Small Port and Big Valve

[Anonymous]

I have a question;

: When utilizing small high velocity ports (1.6sqin) and big valves (2.19) how do you keep the velocity from slowing in the valve pocket?

: If you were to angle the port to one side of the valve and close in the pocket, a little, on the oppisite side, would that induce swirl?

Just trying to learn a little,
John

 

[Thad]

Good question,
It would have a lot to do with the valve bowl shape and how quickly the shape increases in cross sectional area as the port approaches the valve set. Also the amount of valve opening would effect it.

You mentioned the 2.19 intake, several people, IIRC FTF included, noted that at 1.92" shrouding starts. Anything bigger gain is lost to deminishing returns.

 

[Anonymous]

I was actually looking at a 351C 2V head when I asked the question.

The Cleveland head will unshroud when opening, but doesn't offer any swirling action. That's why I asked the question about making the swirl happen inside the valve pocket.

I'm just trying to picture what the perfect performance 300 head would look like with raised intake and exhaust and a Cleveland valve train.
The fun part is getting the stock intake and exhaust to fit. That threw out the normal Cleveland and Windsor intake shape.

My thought was to take a small intake port, coming in at a high angle, and have it offset the valve slightly so that the high speed flow would run around the large valve with out to much drag.
I'm sure this has been tried and thrown out, but I can't find any record of it.
It would make a good head, if it worked.

John

 

[Thad]

John,
What are you doing?
I'm playing the devil advocate again, don't you think too much air flow ability will exceed what the 300 can best use, moving the flow capabilities above the usable rpm range .
Dad and I once built up a pair of SCJ heads for a 429, flowed like a flush toliet. But on the engine were not as good as before. Went to 460, the heads started to work. But the real kick-in -the-butt came when we went to 514, a whole new world, 5,000# car C-6 running LOW 10.0s

Would it be possible to use some other head design, Trick Flow Twisted wedge or Yates. By using the mirror image it would put the valves in the right sequence. Pistons are available for both, might have to juggle rod length and pin size.

I can see designing so the exhaust ports are in the same place and using existing headers, no problem to increase tubing size. But forget designing intake side to use any existing aftermarket intakes. None are big enough for a truly decent flowing head. You've see the pics of my 300 head, 242cfm and honestly the ID of the intake ports are LARGER than the OD of the Cliffy manifold at the flange. And it is not unusual for a head caster to als cast their own intakes, ala Dart.

 

[Anonymous]

http://www.toohighpsi.com/BudgetTT/alflow.htm
Just thought it would be interesting to note that lightly ported TFTW heads flow that much on a 351, which still has less cid/cyl than the 300. Sure you may not be running the same RPM's but a 351 at 6000 rpm is pushing the same cfm/cyl as a 300 at 5300.


-=Whittey=-

 

[fastback69]

http://www.theoldone.com/

This site has some pretty good info on flow. They concentrate on port shapes that increase velocity over mass. Very interesting reading. The most interesting is the supersonic flow 429.

 

[Anonymous]

To get some basic theories on head flow and mixture quality they're going to send you over to n2performance.com to read McFarlands articles (There are currently 3 lectures, 2 in the archive and the most recent.).


-=Whittey=-

 

[Thad]

Whittey,
Don't know if you thought about it or took it in consideration, but it is important when comparing V-8 to I-6 to remember that the 8 has 33% more valves etc than the 6.

 

[Anonymous]

Thats exactly my point. Those flow numbers are for each cylinder in a 351 which is ~43cid versus the ~50cid of a 300. I sincerely doubt a 300 with similar or even slightly larger flow numbers would be a dog.

What i'm saying is that I doubt anyone here is going to make any head flow worse than stock. Here is some flow data from a k-series head (1.4/1.6/1.8 liter engines): http://members.aol.com/dvandrews/kflow.htm

Sure its a DOHC head, but the engine doesn't care whether the air/fuel came from 1 or 2 (or 3, etc) valves. A 21-28cid/cylinder motor should not have more airflow/cylinder than a 50cid/cylinder motor. Their 'stage 1' motor at 0.28" valve lift will outflow our stock head at 0.50" valve lift. I most certainly see a problem. Their big valve VVC head at 0.23" outflows ours at 0.60". For exhaust the stock VVC head at 0.28" is outflowing ours at 0.60". Their modified k head exhaust at 0.20" is outflowing ours at 0.40". On cylinders that displace ~half of ours. Port your head people. It needs it.


-=Whittey=-