Questions on Porting ohc heads!

[ou812]

Got a Honda V tec head Im going to port, first time doing a 4 valve head. Got some flow numbers:
lift. int. exh.
100. 83 81
200. 149 130
300. 194 155
400. 222 162
500. 239 166
First time flowing a head of this type...pain in the ole rectum! How do these numbers look? Stock valves and ports for now. Questions:
Can I get away with more throat diameter than in a v8 head?
Is there anything that I should maybe be careful of ? Looks like I could open up where the guides are up into the bowl and widen the port and maybe raise the roof some...if anyone has done some of this kinda work Id appreciate some input. Not asking for secret info just pointers! Thanks,
Brian

[cboggs]

Brian,

I've done a ton of those, .. held some records & stuff, ..

1st be VERY carefull around the guide & the guide boss. It's fairly thin
there and they WILL crack if you cut the guide boss down too much.
Don't cut the guides off, I've seen this 100 times and all it does is
increase guide wear.

I still try to keep the throat in the 90% range, .. just like a normal port.
The short turn area I try to get around 98% of the valve, .. etc.

On the exhaust, .. keep the short turn very tall. On the roof I raise the
roof from about the end of the dividing wall out to the gasket. The gasket
& sometimes the header have to be trimmed. Keep the port small for
N/A and turbo cars, .. you want a high air speed.

For intake seat I use a 35º top, 45º seat, 60º then 72º blended.
Exhaust is a 35º top, 45º and radius on the bottom.
These are custom cutters but I think Newen has some stock stuff
that works well.

Hope that helps.

Curtis

[ou812]

Thanks Curt...I was thinking about widening the intake port at the guides opposite the dividing wall. To make room for the air. What about raising the roof on the intake port?
Thanks
Brian

[cboggs]

Brian,

I didn't find much by working the roof, .. seemed to be in the floor &
walls, ..

You should use a Pitot tube and do a velocity map of the port, .. it'll
help tell the story. I map ports in 20 or so locations to get a "road map"
of the flow in the port.

I think it's VERY important to maintain a very even cross secional area
in the two "sides" of the port for each valve. If you try to use
shapes from a "traditional" head like a small block Chevy you'll get
in trouble.

When I first started the multi valve stuff, .. I made a rubber port
mold so I could see what the port really looked like, .. and MAN
did it open my eyes! If you can, make a "rubber" of the port.

I hope Darin rings in on this one, .. he's done some multi valve stuff, ..
and since I do so much multi valve road race stuff, .. I'd love to
hear his take on it, ..

Curtis

[ou812]

Ok Curt...I will probe the intake port to get some idea of how the port works. I have never done the rubber mold but I guess I could. This customer brought me a damaged head that has been ported by someone else to compare my work against his...but after mapping the ports out with my calipers Id say this guy is ROBBING people! His ports are about the same size as the stockers, cut down exhaust guides, and he opened the intake up and squared it! Im going to flow this head tomarrow to see just how it compares to the stocker. Hopefully I can do a better job than this guy and bring in some of the local ricers!!!!
Brian

[SWB]

"square" the port floor next to the divider and make the divider more concave. Keep a small radius on the leading edge of it and otherwise do as Curtis says.

[cboggs]

Brian,

Do you know who ported that other head?? I'd find out.

It takes VERY little material removal to make those heads work, ..
big ports are not the way to go, . so be careful.
The cost of porting a head isn't tied to how much material you remove.

If you take your throat and make it 90% of the valve, then make the cross section at the short turn apex 98%, .. it's not too far from what the stock port is, . .

Curtis

[mike_belben]

curtis, what brand/type rubber compound have you had success with in making molds, and do you recall where you sourced it?

[ou812]

This ported head has the intake port entrance "squared" vs. oval. All for corners are squared up. Then they use a square intake manifold. Ill have to flow it to see...it may flow very well. If thats the case, it really wont take much to make these heads flow well!!

Brian

[cboggs]

I get the mold compound from Cylinder Head abrasives, ..
http://ruffstuff.com/pages/kits.html
scroll down the page, ..

Works well, .. hardens in 18 -24 hours, .. fairly easy to remove.

Curtis

[PFM]

The rubber mold helps to "see" the port, and should help in a huge way with cross sectional area. The best performance per dollar I found so far is VI-SIL, GP-25 with the blue 6 hour hardner. This is a RHODIA product, on the left coast Walco Materials sells it, 1-800-297-4541. It is pretty soft 23 durometer, mixes well and pushes out well. I use silicon lube spray as the mold release. Make a second one and cut it apart with a sharp knife ink it on a stamp pad and print to .1" square graph paper. Count the square and there you have it. You may drop Rick360 on this board a note to see about a scanner program for a high tech process better than counting the squares.

It is no substitute for mapping the port and doing your home work but not much hope in just going big for bigs sake.

PFM

[mike_belben]

cool. is one kit enough for one port?

[cboggs]

Mike,

The stuff I use from CHA does several ports, .. but I'll have to look
into the stuff PFM uses, .. sounds good, .. and I'm always for saving cash.

Curtis

[PFM]

The rubber comes in quarts, or gallons. As for how many ports it will do a gallon does lots and a quart a few. A gallon would do 15, 250 cc ports to give you a rough idea. If my memory is working a gallon kit was around $80 plus shipping. The best value I have found, it has about a year or two shelf life so you may want to work out the numbers. I will warn you once you start you will do more ports than you think.

I am working on a clean sheet head at the moment and I need to build a flow box the post on this site has great info on it and works with the rubber plugs. I have done some in the past but this clear pourable plastic looks like a great way to build a flow box.

I hope the info helps.

PFM

[cboggs]

PFM,

Clean sheet projects are fun, ..

yes the info on the plastic for the flowbox is awsome, .. I've also
used the blue machine wax, comes in blocks for around $100 for a
block big enough to make a set of ports & chamber.

It's been a few ( ahem, . ok several ) years since I did one like that, ..
had to remember where to get the stuff, .
http://www.freemansupply.com/StandardSizeBlocks3.htm

Curtis