Tommy Posted September 18, 2009 Share Posted September 18, 2009 I'm running a slightly bored L28 aftermarket cam, into a 240z with triple webers. Ignition will soon be PS91 with HI-6 from crane arms. Currently, I have a 280zx Distributor without the vaccum advance hooked up (bad). I am looking for a new distributor, and would like to hear any thoughts on weather to go with vaccum and mechanical, or mechanical advance only. I know that triples are not usually set up for vaccum advance, and if I drill, it must be before the first butterfly nut on the manifold. This is not where cannon want's me to drill (there are preselected holes), but that's fine with me. I have also heard of possible problems with vaccum issues when more carbs than stock are used. I need midrange peformance, because this is primarily a daily driver. There is a mallory unilite with vaccum and mechanical on ebay right now, and I am considering buying it. My question: Should I go with mechanical advance only, or mechanical and vaccum? Thanks for any input. Quote Link to comment Share on other sites More sharing options...
Lazeum Posted September 18, 2009 Share Posted September 18, 2009 I have a mallory Unilite with no vaccum and it works good. It is tunable as long as you purchase the springs kit. In addition to the distributor I have a Hyfire unit (equivalent to the MSD 6AL) People are saying the unit is fragile, some high tension can destroy it but so far so good. I kept the stock ballast for this reason. You'll need also to rewire a little bit everything with an adapter if you want your stock tach to work properly. Regarding vaccum location, it does not really matter anyway since all intakes runners are linked together (the web between them is hollow) Quote Link to comment Share on other sites More sharing options...
JMortensen Posted September 18, 2009 Share Posted September 18, 2009 If you're going to shell out the king of money you would need to for a Unilite, go get a DIS crank fire ignition system. Crank fire is far more accurate than ANY distributor will be. If you have to keep a distributor, I'd pick a 280ZX distributor and then eliminate the vacuum advance. In fact, I'll sell you my old one if you want (going V8). I'd do the MSD 6AL, the 280ZX distributor and Master Blaster II coil for $150. The vacuum advance has been JB Welded so that it can't move and the bushings in the dizzy were just checked about 5000 miles ago and are in good shape. You would need cap, rotor, and wires to run it. As to the MSD type ignitions, you should jump the ballast when you run them. You'll get a MUCH hotter spark with the ballast jumped, and they're designed for a full 12 volts. Quote Link to comment Share on other sites More sharing options...
rucus01 Posted September 18, 2009 Share Posted September 18, 2009 If you're going to shell out the king of money you would need to for a Unilite, go get a DIS crank fire ignition system. Crank fire is far more accurate than ANY distributor will be. If you have to keep a distributor, I'd pick a 280ZX distributor and then eliminate the vacuum advance. In fact, I'll sell you my old one if you want (going V8). I'd do the MSD 6AL, the 280ZX distributor and Master Blaster II coil for $150. The vacuum advance has been JB Welded so that it can't move and the bushings in the dizzy were just checked about 5000 miles ago and are in good shape. You would need cap, rotor, and wires to run it. As to the MSD type ignitions, you should jump the ballast when you run them. You'll get a MUCH hotter spark with the ballast jumped, and they're designed for a full 12 volts. Why would you elmeniate the vacuum advance? Without a load compensation device the timing will be well below optimal when driven on the street. A properly tuned vacuum advance will yield to a much cleaner idle along with a much more effecient cruise. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted September 18, 2009 Share Posted September 18, 2009 Tommy, I didn't read your original post very well. I'd suggest you take the distributor you have apart and then disable the vacuum advance. This site will help with disassembly and reassembly: http://www.jrdemers.com/280ZX/distributor/distributor.html Why would you elmeniate the vacuum advance? Without a load compensation device the timing will be well below optimal when driven on the street. A properly tuned vacuum advance will yield to a much cleaner idle along with a much more effecient cruise. Vacuum advance is for mileage. There are a couple reasons why you wouldn't want vacuum advance. 1. If you have triples and a cam it's possible that you don't have the vacuum to operate it properly. 2. If you have triples and a cam you're probably more worried about getting maximum hp at WOT, and vacuum advance doesn't allow that to happen. Examples: By running mech advance only and running a small amount of it like the ZX distributor has, the static timing can be advanced. Instead of running 8 degrees BTDC, you might run 18 at idle. This makes up for what the vacuum advance does at high vacuum situations. The mech advance mechanism from the 280ZX has ~18 degrees of advance in it, so 18+18=36 degrees of advance. Just an example, it might be better to run 14 or 20 degrees at idle, it depends on your particular build. Running vac advance means that you lower the static timing to the factory spec of 8 degrees or whatever it is. Then when you punch it and vacuum is at it's lowest (so you're not getting any help from the vac advance), you'll be left with ONLY what the static timing + mech advance yields. In the case of the ZX distributor that is ~26 degrees (8+18 degrees). As a very general rule, most L series motors make best power at mid to high 30's total advance. The advantage with the vacuum advance is that at highway cruising rpms and vacuum it will add vacuum to the mechanical advance. You might be running 40+ degrees BTDC in this scenario, and that might not be a detriment because the engine can handle it without pinging and will get better mileage for it. In every other situation, I would say that the mechanical with a much higher static timing setting has the advantage of making more power. Quote Link to comment Share on other sites More sharing options...
Tommy Posted September 19, 2009 Author Share Posted September 19, 2009 Lazeum -- Zs-ondabrain from classiczcars responds: "Yup, I had similar issues with my triple 40DCOE's and advancing the timing helped a little. Different altitudes will also effect the timing. Advancing should also bring up your idle. The only problem with running Vaccum advance on triples is they are not typically set up for Vaccum Advance. The VA has to be place before the buuterfly on the #1 Weber. If you put the VA after the butterfly, on the intake manifold, you'll suck your vaccum advance diaphram out or suck a hole into it, causing it to malfunction. I blew out my $30 diaphram on my Mallory Unilite by doing that exact wrong thing. Dave" Jim -- I currently run a 280zx with no vaccum from a PS92 and Fireball XR700 (crane arms CD ignition) Rucus -- The Unilite I'm looking at now it listed as much cheaper than the crank-fired ignition from DIS. Jim and Rucus -- This car will be driven 95% street. I wouldn't mind a little more gas mileage, either... Although it would feel good to have max HP at WOT, it's not too practical outside the track. So... so far, I think I'll go with this unilite and hook up the advance? Anything else I might want to know? Quote Link to comment Share on other sites More sharing options...
Tommy Posted September 21, 2009 Author Share Posted September 21, 2009 Talked to my dad last night, he strongly advised against hooking it up, especially before I can get it running again. Swapped the old PS92 for the new one. Haven't hooked up the HI-6, and I'm looking for the manual on how to do it. He said that the PS92 and HI-6 might even work in series with the XR700 ignition. Apprantly Crane just went out of busines. I'll keep looking, and leave the advance until (at least) it runs. If I swap an old PS92 for a new one (it's currnetly hooked up to the 280zx dizzy with no ignition amplification), do I need to take apart the dizzy and recalibrate it? I remember reading something about this... Quote Link to comment Share on other sites More sharing options...
Tommy Posted September 22, 2009 Author Share Posted September 22, 2009 Found both manuals, unfortunatly I need to setup the current 280zx dizzy with an optical ignition to run the XR700 from fireball. Seems like a common/straightforward mod to the dist., but requires another part... No more questions Except if anyone knows the part number to change an OE 280zx dizzy to fire from optical cables... And I'm going mechaincal advance only with the XR700, HI-6, and PS92 coil in series with the tach adapter. Quote Link to comment Share on other sites More sharing options...
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