datzenmike Posted September 27, 2008 Report Share Posted September 27, 2008 Never hurts to smooth any irregularities between the exhaust valve and the manifold. I've seen burs from machining to install valve seats and casting ridges in the pocket below the seat. Smoother the better to prevent combustion deposits collecting. Porting the head AND the exhaust manifold to match the gasket won't hurt either. Because the exhaust is under extreme pressure the gasses will find their way out even if there are some rough areas anyway. The intake relies on only 14.7 lbs (sea level) of atmospheric air pressure to push through the intake port and valve. ANY restriction is to be avoided and every advantage for good flow given to this area. L heads have very nice runner design begin with. On a stock motor the initial timing is set at 12 degrees. As it revs the centrifugal or mechanical advance slowly add another 20 degrees advance. More gas and air from cam/carb upgrades will need slightly more time to fully ignite and burn in the cylinder, requiring it to be lit slightly sooner than stock. Advancing the initial timing will give better mid range power BUT the stock advance will still add another 20 degrees advance on top of that and run it into the detonation zone. The best cure it to change the centrifugal advance curve by modifying the distributor. This will reduce the mechanical advance curve to say, only 15 degrees. This will keep it close to the total stock advance of 32 degrees but will bring it in sooner. More advance sooner but same total advance. Quote Link to comment
datsunfish Posted September 27, 2008 Report Share Posted September 27, 2008 AH HA. I get it.:D Quote Link to comment
stilltwisted Posted September 27, 2008 Report Share Posted September 27, 2008 great explanation on centrifugal advance curve ,, that is the best way to make a dizzy perform for mild street eng... Quote Link to comment
DISLEXICDIME Posted September 27, 2008 Report Share Posted September 27, 2008 Some of that makes sense but the other half:blink:???Too much timing??? What does that mean?? And no one,ever,in the history of datsuns has ever said an EI dizzy was problematic. What could go wrong?? There is nothing that a points dizzy could do that a matchbox could not. I run a un resisted msd blaster 2 with a matchbox dizzy and it works great. Plus you never have to do any thing to it ever? Too much timing????? Some one please help explain this. And porting the exhaust? Never heard of that either. if you are running a engine that revs past 7000rpm you are better off running a sss points dizzy is what i have ben told it will run up to 7500. the spark is more stable at high rpms with the sss dizze. but i used to runn my l16 to 7500 all the time with a el dizzy and it seemed to hold up. I am trying to figure out what i want to do about spark for my l18 since the red line is 8000. for now i am just going to run the eldizze and see what happens like the nw starquest guys say "ride or die no regrets" lol thats the only problem i have heard about the el dizzy Quote Link to comment
Cuts metal like mad Posted September 27, 2008 Report Share Posted September 27, 2008 the sss dizzy is no different than a standard points distributor where rpms are concerned, safe operating limit is about 7000 rpm, the EI dizzy is about 7500, racers will disable the centrifugal advance by welding it thereby keeping it from over advancing under ANY conditions. Theres no reason to run an L motor up that high on a street motor anyway. Your not gonna be getting there that much quicker if at all... more than likely you'll get there slower. For racers they run high rpm because thats where the powerband is, not just cause they can. Quote Link to comment
DISLEXICDIME Posted September 29, 2008 Report Share Posted September 29, 2008 the sss dizzy is no different than a standard points distributor where rpms are concerned, safe operating limit is about 7000 rpm, the EI dizzy is about 7500, racers will disable the centrifugal advance by welding it thereby keeping it from over advancing under ANY conditions. Theres no reason to run an L motor up that high on a street motor anyway. Your not gonna be getting there that much quicker if at all... more than likely you'll get there slower. For racers they run high rpm because thats where the powerband is, not just cause they can. 1 st he asked about a performance build 2nd with the cam i have that is where the power band is . And that gives me a reason to rev my l that high. Quote Link to comment
slodat Posted September 29, 2008 Report Share Posted September 29, 2008 Maybe an EDIS setup is the ticket mr. dislexic... Quote Link to comment
DISLEXICDIME Posted September 29, 2008 Report Share Posted September 29, 2008 Maybe an EDIS setup is the ticket mr. dislexic... thats what i am thinking you still have any wheels left Quote Link to comment
Rubberman Posted September 29, 2008 Author Report Share Posted September 29, 2008 If you got the coin get the dizzy. If not, check the wrecking yards for one of the cars I listed and get one. They never wear out, put it in and forget it. Oh yeah.... you will need a matching EI coil preferably. Weber? New to prevent headaches troubleshooting a used one. If you are using the U-67 head find this manifold: http://i138.photobucket.com/albums/q251/datzenmike/motorL16exhaustmanifold.jpg[/img]"] This is as close to a perfect exhaust header as you can get for a mild engine. It's from an early L16 and may have the air injection tubes... just remove them and install pipe plugs. What kind of manifold came on a 1968 roadster? Would it possibly be this one? Of course the roadster is sitting in my backyard, but it's 2 in the morning here and I probably couldn't tell anyway. Quote Link to comment
ppeters914 Posted September 30, 2008 Report Share Posted September 30, 2008 What kind of manifold came on a 1968 roadster? Would it possibly be this one?Of course the roadster is sitting in my backyard, but it's 2 in the morning here and I probably couldn't tell anyway. Outside of the clutch, SU's and maybe a couple other nickel-dime parts, nothing on the roadster engines (R16 or U20) fit anything else. Here's the stock exhaust manifold for '68-'70 1600 (R16 engine) Roadsters: ...and here's the '68-'70 2000 (U20 engine): Quote Link to comment
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