[T3] Lean Cruise

Max Welton max_welton_2k at yahoo.com
Thu Mar 7 21:25:08 PST 2013


--- On Thu, 3/7/13, Jim Adney <jadney at vwtype3.org> wrote:
> There's a lot of interesting information there, Max. Is the
> coolant 
> temp the oil temp? If so, that's pretty high, so where is it
> measured? Or is that the head temp sensor? 

It's actually a GM-style coolant temp sensor positioned 
in the valve-train galley of the left head. It is clearly 
operating beyond its normal range (for radiator coolant),
but I'm only using it to drive the warm-up-enrichment.

http://www.maxwelton2k.net/squareback68/MST3/clt.htm

> Why did you want to minimize the time you spent at stocio?

I believe that area around stochiometric is where the elevated 
CHTs and EGTs gets people in trouble are. This chart, which has 
been kicking around for a while, shows a relationship between
AFRs and EGT, CHT, ICP and HP. Stochio seems like a bad 
place to be so I just step through it quickly.

http://i165.photobucket.com/albums/u45/CDNBullyboy/LM2%20logs/435515.jpg

BTW, while that coolant temp isn't particularly accurate, it 
does show trends nicely. And when in lean-cruise, that reading 
is lower than it is when I run a flat 13.1:1 across the whole map.

> Another thing that has lots to do with economy is the
> advance. The 
> D-jet distributors give extra (10 deg) vac advance under
> your light 
> throttle conditions. That gives 40 deg of advance when
> cruising, 
> which is WAY more than you can tolerate with WOT, but
> perfectly 
> acceptable with light throttle.
> 
> Does your system give you any control over the spark timing?
> If not, 
> what distributor and timing are you using?

I am using the stock type-3 distributor connected to a 
stock type-3 throttle-body. Even though it's a 1776, it 
should be giving a near-stock advance profile. Here in 
the mountains I am running it with a few degrees more
than stock. The engine seems to like it.

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




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