Hi Dave, for those of us still learning, could you define "high compression
engines"? Is a stock rebuilt 3000 Healey engine a high compression engine?
Thanks,
Ron
----- Original Message -----
From: "Dave & M" <rusd@velocitus.net>
To: "Michael Salter" <msalter@precisionsportscar.com>
Cc: "HealeyList" <healeys@autox.team.net>
Sent: Tuesday, January 09, 2007 12:23 PM
Subject: Re: Pistons damaged again
> Hi Folks,
>
> I tell this to everyone who will listen, but few apparently do.
>
> On high compression engines, it is important to set ignition timing at
> an rpm where maximum static plus centrifugal advance (vacuum advance
> not connected) is all of the way in. Depending on the particular
> distributor, this could be anywhere from 4,000 to 5,000 rpm. Most
> engines will tolerate between 32 & 36 degrees of total maximum
> advance, depending on engine tune, fuel grade, & altitude. In other
> words, set for maximum advance & let the idle advance fall where it may.
>
> It seems that many folks still insist on setting advance at idle &
> letting the maximum advance fall where it may. This method is not
> precise. The distributor's initial centrifugal advance curve is very
> steep (advances quickly) at low rpm. Only a small error in the rpm
> that the advance is set at can make a very large error in the total
> advance at high rpm.
>
> Seat of the pants timing is never reliable. A few degrees of over
> advance "may" give better throttle response & a bit more overall
> power, But the risks are great.
>
> ------------------
> Quote Michael Salter:
> Detonation can be quite serious at highway speeds but completely inaudible
> to the driver. You can buy knock sensors which will turn on a light when
> detonation is occurring; might be a good investment.
> ------------------
> Quote Bob Spidell:
> "I'm not convinced that the fuels that are available today,
> particularly in
> CA I understand, are good enough to handle the amount of advance that the
> original distributors can produce. "
> -----------------
>
> I agree completely with Michael & Bob.
>
> Regards,
> Dave Russell
> BN2
>
> Michael Salter wrote:
> > Hi Ken,
> >
> > I would say, largely because of the way the pieces have broken off
> > the top ring land, that there is little chance that that damage is
> > attributable to anything but detonation. The other marks in the
> > pistons are probably the result of the broken off pieces hammering
> > around before they went out the exhaust port.
> >
> > There appears to be a cracked piece just hanging on in this
> > picture.
>
> > I have seen similar damage several times particularly on MGBs and
> > would suggest that you check your distributor advance curve
> > carefully both before and after you have the engine rebuilt.
> >
> > I'm not convinced that the fuels that are available today,
> > particularly in CA I understand, are good enough to handle the
> > amount of advance that the original distributors can produce.
> >
> > Detonation can be quite serious at highway speeds but completely
> > inaudible to the driver. You can buy knock sensors which will turn
> > on a light when detonation is occurring; might be a good
> > investment.
> >
> > Michael Salter
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