Piston to valve clearance?

CaptainChrysler

CaptainChrysler

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Feb 8, 2008
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I was wondering what the recommended piston to valve clearance was for a 12 valve? It will be in a pulling truck.

I did a search and didn't really find anything.

Thanks
 
100k clearance is a good starting point to shoot for if running high RPM's....some drop in cans have as little as 15K clearance...

Lavon
 
You can get by with as little as .030 on the intake, but .050 is what we shoot for , the exhaust needs a little more , on the order of .050 to .075.
Remember the pistons chases the exhaust valve shut, and the intake valve chases the piston down
I have run a lot closer than this, but that’s just getting by with what you have to do.

Well designed cam profiles do not require big valve clearances cuts on the piston. The days of cutting pistons .100 to even more is over, if a cam requires that kind of clearance it’s poorly designed.
If you need this kind of piston clearance cuts, then you have excessive overlap. In a properly designed diesel cam program the overlap is minimal. Mu new 24 valve race cam profiles lift the valve .0600+ and require pistons valve reliefs of around .060 .
In proper engine assembly, you should trial fit the cam, check clearance, and then cut the pistons the minimal amount. The more you cut pistons, the more compression you are cutting out of the engine, and compression is power
 
Mu new 24 valve race cam profiles lift the valve .0600+ and require pistons


.0600+? very impressive that you can make power at .060 lift!
 
The days of cutting pistons .100 to even more is over, if a cam requires that kind of clearance it’s poorly designed.
Click to expand...

Interesting, to say the least!
 
With the latest competition 24 valve heads, the ports are moving air all the way up to .600+ valve lift. A lot of air flow has been left on the table with current cam designs. On forced induction ports, moving the valve out of the way yields even more flow, and cylinder fill.

I have been doing cam design for 20+ years on multiple engine programs. I love the challenge of this diesel program. We started with a horrible small port, and intrigue manifold head. The rocker ratio was terrible, and the cam core would not support the correct timing I knew what it wanted, and worked in that direction as far as possible. 5 years ago I scribbled down a design, which the math pointed to. The more I progressed in that direction. The better it ran, Rich Buckley was brave enough to let me get outside the box and we both went back and forth of his cam , he’s made a trip or two Bullet to pick up the latest of my renderings . The results are apparent
.. The new MaxSpool Pro series 54.5 and 60 mm Tool steel cams will deliver more air then any cam to date
These cams are huge, in airflow potential up to .525 lobe lift , intake lobe center lines any where you want them , and wide lobe separation angles

My 2.6 pulling cam is on a 122 intake love center line with a 125 lobe separation angle , and requires a little less than .030 valve relief , and this with .605 gross valve lift

The old cams that needed huge valve reliefs were just gas lobes on a diesel , with a tight LSA
 
Greg, my man. This doesn't need to turn into a Max-whatever commercial. Captain Chrysler, asked a question which you answered to the best of your knowledge,which by the way is contradicted by pretty much everybody who is winning in pulling. A lot of the pullers have .200" or more cut off of their piston Captain Chrysler. Greg is giving his opinion which is better suited for engine that need to accelerate like in drag racing. If you are only concerned in making power from 4500-5500 and don't need to accelerate lower than that, then scheid and Haisley have shown that cutting more than .100" is almost a necessity.

Also greg I didn't need a full explanation. I was just giving you a friendly jab for saying that your new race profiles lift the valve 60 thou. Although I know it was a typo(i hope) I have never heard anybody bragging about such meager amounts.

Since we don't argue much anymore, would it be too much to ask for you to put a diesel dragster in your avatar instead of your v-6 gasser? It is kind of like the Helix cam in all of their ads being from a Datsun, It just ain't right.

Captain chrysler- Most people say .050" is minimum. i have run much less on street trucks. Remember, competition engines run hotter. The more heat, the more the piston and valve grow which means you need more clearance at room temperature to make sure things don't touch when they get hot. .050" is a good number for competition engines.

Zach
 
Thanks for the useful responses guys. We have 0.083" on the exhaust side. The intake is too tight. I need to do some more checking before we cut any thing though.
 
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