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MG Midget and Sprite Technical - Sprite/Midget 1275 Turbo discussion

I have just joined this group after reading a recent discussion on someone wishing to Turbo their Sprite/midget 1275 motor. I have successfully done this to my car here in Australia and have gone fairly high tech because it was the best way to go. Hence, no carby through a turbo, fuel injection, higher comp ratios than old thinking and I am running 17 lb boost regularly in a very tractable and quite quiet road registered car that is very fast on Track days. I thought that my experience might be helpful to others contemplating going down this road. Please see details therefore at the blog below (just click)http://pulse.yahoo.com/_HV2XWHQ5H4OIN2T7VUJCE4SW7Q regards Bruce


Bruce Roberts

Hi Bruce,interested to see another turbo car on the strip,especially with all the electronics.What time did you run?
steve cowling

looks like an impressive build, welcome to the forum!
Alexander Sorby Wigstrom

That's a fantastic car!

With an engine like that, with those sticky tyres you could have a big accident. if it was my car, the next thing i would buy would be a roll bar, high back seat and harness!

d cusworth

Now this
http://pulse.yahoo.com/_HV2XWHQ5H4OIN2T7VUJCE4SW7Q/album/photos/125464
Realy sparks my intrest!!!

As far as i can see and understand it is a crank angle sensor that fit's the distributor hole?!?
Where did you get it and is it compatable with most aftermarket ecu's that normaly use a 36-1 tooth trigger wheel?
Onno Könemann

Onno, I missed that. Looks nice!
d cusworth

yep and if it does what i think it does it would mean that you can make a bolt on EFI pack for our A-series.
Would save me a lot of hassle as I have very limited space in front of the crank balancer to fit a trigger wheel
Onno Könemann

I fitted a trigger wheel from a ford sierra 2ltr twincam from about 1993. it was pressed on the the front pulley. it's outer diameter is exactly the same as a 1275 pulley, so I turned the inner face of my pulley down, and now its a flush fit!
d cusworth

thanks for all the comments and interest. Let me add a few thoughts,

To D Cusworth, I appreciate your observations. Yes I do run sticky tyres on track days and they are great in terms of lap times. The car is faster on the circuit than gaggles of Lotus 7's, light-weight E-Type, Lotus Elite, hot Escorts etc. These tyres in no small way help the car achieve that! I agree that the roll over bar is important (even though I had none in my rare motor cycle comp days or when flying aerobatics!!!) but I now have one since that photo. ...I am seat-belted of course and again I agree that I could go better there.

Onno Könemann and D Cusworth on the Crank Angle Sensor:- Yes this fits into the usual distributor take-off position. The 'case' is from a Magna sedan about a 2000 model, slightly shortened in the shank if I remember correctly. I found a number of dizzy experts that could do the mod and they rebuild the internals to make it into a crank angle sensor. Advice; dont go optical, that is old technology now and has problems. This is built on the very latest "Hall Sensor" technology, sends the info to my Microtech after-market computer, (there are lots of differnt brands that would do) which in turn sends signals to the Microtech 'exciter' module, then down to the four individual coils. I shall try putting a photo up of the CAS in position with this thread
Bruce




Bruce Roberts

Very nice! I have gone for a suck through supercharger setup on my Midget build, which can be seen in the Supercharging section of the forum and hopefully will be completed in the next few weeks. I have another car in the build with a turbo and aftermarket injection setup (a rotary Mazda) and so decided to try something different for me and more traditional with the MG. I am shooting for decent boost figures though (~15-16psi), with water injection to cool the intake charge and keep detonation under control.

I am also looking at a highish compression ratio for forced induction at probably around the 9.5:1 mark, but am impressed that you are using as high as 10.5:1 at your boost level. I guess that with the computer controlled spark and fuel you are able to push things closer to their limits more safely.

I have a few questions if you don't mind me asking: How many kms have you put on the car since the conversion? Have you had any problems, perhaps with other components not coping with the power? Do you perhaps have you any power figures and/or 1/4 mile times to share?

There is another person here in Sydney who is also building a supercharged setup, but blow through using fuel injection and an intercooler as yours is, with the addition of a crossflow head as well.
AndrewF

Hi Andrew,

I have been operating the car for a couple of years now but am unsure of the ks. Not high, probaly a couple of thousand at a guess.

Fundamentally no real problems engine wise, though I once popped a head gasket which I quickly replaced. That was in the early stages of tuning. I have experimented greatly with varying computer mapping and turbo tuning and continue to do so. I have come to believe that this little four cylinder "A"series is very very strong. I'm using standard rockers and standard crank BUT have bridged the centre main so that a max of only one thou whip can occur. I converted my head to eleven bolt. Outside the engine, axels (or axles), diff and drive shaft have been beefed up due axels and diff failing. Gearbox has been fine but I do drive carefully even at the drags though diff and axels suffered didn't they. Best time with my inexperience in this type of event has been a consistent 14.8 ( about same as the earlier WRX and current ss Holden and a fraction faster than the -12 E-Type could do when it was new). I know I'll get that down a bit more with some improvements to the car and my driving!).

As my Blog said, modern thinking uses higher compression in boosted cars, (they perform much more acceptably when off boost) and modern computer control means that all the factors are very precisely managed... input from the various sensors is processed six times a second in my car! That type of precision requires FUEL INJECTION AND SPARK managed by the computer along with the other components.

I use water injection too but call on it only rarely. I deliver it, like the WRX, to the intercooler (though theirs is automatic to the intercooler during boost) and mine can also deliver to the radiator core.

That chap in Sydney with a cross flow head will do well if he gets the boost tuning just right.

I'm happy to share my experience cause I'd love to see more Sprites with genuine Sprite motors going this way. I'm anxious to see your car's details and will go looking for it on this forum as soon as I've sent this off

Cheers

Bruce





Bruce Roberts

Very interesting stuff Bruce,

My car uses water injection directly into the inlet tract before the blower - i.e. the engine actually swallows a small amount of water with the intake charge. It is not uncommon for this to be used on street fuelled suck-through supercharged cars (like mine, where an intercooler cannot be used) and is also often used in turbocharged rotarys where detonation will kill an engine far more quickly than in most piston motors. It's something that was used in WW2 planes among other things, and acts a bit differently than a water spray on the intercooler as the water also acts as a detonation suppressant in the cylinder after helping to cool the intake charge.

A 14s pass is very respectable for a Sprite, though I too think you should go a bit quicker if you get some grip and a good pass. What tyres are you running? What upgrades have you done to the diff and axles? I have installed a 5 speed Toyota box in my car and am fitting a 7.5" clutch, but I haven't yet done any upgrades to the rear for the extra power. I will want a limited slip centre for motorkhanas, but have not yet decided which way to go and what to do for axles - whether to buy uprated ones or to just try machining the standard ones to eliminate the weak point on the inner splines.

Interested to hear back from you,

Andrew.
AndrewF

Andrew, I checked your posts on your car. Looks like a very interesting project. Colin Dodds has a S/charger set up on one of his Sprites but I'm not sure of the details. Have you seen that one? One of our Qld Sprite Club members has one for his amazingly immaculate Mk4. Interestingly there is a nice a high tech one advertised for Sprites in Melbourne but I'd have to check details when I get home. (I'm being a grandfather at the moment, helping out a very sick grand-daughter in Sydney)

But to go to your question, I now run an RX2 L/S diff (it ran numerous low 11's so it can certainly take the heat!)with RX2 axels which are so much beefier than original Sprite stuff. And for good measure I use the Mazda drive shaft as well. There is info I think on this in the blog site I quoted in my first post.

But I was interested in your comments about being involved with Rotaries and the Rotary drag scene. I love them and have had a lot to do with them through my kids who have been very involved. What rotaries did you have and what times were you getting?
Bruce Roberts

Bruce,

it's good to know you are embarrassing some expensive machinery!
d cusworth

An Rx2 diff, interesting! I have heard of a few people using a narrowed rx7 rear end in Sprites Misgets which are the same basic thing. I assume it required narrowing for use in the Sprite? And you redrilled it for Sprite stud pattern? I don't see any information on this on the website you provided, but I'm probably being blind!

Colin has helped me a lot with my setup, has provided the specs for the engine and will assemble it for me as I am running very short on time to get the car back together for my wedding using wedding cars tonbridge on the 6th of March! It is at his workshop that I was having a conversation about the supercharged setup I referred to above, and Colin has built and worked on engines for a number of supercharged setups, including a Moss setup on one of his own cars. If you are referring to the Hi-Flow setup, he has built a few of these and power has been a bit disappointing compared to a built n/a engine as the blower is on the small side and is working too hard to provide decent levels of boost.

As for my involvement with rotarys, I previously had a 12a extend port powered 323, and for the past few years I have had a 12a bridgeport turbo 323 in the build. It has been put on hold the past ~12 months as I have done the Midget, but will get some attention again soon. It runs on straight lpg, using an lpg injection setup with an aftermarket computer (Profire) that also controls spark. It has a hilux diff with series 5 rx7 brakes, and the entire front steering/suspension/crossmember/brakes also from a series 5 rx7 fitted. The front wheels are set further forward than standard and the engine set further to the rear than it does with standard rx3 mounts, so the engine is entirely behind the centreline of the front wheels. Shortened series 4 turbo rx7 gearbox, brass button clutch, water injection, bridgeported, doweled (before I got the motor), and with a 6mm thick plate between sump and block for extra rigidity. It is a genuine 12at block but has been fitted with n/a 12a rotors for their higher compression ratio, I have a small T04 for it and am shooting for ~400rwhp. It actually doesn't require a lot of work for completion - a gearbox mount, exhaust, driveshaft, modification to the steering rack, finish off some bodywork (mostly the flares required front and rear) and then paint it and put it back together. It has not seen a workshop for anything, and the aim is to get it together and on the road without any outside work barring a driveshaft and brake lines. I can't wait to get it on the road to go and hit some track days and a Wednesday night at WSID! I have more interest in circuit stuff than drags, but still enjoy going to WSID and enjoying the machinery there and will definitely take the car for a run when it is complete. I have also been helping my best mate put together a Series 5 rx7 track car on a tight budget over the past couple of years - it is now nearing completion and we are looking forward to seeing what it will do.

I am sorry to hear about your grand-daughter, I hope her health improves soon.

Cheers,

Andrew.
AndrewF

Hi D Cusworth...Is it Dave or Don or Doug or what???

I just found a site that shows some of the other machinery I was talking about though I haven't tried it against the Maserati in the first shot!! See:- http://www.catchfencephotos.net/viewtopic.php?f=8&t=2595 I don't run against the faster open wheelers though have been faster than some of the slower ones.

Hi Andrew What a great project. Best of luck with it. I really love the power of the Rotaries and as long as I am away from a heavy population, I love the bridge port sound! Too much attention in dense population areas. I have driven just about every kind of Rotar you can and enjoy them all (right through to the beautiful 20B Cosmo my youngest son used to own). I fully recognise however that it doesn't matter what you do to a Sprite motor it will never end up with the absoliute brute power of a competition Rotary. Look at what the Pac Performance cars are doing... and the South Americans.

Congratulations on the wedding coming up, I hope you will have permission to keep working on your cars. I'd love to hear your time when the Bridgeport runs at Eastern Creek.

By the way, if you look at the shots in my blog there is a recognisable RX2 rear Fluted Brake drum (the non-Rotary Capella did not have these nor did any other car). I had my RX2 diff cut down to correct width and the actual Sprite bracketry jigged onto it. Photos of the diff show its near size to the Sprite but its re-enforcing moulding is different and it is 10kg heavier. Axels (diferent right and left lengths)were appropriately splined and hub plates were modified to fit the Sprite (old holes welded over, new studs, patterned correctly . Currumbin Diffs (just over the border in Qld) did a great job for about $1,000 cheaper than most Sydney specialists charge. By the way, I bought my car from Colin, it was his Chook Shed car!(See Blog)

Thanx for the thoughts on our little Evie, she is just over two weeks old and having a bit of a battle in life. Seems she is winning so that's good. She is our eighth grand child. Comes from being an old bloke!

Best of luck to your Mate with his Series 5 too.

Cheers

Bruce

Bruce Roberts

Bruce - It's Danny! some good photo's That Morgan was trying hard to clip the apex!
d cusworth

Nice work mate.

I too am impressed with the dissy sensor. I have programable ignition with a machined front pully and sensor mounted to it. I think it would have been pretty easy to make a dissy spindle with a number of holes in it. But just wondering if the accuracy would be adequate? obviously is.
Robert (Bob) Midget Turbo

Now here is me thinking
Could you use a normal conversion kit for a distributor to pull the signal from?

You would have to set TDC for nr 1 and then see how many triggers you get for 360 degrees of crank rotation.
And see if you can get the ECU to understand this

Other wise indeed make a small 36-1 wheel in side the housing.
But how to compensate for the dist going at 1/2 engine speed......
Onno Könemann

I think that is the problem Onno although I suspect you could progam the ignition module to time itself at every SECOND blank! :)
Robert (Bob) Midget Turbo

The megasquirt system is capable of using a distributor trigger, but clearly it is not as accurate as a crank wheel sensor.
Trevor Jessie

Onno,

I think you would need a 72 - 2 trigger, 2 36-1 in succession, wheel in the dizzy housing to use it instead of a 36-1 crank fitted trigger wheel. I would be interested to know how much mechanical jitter in introduced in the system compared to the crank trigger and whether its important.

Years ago I was wondering about making a mapped ignition and had some trigger pockets milled into the front face of the flywheel and a sensor in the backplate, never came to anything though, but they're still in the engine and gave good signals when hooked up to an oscilloscope. Maybe on those lines a trigger wheel could be made to fit the flywheel rather than the crankshaft pulley.
David Billington

Hmm the accuracy i had not thought about.
It would be play up on play op on play and kind of defeat the exact nature of an ecu setup!

And i think it would cost more to modify a dissy for this use than machine the slots in the crank pully.

Since i have several of those and still have to have the balancing done i might go that way
Onno Könemann

For forced induction over say 5-7 lbs, a 3D mapped ignition is really essential... you need significant retard for boosts of 1-bar or more.

The normal vac unit only operates between 0-bar and max of 1-bar vacuum (actually I've read -10 lbs /sq-in for some units).

This means you need to set the ignition severely retarded for most of its range to accommodate the timing needed for full boost. Engine runs with this, but to the detriment of part-throttle torque / economy.

Or you can reduce the mechanical advance rate (on basis that boost increases with revs) - again, far from the optimum.

You could spring-bias a normal vac unit to work in the range 0-bar to 1-bar boost, but again sub-optimum.

Modern engines with 3D maps use a MAP sensor, which is calibrated for both vacuum and boost; this is used to determine the ignition timing along with rpm.

Anyone tried fitting one of these to a manifold/ECU for Aseries?

A
Anthony Cutler

Anthony
No one is debating the need for mapable ignition.
Just how to trigger it.
A map sensor or tps (or both) are esential for this.

Kindof saying i don't understand what you want with your post
Onno Könemann

You need both

A
Anthony Cutler

May I just say a couple of things about the extremely successful Crank Angle Sensor that I have fitted.

Firstly it is state of the art technology and the most advanced competition cars at the track and drags are using this design. Remember it is "Hall Sensor" technology. Please read about this by Googling the subject. I can suggest a couple of sites to start on which I'll put down below.

In my blog I refer to the help I've had behind my project... my son in law Dom. He is one of the BMW company's top tuners, succesfully races his own Rotary drag car, is a qualified auto electrician and a qualified mechanic/technician. He is an expert on after market computers and has prepared lots of rotary engines for very happy clients and is an excellent tuner of high performance turbo cars.

Dom put me onto this idea rather than a device on the end of the crank, definitely turned me away from optical technology and moved me beyond carbies when using forced induction. That's why we went to EFI, so very important when linked to a sophisticated computer that uploads so many inputs and is programmed to vary spark advance and retard and injector 'spurts' over timed periods with varying amounts, adjusting temperature by maintaing such combinations of A&R and MIXTURE(the all important factor in this)via the injector control. We map for richer when boosting and leaner when cruising. Our C.A.S. is very accurate and our computer is too. That's why we won't blow a motor, the limits are very carefully set up and all sensors are high quality and accurate.

On the "Hall Sesor" idea see http://www.youtube.com/watch?v=ujc6pjftZ_w and also examine
http://www.google.com.au/search?hl=en&rlz=1W1RNWE_en&q=What+is+hall+sensor+technology+in+a+crank+angle+sensor&btnG=Search&aq=f&aqi=&aql=&oq.

This is a bit long but I have some material from Dom. I'll add it as a second part to this thread seperately

Cheers

Bruce
Bruce Roberts

I received this on the subject fro Dom. I hope it helps those who are trying to set up their own system and who were interested in the way we had gone about doing the C.A.S.


Hi Bruce
The Microtech Lt10s run a map sensor that can read up to 20psi boost and up to 30hg of manifold vacuum. The crank angle sensor has two hall sensors that output a hall voltage of 0v to 5v to the Microtech. One hall sensor has a vane passing through it with four cut-outs one for each cylinder and the other hall sensor has one vane passing through it for camshaft timing to determine tdc number one. The key to making the crank angle sensor work so well (as we discovered) is not so much the sensor but more so how the sensor works in conjunction with the Microtech Lt10s. Some of the leading drag and I guess circuit turbo injected cars do run inductive type crank angle sensors that also work really well, only because they have an awesome engine management system behind them.

Dom

Submitted here by Bruce
Bruce Roberts

Hall sensors or rather the hall effect is not that state of the art.
It is used in most cheap electronic ignition kits.
Works perfectly.


Though i understand your trigger is slightly more sophisticated
Onno Könemann

Hi Anthony,
I run Megajolt with MAP sensor off the inlet manifold,plus trigger wheel off the crank nose for timing.Running about 1 bar of boost,and 19 degrees timing at full load.
steve cowling

Hi Steve

That sounds great. I'm sure your torque would be improved with the addition of a TPS, just like KSeries Ts (and any production forced induction engine).

A
Anthony Cutler

This thread was discussed between 06/02/2011 and 10/02/2011

MG Midget and Sprite Technical index

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