retro fit injection

Its possible to install an injector set, however its not really financially viable , it would require rather extensive re machining of the engine, if memory serves me the cars were positive earth not negative earth systems , so you would need to modify the electrics replace the distributer too , probably up rate all the electrical systems, too

I would get the SUs rebuilt, (or do it myself), for a lot less effort, for something where there is no advice available if it doesn't work. Some things are best left alone.

Yes, there's plenty of systems out there - from the very expensive and professional-installation setups through to cheap DIYer-friendly systems like Megasquirt.

You could use the old SUs as the throttle bodies, but it'd probably make more sense to use something off an injected engine.

Knock sensing and managed ignition won't resolve valve seat recession, of course - you'd still want to fit harder seats.

Alternatively, just see what happens with the valve seats. If they recede, you need to fit harder seats. How do you prevent the recession? Fit harder seats... It's the approach I'm taking with my '80 Landy.

No, it wouldn't. Just fit injector bosses to the manifold, and a trigger wheel to the crank.

They were -ve earth after the late '60s, but changing +ve to -ve isn't a huge job.

This sounds sensible to me. SUs are simple and proven, just rebuild them and get them set up properly.

The idea was to retain some of the original look but end up with better economy, I parked it up 10 years back because the 18mpg didn't compare well with the 70mpg I get from the 206 diesel with much the same performance. It does have a bit of sentimental value and little monetary value.

I still have some additive for that and no noticeable recession as it has not been driven hard. Knock sensing was a wish for being able to keep enough advance under low power on unleaded.

Maybe some time once the problem occurs. I also have a not so old landrover to deal with but that has the V8 and only 8mpg.

This is a 1972 with alternator so -ve earth from new.

AJH

Yes I suppose a decent tuner could get better performance out of the SUs, the car starts and runs fine just a bit too juicy for everyday use.

AJH

I once had a Fiat Croma CHT 1987. The relevance is that this was a last stab by Fiat for carburator with economy. This car had a class winning

51mpg official for a 2Lpetrol, so it can be done. The engine produced a modest 90bhp, but more torque than 120bhp the fuel injected cousin.

You'd probably be best to either have your head converted or look for a used one that already has been.

MegaSquirt is probably the most common aftermarket injection system for DIY fitment, as it was designed with DIY in mind, and all the info you could possibly need is out there and free. But since it is a complicated subject, it will be a steep learning curve.

Lots have fitted MS to both the A and B series engine, which are similar in principle - the main 'problem' being the siamese inlet ports. But MS does have a setting for these.

Usual way it to use later throttle bodies rather than mess around converting SUs.

The obvious way to save re-inventing the wheel would be to ask on an MGB group, and get details from one who has already done it.

No real need for knock sensing on a road engine - but proper mapping of the advance curve will bring very real benefits. The original factory curve was limited by the mechanical mechanism and was never that accurate anyway.

There is a very good MS forum.

I've been running an MS on my Rover SD1 for many years, and am delighted with it.

How was that 18mpg achieved? If on a few short runs to the shops, possibly. But when cruising, it should better 30 mpg.

It will cost hundreds of pounds to convert to injection and add pretty well no value to the car. It might be slightly more economical than the carbs engine in perfect condition, but will take a long time and a lot of miles to save money overall.

SU carbs ain't that difficult or expensive to overhaul. Same with the dizzy. I'd first get the engine into a decent state before deciding on going down the injection route.

Official fuel consumption figures are just that. They have little relation to the MPG the average driver gets.

True, but since it's "official", it means that a standardised test has been used. It may be still used as comparative yardstick between different cars.

Of course I never got 51mpg, but it was nevertheless quite good. The CHT system used high swirl, getting a good mixing of air and fuel.

Not even sure about that. It's only really of some use if those using it to compare understand the likely differences. Which the majority plainly don't.

It's quite interesting to log all the fuel you buy against mileage and work out the true overall consumption in normal motoring. Most would be - to say the least - very surprised.

I log all the mileages from the firm's fuel cards and managers swear blind the cars consumption from the computer is correct when the calculated figure is 5mpg worse.

Even my little 206 van which does 70mpg (@283k miles) is better than an identical but younger one on the fleet by as much as 10mpg.

AJH

It was short runs, unfortunately I never logged fuel consumption when new, we stopped using it as our main car in 1983 and as I said laid it up 10 years ago.

OK I was expecting a big increase in economy, if your experience shows little I may shelve the idea.

I can still just about remember how to fiddle with the SUs and can easily change the distributor to electronic, I need to move it as the property where it is garaged is on the market so I'll bring it home via an MOT appointment.

Thanks for your input.

AJH

Changing from points to electronic may make it stay in tune for longer - but won't make any difference to the MPG when in good condition.

Dave Plowman (News) wrote: [snip]

Corsa 1.3 litre petrol Nov 2003 (new) to Feb 2005 12878 miles 44.2 mpg Still have this - might enter more figures when I'm really bored ...

Avensis 2 litre petrol Jan to September 2009 13431 miles 43 mpg Ran this to Nov 2012 so more figures available ...

Vectra 2 litre diesel Nov 2012 to Jan 2014 20494 miles 56.5 mpg Ran this until July 2015 - more figures sooon

Skoda 2 litre diesel July 2014 to now 1141 miles 55.8 mpg

What type of driving - city, motorway etc?

My 2008 Mini Cooper S (with stop/start) used to manage 37, almost regardless. My current 2010 Civic Type R 25mpg around town and fast A/B roads, 39 on a motorway run. I'm not a light footed driver.

Rural, and long trips on A roads and motorways. The Corsa does fewer long motorway trips. I'm a fairly gentle driver.

Local city once per month on average.

London once per year.

You won't achieve better fuel economy. It would cost more in dyno mapping time than you could possible save.

The single biggest improvement in fuel economy for SI engines has been the introduction of direct injection. This has allowed very lean mixtures to be used at part load. There are no direct injection after market systems as it requires a redesign of the cylinder head and piston.

The only other route to lean mixture for SI engines is "lean of peak", used in long range piston aircraft of the 1940/50's. That requires individual exhaust gas temp sensors, aircraft had a flight engineer to monitor temp and set mixture. There is no current control system that uses this as use was effectively banned by the European Lambda / CAT laws of the early 90's so development stopped.

Knock sensor doesn't give economy. It detects detonation. If it dets you have either too much advance, too aggressive advance curve or low octane fuel. OEM use knock to detect fuel grade and can change map to give more power by running more advance (and/or boost on turbo) if higher octane fuel is used. More power means more fuel is used and worse economy.

Where are you going to "map" this injection system? That will dictate what system you use. If you insist on using a system your tuner/mapper/rolling road is unfamiliar with then you will be paying them to learn how to use the software.

Rip the B series boat anchor out. Go buy a 200bhp Nissan SR20DET including gearbox from a 200SX S14 (the BL box won't take 200bhp), throw in the engine bay. Then splice the whole Nissan engine loom including the NATS security key sensor into the car.

I know they fit, there's more than 1.