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MG Midget and Sprite Technical - lean needle

The 1275 is not so critical on ignition. I tried 2 curves and they do not make much difference in total HP and torque. There is no pinking. The vacuum curve feels better when I drive in the city. The sound is not so “round” as without vacuum . I use lean GX needles, red springs for the moment. (Temp 160-165F). The car drives a wee little bit faster with richer needles and blue springs that gives a lower water temperature 135-140 F. I prefer driving cheap, more MPH. Is it save or stupid Dutch behavior?

BP 98 RON octane, 1300 cc, I guess about CR 1:11 (15.5 bar warm), double HS2, fast road big valve head, maniflow LCB, piper BP 255.


Flip






Flip Brühl

If you are worrying about MPG you are driving the wrong car :-)

How expensive is an engine rebuild when you have melted things from running too lean? ;-)

I am curious, what is the ignition system?
Malcolm Le Chevalier

Yes Macolm, this is exactly what I want to know. I didn't not melt the other engine a 948 which drove 45 mpg.
It is a 123 ignition, with a usb cable and Windows programmable.

Flip
Flip Brühl

Based on the comments about curves and everything being so steady I'm guessing fully electronic dissy (123?), and possibly programmable.
Nigel Atkins

With the 123 ignition I can change between two curves while driving. So I can compare them while driving.
The program can measure time between certain RPM. So it is not a rolling road but it comes close.
Here is a picture of the spark plug NGK 6 ES after 10 minutes with 80 MPH

Flip


Flip Brühl

Once again someone (Flip) posted whilst I was still typing, but I guessed right (and thought I'd remembered Flip had a 123, and it'd probably be the programmable type).

The whole car, and not just the engine and carbs, properly set up will give better performance which will include improved mpg, but only if the car is driven in a steady manner - and what's the point of that with a sportscar.

Having only the other day seen and felt the noticeable difference between the blue and red springs and noting what's in the SU Tuning Guide about them and previous thread discussion on here I'm surprised you're not sticking with one spring for use with both needles.

For the spark plug, the only thing I think I know(?) is you can't tell too much from colour and you need to snatch them out during the run (at the immediate end of the 10 minutes of 80mph) and they were new and/or clean before the run.

Not that I know anything about this stuff anyway, the only thing I can tell from the photo is that possibly you have oil leaking from your rover cover gasket like mine.
Nigel Atkins

Yes Nigel, you are right but not leaking from the cover. I was not using a funnel... Although I had one at hand.
Flip Brühl

I thought the oil looked very clean, I should have known as I've done the same, but left the funnel in the shed and been too lazy to go and get it but then have to go back to the shed to get something to clear the mess up as much as I can.
Nigel Atkins

I've left a funnel in the filler hole and dropped the bonnet on it.
(LandRover not midget thankfully).
Greybeard

Hi,
I am pretty impressed by the difference of temperature by "just" changing spring and needles...
And 135 F is pretty low, no ? That's 57 C... The engine was warm up ? Oil pressure was the same between the two set up ?

(I am not an expert as others here, just being interested in the discussions/trials :))
CH Hamon

Depends on how accurate the temperature readings are. I'd have thought the warmer the engine within a range the more economical running, mpg.
Nigel Atkins

Nigel, yes - that's why I run 88 degree stats, the hotter the more efficient the engine is.
Chris at Octarine Services

Yes but what is too hot. 88c stat might not be fully open until 95-100c. I tried an 88c stat and just couldn't settle seeing the temp needle higher than usual (having had 5 HGFs before). Not that my previous gauges have shown anywhere near what the stat temp is despite the bulb sitting next to the stat, and my latest gauge shows stat opening before the lower calibration marks (70c).

The one that gets me is oil temp, if you're reading from the sump plug position would you want 90+c, or would the reading be taken from elsewhere.

The only time I had a car with an oil temperature gauge all it done was worry me in winter by reading so low for so long. And now my wife's modern car has the facility (same as Dave's) it worries me how high it is with little ambient warmth and only steady driving but it's addictive to switch to the reading.
Nigel Atkins

My (modern) oil temp reached 105C today. I have no idea what it should be.
Dave O'Neill 2

My Golfs Mk2 and now Mk7 oil seems to run at about 105 degrees when hot on the motorway. My Sprite can hit hit 120-130 on track!
John Payne

Boiling point of the water is raised to 111 degrees C with a 7lb cap, 115 with a 10lb cap and a 30% antifreeze mixture raises it another 5 degrees.

So there is plenty of headroom for an 88 degree stat.

All my cars, including the V8 run with the gauge needle a good bit above the N - around 190 on the old F gauges. Never have a problem of boiling over - even with the V8 in motorway traffic jams in the south of France, though the needle does edge up towards the H!
Chris at Octarine Services

Dave,
I've just checked the 'Operating Instructions' ('Owner's Manual' is for the 'Infotainment systems') and it has normal running oil temp 80-110C.
Nigel Atkins

Flip,

I would run an 88°C thermostat and leaner needles if you are looking for economy. Modern engines run hotter (and leaner) to promote more complete combustion. This translates into better fuel economy, lower emissions and better performance.
Glenn Mallory

I tried both ignition curves. The one with vacuum gives some backfire when cold in combination with a lean needle so I changed to the M needle: no backfire anymore. The water temperature is lower as well now. (measure point top right in the radiator. I do have a 88 degree stat.

Here is an interesting graphic from an airplane engine about temperature and mix. EGT (exhaust gas temperature)



sorry that I did answer late but I could started with golf and rowing again after 2 months.

Flip


Flip Brühl

Wow - this is a deep subject and not my area of expertise really but I've picked up a bit of knowledge over the years. First of all the chemically correct air/fuel ratio is 14.5:1 (stoichiometric). Modern engines with high activity ports and combustion chambers could operate beyond 20:1 with stable combustion, however the requirement to keep the catalysts lit off restricts this. At the top end and when extracting loads of power exhaust gas temperatures become a problem, above 950 C engine out temps things start to melt (exhaust valves, seats, pistons, turbines) so in effect petrol cooling is employed. Some manufactures get close to 10:1 AFR and most use some full load enrichment.
I agree with what Chris has said about water temperature, no bulk boiling until beyond 120 C with pressure cap and antifreeze.
On oil temperatures, its common for test bed durability tests to be carried out at a gallery temperature of 140 C. Its desirable to get the oil temperature to about 110 C to lower viscosity and aid fuel economy.
Paul Hollingworth

Ideally oil temps should exceed 100 degrees C so that water produced in the combustion process is boiled off.
Chris at Octarine Services

Nice and interesting graph... Can't deny it took me 10minutes to understand it !

It is interesting to see where you land if you make a 20% error in your mixture set up out of the stoichiometric setting:
> 20% too lean, you are down to 0.055, which is 80% of the engine perf, for 10% more MPG
> 20% too rich, you are up to 0.082, which is...100% of the engine perf! For 10% less MPG

Where you have the "best economy" is a very tight place to be... Low consumption for not a lot of horsepower lost is a specific setting. To me, it looks like a lot of "risks" for a small win in consumption... And I would assume this is on an engine warm-up, so doesn't take into consideration when it is cold and warming up...

I would also say that being able to measure exhaust temperature looks like a great help to find this "economical" setting !

On my modern, 10% of fuel economy would be a great benefit ! On my Midget...not really :P But each to their own !

Looking forward to other comments :) Interesting topic :)
CH Hamon

Couple of points here-
That Fuel/air V Baro ratio catches me every time but that's ok--I just wish we could stick to the common A/F ratio scale
These engines seem to like just a tad richer mixture than non siamese ported engines
Normally best economy is around 15.5:1 and best power 12.5:1 but these engines won't run efficiently/smoothly at 15.5:1 cruising and need to be closer to 15 to get them smooth and the same on full load 12.5 is ok but if it's going to be on full power for extended usage (racing) they need to be closer to 12:1
All this goes out the window if there's any alcohol (ethanol) in the fuel
Stoich for normal petrol is 14.7:1
Stoich for 100% alcohol is 6.4:1 and full power at around 5.5-5:1

Paul mentioned around 10:1 full load mixtures from some manufacturers, That would be the correct ratio for something like 80% alcohol so a safe figure to cover for todays fuels--Most ECU's now, can sense the fuel being used through their knock sensors and adjust mixture and ign. timing to suit

The v8 supercars here and a lot of guys running big boost turbo engines are running E85 fuel which some retail fuel outlets here sell from the bouser
The A/F ratio for full throttle with this fuel is
9.7:1 and alcohol being a very forgiving fuel on the richer end of the scale allows the turbo guys to tip a bit extra in to keep things cool so probably closer to 9:1 for them

Flip
I thought your spakplug colour looked ok ,a tiddle on the lean side but 10 mins at 80mph wouldn't be absolute full throttle so not a 100% acurate reading---At full throttle it might go either way but for a high speed cruise mixture I thought it was close
You had what you refered to as lean GX needles and swapped out to "M" which are leaner still
Be carefull it must be getting borderline lean
willy
William Revit

SORRY Flip
I read my chart backwards-
The M needles are in fact a tiddle richer than GX
So all good
sorry for any confusion
willy
William Revit

This thread was discussed between 11/05/2020 and 16/05/2020

MG Midget and Sprite Technical index

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