providing the proper outlet is drawing adequate vac to match the vac can...I think as soon as you start into bigger valves, carbs and cams it's pure good luck if the vac signal is in the ball park...plus you're only seeing signal for 1 of 4 cycles, unlike a single carb.... I'm not 100% on all this, as I got into it due to the megajolt thing, but I'm pretty sure the theory's right Some of the old Lucas dizzies had adjustable vac cans...which would be nice
Dells come in pairs with a single out for vacuum. I assume they made it bigger to compensate. The T1 solex one has a weeny hole, my dell one is bigger.
I bought an antipulse things yonks ago, which I might fit. It's a small brass affair. I suspect it's just got some kind of damped piston inside it.
That proves nothing though...you'd need to take a gauge reading at idle (should be zero for ported, maximum for manifold) and then measure the signal until it drops out (as the throttle plate gap widens)....if it corresponds with the operating range of the stock vac can on the dizzy, then you're laughing....if it pulls less, then your idle timing is less than ideal (retarded) and you'll run hotter at low load (cruising condition), if it pulls too much, then your timing will be over advancing , early, and it won't run smoothly until the vac condition is no longer present (wider throttle) there's a good article on it here....it's for chevy's but the principle's the same
Yes he probably could and having a quick look at the website there does appear to be an ignition kit for $719.95 – looks like it’s for a type 1 engine and at that price plus taxes and shipping it pushes me towards 123. I doubt if he does anything for a mere Bay with a type 4 but I might just ask the question.
That's all very well, but peeps (including me) do just plug 'em in and go and have for decades. I don't think personally there's much point in getting too scientific about it - as long as it won't over-advance, it's got to be an improvement.
Thanks for the link, a good explanation and I particularly like - ‘What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation.’
He will do it, did me a FI kit complete for a Type 4. Crank fired will be better than a distributor as well, more accurate timing.
But only more accurate if it is programmed correctly and with presumably hundreds of set points to adjust unless you can spend many hours on a rolling road to optimise the settings isn’t it a compromise much like a distributor? Vanorak makes it sound very complicated “say you have a black box and MAP sensor, and you take a vac signal from the manifolds, the vac draw at low load (throttle hardly open) will be 'xHg'....you then programme the black box in such a way that at 'xHg' the timing will be 'Y' degrees (it can even be a negative value)....the black box simply sums the mechanical advance (as determined by rpm) and the 'Y' value together, to give you the appropriate amount of advance. So basically, you can take a vac signal from either ported or manifold, provided you programme the black box to work with the parameters you have. This is why it's particularly good for engines that deviate significantly from stock...” Knowing what xHg and Y are is vital – and that's just setting up the vacuum advance. Incidentally, I see that one of the reasons you went with EFI and crank fired ignition was to keep the temperatures down in your 2056 - was it successful? And are you happy with the choice of cam?
The accuracy of the timing is not to do with the programming of the box, it's just the accuracy of the trigger signal. Using a distributor, you get a scatter (variation) on the trigger signal, whereas the signal from a crank wheel is much steadier. As far as advance goes, you can just program a box (CB / MegaJolt / MegaSquirt) with a simple advance curve to duplicate the distributor function. This will work the same, just with more accuracy. If you fit sensors (Manifold pressure / throttle position / air temperature / Lambda) in whatever combination you want to use, then these can feed into the box (no idea what functionality the CB box has) and allow the advance curve to be different dependent on the conditions. You don't have to do this, but if the box allows it, you can add this functionality later combined with a RR session, but start with a simple advance curve as per the distributor. My EFI engine isn't built yet, in progress with @Paul Weeding
Sorry if i've made it sound more complicated than it actually is. Below is a typical ignition map: In the table, you have rpm and load (ie the actual condition of the engine at any given speed/throttle position expressed in terms of vacuum KPa) To programme the degrees of timing you require, you click on the relevant box and type in a figure. This gives you the ability to create an ideal timing curve based on your particular engine. As the black box takes it's reference point (ie piston position) from the crank, it never deviates, unlike a distributor, so the timing regime you've specified never deviates....once it's propgrammed, it doesn't budge. I admit, it takes some time to get your head round it, but once you have, you can actually change the timing characteristics very easily in real time, via your laptop, and observe the effects, positive or negative. The key is to understand that at any given point whilst driving, (idle, cruising, going uphill, accelerating etc.) there's an optimum firing time...a mappable ignition set-up allows you to achieve this, unlike a mechanical dizzy which is a compromise. It's not for everyone, admittedly, but all modern vehicles employ a similar system as it's inherently more accurate
You'll know what 'xHg' is when you connect a vacuum gauge (or Megajolt, Black Box, ECU) Your engine's just a glorified air pump and develops a certain amount of vacuum when it's running. It varies according to driving style. At 850 rpm the vacuum developed will be x, at 950 it will be x+ and so on...every engine is different depending on what components have been fitted and how it was built. So to assume the timing curve of a stock mechanical dizzy (designed for a stock engine) will be optimum for your engine is incorrect.
I don’t doubt that the signal from a crank wheel is much steadier but doesn’t the accuracy of the advance compared to the optimum for any particular engine depend on how the black box has been programmed? How?
I understand the theory and I understand how you can optimise the ignition curve. It’s knowing HOW to observe the effects, positive or negative that I don’t understand and get it wrong, with too much advance for instance, and a lot of damage can be done to an engine very quickly. It’s a bit late saying I’ll back it off a bit next time after the piston has melted.
You can just program the box with a standard advance curve, then it will work exactly the same as a mechanical advance distributor, but with more accuracy.
You'd start by running your engine up on a 'safe' curve, ie sub optimum. You'd then increase the figures (degrees of timing) in small increments until you're just before the point at which pre detonation occurs...you'd do this for various points along the entire curve. This is why you'd use a rolling road and 'det cans' to detect when this point has been reached. As Owen said, you can simply programme a known safe curve into your table....this can be extrapolated from a Bosch 034 curve for a Type1 for example...
