Spark Retard vs overlap

[Bruce Plecan]

-----Original Message-----
From: Robert Harris <bob at bobthecomputerguy.com>
To: diy_efi at esl2.eng.ohio-state.edu <diy_efi at esl2.eng.ohio-state.edu>
Date: Friday, March 26, 1999 10:12 AM
Subject: Spark Retard vs overlap

That is just a 0 MPH rev limiter.
Now if the control was for boost then that would be something else.
Least to my way of thinking, but I've been wrong before (least twice today).
Bruce
        Doc's been upset.     He's out waxing the boat and trailer.   Had
water
       in everything.   After reading a blonde joke the other day, he found
out
       the boat might be much faster if he takes it off the trailer when in
the water..


>Its an aftermarket thing.  The Buick GN/T Type home pages/mailing lists can
>point to more info.  For the quarter milers, the best I can understand it
is a
>two stage rev limiter.   Stage I - you bring the engine up to launch RPM -
say
>3800, kick the first stage in and nail it to the floor.  This "stutter
fire"
>rev limiter works by progressively severely retarding the spark in selected
>cylinders.
>
>The result of limiting by spark retard is just prior to launch you have the
>turbo spun up to heavy boost, fuel flowing accordingly, launch rpm set, and
>making virtually no power.  The turbo does not need to spin up - its there
and
>the throttle is WOT.   All dressed up with all the air/fule flow possible
and
>no spark to make it go.
>
>Dropping the rev limiter instantly restores the engine to full power at a
high
>boost  making for a very hard and consistent launch.  The rev limiter then
>resets and behaves in a conventional manner.
>
>Since the boost was already very high at this point, turbo lag on launch
does
>not enter the equation - no way to lag if you are already there and no way
to
>improve when you are there so anti-lag is meaningless for this app.
>
>I don't suspect valve life is much concern vs winning the race.
>
>P.S.  It works.
>
>On Fri, 26 Mar 1999 05:00:02 -0500, you wrote:
>>Date: Thu, 25 Mar 1999 13:25:36 -0500
>>From: "Bruce Plecan" <nacelp at bright.net>
>>Subject: Re: Valve Overlap
>>
>>- -----Original Message-----
>>From: Robert Harris <bob at bobthecomputerguy.com>
>>To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
>>Date: Thursday, March 25, 1999 11:03 AM
>>Subject: Re: Valve Overlap
>>
>>
>><Snip>
>>>Now if you want to spin the turbo up in a hurry, you might consider
>>selective
>>>spark RETARD.  Buick GN's do it all the time.
>>
>>Can I ask where in the program this is incorporated?.
>>>
>>>By momentarily retarding the spark, say to 30 degrees after TDC,
combustion
>>>starts way late and slow and the majority of the charge burns and expands
>>in
>>>the exhaust manifold greatly increasing the volume of gas to spin the
turbo
>>>which greatly increases the inlet charge .....
>>
>>Wouldn't that be kinda hard on the exhaust valve?.
>>Bruce
>>
>
>
>1963 Ford C-600 Prison Bus Conversion "Home"
>1971 Lincoln Continental 460 "Christine"
>1972 "Whale" Mustang awaiting transplant
>1978 Dodge Long Bed Peeek Up "Bundymobile"
>
>Habaneros - not just for breakfast anymore
>