I knew this would be a great forum to ask, thanks!
Kendall
> -----Original Message-----
> From: Brian Evans [mailto:brian@uunet.ca]
> Sent: Thursday, June 15, 2000 12:52 PM
> To: Kendall F Jones; Vintage List
> Subject: Re: Ignition timing on a Sprite?
>
>
> Anything that improves combustion - like more compression, more
> cam, better
> breathing, improved combustion chamber - means that less ignition advance
> is needed. Anything that detracts from good combustion - lousy "squish",
> bad chamber shrouding, poorer breathing, high octane gas in a low
> compression motor - means that more ignition advance is needed.
>
> High octane gas is resistant to knock, or detonation. What that means is
> two things - first, it's harder to ignite, so if you have too high an
> octane in a really low compression motor, you can have problems. Second,
> it allows high compression without knock, so that you can get the
> benefits
> of high compression and still have a reliable engine.
>
> With that said, the best ignition advance is as much as possible, just
> before you start to lose power. On a dyno, that's easy to find.
> If you're
> guessing, it's impossible to get perfect (hence your question, I suppose.)
>
> If it was me, I'd run 35deg total advance, and run gas that matched my
> compression ratio to control detonation. Look for detonation as a sudden
> increase in water temp, and as little black balls on the spark plugs. I
> built a 948 engine for a guy up here, and set the timing for 32
> deg. When
> he had it dyno'd, they set it at 35 deg and found about 5 hp from
> just that
> change. FWIW, I run my Martin/Ford engine, which has a remarkably poor
> combustion chamber, at 45 deg.
>
> Advance in race motors is always set as total advance. Your distributor
> will have all of it's advance in by 4000 rpm, so just dial in the advance
> you need and rev the motor till the advance stops moving - that's total
> advance. On my Martin, I run a locked distributor so that I can set
> timing at any rpm. The advance is there (on a race motor) primarily to
> make the engine easier to start.
>
> Detonation or knock, as I understand it, is when the mixture explosively
> combusts rather than burning in a controlled manner. Pre
> ignition is when
> the mixture ignites prematurely but still undergoes a controlled
> burn. Knock sounds like guys with big hammers inside the engine,
> pre-ignition sounds like guys with little tiny hammers going "tink tink
> tink". Passenger car motors of a few years ago ran in pre-ignition
> routinely in order to run lean enough to pass emission test (computer
> controlled fuel injection and ignition fixed that). I'm told that
> detonation can kill a motor in just a few seconds.
>
> Hope this helps a bit.
>
>
> At 12:09 PM 06/15/2000 -0400, Kendall F Jones wrote:
> >Now that I've got a means to set my ignition timing correctly
> (TDC mark on
> >top of the crank pulley & an adjustable timing light), I was wondering if
> >anyone has learned the lesson of what works.
> >
> > Here's what I got - SCCA IT spec motor (very mild by vintage
> specs), .040
> >over, stock head/cam/carbs. Electronic ignition with non-vacuum advance
> >distributor, with 19 degree mechanical advance. I've always set
> the timing
> >but just "twisting it till is sounds good" at idle, however, I popped the
> >dist out during a warm-up and it has not been set back to what
> it was (cause
> >I dont know what I started with).
> >
> >Any hints? Whats a good initial and total advance? I once
> heard 32 degrees
> >was a good total advance, would that get me in the ballpark?
> >
> >thanks
> >Kendall
>
> Brian Evans
> Director, Strategic Accounts
> UUNET, An MCI WorldCom Company
>
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