Short turn shape for carbureted vs multiport injection

[Wesman07]

If an injector is pointed at the back of valve and towards bore center, can the short turn be laid back more?

[mag2555]

Does the short turn need to get layed back more?
As in are you seeing the flow numbers receed once a certain valve lift is reached?

if so the valve job itself can be tweaked to change that condition as can possibly the width and shape of the short turn on each side of the floor as the short turn approaches the bowl.

[Wesman07]

I can’t accurately test it but I think it might. I was seeing and average of 208cfm with a 1.78” valve at .5” lift. It lost 15cfm after a standard 3 angle valve job for a 1.83” valve. Blending the throat into the bottom cut did not help.

I don’t want to take this head back to the machinist as I waited over six months for a standard valve job. Great guys, great work, but dam slow!

[Wesman07]

I also flowed the head with the chamber facing me. I could not find a place where it was unshrouded too much. So I pulled back the chamber from 5 o’clock to 8 o’clock to accommodate the larger valve. This helped the 4” lift the most.

The biggest problem I see separation from the short turn, and it’s starting from the beginning of the ssr. Adding wings or vortex generators help a good bit, but the port is still loud!

I’ve made solder templates of the short turn and compared it to yours… it’s almost identical but they do not act the same.

[mag2555]

So it lost 15 cfm of peak flow?

[Wesman07]

Correct. It’s peaks earlier and 15cfm lower with a valve job and a larger valve.

[PackardV8]

Correct. It’s peaks earlier and 15cfm lower with a valve job and a larger valve.

Well, ain't that the shites!

Would those who know why spell it out in small words? Shrouding happens. Slowing velocity happens.

However, the missing part here is dry flow versus wet flow. Air/fuel mix taking the long road from the carb behaves very differently at the short turn as does dry flow having fuel injected on the back of the intake valve.

To understand this, all one needs do is look at a few OEM intakes today. Convolutions which would never work in wet flow make big torque flowing only dry air.

[steve cowan]

Correct. It’s peaks earlier and 15cfm lower with a valve job and a larger valve.

I would go back
And measure the minimum CSA and throat area and measure your average CSA through h port.
Turbulence is usually SSR but putting in bigger valve and unshrouding chamber without addressing the rest of the port is not the best option in my opinion.

[mag2555]

Could be valve shrouding on the plug side of the chamber.

If you put the 1.78” valve back in and run a test @ .500” lift what are the results?

[Wesman07]

The port and throat are sized correctly for the application. Valve to throat percentage is around 85%

Flow picks up with the 1.78” valve. The port is still louder than before the valve job.

[Tom68]

Got enough margin to try a top cut on thd 1.83 valve ?

[mag2555]

Can you post your flow numbers for the 1.78” and the 1.83” with the valve job?

Are the flow numbers for the 1.83” with the intake bolted on because those numbers are what truly matter?

Can you measure port air speed as taken centered in the port top to bottom and side to side at the flange?

[Wesman07]

It looks like the seat is moved out far on the valve.

Flowed .3”-.6”, 1.78 vs 1.83” valve, after some blending and chamber deshrouding

1.83”

.3 144
.4 170
.5 188
.6 204


1.78”

.3 154
.4 176
.5 192
.6 204

I decided to make an intake manifold so I have nothing to flow test yet. I should see what the runners will flow. As far as air speed. I can measure it but I don’t know how much value it will hold with my pressure drop bench. 17” is about 200cfm.

[steve cowan]

The port and throat are sized correctly for the application. Valve to throat percentage is around 85%

Flow picks up with the 1.78” valve. The port is still louder than before the valve job.

85% is not the best for intake,maybe exhaust depending on flange area and rpm target for application.
89% is where I would be,and you might have the opportunity to shape the throat which is not concentric to valve.

[mag2555]

So with that you posted with the flow numbers the combination of bigger valve and the valve job got you a loss of air flow top to bottom in the lift range your testing in, or at least down to .300".

The loss down there at .300" points me in the direction of the valve job that was done being the main culprit.

That straight 6 head has a lot of short turn height for starting of with a 1.78" valve, its kind of like a 4 bbl 351 Cleveland head in that regard.

A 1.83" valve is only 3% bigger then a 1.78", so I would think that at least short turn wise you have the height there to get it reworked into what's needed, but like I posted I think the valve job that was done is at fault to a large degree.