[joes455]

Porting a set of heads ,best so far with 1.80 throat is 278@ .600 then falls off @610 to 255.My cam will go to .600 lift.Should I be concerned about the tubulance?Also area above short turn to roof is only 1.65,should I grind it down and then reshape the str?

[Jay S]

The turbulence probably won’t make much of a difference with the intake bolted on. If you want to change high lift flows focus on the short side radius, low lift flows are found more up in the ceiling.

[steve25]

What test pressure are you testing at?
Is the valve job still stock?

If you’re using a template made off of 1/4 of the arc of the throat there is not enough short turn height in the 6X-4 head to get the full needed arc so the shape of the short turn below the bottom cut needs to be shaped to slow down the excess velocity.

How much is your head flowing at lifts under .600” as compared to stock?

If you’re porting the -8 heads you may need to go over to a 45 degree seat to get velocity control back since the -8 heads have less short turn height.
I have never ported the -8 heads to over 265@28” so I would have to do such to give you perfect advice on going there.

[joes455]

6x-4 35° seat 83@.100,142@.200,192@.300,236@.400,261@.450,263@50 0,275@550,280@.600,255@.610. Installed North wind intake ,all numbers down about 3-5 cfm but back showed up at.630 vs .610.I would imagine back may have vanished if using a more restrictive intake

[steve25]

A 35 degree seat you say?

[joes455]

Flow bench is a Flow Quik

[joes455]

Don't give away my flow bench design,it's a poncho 455 .060 over cut in half

[joes455]

Fat finger edges flow @ 450 it should be 251 not 261

[steve25]

Are you testing at 28” or lower?

[Jay S]

Very creative flow bench you created there. It must be working if it is showing that kind of turbulence in .010” more lift. More test pressure would likely make turbulence show up more yet.

You should be able to correct that turbulence by contouring the short side and making the CSA at the short side larger. But I think it depends what the rest of the port looks like. On one of the 6x-4 heads I did I made the port to big and couldn’t find flow by grinding on the short side more, I hurt flow when I tried to correct it. It was around 195 cc port volume with a 2.125” valve and 45* seats, seemed like it had to much port volume for the port angle. I ended up correcting it with a bit smaller port, and gained everywhere.

[steve25]

What does the port flow with the valve in upside down and with the stem sticking in the same depth as it would normally?

[steve25]

Am I reading you right in thinking that you have not touched the short turn other then what was needed to get the 1.80” throat in place?

[chiefbigb]

280 at .600 is dam good for a iron d port head. The lower lift numbers are strong also.

[steve25]

Here’s how the floor approaching the short turn needs to be.
This is a 275 cfm 6X-4 .
Notice how the kicking over / widening of the common wall all the way into the bowl has made the floor and the short turn .

Also is a photo of a 1.81” template on the floor up near the window, but not quite there because otherwise you will grind a hole into the common wall just after the head bolt passage near the floor .

Note the round shape of the template as compared to the D shape on the floor near the crown of the short turn.

This is one of the two critical areas to get right to have control of the air mass as it passes around the short turn.

The roof to floor height on the port is 1.708” from a point just after the valve guide and almost going back to the flange.

This gives the roof an arc / bow which it needs to have the overall right shape in that part of the runner.

[joes455]

Good catch 32° not 35,I performed that cut under the 60° and at 14° angle and flow went up some but also went turbulent sooner.Re blend the cut and back to normal.So started to focus on the str at the pr side and was rewarded with even more flow but still turbulent at 600.Idk may kust keep it the way it is until I put 45° seat

[joes455]

No valve installed 260 cfm still backing up

[steve25]

Here’s some more info and photos for you.
In one photo you can see how a 1.77” exh valve fits in the bowl and where it touches the back wall and exh port side of the bowl.
This valves face is .430” down from the chamber floor.

In one shot notice the silver marker on the short turn .
Notice how tall it is and how it spreads out some from the center .
This is a straight area where I ground out the 60 degree bottom cut to get that shape.
What I mean by straight is that it parallel to the 14 degree valve inclination angle.
This is what slows down too high port velocity in that area that makes the flow numbers above .550” lift start to regress.

In another shot that is a 1.820” x 1.70” template sitting like 1/16” above the top of the guide.

In the other shot is the snap gauge sitting in front of the cut back and reshaped guide.
The width here on the very roof is 1.565”

In the next shot is that 1.820” x 1.70” template.
This shows that I still have work to do because the template is still not going in deep enough since the template handle is still .730” away from touching the valve bowl and also it’s not resting right on the floor as you can see I hope.

In the next shot is the .905” short turn template.
Notice how closely the arc, of the template matches the reshaped short turn and how that .905” arc ends , it ends right where I ground in that straight section in the center of the short turn.

The last shot is how the short turn arc in the center looks like.
This arc is what gets extended to each side of the blow to both form a water fall shape that is also D shaped .

If the round shape of the valve bowl is kept above the straight section that I posted about then that shape also leads to flow regression if you have enough air mass passing thru the port that you need to control.

[steve25]

Sorry the site only allows 5 photos so here’s the rest.
PS, in that one photo of the 1.820” x 1.700” template sitting on top of the guide note that the template handle is touching the short turn and also notice with the light showing around the template how square shaped the port has become that deep in the bowl and on out into the runner.

[joes455]

Thanks Steve for your help,What do you mean, that the floor at str should be D shaped?And could you outline it in a pic?

[steve25]

Unlike in one photo here of the port molds of a very high flowing aftermarket race head which is able to maintain the round throat shape all the way around the short side, having any excess short turn height in a factory production iron head to work with would be a luxury.

This means that as in this photo of a iron Ford 460 head ( a head also with minimal short turn height) enlarging the throat size as I did up to 1.88” required the D shape on the short turn that you can see about .150” above the 60 degree bottom cut.

This cut/ shape provided the air mass stability I was looking for to take the intake port up from a stock 257 cfm@ .550” up to 285cfm@ .550” with a peak of 302 cfm@ 700”.

These flow numbers in this 460 were achieve with just bowl work and cutting down and boat tailing the valve guide.
This is a clear sign that the port other than the valve bowl was cast far too large for not just a street motor ( especially in a motor home! ) but for a street strip motor also.


Here also is a photo of a reworked 6X exh port valve bowl and even in this shot you can see the round shape of (1) the throat.

2) the Venturi shape.

3) the transition to D shape as the Venturi expands up the short turn to the apex of the short turn.

In my second photo in post 14 even in the stock 6X intake port on the right you can see the distinct D shape on the floor at the window/ apex of the short turn before the transition down into the valve bowl.

In any other D port head other than the 6X or 5C casting you will find a U shape at the window on the floor.
This shape sends much more air to the center of the short turn.
This is something that the factory did deliberately to pick up air speed by some 8 to 10%.
Remember 99% of all factory 4 bbl or tripower cams had no more then .406” lift and the engineers where more concerned with throttle response then power above 4000 rpm!

Unfortunately once you have bowl ported a D port head with a 2.11” valve along with a 30 degree seat along with a U shaped floor window up to around 220 cfm that U shape on the floor needs to go away to maintain control of the air mass and not have the flow regression that your seeing .