[T3] Lean Cruise

[Keith Park]

Well Im all ears when it comes to better MPG, not so much with the stock
engine but the 2056 gets only 21-22 on the highway and that’s with Premium,
which can be 50 cents higher than regular in the Northeast.  This may be a
showstopper when it comes to putting this engine in the Square when its time
comes... I do so much highway mileage in that car that MPG is important.

Jake Raby says that this is the mileage I should get, and he set up this
engine... but Ive heard him claim much better mileage with similar sized
engines in other builds... maybe they are geared drastically different but I
cant see it making THAT much difference.  Im going to go with the late E
type version of the Djet if I go at this once more... 

Keith


Top Notch Restorations
topnotch at nycap.rr.com 
http://www.a383ina68.addr.com/radiorest/main.htm
71 Squareback "Hothe"
65 Notchback "El Baja Rojo"
65 Squareback "Eggcrate"
87 golf "Winterat"
93 RX7 "Redstur"


-----Original Message-----
From: type3-vwtype3.org-bounces at lists.vwtype3.org
[mailto:type3-vwtype3.org-bounces at lists.vwtype3.org] On Behalf Of Max Welton
Sent: Saturday, March 09, 2013 12:25 AM
To: type3 at vwtype3.org
Subject: Re: [T3] Lean Cruise

The engineer in me needs to explain this. Then I promise to 
leave it be. ;-)

--- On Fri, 3/8/13, Keith Park <topnotch at nycap.rr.com> wrote:

> Well, the D jet can apply a super
> lean condition to light throttle if you
> get the inner stop on the pressure sensor adjusted wrong,
> and I guess this
> has lunched engines in the past.  Im not sure exactly
> how this would compare
> with your profile, but its something to be careful about...
> you don't want
> to hear any knocking and pinging and on a square anyway, its
> REAL easy to
> hear that if its occurring with the engine lid off.

Sure. Makes the cabin smell bad though. ;-)

> Just keep an eye on the oil temp and more importantly the
> head temps.  You
> may be able to get away with things at altitude that we cant
> at sea level.

See, that's the thing. At sea level, as you pointed out, 
aero drag goes up. As I counter with more power, MAP goes up.
If it exceeds 65 kPa, my AFR goes back to the low 13s. 
I might not see the mpg I get at altitude, but the engine 
will be safe.

Now, that 65 kPa will occur at a smaller throttle position 
at sea level because ambient pressure is greater. The
reason throttle position is important here is that it 
effects the vacuum advance signal. The amount of ignition
advance appears to have an effect on measured AFR independent 
of the amount of fuel being supplied.

BTW, that 65 kPa threshold I'm using was arrived at 
experimentally by sifting through hundreds of hours 
of driving data logged through the ECU on a laptop 
riding in the passenger seat. It turns out that 
the coolant sensor mounted in the head reacts fast 
enough to allow me to tell when I'm moving things 
in the wrong direction.

> One thing I CAN say, some of the D jet "experts" get it
> wrong sometimes and
> Have gaps in their knowledge as well.
> 
> Keith

They aren't the only ones (cough). 

OK, I'm done.

Max Welton
http://www.maxwelton2k.net/

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