IDI engine, there IS a future...

[QuickTD]

The coating, which also goes by the name of Turbokoting, is three layers thick, adding a substantial 0.015 to 0.018 inch to the surface.

This is a far thicker coating than the sites I visited offered, and also a different material. Definately the way to go from a thermal standpoint and far less work than inconel liners. Much more expensive than other piston/combustion chamber coatings but if it performs as advertised it would be easily worth the $300 cost. It might allow you to run an 18:1 compression motor and still have it start at -25ºC...

[malone]

Here are some pictures of different pre cups 935racer collected. The 1.9TD version appears polished because it is brand new unlike the others, which were just cleaned.

Note how small the 1.6TD precup (centre) is in overall diameter and the opening.




Note how large the opening is inside the 1.9TD precup (far left).


Internal volumes:

1.9TD: 5.8cc
1.6TD: 5.2cc
NA 1.6: 5.5cc

For specific dimensions that's up to 935racer to bust out his micrometer.

[fspGTD]

Very interesting findings on the prechamber differences... and great close-up pics!  Were both of the 1.6 liter prechambers out of hydraulic lifter heads?

I haven't noticed that "dimple" in the face of the 1.6lTD prechamber on any of the solid lifter 1.6lTD's I've had apart before.

[935racer]

The td is out of a hydraulic lifter head that has never been rebuilt. The other 1.6 was a solid lifter and I have been told it was rebuilt so I am not sure if that precup is stock or not. I have been thinking about porting these cups out a bit to try and get them to flow better, but it seems with every mod there seems to be a negative. I'll dive into the mods this weekend and we can share some ideas, I'll bust out the mics and ive some more accurate measurements later today hopefully. Malone tells me he has a 1.6td solid lifter head that I can bust teh cups out of so I will measure the volume of them as well.

[malone]

When I go home I'll edit my pictures to indicate hydraulic or solid lifter head and then re-upload them. A 1.6TD precup from my solid lifter head and a 1.5 precup from a friend's busted motor will eventually be added in the pictures.

We don't have a precup from a NA 1.6 hydraulic lifter head.. well, we don't really need it but if anyone wants to donate one, feel free. It can be used, slightly cracked, doesn't matter.

[malone]

Flat side (bottom of prechamber) diameter:

1.9TD: 1.2615" (32.0421mm)
1.6TD hyd: 1.179" (29.9466mm)
1.6 NA solid (rebuilt?): 1.261" (32.0294mm)

I've more measurements, but I need to upload a dimension chart to organize them. Coming soon...

[malone]

Basic prechamber dimensions:



1.9TD Hydraulic:

A: 1.0975" (27.8765mm)
B: 1.2615" (32.0421mm)
C: 0.676" (17.1704mm)
D: 0.158" (4.0132mm)

1.6TD Hydraulic:

A: 0.993" (25.2222mm)
B: 1.179" (29.9466mm)
C: 0.677" (17.1958mm)
D: 0.160" (4.06400mm)

NA 1.6 Solid:

A: 1.077" (27.3558mm)
B: 1.261" (32.0294mm)
C: 0.678" (17.2212mm)
D: 0.160" (4.06400mm)

The measurements may not be 100% accurate. i.e. Would VW intentionally change from 1.2615" for one prechamber to 1.261" for another prechamber? Also compare dimension "D" - 0.158" vs. 0.160" vs. 0.160". That's a 0.0508mm difference. So take these measurements as ballpark figures, probably not something you'd take to a machinist right away. The measurements may be enough to help some people figure out a few things though, or at least fulfill our curiousity.

[fspGTD]

Great info, thanks!  The gas port on the 1.9l precup certainly looks bigger from the picture.

I've got a 1.6lTD solid lifter head out of a car, I can measure the precup OD of (malone's dimension "B").

[malone]

The 1.9TD precup has a notch along its outer rim whereas the 1.6TD hydro and NA 1.6 solid precups don't:







Not sure why the notch's there, just thought it was interesting.

Some cracks in the 1.6 TD precup... nothing new but took pictures anyway:

[tylernt]

I too read this thread with great interest. I have a spare warped head and if I can get it straightened, I'm going to port & polish it and I'll certainly consider having the prechambers thermal-coated too. For $100 why not. Coating the piston tops, exhaust valves, ports, and manifold seems a little extreme to me though, unless you were running a TD.

Here's a thought though. If you coated the inserts and the combustion chamber 'bowl' in the cylinder head and trapped all that heat in there, wouldn't that seriously overheat the injector? Wouldn't you want to coat the injector face and heatshield as well to avoid cooking the living daylights out of your injectors?

[VW Smokr]

Seems like the fuel spray(fog?) exiting the injector may go a long way toward keeping the injector sufficiently cooled.

J.R.

[HarryMann]

Fascinating, and lot of great work 'discovering' the truth about these pre-chamber designs by contributors.

Is anyone yet running a ceramic coated pre-chamber?

I was wondering whether a fully polished or ceramic coated exhaust port in the head, would help reduce the temperature differential across the valves, to alleviate the cracking problem, as well as retain more heat in the exhaust gases. This is the first port of call for those hot gases, other than the valve seat, which itself would benefit from slightly better cooling!

[malone]

I am running a ceramic coated pre-chamber cup - just the inside of the cup and not the rest of the pre-chamber. I can't tell if it makes a difference. It'd be a good idea to ceramic coat more thoroughly (the entire pre-chamber and other parts of the head like you mentioned). That's what I'd like to do if given the chance.

[fspGTD]

To add to Mark Malone's prechamber face diameter measurements, I measured a 1.6lTD solid lifter (from a 1984 Jetta) prechamber face diameter today: 32mm.

[TDIMeister]

Whatever happened with the discussion that ran some time ago about the piston cutout that was patented by Toyota?  Did anyone every try the mimic the same thing?