Okay I didn't realize you were talking about operating at an increased boost level. If boost level is increased significantly I agree changing the hole sizes is called for.

If your keeping boost around stock levels enlarging the holes is a bad idea.
Actually I think the velocity will remain roughly the same with the same hole size because the rate of volumetric change between the cylinder and the prechamber will remain the same. The restriction will increase due to increased air mass flow however.
I think this would be next to impossible to calculate how hole size changes would effect things. Only through experimenting and carefully controlled testing could one achieve good results. This would require a lot of engine dyno time and probably some temp probes placed in a glow plug hole to monitor prechamber temps as well.

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Ok so the restriction due to the PC holes is sufficient that the rate of pressure rise due to the combusting fuel in the PC is greater than the rate of pressure rise in the rest of the cylinder... ok so now there is another system to look at... this thing is getting really scary!

EDIT:

i.e. a glow plug

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i.e. a glow plug[/quote]

I have read that others have used the plow plugs as a method of determining, not measuring, fueling changes at idle.

I am going to make a glow plug output measuring machine for lack of a better description. ( not calibration). The purpose is to have a controlled chamber that is instrumented to document the glow plug MV output per X* in temperature. Each plug would be tested and it's output documented for reference later.

Once each plug has a reference sheet they will be installed in the engine. I will then make sure each plug is isolated during operation and will have MV gauges in the glove box to monitor each plugs output live.

If this method of measurement is valid, then it would provide valuable tuning information.

I just got the 4 Speed trans today, ordered new hydraulics, and took the flywheel to the shop to be resurfaced. Once the car is road worthy, the EGT and glow plug monitoring system is the first things on the list.

Having never tried to use the glow plugs as thermocouples, am I missing something?

ConnClark, I am glad to hear that I am not too far off in the woods. Thanks for your courteous critiquing of my ideas and keep them coming.

It might be worth doing a lot of bench testing to see just how useful they really are.. People have talked about using them for doing engine-running injection timing adjustments, but as I recall problems came up with the consistency of the signal plug-to-plug, and variability with time in the "calibration" of each plug... Perhaps a good way would be to just test one plug for all of the above ("calibrate" it), and have that be your "test-plug"... Or you could just measure EGTs. With the rate at which the gasses are moving through the engine, heat transfer should be minimal... or should it?

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It was a big discussion in the past. For me (and nearly all the others) it ended up in nothing. The method is o.k. if you have to balance an IP at home but compared with a bench calibrated one (that's what I ended up with) it is not reliable.
As mentioned the variation in values and the influence on the other cylinder will make you crazy.

Tom

You need a controlled environment to evaluate a plugs consistency and ability to provide good information. The engine is the least consistent environment I can think of.

I won't use the term calibration as the plug is not being altered to produce specific outputs at specific temps. I want to map the plug readings as temperatures go up and down and get a feel for the response lag. This would include actual glow cycles in between tests to simulate starts.

Consistency is a must!! Readings must be with in 2% of total scale in order to be worth anything, IMO. The plug to plug output can all over the place as long as each plug is consistent to itself.

I would use the controlled environment (bench tester) to map all five plugs. If I can get five plugs that are individually consistent, then I will use those in the engine and use the appropriate map for each plug to get an idea of the PC environment in each cylinder.
This idea may very well not work using standard glow plugs.


The next best thing would be an EGT probe for each cylinder.

How did you "calibrate" your plug?

I think your right on with the calibration procedure. It will be interesting to see how/if glow cycles affect the calibration. Your right in that is doesn't matter if they aren't all the same, as long as they don't drift away from the calibration.

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I just made sure all GPs are working, nothing else.
Then plug the tester (voltmeter). It was interesting to increase the lowest cylinder's individual fuel and see how the engine gets smoother.
BUT with that some of the other cylinders changed their values.
You have to be very cool not to go crazy. Starting with an average running engine I ended up with maximum the starting point after hours, not better and far away from any kind of fine tuning.

Tom

You would be calibrating your brain, rather than the plug, strictly speaking. I think using a glowplug to measure the PC chamber temperature might be barking up the wrong tree. What's so special about the temperature up there anyway? Why can't you get equivalently useful information from the EGTs?

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The intention was to adjust the MW individual fuel delivery of each single cylinder to meet the condition of the individual engine. (adapted MW-IP adjustment) in terms of individual delivery.
The temperatures of the GPs (mV outputs) monitor the fuel quantities of the single cylinders. As I wrote it was funny but at the end not a helpful procedure to gain something except a headache and better understanding.

Tom

So, to recap the ideas for a new 617.95 PC;

Can it be agreed on that;

1) The PC needs an insolating thermal coating to reduce the heat losses to the head.

2) Change the strait injector threads to the new angled threads, can use the new 616 PC for parts (if it is pined).

3) Use of the off set ball design change to go along with the angled injector will require a custom made lower half, as the 616 and 617.912 burn tubes are 14mm and the 617.95 is 16mm. Not a huge deal as the 616 PC can be used for a model and source for the new ball (if it is pined).

4) Increasing the burn hole area is justified by increasing boost and fuel.

On a side note, if we make the lower half of the PC, we can try different chamber volumes as well.

Can we get the lower half of the new 616 angled injector so we can convert ours to fit the new angled threads?

Wont coating make the PC holes smaller?

You cant really increase the chamber volume without elongating the timing sequence. Rembemer that whatever changes you make the fuel has to get injected at the same time. Angling etc might make for a longer timing. Distance from the injector tip to the ball certainly has to be the same.

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No, The coating can be inside, if the PC is taken apart, or on the outside of the PC. The holes would not be coated.
Although it would probably be a good place to insolate as the holes see very hostile operating conditions, but achieving the proper bond in the hole might be very difficult. If the bond is not right, any coating will fail. I will need to consult the place that has done it for me in the past to be sure. If it is possible to reliable coat the walls of the holes, the thickness is very controlled and the hole dia could be increased to compensate for any reduction.


[/quote]You cant really increase the chamber volume without elongating the timing sequence. Rembemer that whatever changes you make the fuel has to get injected at the same time. Angling etc might make for a longer timing. Distance from the injector tip to the ball certainly has to be the same.[/quote]

?

Any serious elongation of the PC will retard the timing. The ball acts as a time delay in its own.

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I am thinking the angled 616 PC has a larger volume than the strait injector 616 PC due to the injector threads being at the bottom as if they raised the bottom of the injector cup.

There are a couple of ways to increase the volume of the PC. And yes the balls location to the tube and injector would remain the same unless there was a reason to change the locations due to the way the volume was increased.