WizardBlack Posted August 25, 2008 Share Posted August 25, 2008 I've done some searching and saw a post that had bowtie valves in an L head. From what I have seen in the search results (not much there) you have to install new valve guides with a smaller ID. The benefits include approx. fifty times more aftermarket support (yes, I'm exaggerating, but then again...) for valve materials and sizes and a lighter valve. Evidently the stem length is the same (or very close) as is the tip of the valve? I was curious about this as I am gathering info for a possible head buildup (for turbo) next year. I understand going up to +3mm on the exhaust (+2mm without eyebrowing the block?) is beneficial. I did not find any comments about upsizing the intake valve size for any benefit. Please comment! Quote Link to comment Share on other sites More sharing options...
TimZ Posted August 25, 2008 Share Posted August 25, 2008 I've done some searching and saw a post that had bowtie valves in an L head. From what I have seen in the search results (not much there) you have to install new valve guides with a smaller ID.The benefits include approx. fifty times more aftermarket support (yes, I'm exaggerating, but then again...) for valve materials and sizes and a lighter valve. Evidently the stem length is the same (or very close) as is the tip of the valve? I was curious about this as I am gathering info for a possible head buildup (for turbo) next year. I understand going up to +3mm on the exhaust (+2mm without eyebrowing the block?) is beneficial. I did not find any comments about upsizing the intake valve size for any benefit. Please comment! Not sure about Chevy sizes per se, but the general idea is feasible. Trouble is that you are now talking custom valve guides, custom keepers and retainers, and probably custom springs to make this all work. Plus, all of the required research as to dimensioning everything to come out right for the Datsun head/cam/valve train wll be on you. While you are at it, it would be nice to be able to go to beehive springs - when I looked into this I couldn't find quite the right combo of length, travel, id/od and rate without remachining the valve seats lower in the head and/or making custom retainers. Also for my application, going to a smaller stem size wasn't prudent, given the high EGTs that I was anticipating - especially on the exhaust valve. The intake valve is much heaver anyway, so you could just do this on the intake if you really wanted to. Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted August 25, 2008 Author Share Posted August 25, 2008 Not sure about Chevy sizes per se, but the general idea is feasible. Trouble is that you are now talking custom valve guides, custom keepers and retainers, and probably custom springs to make this all work. Plus, all of the required research as to dimensioning everything to come out right for the Datsun head/cam/valve train wll be on you. While you are at it, it would be nice to be able to go to beehive springs - when I looked into this I couldn't find quite the right combo of length, travel, id/od and rate without remachining the valve seats lower in the head and/or making custom retainers. Also for my application, going to a smaller stem size wasn't prudent, given the high EGTs that I was anticipating - especially on the exhaust valve. The intake valve is much heaver anyway, so you could just do this on the intake if you really wanted to. Hmm, the 4G63 and EJ25 uses smaller valve stems and they get pretty hot. You could probably get sodium filled valves from the 'Chebby' catalogue. I saw a pic of an L head with the valves in it on here somewhere; so someone somewhere did it. I didn't get a chance to see the other stuff, but like you said, the big issue will be getting retainers that fit the new springs and still hold the lash pads. Spring lengths and rates are also pretty easy to get for Chevy. Hmm, I'll have to do some more peeking around. I've even seen Chevy valves used in SBF. Quote Link to comment Share on other sites More sharing options...
Six_Shooter Posted August 25, 2008 Share Posted August 25, 2008 Hmmm, maybe I will need to pull that N42 head off the block and see just what I can fit together. Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted August 25, 2008 Author Share Posted August 25, 2008 Hmmm, maybe I will need to pull that N42 head off the block and see just what I can fit together. I'm surprised BRAAP, 1fastz and some of the other machinists haven't commented. I have a P90 head, but I'm not ready to spend dough on going through it just yet. Quote Link to comment Share on other sites More sharing options...
Z-Gad Posted August 28, 2008 Share Posted August 28, 2008 I have an old E31 head that was used in a GT2 car many many years ago that uses a small stemmed Chevy valve. It was ported for running long tracks and high RPM's with huge intake/exhaust ports. The idea was not only less weight with the smaller diameter valve stem, but better flow around the valve stem as well. The shop owner that built the head used to be buddies with a guy that made aluminum baseball bats. He would do some portwork, and take the head over to have it X-rayed to determine the thickness of the port walls and then would port further and X-ray it again and then flow bench it. This process was done over and over until he was satisfied with having the largest port / best flowing head he could create. Although he used the Chevy valve as a template to do the guides and seats, he had custom valves made to utilize nissan valve train components ... something about class rules back then. Quote Link to comment Share on other sites More sharing options...
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