Experience with combustion pressure measurement and logging?

Hey there, I am looking for some input on measuring and logging combustion pressures.

Looks like I have two options, going with a spark plug based sensor setup, or drilling straight into the combustion chamber.

My concerns with the spark plug based system are kinda obvious, spark plugs are expendable items on a methanol race car and I don't want to be replacing these.

Drilling into the chamber offers its own challenges, but I am leaning more toward this route. Does anyone have experience with either of these?

Next is logging, obviously this will have to be logged very quickly to get a good measurement. Has anyone done this successfully without buying a box specifically designed to do so?

All your input is greatly appreciated.

Zack

I think you've basically answered your own question with regard to the sensors. The instrumented plug is the easiest option but can get expensive when you need to replace plugs. Adding the sensor to the combustion chamber is superior but difficult, particularly since some combustion chambers make this impossible due to the water jacket. Most often the instrumented plugs are used just for the purposes of tuning and then replaced with normal plugs for race use.

In terms of the logging options most people will use a commercial system due to the required logging speed/resolution and the ability to reference to TDC. There's really nothing overly complex about the requirements for logging though and commercial systems are expensive. This is unfortunately above my pay grade so I can't speak about the best way to do this yourself.

You 'might' be able to drill into the chamber - if you do decide to go that route, see if you can scrounge up an old head to cut up and see if it is viable. With some thought, and creative sealing, it may be possible to go through the water jacket if adaquate sealing is used - that you're running methanol 'may' reduce the criticality of cooling in that area.

The other question is, of course, the routing of the wiring.

What sort of sensor are you looking at using?

Optrand or kinsler sensors they end up about $2000 a pop for Optrand I believe Kinsler are more expensive.

I would recommend doing a team viewer session with Plex to see their PCA2000 software.

You could use a generic high speed industrial logger (khz range)but you would have to do some heavy processing work yourself or code something otherwise it will be painfully slow sifting through data.

The plex for 4 high speed channels and base memory (something like hslf hour logging depending on channels/engine speed) worked out similar to tfx with 5 min logging, the Plex has so many more features and software is powerful, and could be used as a chassis logger including gps as well as combustion logging.

I really need to pull my finger out and get some witing done on my rx7 so i can start logging it.

Ive had a small bit of involvement with development of our New Cosworth ECU which has on-board Cylinder Pressure Monitoring.

As explained above the Kistler sensors are one to look at.

You do need a dedicated system to do it if you want usable data, you need to log very fast (200kHz) and you also want this synchronous to your crank/cam angle also.

Thanks for the input here guys. I was already looking into the Kinsler setup before posting here. Looks like their basic system is about 4k USD to get into, so I will have to talk with them and the manufacturer I am working with further to determine if this is going to be what I need.

Zack