[Diy_efi] OL operation - How lean at cruise?

[Michael Richards]

As Hugh mentions EGTs are important to watch as running too lean can 
result in burned valves. I see this a lot in the honda world where kids 
swap their heads and continue to use factory computers that are mapped 
for less VE.

I think you will find the main economy gains under cruise will come 
from ignition and not mixture. Without some special features for lean 
running you will be hard pressed to cruise at 16:1 and leaner without 
mis-firing.

On many V8's you run a lot of advance during cruise. I suspect this is 
related to their archaeic head design (insert other V8 digs here). In 
short if you've got a lot of exhaust left in the cylinder you will need 
more degrees in there.

Realistically you need to put the car on the dyno to find MBT for 
cruise but you can try adding 3-4 degrees in the cruise part of you map 
and seeing how much of an economy effect it has. 

I worked on a 302 powered Ranger some years ago. The customer was 
running 16 degrees of advance during cruise and taking about 22l/100km. 
I leaned it out a bit and found MBT to be up in the 40 degree advance 
range. It's been a while but 44 degrees sticks out in my mind. End 
result was 12l/100km. Don't blindly try this but it is an example.

-Michael

>> -----Original Message-----
>> From: diy_efi-bounces at diy-efi.org
>> [mailto:diy_efi-bounces at diy-efi.org]On Behalf Of hugh at sol.co.uk
>> Sent: Thursday, March 31, 2005 2:59 AM
>> To: diy_efi at diy-efi.org
>> Subject: RE: [Diy_efi] OL operation - How lean at cruise?
>> 
>> 
>> I read on here a while back that an AFR of 16 : 1 was the most
>> economical cruise mixture.
>> 
>> I have experimented with 16 : 1 and 17 : 1 without much to choose
>> between on economy.
>> 
>> My Exhaust gas temperature creeps up to 800?C when doing about 90 MPH
>> on the UK motorways at 16 : 1, so tend to run near 15 : 1 at higher
>> cruise speeds.
>> 
>> I have 280? degree duration cams with 10.8mm lift, so probably
>> suffer a bit
>> from overlap making the Exhaust gas temperature high.
>> 
>> Hugh
>> 
>> 
>> Original Message:
>> -----------------
>> From: Daniel R. Nicoson A6intruder at myo-p.com
>> Date: Wed, 30 Mar 2005 10:20:25 -0500
>> To: diy_efi at diy-efi.org
>> Subject: [Diy_efi] OL operation - How lean at cruise?
>> 
>> 
>> I'm back to tuning my 1994 Mustang GT, snow is gone, the daily
>> driver, an "ultimate driving machine" isn't as reliable as this old
>> Mustang (BMW currently apart in my garage awaiting parts).  So I'm
>> driving the Mustang.
>> 
>> I don't have a very good tune going right now, sucking lots of
>> expensive gas
>> ( I drive about 45 miles each day). So I decided to run Open Loop
>> full time
>> and try to run pretty lean at low LOAD levels (no cats to worry
>> about right
>> now).
>> 
>> I'm just curious what others have found to be good AFR for highway
>> cruise and around town.  I plugged in a program last night that
>> commands about AFR=15.5 at these conditions.  Seems to run fairly
>> smooth down the highway.
>> 
>> My combination is a stock bottom end, AFR-165 heads, cam is really
>> just a high lift version of the stocker, nothing really wild.
>> 
>> Thanks,
>> 
>> Dan Nicoson
>> 
>> 
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