Gaz Posted February 10, 2012 Share Posted February 10, 2012 Question: I have a dizzy that has been locked mechanically and wont use vacumm advance, 13b. Searching all over the E-nets gets me lots of rota heads saying that locking the dizzy is what you do for ported motors cause thats what they do for racing, no real reason. I understand it is so that maximum advance is achieved at top revs but do not see how that can be good for the engine at low revs, how do you stop the detonation?.. A race engine doing high revs all the time, no worries, street use.... no wonder rotarys fuck out so quickly! Why cant I keep the normal mech and vac advance, does the porting act like cam overlap so vaccum is gaylord? Are the counterweights too light at higher revs, why not re weight? Any input from anyone here? Perhaps going electronic ignition is the real answer, anyone set one of these up on a rotary before? Gaz Quote Link to comment Share on other sites More sharing options...
Unclejake Posted February 10, 2012 Share Posted February 10, 2012 Do you mean the dizzy is locked (has no advance at all) or has just had the vacuum advance locked? You need retard to get the engine started (piston engines do anyway). MSD have a solution to your problem of course. The Cortina had a locked dizzy, an electronic retard (fixed curve) and then a separate high RPM retard. You want less advance at high revs than you do at medium revs. Quote Link to comment Share on other sites More sharing options...
Gaz Posted February 10, 2012 Author Share Posted February 10, 2012 No advance at all, it is locked so is advanced manually and wherever it is set is where it stays for whole rev range. Gaz Quote Link to comment Share on other sites More sharing options...
Unclejake Posted February 10, 2012 Share Posted February 10, 2012 You need another dizzy or a retard module/ I know nothing about rotaries. Quote Link to comment Share on other sites More sharing options...
CaMpylobacter Posted February 10, 2012 Share Posted February 10, 2012 no idea why rotary dweebz do this. must make for a lot of the reason that flatpeaker's rotangs wont start when hot/ever Quote Link to comment Share on other sites More sharing options...
Unclejake Posted February 10, 2012 Share Posted February 10, 2012 http://www.trademe.co.nz/motors/car-par ... 549409.htm Cheaper than a new dizzy? Quote Link to comment Share on other sites More sharing options...
Cullen Posted February 10, 2012 Share Posted February 10, 2012 yeah dunno why they lock them for street purposes, loss of power at low revs due to having so much advance early. cant say it will be too harmful though or people would have stopped doing it Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted February 10, 2012 Share Posted February 10, 2012 Maybe it's done to help light the fire when starting? POrted motors would have fuck all cranking vaccuum. (IDK though, Rotors aren't my feild of expertise. Surely if shitloads of early advance is a good thing, you'd just get the dizzy recurved. Although perhaps rotang guys don't have the money for that. I run a locked dizzy on the datsun for the same reason. In a perfect world, you'd use a locked dizzy on a dyno with a dial back timing light. Then you'd test how much advance the engine could stand at 200rpm increments. Note down what those figures are, then have the dizzy regraphed to the same curve. Lots of coin though. Quote Link to comment Share on other sites More sharing options...
Valiant Posted February 10, 2012 Share Posted February 10, 2012 The way I heard it was that a truly big ported motor idles so fast that the mechanical advance would be all in anyway. So they lock the mechanical avance. Quote Link to comment Share on other sites More sharing options...
hmmmnz Posted February 10, 2012 Share Posted February 10, 2012 why not go for a full electronic ignition? the mega and micro squirts work perfectly for na applications, and if you ever decide to turbo or inject then you are 99% of the way there, no more fucking about with points, Quote Link to comment Share on other sites More sharing options...
morkster Posted February 10, 2012 Share Posted February 10, 2012 if you've got a points dissy chuck it away.. get a s2 or s3 (turb or non) electric dissy from fb rx7, the one with modules on the side.. full centrifugal advance is achieved at 1500 or 1750 rpm (depending on dissy model) - timing light tuning at higher revs than this so bit of a non issue.. forget vacuum advance/retard.. [advance (s2 dis on overrun) / retard (turb dis on boost)] i run turbo dis no vacuum unlocked 2.5 deg split this is all i have to say - search rx7.com, ausrotary.com for shitloads of info for africa Quote Link to comment Share on other sites More sharing options...
Grotty Posted February 10, 2012 Share Posted February 10, 2012 Ported motors (bridgeport, j port, pp) locked dizzy's Stock ports/tall ports you can use stock dizzy setup Lots of info on net if you want to know why, plus try tune a ported engine with an unlocked dizzy, it'll have you pulling your hair out to set timing at idle Quote Link to comment Share on other sites More sharing options...
sentra Posted February 10, 2012 Share Posted February 10, 2012 The way I heard it was that a truly big ported motor idles so fast that the mechanical advance would be all in anyway.So they lock the mechanical avance. have read this stated many times, also that the weights mechinism is knowen to fall apart at ported motor rpms, have also heard the whole idea being referred to as a 'hangover from the 80's' ie weights can be changed etc in saying that it worked perfectly in personal experiance, starts easy etc Quote Link to comment Share on other sites More sharing options...
Gaz Posted February 10, 2012 Author Share Posted February 10, 2012 You locked yours Dave? Quote Link to comment Share on other sites More sharing options...
kpr Posted February 11, 2012 Share Posted February 11, 2012 proper ignition "curve" is going to win every time over a fixed. i would think the vacuum advance would be removed due to less /inconstant vacuum in high overlap engine. just like a piston engine with big cams/itb's. removing it wont be the best option but may fix some issues. fixed with no mech or vac would be pretty shit Quote Link to comment Share on other sites More sharing options...
danger Posted February 11, 2012 Share Posted February 11, 2012 My bridgeport would detonate over 7k revs when the dizzy was unlocked due to over advancing the timing. Welded it up and havent had any problems since, also no difference in down low power. It just means you can set it inside the timing window that ported motors run best and dont have to worry about it over advancing out of it and overlapping etc Quote Link to comment Share on other sites More sharing options...
danger Posted February 11, 2012 Share Posted February 11, 2012 And its been as reliable or better than anything else i've owned. Never hessitates to start and its an old motor. Quote Link to comment Share on other sites More sharing options...
danger Posted February 11, 2012 Share Posted February 11, 2012 Ported motors need to run more advanced than unported anyway Quote Link to comment Share on other sites More sharing options...
Gaz Posted February 11, 2012 Author Share Posted February 11, 2012 Ok got my shit sorted. Now have an electric dizzy with modules on the outside. Will be running it unlocked and using vaccum advance aswell. Once setup and engine run in I will then sort if it needs the curve changing and move from there. Im then keen to try running a wasted spark setup with three coils instead of the two and an MSD unit... thats along way away though. Also for reference: Timing chart. Uploaded with ImageShack.us Quote Link to comment Share on other sites More sharing options...
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