OEM Piston Valve Relief Size

Nick_C78

New Member
Random question, but does anybody know the size of the valve reliefs on OEM B16 pistons. I know the intake valve diameter is 33mm, I was just wondering if anybody knows the diameter of the valve reliefs. I would measure them, but I am kind of far from my motor at the moment. Basically I am curious if OEM pistons can run +1mm oversize valves with OEM B16 Pistons and OEM ITR Cams.

Don't lecture me on it not being worth it and why would I do it. This is strictly for research and experimentation.

Thanks in advance if any of you have the answer. Otherwise I will have to wait until I measure them.
 
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Nick_C78

New Member
Same, but it could be slightly larger for assurance. Haha I guess I will measure it when I am up there though.
 

Muckman

Not a M0derator
I have some P72 pistons I'll measure for you
 


Muckman

Not a M0derator
So I measured the diameter of the valve reliefs on a stock P72 piston. Its tough to get an exact measurement because there isn't an exact termination of the relief. Its rounded and the exterior edge is cut back. The best way to measure is to actually put oversized valves in the reliefs, which I happen to have! When comparing the circumference of the oversized valve in the valve pocket it does appear to fit. Of course this does not measure alignment of the valve when in the actual valve guide of the head (ie it may not be centered as I have it). The only way I could sleep at night with this kind of build is to clay the engine.

Here are the measurements of the intake valve relief. Stock and +1mm



Standard size valves


+1mm intake and +1mm exhaust valves




From the top down view you can see it tucks in quite well.

 

96LSteg

Jemel
So flippin thorough Muckman! I swear I idolize you lol I want to be like you when I grow up :lol: Im in for this thread as I plan to use P30s or PR3s in my distant future build and I feel like this is something I need to know.
 


Nick_C78

New Member
I appeciate you taking the time to give that information. I am going to save that post for my files too. That actually appears to fit a lot better than I thought it would. It looks like there is a damn good chance it will work. Especially since I only have ITR cams. With a larger lift and larger duration cam it might not. I will clay it before I start it, but this does make me feel comfortable about giving my head guy the go ahead to install them. Awesome that you had both sizes laying around too. I was going to have to order a valve for that test.
 

Muckman

Not a M0derator
Sure Nick, only for you.

Cams are irrelevant regarding valve relief diameter because if the relief is smaller than the valve than it would hit with any/every cam once the VTEC lobe engaged. The cam would affect valve to valve more than piston to valve clearance. The piston should never be that close unless the surface was significantly milled.

You'd get this. Example: Non vtec pistons dont have big enough valve reliefs for a VTEC sized valve to fit into. Valve doesn't fit into the pocket but there's lots of clearance under.
 

Nick_C78

New Member
Muckman said:
Sure Nick, only for you.
Click to expand...
Damn near sig worthy.

Yeah I have heard about those nonvtec pistons, which is what made me think about my valve reliefs actually. It also got me wondering how people slap vtec heads on stock b20 blocks without issues. hah
 

Nick_C78

New Member
Good point about the cams. I don't see v2v being an issue at 1mm and OEM Cams either though. Plenty have done 1mm oversize. I just wasn't sure if oem pistons could work, but from the looks of it they might. That information can ultimately be a game changer for ballers on a budget, imo. Depending on the gain. Being 1.8 makes the gain a lot smaller, but with the right port job, back cutting of the valves, and supporting bolt ons, I can see 1mm being worth it. Especially if you need new valves anyways.
 

Muckman

Not a M0derator
Are you limited to an OEM cam? Id rather run a large cam instead of an over size valve.
 

Nick_C78

New Member
Limited, no. Curious how much I can get out of an OEM cam, yes. I also save points in HFF Challenge if I keep my OEM cams vs getting after market, but that has nothing to do with my choice. It really just has to do with me wanting to see how far I can go with those cams.
 
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