Don Terrill’s Speed-Talk

I'm not a professional porter, i'm just an auto mechanics instructor trying to help a student with a project.
I've valve-jobbed, flowed, pitot probed, flow-balled, string-wanded & CC'ed this thing.

Of course it flows nicely upto .550, flowing 290cfm@28" and then erupts into turbulence from .600 up.
Interestingly, it flows the same @ .550 as it does wide open with the valve installed upside down.
Currently the port is 215cc. Pipemax says that's about right, but the 420fps SSR floor speeds are beyond my experience level, as this is my first try with a 15* head.

After reading the helpful LS-specific posts from Larry Meaux, Induction Apprentice, Joe Mendelis (R.I.P.) and Airflowdevelop,
I've come to the conclusion that it's time to ask for help.

I have all the pertinent notes & data, and could use about 10-15 min of someones time, if you can spare it.
May i call someone for a bit of help?

If i can't cure this characteristic .600 lift turbulence, i'd like to ask if it would be ok to pay someone to do up a single port that i could use as a baseline to help get this project up and running and out of my hair.

Thanks for looking.
Duke Boele.

Are you flow testing with the intake manifold that will be in use bolted on?

The air volumes needed to kick in the turbulence over the short turn may not take place, or may only take place at a higher lift then what will be run with the intake in place during a flow test.

Is your short turn basically a constant radius back up to the crown once the valve job area is cleared, if so this can be part of the issue.

To visualize that better take a lenght of solder and rap it around the center of the short turn from the chamber floor out to the intake flange, or at least a bit passed the crown of the short turn.

Sir, thank you for your reply.
I bought & sawz-all'ed a truck intake to test that exact condition, and it dropped flow approximately 3% from .300 up...but does nothing to postpone the onset of turbulence. I'm testing 3 different valve backcut configurations to observe effects: no backcut, 30* & 32*. The flow curve shifts around a few cfm but no significant improvements as yet.
I'm hesitant to get too agressive with the SSR enlargement, as Joe Mendelis (R.I.P.) once quipped that the SSR was already too big as-cast, so i'm doing my level best not to do more harm than good.
Ordered a port mold kit from Christine @ CHA & will pour the port in case anyone would like to see where i'm at.

Valves are 2.0/1.55 stock valves.
Valve seat is a NWN-4094 (37-45-64) with a 75* leaving .100 wide 64*.
Throat is currently 89%.
Since this will be a 6.0 liter, i'm using a 4.030 bore adapter.
Average port velocity is 316fps, and SSR apex velocities are 390(L) 425(C) 395(R).
This is my first 15* LS head and I do not have access to a spare for testing, so i'm going slow and making sure i'm not wrecking things from inexperience.

You need to widen the turn & raise the roof into the bowl, give the air more room to make the turn.
Lay the turn back a little (not a lot) & shift the apex on the floor upstream a couple of mm.
Blend in the valve job on the short turn only.
Finish the turn with 80 grit linishing tape pulled back & forth over it.

They will flow all the way to 1.000.. But the SSR is touchy.

TK thank you for your generous advice.
Currently the swirl ramp & rocker bosses are largely intact, are these contributing to the ridiculous SSR floor speeds?
Currently the port pours 215cc.
A 1/4in flowball placed just before the center floor apex helps flow @ .550 from 290 to 296cfm, and against the roof on the swirl ramp hurts it a good 10cfm. Placing the pitot in the same place on the ramp & rocker boss shows approx. 285fps.
I know its trying to tell me something...i'm just not experienced enough to know what it wants.
I just don't have a spare to test without worry of ruining an otherwise serviceable head, and reading back into the Speedtalk archives, the consensus seems divided on the subject.

"Valve seat is a NWN-4094 (37-45-64) with a 75* leaving .100 wide 64*."
What do you guys think of this valve job? Is the 19 deg transition between 45 seat and 64 bottom cut OK?

That's pretty close to what I use.

Remove the rocker boss, that pushes air where you don't want it to go.
The swirl lump thingy gets cut down, but not completely removed (there is water under there), that definitely helps reduce air speed over the turn.

Thank you TK...really do appreciate your help.
I'm totally unfamiliar with 15* heads as far as runner volume cc / engine displacement...is there a basic cc i should shoot for with a 6.0 to 6500?

You can't really, stupid things are too big in stock form.
Concentrate on air speed & stability, just clean up & square the pinch, aim for minimum metal removal to achieve stability & call it good.

Thank you Tony...I mean it.
Also, thanks for the reminder of the Don Terrill "riblet" shoeshine technique...i'd forgotten about that.

fasteach wrote: ↑Mon Jun 07, 2021 10:55 pm Thank you Tony...I mean it.
Also, thanks for the reminder of the Don Terrill "riblet" shoeshine technique...i'd forgotten about that.

Wait what now?

I'm all for new techniques, can you describe this one to me?

Here's info I doug up from the last set that I did which went 315 cfm.

What Tony is describing is NOT the riblet,
It's basically smoothing the apex in the direction of flow.
Speeds are fast and boundary layer thin and fuel is trying to turn.
It's not a cfm gain,more helping with stability.
It's a cool speed secret.