naviathan Posted October 17, 2007 Share Posted October 17, 2007 Thanks to my recent adventures in head work and valve train issues I've had to take my SS valves I was saving for my P90 build and use them in my N42 (They are N series valves not P series). I thought all would be well as they were intended for that type of head in the first place and I didn't read any fitment issues on the website. The valves on arizonazcar.com come in stock and oversized. I got the exhaust in the oversized (3mm) and the intake stock thinking that should be sufficient to improve the flow a bit. Apparently the 3mm oversized exhaust valves are larger than the seats entirely and he would have to cut a bit out of the head for clearance which could cause the HG to not seal... What is the deal here? I wouldn't have figured the fit would be so tight that I wouldn't be able to run this head on anything outside of an over bore...? Anyone have any ideas? HELP!!!! I need this head back quickly! What problems am I looking at? Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 17, 2007 Share Posted October 17, 2007 Big Valves on a stock bore doesn't do a lot because in many cases the bore side shrouds the valve inhibiting flow. Dave Rebello has been doing extensive research on stock sized valves and has them flowing pretty well...in many cases in a stock bore close to what many of the slightly oversized valves will! Really though, 1.5mm Radially should not make that much of a deal with head gasket sealing...though overboring would unshroud the valve quite a bit! (Think L28 Valves in L24 Bore). You may be looking at another set of valves in stock size just to make it fly without eyebrowing the top of the block. You can always run the 90mm bore head gasket, and eyebrow the block heavily down to near where the first compression ring runs. If you saw what we did to fit that E88 Big Valve Head onto the L20A bore block we are currently running in the Bonneville Car... Quote Link to comment Share on other sites More sharing options...
naviathan Posted October 17, 2007 Author Share Posted October 17, 2007 So will this not work without eyebrowing the block? The only reason I'm using these valves is because they're all I have at the right length without pulling apart the other heads. Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 17, 2007 Share Posted October 17, 2007 The only way to know is to install them, and then do a mockup where you rotate the cam through full lift and see if the valves hit the block...clay the area to see clearance. Don't need a crank in it, all you need is the assembled head and a block with your bore---look from underneath if you please! Quote Link to comment Share on other sites More sharing options...
naviathan Posted October 18, 2007 Author Share Posted October 18, 2007 Well, I opted instead to have my machinist cut them down to stock size so we won't need buy new valves just to be safe. Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 18, 2007 Share Posted October 18, 2007 Oh, the humanities! Quote Link to comment Share on other sites More sharing options...
MONZTER Posted October 18, 2007 Share Posted October 18, 2007 I just had a head done by Dave Rebello. I sent him OS 46mm intake and OS 38mm exhaust, as well as stock size Intake and stock size exhaust, all were SS swirl polished undercut. I also sent him oversized seats. When he was done with it he ended up using the OS valve seats, the stock size intake, and machined the OS exhaust down to be only 1mm bigger than stock. He said he does not like the OS valves from his testing. So my head when finished flowed 212 at 25" .5 lift on the intake and 150 at 25" .5 lift on the exhaust. Note: this head was a p-90 for my turbo project and the valves were the SI brand. BTW from what I can tell everybody is using the SI valves and just re-selling them. You can buy the SS swirl polished, undercut ones diretly from them for about $8.00 each and they ship really fast. Nice parts. here is their link http://www.sivalves.com/ocforeign_valvessp_nis.html Hope this helps Jeff Quote Link to comment Share on other sites More sharing options...
naviathan Posted October 18, 2007 Author Share Posted October 18, 2007 Sweet, thanks for that info MONZTER, that will come in handy. Quote Link to comment Share on other sites More sharing options...
kalium99 Posted April 23, 2010 Share Posted April 23, 2010 When he was done with it he ended up using the OS valve seats, the stock size intake, and machined the OS exhaust down to be only 1mm bigger than stock. He said he does not like the OS valves from his testing. Hope this helps Jeff Let me get this straight. Are you saying you've got oversized valve seats with standard size valves....? How does this work? Cheers Quote Link to comment Share on other sites More sharing options...
2eighTZ4me Posted April 23, 2010 Share Posted April 23, 2010 I too, tried the 46/38 route on a MN47 head. If you slide one of each of the valves down in the guides - they're practically touching. You'd have to somehow machine the seats so they'd actually merge together at the center of the CC. That doesn't leave much meat in the seat for a good seal. Other than that - you'd have to somehow space the guides apart further - and then you're looking at totally re-engineering the head - that won't work. I know the MN47 has a smaller combustion chamber - but from what I can tell by this post, you've experienced the same thing I had on your N42 head. Quote Link to comment Share on other sites More sharing options...
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