The truth on bowl sizing

[Dylan Wilson]

Ive been confused here recently over the topic of bowl sizing of a cylinder head, and as i wait for my flowbench to get here and discover for myself, i figured i would pick yalls brain. I have been told both ways of this argument, first that you need to add a bunch of volume to the bowl in order to slow the airspeed down to get better atomization and a better discharge from the short size and valve opening. I have also been told that you need to minimize bowl volume to keep average velocity up approching the throat. So what are yalls tips andtruths about bowl sizing.Feel that both could be true in the end, but overall i feel like you need to retain a taper from the opening if the runner to the throat, what do yall think.

[BOOT]

Is the same for every head?

[steve cowan]

It's a balancing act to try and turn air/ fuel some say make bowl 100 - 105% of valve diameter, some guys blow the bowl out big and install bigger valve to sell flow bench numbers.
There is no correct answer or one size fits all.
You have to test for your application, the only advice I can offer is when you get your bench is don't chase CFM, if the correct size,shape is done the CFM should be there.

[KnightEngines]

Depends entirely on the port shape.
A low port with a big turn angle needs a bigger bowl, a raised runner with less turn angle doesn't need as much bowl.

[mag2555]

I hope your flow bench purchase comes with a Pito tube?

[rebelrouser]

Ive been confused here recently over the topic of bowl sizing of a cylinder head, and as i wait for my flowbench to get here and discover for myself, i figured i would pick yalls brain. I have been told both ways of this argument, first that you need to add a bunch of volume to the bowl in order to slow the airspeed down to get better atomization and a better discharge from the short size and valve opening. I have also been told that you need to minimize bowl volume to keep average velocity up approching the throat. So what are yalls tips andtruths about bowl sizing.Feel that both could be true in the end, but overall i feel like you need to retain a taper from the opening if the runner to the throat, what do yall think.

Lots smarter guys on here than me, but just what heads I have done and flowed, and then built and run on a dyno, the air speed over the short turn is more important than bowl sizing. If you can use a piece of thread on a welding rod and you can stick that thread flat on a short turn and keep the speed down to 400 fps or a little less is seems like they run good. I have seen a couple CNC heads that would back up at higher lifts and most of the time a little time blending the cutter marks and gently shaping the short turn while keeping an eye on the air speed does the trick.

[Tom68]

Well explained in Eric's latest video.

[mag2555]

Sorry make that pitot tube?

[GARY C]

Ive been confused here recently over the topic of bowl sizing of a cylinder head, and as i wait for my flowbench to get here and discover for myself, i figured i would pick yalls brain. I have been told both ways of this argument, first that you need to add a bunch of volume to the bowl in order to slow the airspeed down to get better atomization and a better discharge from the short size and valve opening. I have also been told that you need to minimize bowl volume to keep average velocity up approching the throat. So what are yalls tips andtruths about bowl sizing.Feel that both could be true in the end, but overall i feel like you need to retain a taper from the opening if the runner to the throat, what do yall think.

Here are the results of an engine builder that did not favor big bowls, there are some images of port molds some where in there as well.
viewtopic.php?t=51911

[GARY C]

One follow up to this is what % of valve are we defining as Big vs Small?

[SpeierRacingHeads]

I like big bowls...

[GARY C]

I like big bowls...

You forgot to add "And I can not lie"

[Bob Hollinshead]

Well explained in Eric's latest video.

That's my Son's work. We'll see how it does!

[Wesman07]

I haven’t seen much benefit in increasing bowl volume. I’m curious about those who have. Does it help the short turn?

[Bob Hollinshead]

I haven’t seen much benefit in increasing bowl volume. I’m curious about those who have. Does it help the short turn?

Good question. If the flow is good at .600 but goes backwards at .650 lift on the flow bench will it do the same thing on a running engine if the velocity is lower in real world? I think I'd rather have 20cfm more at .400 when the piston is pulling hard than a 20cfm gain at full lift. Just guesses here...