Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - Exhaust Gas analyzers for Su needle tuning

Can any one point me to a website selling the in-cab LED exhaust analyzers that allow you to see how your SU performs at all needle stations while driving the car? I believe they couple up to a drilled sensor in the exhaust manifold and have been told they available for around $100 US. Any comments on their effectiveness or on the effectiveness of the gunson exhaust analyzers which I don't believe you can use when the car is moving?
K Bannister

Moss sells a wide band sensor that seemed pretty reasonable to me. I'd like to have one in my TF
LaVerne Downey

....why, when I was a lad, you just put your nose to the exhaust....cough, cough, hack, cough....pipe...None of these new fangled LED things for these cars....!!!!

Are you talking about something like this (not LED):

Requires the manifold probes of course.

Gene Gillam

I've installed an Actron 2" Chrome Electrical Air Fuel Ratio Gauge Sunpro CP8200 on our '50 TD. It'll be another month or so before firing up and running, though, so no experience on its behavior, but only expect ballpark indications, not precise readings. Since just adding a Marshall blower and have no confidence the 1 1/4" SU is set appropriately, this should add to the fun. Also picked up a realy cheap single wire O2 sensor off ebay and for the fitting I chose an "oxygen sensor extender." I took a piece of copper pipe and used it on the electric discharge machine to cut a perfect curve on this long fitting, on a skew angle and welded it onto the exhaust pipe about an inch down from the exhaust manifold. I wanted it on a skew angle so it is almost hidden from view and it is off to the side inside the pipe, rather than projecting directly into the middle. Have I lost everyone now? Could've drilled/tapped exhaust maniflod, but worried it could be thinner than I'd like, it will heat up faster on the thin stainless tube and more importantly, read all 4 cylinders more evenly. I also positioned the "choke"/"enrichener" cable right next to the meter so I can tweak the ratio while riding (wife is driver 99% of the time). Something for me to play with.

I've also picked up a "Nocklite" to watch for any hint of preignition. I will know pretty precisely how much advanced it can live with. Ths is a really nifty toy with a built in RISC processor! Something else to program and play with!
Jim Northrup

KB - Narrow band sensors like Jim N is using only give you a correct readout when the mixture crosses stoichiometric, not a lot of good if you are very far off. It can help, if you know how to interpret it. Wide band systems give real data. There is a very informative Aussie website on wide band systems, google "DIY wide band AFR". They supply kits and complete units last I checked, and there are now many suppliers with different WB systems. These were around $500 last I looked, but falling all the time - a few years ago the sensor alone cost that much.

Gene's link is for exhaust gas temperature readout. The full Aussie system has provision to add that to the unit, along with anything up to full engine management.

Jim - That extender thingie is one of the better scams I've met! I got leetle pills that give you 28% gas mileage and 72 more hp! At least it is a good source of bungs, which have been exorbitant, and I think that's how you used it. You really want the sensor in midstream though, since gas flow along the pipe walls is not necessarily a good representation of the overall situation.

"Knocklight" is an expensive way to get the info you need for tuning, and the price would have half paid for the Aussie WB system, which can also deal with detonation sensors.

Fletcher R Millmore

Rather than sensors, analysers, etc.... take your car on the road for a few miles, pull to the side of the road, look at your 4 spark plugs, make ajustments to the richness of fuel, go back to the road for another couple of miles, pull to the side and repeat this procedure until you get the right color on the spark plugs and you will have your car properly set. I do not believe on sensors, etc... just what the spark plugs tell you is the real thing.
Jose Vicente Vargas

You're correct on all points, but I'll explain the methods in my madness for all practical purposes.
Wide band was too expensive and way to much development time just for wifey's TD. My Actron air/fuel ratio package was less than $50 including a cheap sensor and that extender. I selected the Actron because it is part of a set of 6 new matching gauges I wanted that are now crammed into the instrument cluster.
That "extender thingie" is a joke, but it was the long fitting I was after. It provided enough meat for what might be described as a 45 degree fishmouth. Could've used typical 18mm "halfcouppling" but then it would stick straight in and others would point out what a nasty obstruction it is. The sensor is now mounted behind the pipe pretty much out of sight and the sensor is still very well exposed to the stream for steadystate readings. Should be intereseting playing with the "enrichener" cable while cruising!

The "knocklite" itself was barely $100 and coincidently, comes from Australia. Scored a kncok sensor off ebay for less than $3 (under $10 with shipping). It is quite attractive looking and will be a lot of fun, considering you program it to sample noise at idle, half and full throttle and then set sensitivity to suit. Also, it has a "shift light" you program for whatever rpm. I want to set it somewhere around 4 grand in hopes to coax my wife to shift sooner. Right now, she absolutely buries the tach past 6 grand before shifting! There's no convincing her to shift sooner. That's one of the reasons I'm going with a 1 1/4" SU on the blower, to cut down top end power!

These are great conversation pieces, like so many parts of this old supercharged MG. Can't wait to get it on the road to experiment with the gadgets!
Jim Northrup

Jim -
I looked up Knocklite and found like $200. Good you got it for less, certainly beats buying pistons. The real hotrod spirit seems to be alive and really well down under!

Cheap AFR, OK as an in dash monitor = $100
Real AFR that protects your engine and could be set up as a test instrument and be moved to other cars = $600
TD engine = Mucho dinero.
Rev limiter (can be part of Aussie WB) = Mucho lesso dinero
Wife that shifts at 6000 = priceless!
Do you have a spare of the last item?

Fletcher R Millmore

Images of 6 Actron instruments...
Air/fuel ratio meter lower right, enrichener cable just above. Boost gauge above them. Cigaret lighter socket bottom middle. White background on gauges seemed easier reading, but black background would've matched air/fuel meter better.
...maybe next time I'll look to see if it is in focus.

Jim Northrup

Oxygen sensor...image
darn, hit the wrong button, no image.
Jim Northrup

o2 sensor image, inconspicuous.

Jim Northrup

O2sensor up close...

Jim Northrup

While I appreciate that some people love gadgets, and must have them, that "THING" on the TD dash, just bogled my mind. The question I ask is, why is all that information needed for the operation and enjoyment of a "T" series MG. Having an early model TD, I did not have a water temperature guage, and went for many years without one. Not having one to look at, did not seem to be any problem, even when racing, or during other forms of competition. I find that after installing one, I am looking at it as much as the tachometer. I some times wonder if it runs better, or if I'm have more fun because of that temperature guage. If I removed it, there would be one less distraction from the joy of driving it.

George Raham
George Raham

Wow! I guess these diagnostic goodies can get quite involved! What set me on my quest, was an article I came across by Fed Sisson, as an adendum to the 1998 Morgan Driver's Bedside Reader 2/3/98 which read :

"As far as I am concerned, the ONLY way to tune SU carburetors is with an on-board exhaust analyzer ($100 bucks). This way, you can check your car while you are driving it, on your roads (or track). Anything else is groping in the dark.

Many companies make exhaust analyzers today. They run somewhere around $100.00. They use an O2 sensor that fits into your exhaust system and are described in the book. Racer Wholesale (listed in “Source” section or the Bedside Reader) now offers an analyzer that will read two sensors. This is the hot setup for twin carbs as you can exactly balance the carbs.

The analyzer itself is a ‘bitty thing. Mine is about 1 ˝”X2”. It has a series of LEDs that instantly read the fuel/air ratio - as you drive! Real world stuff here.....

I doubt that any standard carburetor will give the absolute perfect ratio at all times. However, you can get darn close and the reward for your time and effort might just be a very dramatic improvement in performance. At the very least, you will have peace-of-mind, knowing that your engine is not being hurt from the effects of a drastically rich or lean mixture

Many of the hot sports racers have the analyzer permanently mounted in their car. They "tune for the course". Exhaust analyzers are available as in-dash instruments also. I personally use the analyzer with the temporary mount as the in-dash units are a bit out of place in a vintage car.

There is also a choice of O2 sensors. I have been using the cheap kind which runs around $30.00. The 70 buck O2 sensor is better as it is electrically heated and comes to the initial readings quicker, but the cheapy works fine once it gets hot. I tape the gage to the windscreen with “racer tape” so that I can see it at all times while driving/testing. It reacts instantly so you can even use it to set the powervalve for a Holley carb. Pretty neat. When I am done - remove the gage and O2 sensor. There is a blank plug that screws into the sensor hole"

On my internet searches I have revealed little of these elusive $100 LED marvels. However, that Gunsen unit appears all over the place but I have read little of how it works or how good it is. Has anyone any insight on the value of this unit?
K Bannister

This thread was discussed between 19/03/2010 and 22/03/2010

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.