Don Terrill’s Speed-Talk

Dear All, often i found some ports that have been reshaped with a small Hill at the center of the ssr. Unfortunately nobody could give me a technincal explanation. Do you know what Is the purpose and how It works such "Hill" on the ssr? (See attachment)

I did not see your attachment on the post. But anything you do on the short side is mainly to turn the air without causing turbulence. Any flow bench should have a velocity probe and you should keep careful track of the velocity at the short side radius. Every head I have done that develops turbulence and starts to drop flow at higher lifts always has velocity numbers greater than 400 fps. A small bump to get the flow to separate and not flow against the valve stem would be my guess on what they are trying. I usually play with the width and contour of the short side. If I lay the short side back a little and still have excessive velocity, I usually widen the bottom of the port to reduce the velocity.
Keeping in mind I am not an expert, but I have been grinding around on heads for about 30 years.

That hill as you call it is a Vein.
It’s purpose is to re-atomize fuel wet flow streams back into a burnable air and fuel mixture so as to not make for detonation issues.

Besides that if the fuel does not detonate then when it does burn it does so on the way out of the motor and just heats up your valves, headers / exh system even more which then only serves to heat up your engine compartment more.

Go on YouTube and watch 3 videos titled de-atomization by Darin Morgan.
Each one is about 30 minutes long, be prepared to take notes.

The way to gain back control of air speed around a short turn that is too low for the volume of air your bringing over it is to grind in a straight section that reduces some of the upper section of the short turn arc above the short turn mid point, but before the crown.

This straight section needs to be made carefully and exactly parallel with whatever the heads valve inclination angle happens to be.

When I need to use this trick I start off with a straight section like 1/16” tall and work my way bigger / taller from there.
A side effect of this is reduced mid lift flow numbers and maybe some low lift numbers also.

The best way to go is to make the height of the short turn greater which of course then means you need to have the play to raise the roof the same amount, plus get the needed arc into it.

Here’s a little drawing of what sections of a short turn controls what lift points.

Note that thd middle section where this if needed straight section should go controls some of both the high lift and low lift flow numbers, and in this drawing the valve job and however many angles are used are part of it.

PS.
If you have a tall 60 degree bottom cut that is a good place to start reducing around the short turn to get that straight section started if you need such to get back control.
Of course the best thing to do is to make geometric templates to first off gauge what your working with before you even touch a grinder to the port in question.

This help to to find out how big in percentage increase relative to the valve OD you should step the throat size up to.

Going up to too big a throat size leads to loosing control of the air mass going over the short turn, that is unless you have a unnecessarily high short turn like in a Ford 2bbl 351 M head casting.

I should also note for you that the overall short turn arc needs to be atleast a quadrant if not a 180 degree arc of what your throat diameter is.

On a lot of heads that where designed to fit under the hood of a production car the short turn is just too low to complement the size you can get the throat up to when you max port them.

Here’s how to make a short turn template ( quadrant) and how to use it.
This template/ quadrant was made to match a 1.66” throat.

Also shown is how a port is geometrically designed, if you care to plat around with such.
Tracing paper works well for this .

mag2555 wrote: ↑Thu Sep 22, 2022 6:30 pm I should also note for you that the overall short turn arc needs to be atleast a quadrant if not a 180 degree arc of what your throat diameter is.

On a lot of heads that where designed to fit under the hood of a production car the short turn is just too low to complement the size you can get the throat up to when you max port them.

Here’s how to make a short turn template ( quadrant) and how to use it.
This template/ quadrant was made to match a 1.66” throat.

Also shown is how a port is geometrically designed, if you care to plat around with such.
Tracing paper works well for this .

Mag,
Are you using the cylinder head deck as the datum for your template?

76% of inlet valve head diameter? Is this port trapped in some way to have to go to this percentage?

I wonder if the OP is dealing with an earlier Italian motorcycle engine, these engines were notorious for not having a port floor to work with.

At times yes if the shallow side chamber wall is close enough to the top cut of the valve job to be considered a extension of the short turn.

A lot of Heart shaped chambers are this way.

rebelrouser wrote: ↑Thu Sep 22, 2022 4:32 pm I did not see your attachment on the post. But anything you do on the short side is mainly to turn the air without causing turbulence. Any flow bench should have a velocity probe and you should keep careful track of the velocity at the short side radius. Every head I have done that develops turbulence and starts to drop flow at higher lifts always has velocity numbers greater than 400 fps. A small bump to get the flow to separate and not flow against the valve stem would be my guess on what they are trying. I usually play with the width and contour of the short side. If I lay the short side back a little and still have excessive velocity, I usually widen the bottom of the port to reduce the velocity.
Keeping in mind I am not an expert, but I have been grinding around on heads for about 30 years.

Dear rebelrouser i attached here the photo. Thank for your comments. When you Say "400 FPS" max velocity on ssr do you mean the velocity you measure on flowbench at 28" of depression?

mag2555 wrote: ↑Thu Sep 22, 2022 6:30 pm I should also note for you that the overall short turn arc needs to be atleast a quadrant if not a 180 degree arc of what your throat diameter is.

On a lot of heads that where designed to fit under the hood of a production car the short turn is just too low to complement the size you can get the throat up to when you max port them.

Here’s how to make a short turn template ( quadrant) and how to use it.
This template/ quadrant was made to match a 1.66” throat.

Also shown is how a port is geometrically designed, if you care to plat around with such.
Tracing paper works well for this .

Dear mag2555 thanks a lot for your comments and advices

Thanks to mag 2555 about info regarding flow and flow separation. Ive been a while now in a process to evaluate my old work and it appears i didn't know what i was doing. However partly by accident, i have made a radical shape that supports volume including neck down valve stems, and may still be practically part of my game plan.

Here just some food for thought using 4 valve as a example:

Intake SAE CD below .65 range throughout the lift curve
Intake valves: 1.35in
Seat ring inner diameter: 1.19in
Valve throats/CSAs at the valve guide area: 0,97in2
Primary choke: 1,76in2 CSA at the manifold flange
SSR apex to deck height: .95in
Port volume: 113cc
Port length: 3.82in


SSR looks a cliff, but it has a nice feeling and a long gradual turn.

If you look close/ understand the geometric drawing that I posted you will see that in a perfect world so to speak the throat size you deside you use dictates the rest of the the dimension that the port will be.
In that example I posted the throat is 1.60".
The center circle that forms the floor arc is then a radius of .800" as shown.

The roof arc/ radius is then .800" plus 1.60" for a total overall arc of 2.400".

If you where for example working with a 2.02" valve and wanted to see what things SHOUD look like when you went with let's say a 90% ( 1.818" ) throat to valve ratio then your center circle would be a a radius of .909".
Your roof arc would then be 2.727".

Now you have the two foundation arcs to superimpose your port onto by starting with the valve inclination angle and how deep your chamber will be.

I make templates from geometric information like this to first judge whatever I have to work with in regards to a to whatever head I am looking to port, besides making templates to guide my porting work.

mag2555 wrote: ↑Fri Sep 23, 2022 6:30 am If you look close/ understand the geometric drawing that I posted you will see that in a perfect world so to speak the throat size you deside you use dictates the rest of the the dimension that the port will be.
In that example I posted the throat is 1.60".
The center circle that forms the floor arc is then a radius of .800" as shown.

The roof arc/ radius is then .800" plus 1.60" for a total overall arc of 2.400".

If you where for example working with a 2.02" valve and wanted to see what things SHOUD look like when you went with let's say a 90% ( 1.818" ) throat to valve ratio then your center circle would be a a radius of .909".
Your roof arc would then be 2.727".

Now you have the two foundation arcs to superimpose your port onto by starting with the valve inclination angle and how deep your chamber will be.

I make templates from geometric information like this to first judge whatever I have to work with in regards to a to whatever head I am looking to port, besides making templates to guide my porting work.

exact hoffman900 quote from another topic.

The optimum port shape is going to have to change along the whole length to work with a change in MCSA. It's not as simple as having something like a camera aperture, so it needs to occur along the entire port / intake tract length

In a perfect world it depends how we want do things. I started messing with the example engine 5 years ago.. crazy times, just put the car on the trailer and go, no dyno, no nothing, but now i see there are different ways to skin a cat. That was a Renault F -series engine i posted above, here is an different head which came waay different from the factory with a smaller valves and bigger port (yes we cut more shape around the valves to handle higher speeds/better pressure recover, or that was the thinking back then without a flow bench..)


I never ran the big bowl high speed port on higher speeds using itbs example. That head combined with a different port recover strategy could be a killer, because there is no that big difference on intake SAE CD, if i example use a restrictive manifold which drops the average port velocity from 300fps@28in to 240fps@28in at max valve lift.

I can see tall enough SSR apex to deck height make sense, but on a 4 valve there is just more area especially when MCSA is further upstream. Yes widening the floor of ssr can be beneficial in that same cylinder head, but it depends the combo



-juhana

Desmoguzzi wrote: ↑Fri Sep 23, 2022 4:08 am

rebelrouser wrote: ↑Thu Sep 22, 2022 4:32 pm I did not see your attachment on the post. But anything you do on the short side is mainly to turn the air without causing turbulence. Any flow bench should have a velocity probe and you should keep careful track of the velocity at the short side radius. Every head I have done that develops turbulence and starts to drop flow at higher lifts always has velocity numbers greater than 400 fps. A small bump to get the flow to separate and not flow against the valve stem would be my guess on what they are trying. I usually play with the width and contour of the short side. If I lay the short side back a little and still have excessive velocity, I usually widen the bottom of the port to reduce the velocity.
Keeping in mind I am not an expert, but I have been grinding around on heads for about 30 years.

Dear rebelrouser i attached here the photo. Thank for your comments. When you Say "400 FPS" max velocity on ssr do you mean the velocity you measure on flowbench at 28" of depression?FB_IMG_1663872924523.jpg

Yes I think Darin Morgan also talks a lot about velocity on the short side and ports. https://www.motortrend.com/how-to/1006c ... rt-design/

I even put a floor wing in my personal Super Stock heads. There is nothing in that head under 400fps..

And that guy that did that port in the picture is my kind of guy!