before turning.The header flange should overlap the port at the top for antireversion purposes

[blykins]

Didn't catch the engine description....I saw the 354 and thought it was a slightly overbored 351.

There's nothing efficient about a Cobra header/sidepipe setup, so there's no use in sweating the details.

The trend I usually see, however, is that people tend to go too large on header sizes and carb sizes.

[ERA Chas]

Stroker 302's are fine with 1 3/4" pipes. Keeps velocity up with excellent flow. The sidepipes are where the loss is.

[Rare Iron]

Back when I worked for Dynomax, our smallest header primary sizes were 1-5/8", with some big block headers at 1-3/4".

[Dwight]

I wanted to improve my old sidepipes so I bought a pair of Classic CobraPack 3" mufflers with packing. When I cut the old muffler off, I found they were 2 1/2" packed. I may not gain a lot from the new mufflers, but I'm going to install them.

Dwight