Thread: header size

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We do 4/7 swap on almost all the chev engines we build for customers

and use bigger/shorter headers to move the curves higher in the power band--if you are building for more power the engine will compromised with smaller longer headers!!!!!

Use as big as primary tubes as you can and still get a sparkplug and socket to clear---you can pair cylinders into 2 different primary lengths to spread the tuned rpm range of the engine--especially with tri - ys


Jerry

i used the bigger size tube when i build headers for small blocks a 383 is not that small cid 1 3/4 or 1 7/8 you may have to use a stall plates for the 1 7/8. i buy all the sbc stuff from a guy i know that cuts the header plates on a cnc mill you can go to 1 7/8 with no stall plates if you work the tube and going to a small head bolt head and a small bit of work on the tube and go to a 28+long primarys and go with a X tube ex cross. as for the 4/7 swap i use them all the time there not that much more money were i get my cams there not any more then buying a stock firing cam from jegs or summit. i run them for less crank twist then the small amount of power you may see .i think you will see more power with a good built headers and ex then the cam but it all adds up i doing a 4/7 swap on two bbc blower engines for a boat i going to have the new firing order on stickers on the valve covers so some one will not try wire it with the stock firing order.if i go to a custom grind i use the 4/7 swap all the time on rollers cams

For you chebbie guys again...HELP!

I was looking at the arrangement and tube size on some 4 into 2 into 1 stepped headers for a small block, here's what I found for a sbc with a 1-8-4-3-6-5-7-2 firing order:

On the left bank, the first two clinders are paired, and the back two cylinders are paired, same thing on the right bank. Tube at header is 1 3/4" stepped to 1 7/8" 10" out from the header flange...... If I change the came to the 1-8-7-3-6-5-4-2 firing order, what is the best way to pair up the tubes on the 4 into 2 collector to maintain the same scavenging effect as the standard firing order??????

If all this confuses you, join the club!!! I spend a lot of time confusing myself!!!!!

Maybe I'm just playing with something that doesn't matter a whole lot, but it IS a chebbie, and needs all the help it can get in the horsepower department......