Thanks for the info, I see Turner do a 9:1 head but have heard that reliability goes out the window above this. Perhaps this relates to petrol rather than gas. I also intend to fit electronic ignition any thoughts on whats best?
Ref Andy's advice not to go over 9:1 if you want to use petrol; that is about the 'accepted' limit for an old two-valve motor running unleaded 95, over that, and only a bit, you really need to be running 97RON 'Premium'.
Suggestion you looked at very high C/R was IF you optimise for gas, in which case the stuff can stand C/R's up into diesel figures!
If you were to optimise a series motor to run 'dedicated' on gas, you could probably use a C/R around 14:1, the kind of C/R they used to use on old methanol engines that have a similar 'soft' burn charecteristic, BUT you'd struggle to get it to run on petrol....
Advice centered on the notion of using an ignition advance module and setting the petrol mixture ritch. With the advance module switching in on gas, for which timing would be optimised, module would effectively retard the timing for petrol, which with ritch mixture, would help avoid knock.
Wouldn't give best ecconomy or power from petrol on such settings, but then presumption is, you would only use petrol for start up, where power and economy isn't an issue.... choke on for instance! Or when unable to use gas, in which case, loss of petrol ecconomy, for little use it would get, compensated for by greater gas efficiency you'd exploit more often.
RIGHT!
Electronic ignitions..... have intended to write a piece for mi webby on this one for years, but never got round to it!
So, sucking eggs time, but bear with me, what you got, or should have is points. Mechanical switch worked by a cam, and rotated about that cam to adjust the timing by being sat on a plate, thats tugged on at one end by the vacuum advance and pushed on the other by the centrifugal advance mechanism.
So, fully mechanical, bob-weights underneath, diagphram on the side, switch on the plate.
When cam opens switch, breaking circuit, takes volts off the coil, which reacts with a huge 'reverse EMF' that will jump the gap in your spark-plug.
Meanwhile, a condensor, bridging the points accepts the volts that would be going through the points were they closed, to detur them from trying to jump the gap and not get the coil to react.
Everything apart from the coil, normally sits in the distributor, which directs the 'high tension' volts from the coil to the desired spark-plug.
All the mechanical bits controlling the 'low tension' electrickery, sit underneath.
OK..... 'electronic' ignition. Been around a long time, and there are a LOT of different variations on the theme.
Most advanced system is an entirely microprocessor controlled system, which does away with ALL of the mechanical bits and bobs, including the switches; you have a black box, and it takes a signal from a sensor on the engine to tell it the engine speed and crank possition.
You still have something a bit like the old fasioned 'High Tension' circuit, but no distributor. Instead you have a number of coils, most simply one per spark-plug, and when the brain decides one sparker ought to spark, it simply takes the volts of that coil.
Advantage of these systems is that there are no moving bits and bobs in it to wear out, break down or generally go wrong..... just transistors and integrated circuits, which ALSO wear out, break down and go wrong..... but dont need any maintenence until they do!
Electric brain, can also vary timing according to multiple sensors on the engine, so can vary the ignition according not only to inlet vacuum or engine speed, but also say engine temperature, emmissions or even a 'knock' sensor... so it can 'self tune', and thats what they normally do when set up to work with fully managed fuel injection system, and the ignition and fueling are both controlled by the same brain.... or two brains that talk to each other!
This means they can be more accurate, and more efficient, more often.... note the use of a 'possibility' in 'Can', not a 'definative' as in 'are'.... they can be set up as cokeyed as points!
OK, two options for you at THIS point; Mega-Jolt or Mega-Squirt.
Mega-Squirt, is a fully mappable Engine Management Unit, that can be DIY built from a kit, attached to stock fueling and ignition components from Ford or Boche etc, and programmed from a PC.
I mention it, becouse you COULD use just the ignition control part of the system for your ignition; expensive but gives scope to go for LPG and or Petrol injection, either single point or sequential, and only have to plug in the hardware, and down-load a new map for the controller.
Mega-Jolt is a stand-alone fully-mappable ignition controller, effectively just that bit of the complete Mega-Squirt controller that controls ignition timing.
And its a bit cheaper, if you dont envissage going any further with the electrickery... though having done a mega-jolt, youd probably wish youd gone Maga-squirt, becouse once you have looked at the sensor ring you have attached to your front pulley, you'll be thinking its such a waste to ONLY have that drive the ignition when it COULD be driving a fuel map....
Anyway, as a system, either or, neither are exactly 'cheap', I think you are looking at around the thick end of £300 for a full mega-Squirt controller in kit form for you to solder together, which is not a LOT more than a fully-built -jolt. after that, though, next big expense is the sensor ring and pick-up to drive the timing, which depending may be around £100ish, but after that rest of the necessary hadware, (ignition only), basically coils, is available in any scrap yard from almost any car with 'modern' mapped engine management. (as is the rest of the stuff for petrol injection)
So, moving on, we come down to the 'electronic ignition' kits that have been around since the late 1970's, Piranah and Sparkrite being the two names that spring to mind......
I cant remember which way round they were, but one, and I THINK it was the Sparkrite, wasn't ACTUALLY an electronic ignition, they used the word 'transistorised' I believe, and basically all it did was amplify the voltage from the points to the coil, so that they were less likely to arc, which if you had a decent condensor they shouldn't anyway, and the points were a BIT less prone to eroding or sooting up. And you got a SLIGHTLY beefier spark from the coil...... but, points were still in the system, and prone to almost anything they were before, and still timed by the diagphram and bob-weights.
I think that ****-part sell a 'generic' electronic ignition system for about a tenner, thats pretty much the same thing....... but even MORE useless.
I HATED the dang things, they were usually fitted for no other reason than idiot mechanics couldn't diagnose a duff 50p condensor, and introduced a host of crimped together conections grafted into the system to give you even more hassle than you had to begin with.
Onto the next system, I think it was the Piranah, who I know are now defunct, but some-one is still making thier old kits here in the UK....
These used an amplified low tension circuit, like the sparkrite, but triggered by an optical pick-up that replaced the points. You got in the kit, a little metal fan with as many blades as you had cylinders that clipped over the points cam, and a little led lamp and LDR with a gap between them, that the fan turned in, that sat where the points did.
LED shone on the LDR and you got volts to the coil, when the fan blade cut the beam of light, volts stopped.... pretty simple stuff here!
No more risk of points eroding or arcing.......... but still mechanically timed by the bob-weights and diagphram, AND a whiole bunch of new problems usually casued by poor fitting and wiring............ 'breaker fans used to get bent a lot and or run out of true, or crud would get on the LDR... LED/LDR wires would jam the advance mechanism.... they were HORRIBLE!
I am NOT a fan or either after-market set up. They are NOT fully electronic systems, and have few if ANY advantage over a properly set up points system.
If you want a 'contact-less' ignition, which is essentially all these are, well, the piranah is at least.... then you CAN I believe fit the Lucas distributor from an old Metro, Meastro or Montego from the late 80's or Early 90's.
Same Distributor body as the original Series Dizzy, BUT inside it is a propper, factory set up 'hall effect' pick-up. Basically a sharp steel 'tooth' on the dizy shaft instead of a cam, and as it passes a coil, it induces a TINY current. An amplifier, depending on variant, either on the side of the dizzy, or on the wing under or besides the coil, inverts that 'signal' and boosts it to drive the coil, and do what the points used to, without points or condensor.
Its a bit like the Piranah optical system, it ONLY removes the points and condensor, advance is still mechanical, BUT, the system is a lot more reliable.
First, becouse the hall effect system is more robust in the principle it works on; Second, the system got a lot more and better factory development to make it robust; Third, it was designed to be manufactured and assembled reliably and repeatably to a standard, and fit inside the distributor body it was put in.
Rather than assembled as a kit from the cheapest available catalogue components, that might hopefully fit into a any of the proprietry dizzy bodies some-one might want to put it in, AND that person has some commonm sense, and follows the instructions and doesn't decide to take any short-cuts along the way.....
I have NOT used this a Montego/Meastro dizzy myself on a Series, but I have used it on a lot of tuned BL A's, and it DOES work, and work well, and work reliably. Timing is accurate, and reliable, and they are pretty much maintenence free.
I know people that have used Montego 1.6 dizzies on SIII engines with NO mods to the bobweights, springs or vacuum advance, and reckon that static timed for the SIII engine, the advance curve is close enough, and allows the motor to rev out a bit further.
On a tuned engine, you'd be starting from scratch with the desired advance curve, BUT given a higher compression ratio, I'd expect, that a Montego dizzy would probably be as good a starting point as any.
So, getting practical;
If you want to go for it, no expense spared, I'd use a Mega-Squirt. Going LPG, I'd be just SO tempted to do the job propa and go for an LPG injection front end, and enjoy the benefits of mapped fuel and ignition on gas.
On an SIII engine, probably keep it fairly low tech and not go sequential, but use a single point Bosh injection block from something like an old Golf or Escort for the petrol side of things, but for the gas, as thats what I'd want to use most often, and its just as easy, probably use a four way squirter block, though I'm not sure whether I'd sequentially time them, or run them on an 'average map'..... which is probably loosing you a bit, but IF you go down that route, you'll soon find out what I'm ranting about!
Next, having suggested high compression gas, and ignition advance modules, well, you can run an advancer on a points system.
Its a bit like the old Spark****e amplifier, but a bit more sophisticated, and instead of simply boosting the signal from the points, when switched into the circuit, it adds a 'phase change' shifting the voltage cut a few degrees forwards.
Most basic advancers have a fixed phase shift, normally around 4 degrees, more sophisticated ones have a pottentiometer that allows you to 'fine tune' the amount of advance they give by a couple of degrees either side of thier nominal, so from perhaps 2 degrees to 6.
Some, but I've only ever come accross them for motorbikes, have a 'sort' of 'pseudo-mapped' advance curve; they cant adjust the timing according to vacuum, but they can adjust it according to speed, and for high performance bikes, which used to use fixed, static timed, points ignition, you could get advance modules that 'emulated' a mechanical advance curve, increasing the phase shift according to the frequency of pulses from the points...... which is probably beyond what you need, if you go down this route.
Anyway, a simple advance module is as 'good' as any of the cheaper 'electronic ignition' kits, like the old piranah or spark-rite, and for a gas system probably better.
Module sits on the feed to the coil, and it will boost the spark on gas, which is when you want it, without making things over-complicated.
If I was doing things on a budget, or tyring to keep mods to a minimum to retain classic 'authenticity', that's the route I'd go; reconditioned points distributor, and the advance module reccomended by Turners or whoever I got my LPG kit off.
BUT, going for some 'mild tuning' and not wanting to go silly with a Mega-Jolt or Mega-Squirt, then I'd be very tempted to go find an old Montego Hall effect distributor, and use that with an advance module.
On the comment of reliability....... well, old engines aren't that reliable to begin with you just dont know what, if anything, or when, if everything might go wrong with them.......
When you start tuning engines, you are not denting 'reliability' but life expectancy, which is a slightly different thing.
Bearings that can stand the load of 75bhp for 100K miles, reduce in life expectancy by an inverse square rule; double the power, so 150bhp, and life expectancy drops by the square of the multiplier, so 2x power becomes 1/4 life, or 100K miles life becomes 25K miles...... and its pretty much the same for bores, rings, seals, gaskets etc etc etc.
So start from fresh, a tuned 'built' engine, using new or reconditioned parts, provided theres no assembly flaws in it SHOULD be as 'reliable' as a new or reconditioned engine..... becouse you still have a reasonable certainty over how much life is in it. It will be JUST as reliable...... just not for as long!
Start with a tired old engine, with unknown life left in its variouse components and you will accelerate the wear on them, they will be just as 'unreliable' due to age, but more likely to break or wear out becouse of the increased stresses placed on them.....
Its a bit of symantics, but important, becouse if you are tuning your engine while reconditioning it, you are putting more life into it from the reconditioned bits, and taking it away again from the tuning.....
How much new life you breath in and how much you take out depends on how you build it, and the question of 'reliability' is then entierly subjective!
Provided you dont go stupid in the tuning, there's no reason why it shouldn't last a very loing time, and be as reliable as anything else out there.
And, on gas, you are onto a winner from the beginning, as I aluded to its 'soft burn' properties.... it burns pretty slowly, so you dont get the peak pressure loading as it all trys to go bang at once that petrol gives, it spreads the pressure out more over the combustion stroke, which TENDS to give rings and bearings and stuff a slightly easier time, as they dont get the big peak loadings petrol imposes.
And, though petrol still gives them, on an engine optimised for gas, and set up 'wooly' on petrol, you are not going to get the violent loadings petrol COULD give on a tuned engine, while optimised for gas, which is the fuel you are going to hope to be using most often, so petrol would only be for start up and the few occassions that you cant find gas, so you shouldn't risk stressing the motor out, very much, very often, or for very long, if at all.
Three bearing 2.25 is good for around 100bhp, five bearing motors 120-140, without significantly risking premature failure.
In hard terms, reconditioned 'standard' engine, you could expect to last maybve 100K Miles without needing major attension above routine maintenence. Tune one to 100bhp, and reconditioned to the same standard you can reasonably expect around 70K Miles without major attension, above routine maintenece, provided you do give it that maintenence and slightly more frequently
Going by the same numbers, good guiide would be if you changed the oil every 5000 miles on a standard engine, then tuned, you should be changing it every 3,500 miles, and tappets plugs points etc at similarly reduced intervals.
If you are ONLY going for a high-compression head, and a gas conversion, and keeping it otherwise pretty tame, single mixer gas system, and possibly no more than an advancer on points ignition and a vacumme mixture valve on the gas; then really, the tuning would probably do little more than compensate for the 5-10% power loss you get on gas from its slower burn, and the reduced flow of having a venturi mixer in the inlet above the carb.
Which is a point worth noting; as said, advantage of a flowed cylinder head is it allows a bit more gas into the pots under peak flow conditions, ie with the throttle wide open, and it gives most effect at higher revs where the flow volume is the greatest.
BUT, if you have artificially 'choked' the air-flow up-stream of the head, to get a venturi effect to suck LPG out of an evaporator......... You AREN'T going to get the benefit of it.
Unless you over-size your mixer, so it presents less of an impediment to flow..... in which case you'll need to increase the delivery pressure at the evaporator, and in order to stop that over-fueling, you'd then really need either a vacuum mixture valve between the evaporator and mixer, or a closed loop, lambda sensor controlled steeper valve, and we are back into the realms of added complexity and cost, that makes a Mega-Squirter system start looking not that much more effort and probably less hassle.
I think its back to Turners, for advice, really. You want to do this as an alternative to a TDi, essentially for ecconomy, so you dont want to be chucking shed loads of money at it or making the job more complicated than doing an engine swap.
So, getting back to the real world; Turner head, open loop gas conversion, with vacuum mixture valve, points ignition and advance module, and with the head specced to Turners reccomendation, probably 9:1, unleaded, which isn't really 'flowed' just tidied up to avoid hot spots, and a mixer sized to suit, you should be pretty well sorted, and that should all bolt onto your original bottom end without significantly harming reliability.
While I was digging about down there, though, I would spend a bit of time to check the timing gear, and probably replace the timing chain and gears as a matter of course.
I'd probably also pull the sump and drop a couple of braring caps just to check there was a reasonable hope of there being life left in them, and that, presuming the motor had decent and even compression on test, and wasn't using too much oil.
And I'd overhaul the dizzy, for sure, with new points and condensor, vacuume advance unit and bob-weight springs; and use a new coil, just for piece of mind, along with new dizzy cap and rotar arm, of OE spec, becouse gas likes a good spark.
Probably also change the water-pump while I had the timing cover off, and head out the way, and almost certainly 'back-flush the coling systemn before I took the old head off, and look for any leaks afterwards from the rad or heater matrix.
Standard 2.25 Petrol is 'rated' at around 75bhp. A tired old one isn't going to be making that, even if one made close to it out the factory.
If you aren't doing any more than head and gas conversion, where you are starting is with an engine probably making something like 60-65bhp.
If you fit new timing chain and gears, and do no more than settle the rest of the engine, like set the tappets, timing and carb up nicely, you are likely to get the thing back up close to 70bhpish.
A reconditioned head on that, with new valve guides and sharp valve seats, on its own would probably have negligible effect on peak power.
Upping the C/R a point from 7:1 to 8:1 would probably give you 5%, taking you close rto the quoted factoy rating..... uping it another point to 9:1 would probably give you another 5%ish so maybe nudgingf towards 80bhp.
It's tuning, but a legue away from anything that might be considered a bit 'warm'!
And, of course, sticking the gas mixer on there, you are going to drop more off the peak power than you have gained, even on petrol.... so you are running quid-pro-quo.
BUT, it will FEEL like you have endowed it with HUGE amounts more power than you really have; becouse what you will feel, from a nicely shaped head, a higher compression ratio, and well controlled ignition, is 'throttle response'...
The engine will be eager to do its job and react to the throttle, feeling tight and crisp, and 'lively'........ well as lively as a 75bhp engine with a heavy iron flywheel can in a two ton vehicle!
So the behaviour of the engine will be much more akin to one with a lot more power, and should be a lot more rewarding to drive......
BUT, gas blunts that, especially open loop gas set ups; hence my reccomending the ignition advance module, becouse that really helps throttle response, as does the vacuum mixture valve.
