Don Terrill’s Speed-Talk

165 cast dart heads cc at 173
as cast port flows 209 @ 500'' lift @ 28''
factory valve job from dart
got 5 angle on intake and 3 angle on exhaust,both 45 deg seats
valve throats at 88-89%
i have thinned guide bigger bowl and layed down SSR slightly and widened slightly i am at 237 @ 500'' @ 28''
speeds on SSR are to fast at different depressions
using J pitot tube 1/2 inch before SSR and off floor 1/2 inch as well speeds as followed
10''-410 ft/sec
20'' - 460 ft/sec
28'' - 480 ft/sec
35'' - 470 ft/sec
40'' - 440 ft/sec
if i hold a 8mm flow ball above SSR flow goes up and air sounds better must be re-attatching to SSR maybe,can you give me hint where to go to next,i want airspeed around 370 ft/sec average if that is possible ,
i dont expect all the answers just where i should look at next
thanks for any help

Your in a good place as you have enough port area at the apex of the short turn to pass 237 or more cfm, but now you need to get control of that air mass!
Judging by what you posted I am assuming a 2.02" Intake valve your saying that your Throat in the valve bowl is 1.77" in diameter judging by your statement of 88 to 89%.

If this is so then your short turn arc likely needs to be layed back more and the floor needs to made wider.
To be on the safe side and to not grind out too much floor I would re-arc the floor to .925"
This new arc should start at 1/8" below last bottom cut of the valve job .

You really should be using a simple template to do this as in this photo
This is a 1.71" template in my photo.

When you widen the short turn try to keep the same common wall to floor arc ( left to right) as you see in the stock port when you view the apex of the short turn from looking down in from the flange, yes make the floor wider but with the same contour in that area.
On the Exh port side of the short turn you in effect make that transition more like a 90 degree by using a template made to the starting point .925" arc I posted about before .

Since you have the blessing of working from home take your time and make these changes slowly as you widen the floor as this is a big part of the key to getting the port velocity down to what your looking for, but I must say this too you now , 370 fps is great for racing / top end power, but if your using these Heads for more of a street drive motor I would be very happy with 425 fps as long as my test pressure manometer was not bouncing up and down at the max flow rate the head Cam muster!


And don't forget to check your fps and manometer situation with the Manifold bolted on .

How are you guys measuring throat %'s? Using seat OD.. or ID?

groberts101 wrote: ↑Sun Jul 15, 2018 9:32 am How are you guys measuring throat %'s? Using seat OD.. or ID?

Personally, I use the seat O.D. however, that is not usually the same as the valve O.D. - maybe .010" smaller or so.

groberts101 wrote: ↑Sun Jul 15, 2018 9:32 am How are you guys measuring throat %'s? Using seat OD.. or ID?

Why would you ever use seat od?

ok guys,
looks like i have messed up my throat % calculations and measurements
do i measure the bottom cut diameter??
i am assuming it is the transition of the throat to bottom cut transition is critical,i just hope i have not taken out to much material in the throat,this is a test head so mistakes are permitted but if i can make a nice performance cylinder head i will copy another one to run on my 327 short block.
the airspeed previously was around 410 ft/sec before the valve job,looks like i need to read up a bit more before i proceed

1.94'' intake valve
1.5'' exhaust valve
sorry forgot to mention

i am only concerned about intake port at this stage
1.94'' intake valve
ID of seat cut 1.866''
bottom of throat cut thats blended in 1.73''
pushrod pinch 1.01'' x 1.83''= 1.85''
apex of SSR in centre of port 1.10''
stock centre of SSR apex 1.116'' comments and advice appriciated,i figured i made a mistake by making the throat 90% max of the OD of the valve,
the throat blends into the bottom cut of the seat job real nice and i did this before the 5 angle was done,i wanted to compare a before and after valve job on the port in progress.

Ok , I can see from your photos that your still in a good way and have not taken out too much meat anywhere yet!
I think most of use use calculate the Throat percentage off of the valve OD, I can't see why you would go any other way?

So now with a 1.94" valve we 88% giving a number of 1.70" , and for the Exh valve 1.32".
Your new minimum short turn arc below the bottom cut is now .835".
SB Chevy 23 degree heads respond faster with flow gains by increases in port width , followed by changes in port height.

Your common wall should be as dead straight running into the back of the valve bowl as you dare to make it while keeping in mind the left to right floor arc I posted about before .

237 cfm @.500" is a good number , what do have for air flow at .200" lift and what are you Exh flow numbers as it stands now, as with a 1.50" Exh valve if you need to you can yank out more high lift flow , but maybe at the expense of low lift flow which you never want to have to do!

In other words with current 237 cfm@ .500" lift what is your Exh to Intake ratio looking like with the Intake Manifold bolted up?

Here's a shot of a iron LT1 head ported to 275 cfm, note how straight the common wall is and how it goes that way right on back to rear wall of the valve bowl.
Also note that I do not have enough floor to wall arc going on ( left to right) on that common wall, as it's too far removed from stock.

Not trying to start trouble, but there is no way that iron lt1 flows 275. Unless the bench leaks like a siv.

True enough with a 1.94 valve , this is fitted with a 2.02" and the last 15 cfm was pure hell to get as the floor had to layed back way more then I thought it should and the roof is thinner then I would like !
Oh , and where taking at .750" lift also, but that shot I posted was to show him the common wall.

Headguy wrote: ↑Sun Jul 15, 2018 1:06 pm

groberts101 wrote: ↑Sun Jul 15, 2018 9:32 am How are you guys measuring throat %'s? Using seat OD.. or ID?

Why would you ever use seat od?

ONCE AGAIN; you show little clue about what is going on ... you need TWO factors to derive throat percentage.
Most people use Valve O.D. as one of the factors which should be close but, not really correct.

mag2555 wrote: ↑Mon Jul 16, 2018 8:56 am True enough with a 1.94 valve , this is fitted with a 2.02" and the last 15 cfm was pure hell to get as the floor had to layed back way more then I thought it should and the roof is thinner then I would like !
Oh , and where taking at .750" lift also, but that shot I posted was to show him the common wall.

These went 275

Matt, those the EQ vortec?

Wrong bolt pattern.