Basically, a standard dizzy is fitted with a vac unit and in order for it to do its job the breaker plates are in two pieces one of which is attached directly to the vac unit, and also they usually have dual return springs fitted to the solid plate. This standard vac advance/retard system allowed dwell variance which relates directly to points gap variance and this is a bad thing especially in a competition engine. Dwell variance is also caused by a worn dizzy, as in loabs and shaft bearings etc. Dwell is the number of degrees that the distributor shaft rotates with the points closed (and therefore charging the primary coil) and when the points open the coil fires. Points gap is directly related to engine timing ie if an engine is timed with the correct points gap and then the gap is made smaller, the timing will be less and the dwell will be higher and the opposite also applies - Ppl who use a dwell meter (recommended) instead of feeler gauges to set the points gap will have seen this. The correct dwell angle is far more advantageous than the correct points gap, and setting the points gap get more inaccurate if the points are used.
As Errol alluded to the timing spikes at certain rpms (usually high rpm) was why the solid or welded breaker plate was use in racing with carbies that didn't come equiped with a vac unit metering device, the downside is the engine can be a bit cranky on cruise below 2500 - 3000 but the performance gains are really noticeable from 3600 - 4000+ rpm to as high as your game to go which is were most L series engines are running most of the time.
regards Terry
Topic: Dizzy ======= Date: Sat, 17 Apr 2004 08:07:14 +1000 From: "Errol Smith" <[EMAIL PROTECTED]> ---------------------------------------- The main reason for welding or replacing the breaker plate with a solid item is to help stop timing scatter. With the standard diaphragm plate the timing can move 4-6 degrees at high engine speeds. Disadvantage of making the breaker plate solid is the lack of cruise advance from vacuum.
Cheers Feral Errol Get Serious! http://www.datrats.com.au/
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of James Fitness Sent: Friday, April 16, 2004 11:13 PM To: [EMAIL PROTECTED] Subject: Re: Dizzy
My old turbo 240z had the plates welded up... static timing - best thing for a Big boost carby turbo... (probably good with fuel only efi too?)
mark krawczuk wrote:
dont they either stretch the adv springs or elongate the adv spring holes in the plate? i think they usually recurve the dizzy according to what engine setup u have??
mark k
----- Original Message ----- From: "maldat" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Friday, April 16, 2004 4:03 PM Subject: Re: Dizzy
gainsYou dont have or need Vac advance for twin side drafts , hence remove it from the dizzy graph it and weld it up.
The timming does not change , I think they call it dwell angle? with high/low Rpm.
Malcolm ----- Original Message ----- From: "Jeff Oldham" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Friday, April 16, 2004 5:09 PM Subject: RE: Dizzy
and to add my 2 cents worth WHY is it welded up.....what performance
?
ta Jeff
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