Short turn shape for carbureted vs multiport injection

[Wesman07]

Mag,
I think I misunderstood you. Those numbers are how it flows currently with a 1.83 valve and with a 1.78” valve in the new valve job.

Did you want pre valve job numbers?

[Wesman07]

Pre valve job with 1.78” valve

1) 52
2) 114
3) 164
4) 180
5) 198
6) 200

New valve job with 1.83” and blending

1) 52
2) 100
3) 144
4) 170
5) 188
6) 204

[Chris_Hamilton]

Back to the OP's original question. Does the SSR need to be different for carbed versus fuel injection? If so what would be the differences?

[Wesman07]

I believe the GM LT heads (direct injection) have a short turn that’s laid way back because it doesn’t not need to turn the fuel. Darin Morgan gives a good explanation of this in one of his videos. What I don’t know is if spaying at the back of the valve is the same.

I am very curious what Mag has to say. He has helped me out tremendously. The more I look the more I think there could still be a shrouding problem. Is it possible that a shrouded short side would cause a separation problem? Like air rolling around in a pickup truck bed?

[Tom68]

Thought it was about turning the air and keeping full airflow around the valve at high velocities.

Screw the fuel, look at how good direct injection works.

One thing for sure is, old school heads with low short turns flow lower amounts of air.

[BLSTIC]

The new Honda k20 turbo motor is a 4v head with something like 150cfm. They straight up dropped airflow for charge motion at all costs

[Tom68]

The new Honda k20 turbo motor is a 4v head with something like 150cfm. They straight up dropped airflow for charge motion at all costs

Dropped airflow ? 4 valve with a turbo.

[BLSTIC]

Yes. The naturally aspirated versions of that engine flow a lot more. Turbo versions skip out on short side flow altogether in favour of charge motion for detonation resistance and better efficiency, then add a comparative ton of boost.

[dannobee]

The low valve lift numbers are usually due to the valve job. Does the tulip on both valves look similar? Did you try back cuts? Are the margin widths and angles the same as before? Obviously something changed.

One trick for the unshrouding part is lift the valve off the seat with your tool and lift of choice, then flip it over and use a flow ball around the valve and see where the flow ball hangs up.

[mag2555]

If you can afford to sacrifice that 1.83” valve then grind its OD smaller by .025” and make a flow test starting at .200”
If the numbers go back up near that of the 1.78” then you know how much unshrouding work you need to do on the deep side of the chamber.

If not much improvement takes place then your dealing more with the difference in the shape of the back head between the two valves.

[mag2555]

I getting back to your original question, are you talking about having the injector in the intake or the head port?

If in the roof of the head then even a minimal bulge would have to make for a reduction in air flow passing around the long side of the port so in that case I can’t see why laying back the short turn might be needed if your not having a velocity issue calling for such.

Here is where Brodix places there injector holes, right on top of the rear of the valve bowls.

[Wesman07]

Hmm. I could grind a flat spot in the 1.83” valve. That way I could rotate the valve and pin point where the chamber wants to be pulled back.

The original question was referring to an injector in the intake manifold that has a good line of sight into the chamber. See photo of stock manifold. Does the requirements of that short turn change?

What had me thinking about it was the separation problem was easier to manipulate before the turn rather than after. Although, I’m starting to wonder if both the separation and shrouding problem are related. Shrouding under the SSR could reduce the amount of depression in the bowl to keep the boundary layer attached…

[BLSTIC]

Thought much about port texture? It probably has a bit to say in the matter too

[mag2555]

Very simply put , to me if you have air flow available above let’s say .300” lift or so that can’t get out passed the valve on the plug side then that will force the short turn to try and pass that air volume, and if it’s already near the limit of controlling the air volume to begin with then one can only expect the flow to back up.

Also a bit of turbulence is not a cut in stone bad thing.
If it takes place up at the peak valve lift your running and your head happens to have a wet flow issue the turbulence can help shread the fuel back up into a more fast burning state.

[Wesman07]

Wouldn’t the opposite be true? If the long side had some shrouding and the short did not, there would be lower pressure at the short and higher at the long. That should help the turn. I’m interested to try both.

A good buddy of mine is an airspace engineer and I work for him when I can. He explained a few things that were real eye openers (to me at least).

Turbulence is not bad. Quite often is necessary to keep the boundary layer attached to the wing. Many times extensive efforts are made to ensure the layer stays turbulent to reduce stall speed.
https://en.m.wikipedia.org/wiki/Vortex_generator

Also, we commonly use the term turbulence incorrectly. The reason a port has a maximum flow limit is typically because of “pressure drag”.

I’m not saying anyone has it wrong. I’m just saying it found that to be interesting.