[Fot] TR6 race engine with 45DCOE triple Webers

[Duncan Charlton]

There has been discussion on this lately on one of the DCOE tuning discussion groups ("sidedraft_central" Yahoo group) and I learned a couple of things: If the sensor is too close to the exhaust valve, the sensor can overheat, give faulty readings and perhaps damage the sensor, so in that regard, too far away is better than too close.  Most sensors have a heating element to keep them operating properly if they are far enough downstream that the exhaust gases are below the optimum level, so I don’t think distance from the exhaust valve is necessarily wrong.  

The sensor has to be far enough from the outlet that the exhaust gases are not diluted by fresh air cycling back in.  I don’t know what that minimum distance would be but my local dyno operator attaches a copper pipe to his sensor which he then inserts perhaps 18-20 inches into the exhaust pipe.

I assume you already know that the sensor can get out of calibration of you disconnect the sensor from the gauge and then power it up, power it down, and then reconnect the sensor.

Duncan Charlton
Elgin, Texas USA



> On Dec 30, 2016, at 11:25 AM, Marcel Van Mulders <van.mulders.marcel at telenet.be> wrote:
> 
> 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 <mailto: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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