[Fot] TR6 race engine with 45DCOE triple Webers

[Marcel Van Mulders]

Duncan wrote :".... how far downstream of the exhaust valves is the Lambda
sensor installed..." : this may well be the culprit. It is installed at
130cm/4ft of the exhaust valves because of the long primaries and
secondaries of the exhaust. The Lambda sensor is part of the dyno. Exposed
on the open air it is reading 22.37 so I suppose it is working correctly. I
can't find any leaks on inlet and exhaust side. The engine is running
sweetly and crispy, so I wonder if  I get a false ARF reading. Can the
distance to the exhaust valves have such an influence on the ARF reading?
In fact, also at lower RPM the ARF is much too lean,  but that can be
corrected by turning out the idle screws way too far (4 complete turns or
more!), so I was misleading you by speaking of "leaning out at the higher
RPM."
Should I install the Lambda sensor in one of the primary or secondary
exhaust pipes (and check the spark plugs if they all get the same mixture
strength)?
Marcel
 

  _____  

Van: Duncan Charlton [mailto:duncan.charlton54 at gmail.com] 
Verzonden: vrijdag 30 december 2016 13:53
Aan: Van Mulders Marcel
CC: Duncan Charlton via Fot
Onderwerp: Re: [Fot] TR6 race engine with 45DCOE triple Webers


How far downstream of the exhaust valves is the Lambda sensor installed, and
how far from the exhaust system outlet is it?  You mentioned having checked
for air leaks, but didn't say whether you checked both intake and exhaust.
Is the dyno operator also using a lambda sensor?

This comment is not specific to the TR6 but since it's leaning out at the
high end I would have initially guessed that your air correction jets are
too large, but one typically expects the AC jet to have a number about 50
higher than the main jet, whereas your AC jets are nearly the same number as
your original main jets and a lot smaller than your second main jets choice.


According to the Weber choke selection chart the 35mm chokes correspond to a
maximum output of 6000 rpm so 36mm seems fine unless the engine's desired
max output is a lot higher than that.

Duncan Charlton
Elgin, Texas USA




On Dec 29, 2016, at 3:45 PM, Van Mulders Marcel via Fot <fot at autox.team.net>
wrote:

The engine for a friend's TR6 racecar is finished at last and it has run a
couple of times now.
I have a problem with the mixture : the air correction jets are 155, I
started with 140 main jets but the mixture was much too lean : AFR was 14 at
idle and 17 at 5000 rpm. Even with 180  main jets, the AFR  is still 15 at
4000 - 5000 rpm. The engine is 2720 cc and 12.6 volumetric CR.
The Webers are secondhand, 45DCOE type 152 and they look as new
The venturis are 36mm, emulsion tubes are F16, idle jets 55F8 and aux.
venturis are 4.5. Pump jets are 40 without a bleed hole. The plugs have a
correct colour, no sooting, no signs of overheating. The engine is on a dyno
but I didn't risk so far to really load the engine, so the plugs doesn't
tell much. The lambda sensor is a wide Bosch sensor, about new and with an
Innovate controller. I suppose 180 main jets are already too big. I can't
find any air leaks and the spark plugs have all the same colour. Is it
possible that 36mm chokes are too big? Any idea's why the mixture can be too
lean, even with 180 main jets? Should I suspect the lambda sensor/Innovate
controller? What venturis should I start with? 
Another question : I have no experience about the range of total ignition
advance a full race TR6 engine does need.
Marcel 
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