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TR% Air to Fuel Ratio

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hondo402000

hondo402000

Darth Vader
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Well to get every one up to speed, I rebuilt my TR6 engine last year, bored to 2.7 lots of goodies, I have 40DCOE webers on it, and been trying to get the Air to fuel ratio set, and as they say webers are great because they are infinately adjustable and they are bad because they are infinately adjustable. After spending a lot of time adjusting the carbs, which means swaping out jets which isnt cheap, I think I am pretty close, I have an Inovate motorsport AF meter in the car. I have pretty much dialed in the webers, I know modern cars run 14.7 AF ratio which is the best for fuel economy and hard to do with carburators
I have read that 13.1 AF ratio is the best for power.
Now my stats
at Idle I am runing 12.5
crusing at 35 to 45 MPH in town its around 13.4
on the highway at 2700 rpm and 70 MPH its in the 12.5 to 13 range
and believe me I have read up on adjusting webers,and all the circuits that come into play, bought a set of micro drill bits in MM sizes so I can drill the jets out instead of purchasing a ton of jets,(found that on the NET)
one question is any one with an AF meter have any stats on what their AF ratio is and what carbs are you running, it would be nice to see someone running the original Strombergs and what readings they have
I just dont want to wash the cylinders and wear the rings out prematurally, plus I dont want to get too lean and burn a piston up
but since I only have 800 miles on a new engine doubt it will happen soon

I did take it out for a 60 mile drive around charlotte this morning

Hondo
 
Hondo, I have found that through tuning my carbs with the A/F meter on the car and then running to verify on the dyno, that my best results are at 12.5/1 for WOT. Dyno results in 2010 here: https://www.74tr6.com/dynoday2010.htm Note that I have tweaked them slightly leaner since and found this to be better for overall driving and I also have my temperature compensators all working properly for hot weather conditions.

I now have mine at idle running closer to 13.5-13.9 fully warmed up and I can cruise at the 14.1-14.3 range, with a nice tan color on my plugs after a few hundred miles. That is in the hot, muggy weather that we are experiencing now. I use the Zenith dashpot oil in mine, or 3 in 1 oil, which reacts the same way (20W).

All of these cars are a little bit different, so I just gave you his for comparative numbers only. With my cam, tri-carbs, headers, compression and electronic ignition, reworked curve, etc., plus running high test gas, this all works for me.

Don't become a slave to checking plugs after every run. Give the engine another 200-400 miles to fully break in and check your plugs after about 500 miles, but do no more tweaking in the mean time. If you have the nice tan color, even across all plugs, you won't be too rich or too lean overall and that is what you want to achieve.
 
The 14.7 to 1 is the stoichiometeric figure for a gas and air mixture. It is the ideal air to gas mixture for complete burning of such a mixture. To my knowledge this provides best power and least emmisions and that doesn't change. Any more fuel and you will just be dumping unburned fuel (like the chipped WRX's...black smoke out the tail pipe, any less to will run lean and have to deal with all the problems associated with that.
14.7 to 1 is what you should always be aiming for...modern cars use the O2 sensors to adjust the fuel trim, making it easier to get to stoichiometric.
Other types of fuels, like alcohol or methanol, have different stoichiometric values, but gas is 14.7:1.
That is what you should be aiming for.....at least that's what they talk us in school.
I don't think it matters whether it is new, old, British, Japanese, American.....you want a complete burn of fuel to get the most power.

Mikey
 
Mikey, hate to argue with you but Keith is right with that 13 #.
For complete power I think that what you shoot for.
In fact car makers and new engine makers are trying to shoot for the 20's and will soon be there
 
thanks guys, I will keep proding along, think I need leaner Idle jets to start with ,since most of my driving appears to be done on the idle circuit

Hondo
 
I running SUs on a modified engine in my TR3. My O2 sensor shows between 12-13 when I get on it and around 14 when cruising. Unfortunately, it runs rich at idle. For now, I'm going to leave it that way, as I get proper enrichment at WOT. If I set the mixture on the SUs at idle, then I'd be lean at WOT, which is a definite no-no. That's why it's important to see what the numbers on the fly or the dyno so you can set the carbs accordingly.

It's good to see more guys applying some modern technology to these older cars.

There are a bunch of Chris' (MadMarx) videos that show his AFRs while racing his TR4. He has Webers on the car.

Here's a recent one.
 
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]In fact car makers and new engine makers are trying to shoot for the 20's and will soon be there[/QUOTE]

With computer controlled fuel injection/timing and the sensors that watch over temperature, detonation and many other variables,it is possible.

On our cars, it would be holes in pistons.

I finally found a happy compromise between being too rich at idle, versus to rich at WOT and got the too lean scenario under control, but it does take having a a sniffer in the tailpipe, or an on board gauge, which is what I use.
 
Shameless Plug, I have an Innovate Gauge and O2 set up in the classifieds fight now.
I would really like to unload it before I move.
I bought 2 for the Wedge and after learning more on my PI set up I can just plug my computer into that to see what I am running.
Randall got 1 a nd I still have 1 more
 
Don, went to send you a PM about the O2 sensor and gauge, but you're over the limit. Couldn't find it in the classified.
 
Paul, What ever the Innovate uses
Bosch style I would imagine
 
Brosky said:
What size is the sensor thread Don?
Click to expand...
Same as a common spark plug, M14x1.25 I think.

The Innovate kit originally came with a suitable bung, but Don apparently already used them.
 
Thanks Randall. I have a bung in my header already. I was wondering if this would thread inside of it.
 
Brosky said:
I was wondering if this would thread inside of it.
Click to expand...

Most likely it will. Seems like pretty much all of the O2 sensors (and I think EGT too) use the same thread.
 
Randall is correct (Duh!)
But I seem to remember at least 1 funky threaded one.
Could be fuzzy knowledge though
 
well I would pay to use a chassie dyno, but seems I cannot find one thats within the charlotte NC area, anyone know of any?

HOndo
 
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