D83ZXT Posted October 17, 2002 Share Posted October 17, 2002 Ever try going to sleep with motor rebuild running through your mind? Grrr...... Exhaust valves... I am getting confused as to whether or not this should be done. P-90 Street/Race Sunbelt "doesn't" recommend larger exhaust valves over stock. They say the durations of the exhaust valves stays open more then closed. That's from their head flow tests results. Geromaly's doesn't seem to see this necessary either, as long as a street/race port & polished job was done correctly. I do know a few who was has Robello work, and Dave does open them up. Any body else have evidence that larger exhaust valves does make a difference or not? So what give here??? Think that was fun, try going over cams with different people... lol Donna Quote Link to comment Share on other sites More sharing options...
240Z Turbo Posted October 17, 2002 Share Posted October 17, 2002 I run the larger exhaust valves, but have also heard that oversized exhaust valves gain little. I think you would be better served oversizing the intake valves and I wish I had done the same. Quote Link to comment Share on other sites More sharing options...
TimO Posted October 17, 2002 Share Posted October 17, 2002 Donna- Can't sleep huh! With all the cam specs and confusing opinions going through your head....gee I wonder why! As you know I run the larger exhaust valves. I don't know if they make a difference in my set up or not! I don't have a baseline for comparison. I would think with some of the Nissan builders and cam grinders such a Isky emphasizing the intake side on their cam specs for turbo z motors, maybe larger exhaust valves are not the way to go... only a guess. I would spend the extra money on porting your head, focusing on smoothing out the runner walls and concentrating on blending and smoothing the pockets around the valves. Or you could buy chocolate and send it to Sacramento!! On the left TimO Quote Link to comment Share on other sites More sharing options...
D83ZXT Posted October 18, 2002 Author Share Posted October 18, 2002 ROFL.... Now, how I can pass you, if you're always on the left? Just you WAIT!!! Thanks for the input, I do believe that's the plan for now. Keeping exhaust as stock size. James, thanks for the addition insight. I will discuss this further, while my head is being opened up even more then before. Tim, your right about the larger intake over exhaust cam findings. Boy, wasn't that fun... Talk about flipping durations around.. Hey, at least I know what center lobes to go with my Turbo unit (per Reed) LOL.... I am waiting for recommendations from Elgin's. (faxed motor info spec sheet today) So far, I am leaning towards the ISKY, over Sunbelts $600 cam/springs. That's quite a bit difference in price. Trial and error, but we'll see what works. Tell you what... Why don't "You" buy it, then you can show how it runs on the dyno SEE's....Yummie Hey! Now that's a way to add more weight!!! Since you already know about the bag of cement that I was planning on slipping into your Z.... Me Evil? Nahhhh.... Donna Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted October 18, 2002 Share Posted October 18, 2002 When I had my performance turbo cam installed I had a minimal amount of head work done too. I had the opportunity to install a larger exhaust valve, but my builder commented on the fact that since I was running the stock bore, a larger exhaust valve would be significantly shrouded by the cylinder wall. He had a flow bench set up with a junk P90 and said he got better results flow-wise by simply unshrouding the stock valve instead of installing a bigger one. Quote Link to comment Share on other sites More sharing options...
RB26powered74zcar Posted October 24, 2002 Share Posted October 24, 2002 So........ whats the verdict Donna? Is the jury still out, or have you made up your mind already?? Quote Link to comment Share on other sites More sharing options...
David K Posted October 26, 2002 Share Posted October 26, 2002 i think the piston size and compression matter more than exhaust valve size. you can only push out as much air as your piston will let you, right? i think the intake valves will gain you more since you can stuff more air into there. Quote Link to comment Share on other sites More sharing options...
D83ZXT Posted October 26, 2002 Author Share Posted October 26, 2002 LOL... Joel How's your beast doing? I am keeping the exhaust valves stock size. Maybe someday TimO and I could swap heads around to see if there's really a difference. I believe he's going to get the same cam as I am. It would be interesting though to see Donna Quote Link to comment Share on other sites More sharing options...
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