Right then hope this makes sense - V8 Dizzys Q

[geoffbeaumont]

Before you fit any EDIS or anything try advancing your existing dizzy until you can generate some knock. Read off the advance with a strobe to give yourself a limit to the advance when doing your tables.

That's the general idea - although I've played with it before and never managed to get an audible knock on LPG, even though it was massively over advanced and barely drivable.

As a precaution have you thought about obtaining a knock sensor from a modern motor and trying get an output to light a led or something when knock occurs? I believe they are pieso-something or other which will resonate when knock occurs. Thus any output, amplified and then rectified could turn on a led. You do not need to know which cylinder is knocking, just that one or more are. Worth thinking about?

Yes, I have though about it - although not just lighting an LED. Megasquirt can use a knock sensor (think that functionality is reasonably stable now - it was very experimental when I started out on this...far too long ago).

The trigger wheels are designed to be clamped between the pulleys not welded to them. The welding is just a catch to prevent any rotation.

That's how mine is done at the moment , but there's only room to fit a 1mm thick wheel into the pulley stack on a '93 Range Rover without displacing the pullies. I think the wheel with the large inner diameter is designed to be welded on rather than clamped (read the description on the eBay sale) - with that thickness of wheel that would be the only way to do it on mine.

[FridgeFreezer]

jw - knock sensors are often engine-specific, without going into lengthy discussions about it it's a complicated business:

- Each engine has it's own knock which can be very different

- Each engine makes any number of other noises in normal operation

- You only want to listen to the knock sensor at a certain point after a cylinder has fired

- Many knock sensors are "tuned" to a specific engine or family of engines

Also, a knock that we would hear is many many times over the safe limit for an engine, if you can hear it knocking it's well outside an acceptable advance setting.

As Geoff has said (and he's probably more up to date than me) work is afoot to devise a universal-ish solution, the new ECU / CPU upgrade can more than handle it, it's just writing the software (and testing it without destroying too many engines!) that's the hurdle, but then "they" said they'd never make the ECU's work in the first place...

Roll on Ion-sensing ignition I say (yes they're working on this)

Full discussions of it in laboriously technical detail: www.msefi.com search for "knock".

[jwriyadh]

4.0 and 4.6 V8s with GEMS or later?

jw

[FridgeFreezer]

I suspect whatever they come up with will accept a "tuned" sensor if there's one available.

As for just connecting it to an LED, you still have the problem that the sensor is basically a very sensitive microphone and may be "triggered" by all sorts of things within the engine unless you can only sample it's output at the point where knock would ocurr. From what I can tell you will always need a fair bit of signal processing on a knock sensor. I'm waiting for the grown-ups to develop something that definitely works

[Astro_Al]

Just to confirm what Fridge said - before relying on any non-standard knock sensor you have bolted on, make sure it's working properly.

I know there were big headaches with building custom GM aluminium V8 (LS series) engines. People where trying to use the newly introduced (then) LS6 block or heads with the older LS1 knock sensors (so they could, for example, keep their LS1 blcok and loom/ecu and just add the improved LS6 heads), but since the knock sensors where located in different places they looked for different characteristic signals to indicate knock (or technically could have done - it all panned out ok in the end).

So even between similar engines and sensors you need to be careful that they will correctly diagnose knock when it occurs.

Al.

[Bull Bar Cowboy]

Nige,

Some is a bit granny and eggs , but using these fundamental principles has always given me good results.

For the purposes of completeness we will assume Type 1 & 2 have very similar curves as they were both used on the EFI motors with similar cams, the major difference being the ignition amp. The type 3 dizzy will have a longer curve and max advance will be at higher rpm. The static will vary a lot due to different markets for the same product. This is mainly emission related.

As regards spark intensity the 35DLM8 was always reputed to be the best, although the amp suffered reliability problems with heat. Its position on the dizzy took direct heat from not only the engine but also it was in the hot air path from the radiator. On TVR’s where space is even tighter and consequently under bonnet temperatures are higher the reliability problem was more noticeable. On the RR it was more noticeable under extreme conditions (i.e. hot ambient air temperatures). These facts mainly applied to the early 2 pin version. The later 3 pin amp seems better in all respects. I currently run the 3 pin amp and have had not heat problems to date.

If you are playing modified timing curves then the following may help. Most of this is from my days of building highly tuned A series engines. Most engine tuners tend to use smoke and mirrors when describing this subject but it is in fact very easy to digest and does not require the use of Paracetamol.

I suppose its best to run through the fundamental principles of petrol internal combustion engines. Ignition timing is required to ensure that the mixture completely combusts at around 15 degrees after TDC to give the piston a healthy shove on the downward stroke (peak cylinder pressure). The rate at which the mixture combusts, called the flame front, is dependant upon fuel air ratio, compression ratio, cylinder filling (volumetric efficiency, say, throttle wide open), and combustion chamber shape. As these are fixed entities then the combustion time is a finite process. So in order to meet the above requirement we have to advance the ignition of the mixture as the PRM increases to ensure we meet the 15 degrees ATDC criteria. If it happens too soon then the combustion will happen as the piston is on the rise (or at TDC) causing pinking (or pinging by its correct term). If it happens too late then the piston will be well on its way down and the engine will give the performance of a TDI !!!. (Detonation is a another product of incorrect engine tuning that will destroy a piston very quickly but should not be confused with pinking).

The combustion chamber shape of the RV8 is an open wedge and the overall max advance for this type of shape will be 34 – 38 degrees. The A series engine with which I am very familiar utilized the heart shape (carotid) which would allow a max advance of 32 – 34 degrees, so there is a great deal of similarity between the timing process on these two engines. Of the older engines the pent roofed xflow was the most efficient shape, bring the advance needed down to 30 or less degrees. However, Mr land rover would have wanted the engine to always perform well under all sorts of conditions and sometimes running on the sh!test fuel in the world, so the land rover V8 dizzys are limited to 28 degrees max advance. Knowing this allows you to easily work out the mechanical advance supplied by the dizzy (i.e. what’s stamped on the bob weights OR the advance cam). If the manufactures data says the static timing is TDC the calculation will be 28 – 0(static) / 2. So in this case 14degress. If the stated static was 6 then the calculation would be (28 – 6) / 2 = 11 degrees.

The first step in tuning an advance curve is to determine the maximum ignition advance the engine can tolerate, and subtract from that figure the initial static advance. The distributor mechanical advance will be ½ that figure. So from the above we can safely assume that the max advance for the RV8 will be around 34 degrees (in fact many of the RV8 high performance engines are set up by running the engine up to 4750 rpm and setting the dynamic timing to 34 degrees). The static timing is generally a function of the cam profile. Serious race engines use overlapping profiles of 300 degrees or more giving a tickover of 2000 rpm and the useful power would not kick in until 3000 rpm. An engine with this type of cam would also spit flames (due to the overlap) and would have a high level of emissions (mainly unburnt fuel). This type of cam would require a static of 16 – 20 degrees. Most tuned road engines will have a cam of 270 degrees of less, thus giving a static of 8 – 12 degrees. A 280 degrees cam will require a static of 10 - 14 degrees. The golden rule of the tuners was always use more than 10 and less then 20. So if your engine currently performs well on a static of 10 degrees then the mechanical advance that is required will be 34 – 10 = 24 degrees. Therefore a pair of weights and cam marked 12 will do the trick nicely. An alternative that we used to use, because you can never get the right bits in a hurry, was the empirical method. Use the nearest weight that you have and adjust the dizzy cam stop the give the required result. To do this you will have needed to replicate your crank pulley timing markings right up to 34 degrees. This is easy as real steel a premarked tape for this purpose.

The springs give the rate of advance. Generally a tuned engine needs max advance earlier than its factory standard brother. On a tuned V8 then max advance would need to be a 4000 – 4500 rpm. So from static to max mechanical you really need it to be almost linear. Usually the factory setting springs are too strong, therefore slightly weaker springs are required. The differences are small and you can sometimes get the required result by carefully adjusting (bending) the spring retaining pins. Any scrap Lucas or Bosch dizzy is good for the supply of alternative springs. Also Real Steel do a set of 6 for the RV8.

Well sorry if its been boring but a correctly timed engine will maximize the performance and make it very tractable. Modern engines with electronic management of the timing have a lot to be said for them with just a quick remap required.

Ian

[FridgeFreezer]

I was with you up to "Paracetamol", then I had to go and take one!

Really must get that EDIS sorted...

[Bull Bar Cowboy]

Nige,

From our conversation your task is looking very much like this ,

Ported and polished heads help the flame front burn faster, so your max advance is probably going to be around 30 -32 degrees. From what you tell me the static is currently 14 degrees. That would indicate a cam of around 280 degrees and I therefore expect that your tick over speed is not much less then 1000 rpm. So, what you need to achieve is,

32 – 14 = 18 degrees advance required between 1000 to 4000 rpm.

As the dizzy runs at ½ engine speed then you are looking for 9 degrees mechanical advance at the dizzy. Your quest is to find a dizzy cam & weights that are marked 9.

Standard springs will be too strong. The springs must always be under a little tension otherwise you get a kick in the ramp and the engine will pink. Ideally you want the advance ramp linear. This can sometimes be achieved by careful manipulation of the springs and anchor posts. This is a tedious process but well worth the effort to get it right.

My 3.5 runs with a CR of over 10:1 together with polished and ported heads. However, the cam is mild (3.9EFI) as I wanted to retain the low down grunt that you tend to loose with hotter cams. Consequently I run a static of 4 degrees and the engine max advance tolerated is 32 degrees. I have played with the springs (stolen off another vehicle) to give me the linear ramp.

Ian

[Hybrid_From_Hell]

Ian,

Cheers for the chat and info today .................and the post.

As I said work is a REAL PITFA at the mo, .................

so I have printed off this entitre thread

so I can give it real thought and study tommorow.............. when in a "Big Time" seriously boring and uninteresting and frankly mind numbingly dull "lose the will to live" type meeting....

Be in touch

Nige

[Diff]

Hi Nige,

Further to Ian's excellent posts, here is an article on adjusting timing for modified engines, which you may find very useful:

http://members.aol.com/DVAndrews/timing.htm

I have modified a few dizzies in the past too, and the results can be rewarding, but it can be VERY time consuming because without a proper tester, the only way to plot your curve after each 'adjustment' of the weights, stops or springs, is to refit the dizzy, start the engine and get out the timing light, tacho, graph paper and pencil!

I should point out that the max advance for each head design will vary slightly according to a number of factors including most significantly, the compression ratio and the fuel octane rating.

High compression causes fuel to burn faster so less advance needed.

Regards,

Diff

[Bull Bar Cowboy]

Diff,

Yes, one of many excellent articles that detail much the same information (although I question the cam static settings ..... bit high ). I suppose where the info given is similar (or shall we say, not too dissimilar), then we can all be sure that we are barking up the same tree . Hardcastle also gives some useful gen in his tuning the RV8 books as also does Marcel at TDC engineering. Most of mine was gleaned the hard way [violin mode on] ……. hard facts coupled with empirical trial and error testing …………… in the early days there were lots of errors, but results began to pay off in the end ….. with the old A series producing the magical 100 + ponies from an engine that was well sub 1000cc ( 850 & 970) and originally designed to do 58bhp. We used to get them singing at 8000 rpm flat out with no power at all below 3500 / 4000 rpm …… using silly cams like the 649 etc. Many a mistake has been made on the timing ……. usually noticeable by the lack of grunt and the exhaust manifolds glowing cherry red after the first ¼ mile . In those days we didn’t have the internet (it would have been really useful). However, I’m not one for looking backwards, life is just a series of chapters in a long book ……..

Agreed, compression ratio and combustion chamber shape are the key to the speed of the flame front as these days there aren’t too many choices with regard to high octane road fuels. Sadly, gone are the days when we could get 101 octane at the pumps !!!

Sun indeed did make a tester for dizzy’s which enabled you to plot the curve, although I have only ever seen it in American books & catalogues.

I am sure that we all agree ………. this is a dying art , because electronic engine management beats the old mechanical dizzy on every front …. and remapping the curve is just soooooooooooo easy to do with the aid of a lap top and a good understanding of the engine / principles B) .

Ian

[Diff]

Hi Ian,

I would love to have had a go in one of those minis! With over 100bhp and able to rev to 8000rpm they must be an absolute hoot!

I had a relatively standard mini 1000 years ago which was fun, I can only imagine how much more fun it would have been with one of your engines.

Regards,

Diff

[Bull Bar Cowboy]

Diff,

The sort of spec that we were producing from our garden sheds were,

CR of 11.5:1 …. achieved by shaving both the head and the block ….. if you got a bit over ambitious then a loud knocking developed at high rpm as the piston touched the head !!

The heads were ported and lovingly gas flowed by polishing to a mirror finish. The rules did not allow larger valves !!!

Forged pistons, lightened conrods & crank and both were shot peened, balanced & nitrided.

Lightened flywheel & clutch ….. paddle clutches were not readily available in those days

To stop valve bounce, which was the limiting factor, the cast rockers were carefully lightened by hand and each was weighed to ensure uniformity. Hollow push rods and the cam followers (tappets in the true sense of the word) were carefully lightened to be eggshell thin.

Timing gears also got the same weight shaving treatment.

Top speed was a ton + and 0 – 60 times of well sub 10 seconds …. common place these days even for a road car, but 25 – 30 years ago that was a flyer.

I'm bl00dy sure that I wouldn’t have the patience to do it now

Oh, and the most embarrassing incident ……………. Having a flywheel come off at 8500rpm ………it went through the bell housing and lodged in the grill, buckling the front sub frame in the process. Oh yes, another time in my road going Mini I was at he lights in our home town and decided to beat an Anglia (Dagenham dustbin) off the lights. At amber I raised the revs and at green dropped the clutch …….. forward motion didn’t happen, one loud bang and several bits of the gearbox were laying in the road …….

Ian

[Diff]

Brilliant! I know what you mean about patience, I seem to have less of it these days too! I think it goes hand in hand with having far less 'tinker time' these days.

My old trials buggy has been languishing in a lock up garage for years waiting patiently to be resurected!, My Montesa 248 trials bike needs a bit of tlc as it keeps weeping its gear oil on the floor, my 1978 Guzzi LeMans has not been ridden for years, and the 110 gets just enough maintenance to keep it reliable.

Regards,

Diff