Guest 73Turbo240z Posted March 11, 2005 Share Posted March 11, 2005 I've been researching my options for my head on my motor, it's a p90a hydrolic setup, i'm wanting to do some kind of valve upgrade, but after taking a look at it last night, there really doesn't seem to be a whole hell of alot of room to get bigger valves into that puppy. i'm currently on campus so i can't post photos, but the intake and exhaust valves are very close proximity to one another already, so i worry that going to larger valves would make that thin wall between even worse off structurally when material gets removed for the larger valves... anyone care to speculate on that? and the quest for better valves is what led to the question of cam tower shimming, i was told i could run stainless valves for an N47 head which are longer than the p90a valves by shimming the tower. I know what shimming is, but when i think shimming i think washers used to level out bumpers and whatnot, when messing with somthing as precise as a camshaft though... i'd like to know more about how it's done right. anyone done this and care to shed some light? Quote Link to comment Share on other sites More sharing options...
datsunlover Posted March 11, 2005 Share Posted March 11, 2005 Shiming the cam towers is similar to what you're tinking of, just not using washers. Basicaly it's putting thin pieces of metal (same shape and with the holes matching the bottoms) in between the towers and head, in efect raising the towers any amount desired. I've never heard of doing it to suit longer valves, but I know for sure you have to do it when you mill a lot off a head (to raise compresion) as the timing chain tensioner will not take up enough slack after a ceartian point. IE; shaved head sits lower on block, making cam sit lower/closer to the crank. Quote Link to comment Share on other sites More sharing options...
Guest 73Turbo240z Posted March 11, 2005 Share Posted March 11, 2005 Shiming the cam towers is similar to what you're tinking of, just not using washers. Basicaly it's putting thin pieces of metal (same shape and with the holes matching the bottoms) in between the towers and head, in efect raising the towers any amount desired. I've never heard of doing it to suit longer valves, but I know for sure you have to do it when you mill a lot off a head (to raise compresion) as the timing chain tensioner will not take up enough slack after a ceartian point. IE; shaved head sits lower on block, making cam sit lower/closer to the crank. what kinda metal would you use to shim though, it has to be pretty precised and level across the board i'd imagine, so hacking up sheet metal to the shape and then stacking to your liking seems a little archaic... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 11, 2005 Share Posted March 11, 2005 As to what to use, how about shim stock? Or buy them from ISKY or whoever has them these days. Machinists can order them for you, they aren't hard to find. More important question is WHY you would do this? The longer valve stem doesn't do you any good unless you're going to shave the head to boost the compression. The common setup is to shave .080, then use the N42 valves because they are .080 longer, and shim the cam towers up. The shims return the cam towers to the right height with relation to the timing chain, and the longer valves put the rockers in the right location with relation to the cam and lifters. Your original post seemed like you were trying to get the biggest valves into the head that you could. The P90 valve is the biggest Nissan put in, and it has the same size head as the N42, so there is no advantage to swapping out one for the other in terms of flow capacity. Quote Link to comment Share on other sites More sharing options...
Guest 73Turbo240z Posted March 12, 2005 Share Posted March 12, 2005 the end goal is a p90a with a yet undecided head upgrade, and my current research had yielded nothing it terms of "bolt in upgrades" for the p90a, the n42 had stainless valve offerings which was my only real reason for interest in the n42 valve, i'll be running the stock CR as my motor will see a good amount of PSI and i'd rather not play the russian roulette of higher compression + boost. the goal of this is a upgraded p90a, of which how i'd do that is still up in the air, since i'm still not fully aware of my options. Quote Link to comment Share on other sites More sharing options...
Guest jlg111286 Posted March 13, 2005 Share Posted March 13, 2005 Hey i have a E31 thats shaved, i put shims in there that way the chain doesent get slak too much. Quote Link to comment Share on other sites More sharing options...
DeusEx Posted March 13, 2005 Share Posted March 13, 2005 Shimming the cam towers will throw of your cam geometry a little though..... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 13, 2005 Share Posted March 13, 2005 Shimming the cam towers will throw of your cam geometry a little though..... If you shim the same amount that you shave off the head, it puts the cam geometry back in the right spot. Quote Link to comment Share on other sites More sharing options...
RB26powered74zcar Posted March 16, 2005 Share Posted March 16, 2005 There are the correct stainless valves for the P90 head out there in Z land, if thats all your after.... I know a few folks here on this board that have monster turbo L6's, using the P90 with custom stainless valves, so they are available... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 16, 2005 Share Posted March 16, 2005 That's not the cam geometry he's referring to...shimming he towers changes the relationship between the cam and the rockers/pivots/lash pads/valve stems. There are secondary effects when restoring the crank center to cam center distance to compensate for a shaved head. Read up on it in the "How to Modify...;and the How to Hot Rod Datsuns..." books for details. DAW That's why he was talking about installing the N42 valves. Basically he wants some stainless valves and can't find them for a P90, so he's thinking about modding the head to fit the valves by cutting the head and shimming the cam towers and installing the longer valves. All the geometry would be correct but this would raise the compression ratio quite a bit, not good on a turbo motor. And as J. Soileau 74260zt says, somebody has to make them for a stock length P90. Quote Link to comment Share on other sites More sharing options...
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