So I've been playing with this 6 cylinder I have in a '63 F100 and the head has me a bit stumped as to which direction I should go.
A little background on the 215/223/261 motor series in case anyone's unfamilar. The head is a 10 port design. Yep, you read that right. 6 seperate exhaust ports, and 4 intake ports (2 are straight shot and 4 are siamesed). WTF? Otherwise, it's pretty conventional: OHV, typical valvetrain, roughly "square" bore/stroke, etc.
While the exhaust ports are pretty small from the factory, with a bit of exploratory surgery it looks like it can flow OK for an engine of this size. What I did was take the ~1.1875" square port and shape it into a trapazoidal shape. I wanted to preserve the velocity as much as possible while still gaining a bit more flow to extend the rpm range somewhat. My gut told me to leave the floor pretty much untouched, except for mildly reworking the short turn radius, and work on the roof and upper sides. Looks like it'll be OK.
The intake is where I'm stumped. If they were all siamesed, OK fine. Again, if they were all independant, OK fine- I can work with that. What I'm not sure about is how to go about balancing the flow as much as practical between the sia. vs the ind. The siamese intakes share
some features with the Chevies, but they don't have the head bolts going through the middle. What they do have is "wings" right at the valve bowl/seat area on the floor. Actually, they seem to have more in common with the 235 heads, portwise. I'm not sure if lumps would really work here. I suspect they would, but I'm worried they would make the port volume too small as compared to the ind. ports. I realize I'm not looking for double the volume of the single ports, but still...
All this leads to my questions: (and thanks, if you're still hanging in there after this lengthy diatribe
)
1. Should I eliminate the wings or just profile them bit?
2. What's the best way to balance the flow between the differing configurations?
3. Thinking of the intake as an extension of the port-should I build a: A) divided plenum, B) log plenum, C) IR-ish intake with 4 carbs.
Are the wings sorta like a prehistoric ditch cut to help "bounce" the intake charge into the valve seat at a straighter shot (vs. just spilling over the sides)? Do they help with shared cylinder reversion?
I'm thiking an IR setup, such as it is with
some sia. ports, would help from a reversion standpoint but probably not be so good from a flow balance perspective. That leaves the log and the divided plenum. The log won't help with either the balance or pulse reversion-but lots of manufacturers have built them that way over the years, so am I overlooking something? That leaves the divided plenum by default. What am I leaving out?
Finally (hang in there, almost done), the truck will be used as a daily beater/hauler/sometime tow vehicle. So economy and efficiency are probably more important than raw horsepower. I'm looking for a good torquey motor in the 1500-4000 rpm range, and a smallish cam is in the cards once I have some flow numbers on the heads. Headers are being built now; 3-1.5" long tubes per side(about 30-32" if I can make them fit) feeding into a Y after the collectors to a 2.5" exhaust is the current plan. As is a duraspark conversion.
I'll try to post some pics to better explain what I'm rambling about
