Flow on bigger bore size.

[Steve.k]

IMG_2600.JPG

Here is a head test done on different bore size. Why does the flow increase then drop at .800 on bigger bore? I can understand bigger bore less valve shroud which is apparent all the way till .800?

[pcnsd]

Because the flow is becoming unstable at the combination of higher flow at lift on the larger bore. Which bore size is important to you? If the smaller, I would test at a higher lift (.900") to confirm the flow stability on the small bore size or test to the same lift (.800") at a higher depression 36"+h2o if you can. Flow backup near your max lift is not a the best of signs. What is your actual expected valve lift in use?

[Steve.k]

The bigger bore would interest me Paul. I knew from our own testing that big bore helped flow which that shows. However i have not seen the drop at .800 or know why it was happening. Its good to learn something everyday. Thanks. There is more than meets the eye to flow.

[cjperformance]

Contact Dave at AFD as he will have some good input on this but did you try shifting the head a little on the 4.125" bore adaptor by any chance?

[GARY C]

Contact Dave at AFD as he will have some good input on this but did you try shifting the head a little on the 4.125" bore adaptor by any chance?

Thats what I would try, if the chamber is smaller than the bore then the lip could be causing a pressure recovery issue.

[JoePorting]

How did you get a 2.19/1.65 valve set to fit in a 4" bore? Isn't the valves hitting the bore? Not familiar with that head I guess.

[cjperformance]

How did you get a 2.19/1.65 valve set to fit in a 4" bore? Isn't the valves hitting the bore? Not familiar with that head I guess.

Canted valve based on the Ford Cleveland cylinder head.

[user-23911]

Don't know why you're even worrying about it?
How many crank degrees are the valves open by 0.8 inch?

You should be fucussing on lift at 0.3 inch.
It's the low lift flow that's important.

[user-30257]

Don't know why you're even worrying about it?
How many crank degrees are the valves open by 0.8 inch?

You should be fucussing on lift at 0.3 inch.
It's the low lift flow that's important.

I sure hope to God you are kidding.

[user-30257]

IMG_2600.JPGHere is a head test done on different bore size. Why does the flow increase then drop at .800 on bigger bore? I can understand bigger bore less valve shroud which is apparent all the way till .800?

That bigger bore can cause air that was flowing more on one side of the valve, to now switch to another. That can be found by pitot testing around the valve seat.

[mag2555]

The bigger Bore has changed how the air mass is passing thru the port and out thru the valve and out into the chamber.

You are now able to pass more air thru the minimum port area of the head and this added flow has kicked up the port velocity to the point that your your short turn arc can't control it so in turn you get flow regression .
There are a few things you can do to gain back control .
1) rearc the top of the short turn to push the apex back more towards the port flange.

2) blend off a good amount of the valve job bottom cut around the short turn.
This needs to be done carefully and in line with the valve inclination angle of the Intake valve which in your case is canted so you will need to make a template the locates off of the valve stem.

[user-17438]

The bigger Bore has changed how the air mass is passing thru the port and out thru the valve and out into the chamber.

You are now able to pass more air thru the minimum port area of the head and this added flow has kicked up the port velocity to the point that your your short turn arc can't control it so in turn you get flow regression .
There are a few things you can do to gain back control .
1) rearc the top of the short turn to push the apex back more towards the port flange.

2) blend off a good amount of the valve job bottom cut around the short turn.
This needs to be done carefully and in line with the valve inclination angle of the Intake valve which in your case is canted so you will need to make a template the locates off of the valve stem.

you know this how?

[user-23911]

Don't know why you're even worrying about it?
How many crank degrees are the valves open by 0.8 inch?

You should be fucussing on lift at 0.3 inch.
It's the low lift flow that's important.

I sure hope to God you are kidding.

So how many crank degrees do you have 0.8 inch valve lift for?
Can you answer it?

Or you can't answer it?


Normally max flow is roughly at D/4 so any lift over .55 inch is determined more by the port than the valve size or curtain area. It only flowbench numbers which aren't real anyway, not at such high lifts.

[mag2555]

I know this by curing such issues with heads that exhibit these symptoms either in stock form or during porting !

Try this fellow ports here, take a big nice stable high high flowing Intake port and make it smaller and reshape it until it goes into port sheer/ tumble at say .450" lift, you will learn a lot from doing that if you already don't know what I mean!
In short , learn how to make it wrong and you will then know how to make it right!

[zums]

Don't know why you're even worrying about it?
How many crank degrees are the valves open by 0.8 inch?

You should be fucussing on lift at 0.3 inch.
It's the low lift flow that's important.

I sure hope to God you are kidding.

So how many crank degrees do you have 0.8 inch valve lift for?
Can you answer it?

Or you can't answer it?


Normally max flow is roughly at D/4 so any lift over .55 inch is determined more by the port than the valve size or curtain area. It only flowbench numbers which aren't real anyway, not at such high lifts.

.3 is a waste, mabey you should get in touch with your degree wheel and indicator and do a sweep from .25-.35, then try it again from.7-.8
Tom