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Old 11-30-2008, 01:55 PM   #1
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12 valve head and 24 valve head

I am thinking about building a 12 valve and was pondering what the difference in the valves are. When they developed the 24 valve head did they take the size of the valves in the 12 valve and reduce them 25% then add 12 more, or did they just use the same size valves. What I am getting at is will the engine flow more effcient with a 24 valve head on it vs. the 12 valve.

More questions to come.....
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Old 11-30-2008, 02:13 PM   #2
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Smaller valves in the 24v head because there is less room. 24v head stock will out flow a 12v head stock.
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Old 11-30-2008, 02:25 PM   #3
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i've heard a ported 12 valve will flow more than a ported 24 valve though
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Old 11-30-2008, 02:30 PM   #4
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Quote:
Originally Posted by j-rod View Post
Smaller valves in the 24v head because there is less room. 24v head stock will out flow a 12v head stock.
Now see thats what I figured. They had to reduce the valve size to fit 12 more. I guess that was a no brainer. But again does anyone have hard evidence that the 24 valve head will flow better then 12 valves. Even if they are comparing P&P heads one should be better then the other. If you reduce the size by 25% but then add one more on the intake side and one more on the exhuast side you have increaseed your size by 50%. Just rought numbers, I dont know if that is the correct sizing.
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Old 11-30-2008, 02:55 PM   #5
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the 24v will outflow a 12v. a max effort 12v head seems to be maxed at about 200-210 cfm a 24v head can be ported to flow 240+ and ive heard of up to 260 however ive never seen it on the bench myself.

It also will flow more at low lift and should have a higher port velocity
but theres more to it than flow. swirl, port velocity, flow at lift, all play a role, plus the 12v runs a much higher rocker ratio which would help make up for some of the loss of the low lift flow by having a quicker valve action off the seat

the 12v is still the horsepower king as of now, however I think there is some untapped potential in the 24v that has yet to be found because people are trying to apply things that work with a 12v directly to a 24v and bigger is not always better
 
Old 11-30-2008, 03:51 PM   #6
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A ported 24v head will out flow a ported 12v head.
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Old 11-30-2008, 04:18 PM   #7
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So is it possible to upgrade the 24 valve head with the 12 valve rocker arms so you can obtain maximum flow through a 24 valve head. I know for sure now I want to run a p-pump but do not know if I should keep the head that comes with it. I am trying to pre plan how I can put together the ultimate head and squezze out the full potential of it.
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Old 11-30-2008, 04:25 PM   #8
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I guess the question is what your trying to acomplish?
there are higher ratio rockers out for 24v but still not as high as a stock 12v

the 12v will be cheaper and easier to build. the 24v also has the disadvantge of piston and injector combo choices.

On the engine dyno the 24v is still about 100 horse shy of the best 12v combos. so unless your wanting to spend abunch of money on r&d id stick with the 12v
 
Old 11-30-2008, 04:34 PM   #9
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Quote:
Originally Posted by gotta12v View Post
the 24v also has the disadvantge of piston and injector combo choices.

What are you talking about?
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Old 11-30-2008, 05:13 PM   #10
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there is not an 5 hole injector nozzel outside of a custom billet nozzel that I know of for an overhead setup and the 5 hole injectors seem to work best with an inline pump. also the vp 24v pistons bowl is small the early cr piston has an chamfer that would possibly cause rim fire.

the later cr has a larger bowl but a mild radius into the bowl which may not mix the fuel as well as a bowl designed for an lower injection pressure system.

a custom piston and injector setup could be made but the cost would be much higher than in a 12v and the gains are yet unknown
 
Old 11-30-2008, 05:34 PM   #11
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Ok I am kind of lost now. Let me break this down Barney Stlye for you. I am going to pick up a 94-98 12 valve truck and build it for racing only. I am trying to find out if I can increase the performance of the motor by removing the stock 12 valve head and slapping on a Port and Polished, bigger springed, and posibly different other things to. Pistons will more then likely be Marine pistons and shaved to match the over sized Cam I want to install. Hope that clears up the water for ya'll.
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Old 11-30-2008, 05:45 PM   #12
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12v pistons have an offset bowl to match the injector location so which ever head you use you must use matching pistons.

If i were you id use the 12v head and marine 370 pistons flycut not shaved and coated (to keep compression up as much as possible since a 370 piston is already 15.3 factory)

port the head concentrating heavily in the bowls, working down the valve guide castings ect..

use a good valve either ss or inconel and a good spring retainer combo. if money allows remove the intake shelf and true the runners focusing on straightening the runner in reference to the valve.

the cam, injectors, ect.. depend on the application
 
Old 12-01-2008, 01:41 AM   #13
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i hear the 12v heads are more capable and reliable at higher rpm than the 24v heads. Maybe if some one made a rail system for the 24v head like the top fuelers.
 
Old 12-01-2008, 05:54 AM   #14
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I personally like the 12V head better, mainly because I have never had an issue with one and I have a 24V head in the shop that dropped 2 valves....not good. You are correct on the 12V flow numbers......mine is 214 intake / 191 exhaust @.500 and I have a flow sheet, if someone SAYS a 24v head ported will flow more I'll challenge them to produce a flow sheet.

Jim
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Old 12-01-2008, 06:01 AM   #15
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I don't have a flow sheet, but the guy building my engine did some extensive dyno work for a pretty well known diesel shop. He picked up 50-75HP on the dyno going from the ported 12V to the ported 24V. Said he couldn't convince them to go to the 24V setup.

Now supposedly you start getting into the high lift numbers the 12V will start to outflow a 24V, but the low lift numbers of the 24V eat the 12V up. So if you figure cam profile in and that fact that the valve doesn't open fully instantaneously, then that is where the 24V starts to shine.

There have been issues with valves on the 24V. You should absolutely go with a better valve if your gonna run a 24V head. The 12V are definately cheaper to build.
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Old 12-01-2008, 08:09 AM   #16
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Quote:
Originally Posted by zstroken View Post
I don't have a flow sheet, but the guy building my engine did some extensive dyno work for a pretty well known diesel shop. He picked up 50-75HP on the dyno going from the ported 12V to the ported 24V. Said he couldn't convince them to go to the 24V setup.

Now supposedly you start getting into the high lift numbers the 12V will start to outflow a 24V, but the low lift numbers of the 24V eat the 12V up. So if you figure cam profile in and that fact that the valve doesn't open fully instantaneously, then that is where the 24V starts to shine.

There have been issues with valves on the 24V. You should absolutely go with a better valve if your gonna run a 24V head. The 12V are definately cheaper to build.
True, but stock 24V exhaust valves are inconel IIRC and as far as strength and reliability U will not beat it. I have talked to a source that has ran aftermarket valves and he has seen them crack and mushroom and im pretty sure he has seen and built a few motors.....
Brandon
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Old 12-01-2008, 05:43 PM   #17
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Okay so the 12v head is far superior I gather.So here is my next question for ya'll.

Has anyone flipped over a head and measured the CC's of the combustion chamber and then balanced all 6 of them to hold the same CC's? Just some stuff I have been thinking about.

Also has anyone pulled all the connecting rods and the push rods and re-match them with parts of the same length?
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Old 12-01-2008, 05:46 PM   #18
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It is pretty much zero CC
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Old 12-01-2008, 05:49 PM   #19
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Quote:
Originally Posted by SmokinRamMike View Post
Okay so the 12v head is far superior I gather.So here is my next question for ya'll.

Has anyone flipped over a head and measured the CC's of the combustion chamber and then balanced all 6 of them to hold the same CC's? Just some stuff I have been thinking about.

Also has anyone pulled all the connecting rods and the push rods and re-match them with parts of the same length?
Dan do u wonder...Cause I sure do.
Brandon
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Old 12-01-2008, 06:01 PM   #20
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I sure am cornfused!
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