Thread: 302 cyl head print (needed!)

Tweet

Sorry about the mis communication. The only thing im confused on is the bolt hole center location compared to the port hole center. These must be exact because if they are off then, bolts, ports, and everything could be not lined up correctly.
I am having a hard time finding this.

I think that the reason that you are having trouble finding the tapped hole location relative to the port is that it is not an exact dimension.....the ports are cast and the header bolt hole locations are machined when the head is clamped against some reference surface...usually pads at the ends or head bolt surfaces that were machined in the first operation. The casting cores are not in a terribly precise location....so things vary among heads.

I think the suggestion of taking your heads and doning a real measurement on them is the best if you want precision......OR you could make your plates and hand fit them to your heads.

mike in tucson

if they are made in the prosses that you describe, than any aftermarket header that you buy will not fit on any head, because it is not "in a terribly precise location".

The factories MUST have some talerance for the casting.

Well my plan is to make the flange, then make tools (inside and outside die/madrel) to flare the pipe to a more oval shape. and directly match the port size. (or bigger).
The pipe will then slide into the flang then be tig welded on the inside, (head side).
Any comments?

First of all, if you take a stock factory exhaust manifold and match it to the head, you will be shocked at how far it can be off......1/8" is not uncommon. Some exhausts are made
bigger all around the port on purpose so there is a drop off going into the exhaust.

Headers are'nt much better; I've had to move the header bolt holes by almost 1/4" on some header models.....if I didnt, the flow would be terrible at the junction.

The best way to start the process is to find or make a gasket that matches your head....check both heads to see if they are the same. Take that new gasket/template and put it on your exhaust and see where you fall......then, make your new flanges from your template so they fit.....

What you are describing as to your fabrication of headers is essentially what the header guys do.

From my discussions with the custom header guys and my experience on one set of headers, the flanges you buy have the ports sized to match the OD of your prescribed primary tube. For a 302 the "normal" is 1 5/8" primaries and the tubing is a controlled OD which gives you a circumfurence of 5.11" so the port perimeter will be about 5.15" or so. When you form your tube to fit and tap it into place you'll get nearly a zero gap fit. Header guys I talked to said to weld on the outside, leaving the machined surface of the header flange unmolested, but to never weld both sides of the flange.

Sounds like you already know exactly what you want to do, and that you either own or have access to some pretty sophisticated equipment. Not many people can afford to spend time making things like custom header flanges and make it pay off so you are in an enviable position. Good luck with your header build. I'd love to see pictures of your process as you move forward.

Originally Posted by Henderlong

if they are made in the prosses that you describe, than any aftermarket header that you buy will not fit on any head, because it is not "in a terribly precise location".

The factories MUST have some talerance for the casting.

Well my plan is to make the flange, then make tools (inside and outside die/madrel) to flare the pipe to a more oval shape. and directly match the port size. (or bigger).
The pipe will then slide into the flang then be tig welded on the inside, (head side).
Any comments?

From someone who's fabricated many sets of SBF headers, I have to say I think you're making the process way too difficult.....

As others mentioned, use the gasket that most closely matches your exhaust port opening, then grind the od of the flange to match... I usually by a header kit, with flanges, tubes, and collectors from Speedway. Once I get the flanges to match the ports, it's a simple matter of dingin' the round tubes to an oval shape on the end with a body hammer and some solid round stock with the correct radius held in the vice.

Unless you're tuning for one or two horse on the dyno, don't really see where anything more exotic would be required.....and if you are looking for the absolute best horsepower, then you've got the wrong set of heads anyway...JMO

Hha, ya i know these heads are not the greatest....
I used a cmm machine to answer my own question.
If you were to draw a line down the center of the bolts, the port ends 18.5608mm in one direction, and 12.9901mm in the other. So i took a persentage of that and apllied it to a 1.8inch (h) x 1.32inch (w) port on the flange
I will post a picture once i finish the design

idk if i want to use a ball pean hammer to shape the tube. I sorta want to flare it out useing a press and some custom tools. This would be better for production if i wanted.

I have axcess to a 3 axis cnc machine at school. All i have to do is build it on CAD and convert it to a txt doc. Then i take it over to the cnc.
However i first want to mill it out of wood, to ensure that it fits correctly. I will of course use a wood cnc mill for this, not a metal one.
Just give me a few hours to make a mock up design.
STAY TUNED

K heres my mock up. Dimentions are exact. Im not sure how i want the outside too look yet?
Like i said before. the pipe will be flared so that the outside diameter fits snugly inside the flange.

Originally Posted by Henderlong

K heres my mock up. Dimentions are exact. Im not sure how i want the outside too look yet?
Like i said before. the pipe will be flared so that the outside diameter fits snugly inside the flange.

The bottom edge is only important for plug clearance, and then mainly for angled plugs which can be a pain with some headers. If you're making them out of wood first you can check plug clearance and tweak if necessary, right? Telling us that you're a student with access to the school tools and the blessings of your professors/shop manager brings some sanity to this thread, at least for me. It's a great project given your situation

PS - on the welding I looked at Don's thread http://www.clubhotrod.com/forums/sho...threadid=46852 and Hedman does theirs the other way, letting tubes protrude on the head side, welding a solid bead and them machining that flat. You would at least need a belt sander large enough to do all four ports at once, if not a mill to keep it flat I would think. That keeps the front side cleaner and gives a little more room for header bolts on the flange.