ggzilla Posted February 8, 2012 Report Share Posted February 8, 2012 within a few thousanths of the thickness/height That can make a substantial difference in compression ratio. Generally 4 thousands will still run pretty much the same, but guys who have the head skimmed every time they change the head gasket (even though it doesn't need it) will end up with an unexpectedly high CR. Quote Link to comment
Dirttrack510 Posted February 8, 2012 Author Report Share Posted February 8, 2012 What number on the cam gear is for what? 1,2,3 i was told #3 was for more torque. I'm assuming it's really for when you resurface the head to correct the timing Quote Link to comment
banzai510(hainz) Posted February 8, 2012 Report Share Posted February 8, 2012 I'm assuming it's really for when you resurface the head to correct the timing YES or chain stretch or move the power band up or emissions L20s came on #2 from Factory Quote Link to comment
Laecaon Posted February 8, 2012 Report Share Posted February 8, 2012 I thought it was to account for more chain wear. But probably could be used for other purposes. Quote Link to comment
Dirttrack510 Posted February 9, 2012 Author Report Share Posted February 9, 2012 I called REBELLO... The 1 is factory, 2 is slight advance, & 3 is the most advanced. For more cam advance slot #3 hole. Quote Link to comment
datzenmike Posted February 9, 2012 Report Share Posted February 9, 2012 One may be factory for the L16 but L20Bs are on number two. Quote Link to comment
datsunaholic Posted February 9, 2012 Report Share Posted February 9, 2012 The factory manuals (at least for the 610 and 620) for '75 says #1, BUT it's reusing the L16/L18 paragraph and it's corrected to #2 in the '76 manuals. What's funny though is EVERY L20B I've ever taken apart has been on #1. However I'm pretty sure every L20B I've taken apart has been apart before. For more cam advance you can always drill a new hole... if you know where. Or buy one of those REALLY expensive adjustable sprockets. Slotting the hole is simply asking for it to back itself off. Quote Link to comment
Dirttrack510 Posted February 9, 2012 Author Report Share Posted February 9, 2012 Dave at rebello says its common practice to slot the stock gear on the race engines they build & torque it to 125 lbs. Claims they've never had one move. Quote Link to comment
Dirttrack510 Posted February 9, 2012 Author Report Share Posted February 9, 2012 On the other hand... Maybe these numbered gear holes are like TOOTSIE POPS... The world may never know... Quote Link to comment
docbainey Posted February 9, 2012 Report Share Posted February 9, 2012 Dave at rebello says its common practice to slot the stock gear on the race engines they build & torque it to 125 lbs. Claims they've never had one move. On a race engine? I'ld like to see how long it takes to degree a cam that way, or adjust it for chain stretch, Sounds like BS. Take it apart and you are F'ed. Whatever. You can also use offset bushings if you increase the diameter of the pin hole on the sprocket. Any muscle car speed shop sells them. But if you you don't put a degree wheel on it, your just guessing. Quote Link to comment
Dirttrack510 Posted February 9, 2012 Author Report Share Posted February 9, 2012 He said to put #1 @ tdc, get #4 cyl valves at overlap, with #1 intake opened to30 thousanths and lock it down. He said that should be the perfect setting. Quote Link to comment
docbainey Posted February 9, 2012 Report Share Posted February 9, 2012 He said to put #1 @ tdc, get #4 cyl valves at overlap, with #1 intake opened to30 thousanths and lock it down. He said that should be the perfect setting. All you need is a degree wheel and a positive stop to be able to find TDC. Almost forgot, a dial indicator on your #1 intake valve also. Quote Link to comment
DAT510 Posted February 9, 2012 Report Share Posted February 9, 2012 On a race engine? I'ld like to see how long it takes to degree a cam that way, or adjust it for chain stretch, Sounds like BS. Take it apart and you are F'ed. Whatever. You can also use offset bushings if you increase the diameter of the pin hole on the sprocket. Any muscle car speed shop sells them. But if you you don't put a degree wheel on it, your just guessing. You know Rebello has been doing this for over 30 years right? Quote Link to comment
Dirttrack510 Posted February 9, 2012 Author Report Share Posted February 9, 2012 If you all think the slotted hole is a bad idea, maybe I'll try drilling a 4th hole. I think I can figure out where to put it by mic-ing the distance between the other holes. :unsure: Quote Link to comment
ggzilla Posted February 9, 2012 Report Share Posted February 9, 2012 It is a great idea. It's not going to slip if you use a torque wrench. Overtighten it, and it may slip. Tighten it properly. You can mark the pulley and cam so that you can later disassemble and reassemble it in the same position. Advancing the cam will shift the power band down in the RPM range (or correct for chain alignment). So measuring the exact timing and setting it there via a dial indicator is the best way to do it. Better than picking a hole to use. Quote Link to comment
docbainey Posted February 10, 2012 Report Share Posted February 10, 2012 You know Rebello has been doing this for over 30 years right? Quick and dirty. It's great if you never take it apart, Try and adjust cam timing at the track. Slots don't get it, to much screwen around. I dialed my first cam in. in 1976. When you have the cam properly dialed in, you can make educated changes with off-set bushings without having to dial it in again. Read the Racer Brown section in the orginal HP book. Quote Link to comment
Sealik Posted February 10, 2012 Report Share Posted February 10, 2012 (edited) http://www.datsport.com/racer-brown.html Actually....this link should be "Pinned"...lots of good info Edited February 10, 2012 by Sealik Quote Link to comment
Dirttrack510 Posted February 10, 2012 Author Report Share Posted February 10, 2012 http://www.datsport.com/racer-brown.html Actually....this link should be "Pinned"...lots of good info I second that motion... I never thought this thread would get this involved, but it does have lots of good info in it. :D Quote Link to comment
Dirttrack510 Posted February 10, 2012 Author Report Share Posted February 10, 2012 By the way, I talked to my machine shop today... They claim those 46mm Intake valves will fit! I have a U67 head that was already in the shop, before this thread started and they're gonna try and put em' in there. I'm rolling the dice on it. I talked to ISKY CAMS about the 46mm valves and they said they will be sort of a wash performance wise vs. the 44mm intake valves on my L16 race engine, but that they should be great in something like a LZ22 race motor (yummy). The U67 head I have wasn't a great head to start with, so I'm not risking much, besides my money. :rofl: If nothing else it'll be good info for RATSUN as to weather they will fit or not. Wayno says they won't fit :no: , I guess I'll know for sure soon enough. :sneaky: This head is gonna get the works if they fit... full port and polish, 5 angle valve job, opened up intake ports, welded up intake water ports, and those BIG ASS 46mm intake / 38mm exhaust valves. This should work great with my L4 ISKY CAMSHAFT (.580 lift) :thumbup: I wanna go fast :P Quote Link to comment
docbainey Posted February 10, 2012 Report Share Posted February 10, 2012 [ This head is gonna get the works if they fit... full port and polish, 5 angle valve job, opened up intake ports, welded up intake water ports, and those BIG ASS 46mm intake / 38mm exhaust valves. This should work great with my L4 ISKY CAMSHAFT (.580 lift) :thumbup: I wanna go fast :P Instead of welding up the water ports just drill & tap for pipe plugs. Quote Link to comment
Dirttrack510 Posted February 10, 2012 Author Report Share Posted February 10, 2012 Why not weld up the ports and be done with it? :unsure: I've had problems with water leaks at the intake :angry: and figured I'd just do away with em' for good. It's not a street engine, so I shouldn't need em' anymore... Quote Link to comment
datsun510 Posted February 10, 2012 Report Share Posted February 10, 2012 Use a round port head for even more top end. Quote Link to comment
Dirttrack510 Posted February 10, 2012 Author Report Share Posted February 10, 2012 Use a round port head for even more top end. My W58 head is round port, but it has the sleeves in the exhaust ports. I know those can be removed though, but I heard they help with scavenging the exhaust and improve with flow. Quote Link to comment
wayno Posted February 10, 2012 Report Share Posted February 10, 2012 By the way, I talked to my machine shop today... They claim those 46mm Intake valves will fit! I have a U67 head that was already in the shop, before this thread started and they're gonna try and put em' in there. I'm rolling the dice on it. I talked to ISKY CAMS about the 46mm valves and they said they will be sort of a wash performance wise vs. the 44mm intake valves on my L16 race engine, but that they should be great in something like a LZ22 race motor (yummy). The U67 head I have wasn't a great head to start with, so I'm not risking much, besides my money. :rofl: If nothing else it'll be good info for RATSUN as to weather they will fit or not. Wayno says they won't fit :no: , I guess I'll know for sure soon enough. :sneaky: This head is gonna get the works if they fit... full port and polish, 5 angle valve job, opened up intake ports, welded up intake water ports, and those BIG ASS 46mm intake / 38mm exhaust valves. This should work great with my L4 ISKY CAMSHAFT (.580 lift) :thumbup: I wanna go fast :P I don't recall saying one way or the other on valve sizes, I don't even know how big the 280Z valves are, the intakes could be 46mm as far as I know. I just have 280Z valves put in my heads, and the intake seats are notched a little so the exhaust seats will fit, as the intakes are cooled by the cool air/fuel mixture flowing in, and the exhaust valves are left un-notched as they have no cooling except from the water jacket cooling the head itself. Quote Link to comment
ggzilla Posted February 10, 2012 Report Share Posted February 10, 2012 What does "notched" mean regarding valve seats? Quote Link to comment
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