24v head vs 12v head

CorneliusRox said:
Calm down internet tough guy.



If you actual read, you'll see that I was saying sorry for when I reread my post and I thought it sounded dick-ish. That's not how I meant it to sound.



That's stock vs stock.
If you take a circle (lets say 100mm diameter) and fit the biggest circles you can in it for a 2 valve setup and a 4 valve setup, you get a diameter of 25mm for the 2 valve and 22.71mm on the 4 valve.
Cross sectional area comes out to:
2 valve = 1347.4 in^2
4 valve = 981.7 in^2

That give the 24v a 37% increase max vs max.

Capture_zpsnw68f9l2.jpg
Click to expand...

the only thing accurate about that is the math, misleading at best, to use that to calculate max flow of a head
 
blackedout12V said:
the only thing accurate about that is the math, misleading at best, to use that to calculate max flow of a head
Click to expand...

Yeah, we've been through this. The math and concept are accurate. Cummins doesn't place the stems where I have them in the picture, and it is only a comparison between the valves and not the runners or connector tubes.
Also, like stated before, there would be more cross sectional area at the same amount of lift even if the area of the valves faces were the same.

blackedout12V said:
higher pressure will always flow more air.
Click to expand...

'higher pressure will always flow more' given the same head and hardware.**
 
Using 9724VF350's info
9724VF350 said:
4v 1.340 valves=5.64 sq in of valve.
2v 1.87/1.75 valves=5.15 sq in of valve.
Click to expand...
Lets just use .4" of lift for both intake and exhaust.
So 4v=1.34 dia valves=16.84 perimeter=6.74 sq in of cross sectional area at lift.
So 2v=1.87/1.75 dia valves=11.37 perimeter=4.55 sq in of cross sectional area at lift.

That still gives the 24v setup a 48% advantage at the same lift. Obviously, we're just talking about the valve aspect here.


If you'd like to contribute, that's great. Otherwise, I don't see the point of your comment...
 
in post #3 you said "a 24v head will always have more flow potential than a 12v head". then proceeded to produce a drawing as to why. my contribution IMO was to the op, is that is not good data to calculate max flow of either head. that drawing would have major valve shrouding issues which impact head flow, which is one reason you cant just slam 2 or 4 of the biggest circles you can fit in a big circle and say, more total area= more max flow potential. also im not following your math on cross sectional area at lift. i thought cross section was the area of a 2 dimensional plane(valve surface area), then you add .400 lift which makes me think your talking volume. which your not because you say 6.74 sq in. i see your calculations on perimeter are what i call circumference, but beyond that you are losing me. if you could elaborate more on how you came up with your cross sectional area at lift totals, then maybe i could learn something new. and lastly yes, more pressure will always flow more air given the same head and hardware, is what i meant. thanks for clarifying that. i should have elaborateed a little further
 
blackedout12V said:
that drawing would have major valve shrouding issues which impact head flow
Click to expand...

That's a good point. I was more or less trying to show that you could take more advantage of the space given with four vs two valves in general.

blackedout12V said:
I'm not following your math on cross sectional area at lift. i thought cross section was the area of a 2 dimensional plane(valve surface area), then you add .400 lift which makes me think your talking volume. which your not because you say 6.74 sq in. i see your calculations on perimeter are what i call circumference, but beyond that you are losing me. if you could elaborate more on how you came up with your cross sectional area at lift totals, then maybe i could learn something new. and lastly yes, more pressure will always flow more air given the same head and hardware, is what i meant. thanks for clarifying that. i should have elaborateed a little further
Click to expand...

Circumference just means perimeter specific to circles. I suppose that'd be the proper way of saying it, just like saying a quarter over a fourth. I usually just say perimeter since it counts for everything.

Anyways, if you take the circumference or a circle, you really just calculated a distance. No area has been calculated. If you picked a start and stop point on the circle, you could essentially 'unroll' the circle and give yourself a straight line.

Now that you have your line (lets say in the x-direction), you can add the lift (the y-direction), and this will give you an area.

Another thing to note, this is also just for ease of explanation and it is a simplified concept. I don't have time to go measure a 12V and 24V head to find out exact dimensions, but I think this will help explain my point.

So here's the circumference, and here it is 'unrolled' so that it's just a straight line.
11_zpsfmgtfyk7.jpg


Now you add the lift to turn it into area. This shows the area in both the straight line and the curve that makes the circumference.
12_zpsph1spihh.jpg


Now if you took the integral of the circumference first to find the area inside of the circle and not the perimeter, then when you added the lift, it would change it to volume.
 
I am fairly certain a maxed out aftermarket 12v head will out flow the best 24v setups. Not to mention it's a more robust valvetrain. I think Zach Hamilton should jump in on this...
 
straight 6 roar said:
I am fairly certain a maxed out aftermarket 12v head will out flow the best 24v setups. Not to mention it's a more robust valvetrain. I think Zach Hamilton should jump in on this...
Click to expand...

I agree. I am not convinced that a Cummins 12v can flow more than a 24v head can.
For that matter, didn't Zach say he has 6.7L custom cast heads on the way?
Three versions from street to full comp.
 
DirtyMaxx03 said:
so was i completely wrong or...?
Click to expand...

I really wish we could get some guys in here with flow numbers. Anything I've ever seen from a shop, the 24V heads have a good margin of flow over the 12V's stock vs stock.

I usually see shops claiming they can get more out of a ported 24V head as well.

CorneliusRox said:
I would be surprised if a fully ported 12v head can flow more than a fully ported 24v head (not including custom cast 12v heads).
Click to expand...
Like I said before, I wasn't counting the custom cast heads. If we do want to count custom cast heads it looks like the new 24V heads Zach is working on will be top fed injectors only, so no connecting tube, and we'll have to see what they flow. I think he said he's making a coolant version, partial coolant, and no water jacket version. That being said, I think it really would come down to the valve size, but we'll see.

If I was sled pulling and pushing serious RPMs, the most appealing part of the 12V head to me would be the lack of moving parts, simplicity, and strength because of that.
 
My understanding is that at low to mid lift 4 valves outflow 2. Once lift gets above a certain percentages (25-30% i think) of the valve diameter flow improvement dminishes rapidly. 2 valves on a high lift cam can usually flow the same or better than high lift 4 valve heads with greater valve area as 4 valve heads shroud themselves to the point were two valves can keep up. Oftentimes with better port velocity.

Some other points that come to mind:

Way easier to control 4 small valves than 2 at high rpm. Probably not important in the 6bt.

Way more valve seat for a given amount valve area for better valve cooling. Might be important for long pulls if your aluminum pistons aren't the first failure point.
 
Just my $.02:

Best overall engine performance, whether a 2v or 4v head is determined by the low to mid lift cfm flow. This section of area is where the valve spends the most amount of its duration of the cam cycle. If max lift is .500, it has to pass .100-.400 twice to get there, making the cfm flow at the low lift is crucial.

The 4v has the advantage in the low-mid lift because the small valve size has reduced shroud time (cfm ramp from .100 to .500 is steeper) compared to the typically larger 2v setup. However, the smaller size reaches the peak cfm flow sooner due to restriction in the valve area.
 
Four valves are better for low lift flow due to increased velocity of the smaller ports. But due to being limited on port volume and port shape by the connector tube, they have limited head room. They have a definite benefit in a street application. With the ability to move more air at low rpm into the cylinders, there is more hp potential at lower rpm with the correct cam. If you get the port volume and shape to do what you want to max high rpm potential, you have to nix the connector tube. As port volume gets larger and larger, this will negate some of the low rpm benefits, getting the correct cam for higher rpm will further degrade low rpm performance. As some of you have pointed out, having a higher flow average across the lift curve can trump a lazy port that has a huge flow number at really high lift. If two heads are being compared and are similar in terms of flow, give me the one with the higher port velocity. There are so few people really taking porting to the next level and so few really informed consumers that expect more of the cylinder head porting shops, that hardly anybody is talking about port volume. I think you guys should start asking for that information.....

The 12v competition head with larger ports gives up port velocity and hence, some low rpm performance. I have one in my tow rig though with 57mm/71mm twins lag is not bad though. For high rpm performance, I have not seen the 4 valve head trump the 2 valve yet in terms of flow although filled heads are getting close. When other factors like valvetrain are factored in, the 2 valve has even more benefits. The simplicity of the KISS 2 valve design gives it more value in my opinion. The other thing that kind of hamstrings the 4 valve is the fact that both valves operate by one rocker, this allows the valves to side load and lift differently, although SMT has a fix for that, it is a little pricey.

The above is only a commentary on what is currently available. The future, given no limit on budget, is with the 3 or 4 valve configuration. The 2 valve is getting a makeover with improvements in the short turn. This dictates a taller and heavier head(good for pulling, bad for racing). I expect development as far as we are concerned will end for the 2 valve after this change due to cost/benefit. The only other thing we could do to really push things further would be to make somewhat of a hemispherical style head. This would greatly lower compression and need a new injector and new style pistons to allow the engine to benefit from the head change. I do not see shops with the necessary resources working together to get this done. If one shop pushed it forward, it would get outlawed, like the 12v heads were in the past. If it gets outlawed, there is no reason to move forward. Sometimes I do not understand the politics behind the scenes of diesels....

The future four valve heads, with larger bore engines, really will have a much higher ceiling for power potential. If gains continue to be made with injectors for four valves, the top dogs in a few years might just be four valve per cylinder engines.

This is only my ignorant perspective on cylinder heads as of now.
 
Last edited:
You must log in or register to reply here.
Back
Top