Geoffrey

Jack, I could find no information regarding cylinder head temps until I spoke with some air cooled aircraft manufacturers. They said that they start to get concerned when the cylinder head temps go above 210 degrees C (410F). I figure they are on the conservative side given the nature of its application. On my turbo car using a factory cylinder head temp sensor with MoTeC logging, I see 180C at .7 bar, 200C at 1bar and 210 at 1.2bar. I would expect to see a N/A engine running in the 150-160 range. I have a lot of cylinder heat temp data from various MoTeC cars and if you are interested I can probably dig some up.

JackOlsen

Thanks. I think before I get caught up in specifics, I'll have to get the gauge in place to see if I'm in trouble or not. The Turbo numbers will be a good reference point.

Why am I concerned about it? Wll, I'm testing out some weird track-only aerodynamic pieces I made for my car. The one that concerns me is a rear diffuser.

I made holes in it that are a little more generous than the 964 undertray, but I want to make sure I'm not cooking the engine when it's in place.

Dave R.

For what it's worth, general design rule for air-cooled piston aircraft is to make the exit aperture area/cross-section for cooling air greater than the inlet area/cross-section. (e.g. cowl inlet < cowl outlet).

bhensarl

Jack,
What are those big fins on the undertray? Heat sinks? Aerodynamics? Scare factor?
Brian

Smokin

Since I have a dedicated rear spoiler I no longer need the spoiler up/down switch. I was looking at places to put the cylinder head temp gauge when it gets here. This seems like a likely location...



What do you think?

Marc Shaw

I think Jack has some better shots of his new undertray here: https://rennlist.com/forums/racing-and-drivers-education-forum/194497-how-many-zip-ties-does-it-take.html (from the racing forum).

Looks cool plus it has that "intimidation factor" if you see him bearing down on you!

Marc

Dunasso

When I use to race aircooled VWs, dirtbikes, and go-carts, using Methanol, the magic number for the temp was around 375F. The dirtbikes and go-carts had a sender ring which went under the spark plug threads, sandwiched between the the SP and the cylinder head. They had a heads up display in the steering wheel or mounted on the handlebars. This would allow adjustments to be made during practice events while driving on the track. The VWs had a sending unit that was threaded into one of the heads. These, used a temp gage mounted in the dash (VDO). It was a bit more tidious to get the temp right because the mixture could not be adjusted while driving.

Duncan

DonW-Cape Cod

Where would you-all mount the guage?

JackOlsen

I've put two gauges in the center console. I'm currently modifying the console to take three of them, which is a little trickier.

Here's the old setup. (Normally, the regular ashtray cover is there instead of the hotlap display.)

Smokin

I just got my VDO cylinder Head Temp gauge from the link on the prior page. It includes a mount for handlebars on a motorcycle! It is the type that uses the ring sensor under the spark plug. I don't see any reason why it wouldn't work correctly as long as the terminal will fit under the spark plug. They certainly give you enough wire to make the run. I think the ad showed motorcycles and VWs in their application.

Has anyone had any experience with this type of installation?

JackOlsen

I just put it in on my car. I wanted to put the sensor on the #2 or #5 cylinder (since they're sandwiched between cylinders, and are likely to get the hottest). I tried putting it in from the top plug on number 5 (passenger-side, middle cylinder), but couldn't get the plug to find its threads, for some reason. I tried it on the plug that's accessed from below on #5 and had no problem.

You have to remove the washer on the plug and replace it with the sensor ring. When you're doing it, I'd recommend putting some electrical tap around the sensor wire until you're happy with the installation. This will keep the woven fiberglass insulation from fraying.

The gauge runs without power (although the gauge light will need it). DO NOT run 12V through the sensor circuit itself. You will destroy the gauge and it cannot be repaired. I'm not sure if it will make a difference, but I wouldn't cut the wires provided with the sensor. It might change the resistance that the gauge is measuring. (I'm kind of ignorant with electrical stuff, so I play it safe).

I tested my sensor ring by dipping it in a cup of boiling water. My gauge read correctly. I put my gauge in a center console.



As you can see, I was driving before I took the picture, and the gauge is 'always on.'

Geoffrey

Jack, I believe that cylinder 1&4 are the hottest due to the 90 degree angle the air through the fan needs to take.

Smokin

Jack... Thanks for the input. I think I ordered it from the link you provided so we have the same one. you have a pretty trick installation! It looks like a stock mount. Unfortunately I don't have that room so I will try to put it in where I mentioned above. It looks like it will fit... Though I would like a voltmeter and/or ammeter too.

I agree about line length. I could swear that I read somewhere that the extra length should NOT be cut because it could change the resistance. Whether or not that's true... I'll keep the stock length... Plenty of places to hide it.

Thanks!

Rick

bhensarl

Let's see yours when you get it installed, Rick! With the full play-by-play if you don't mind.
Brian

Smokin

I'm still wondering exactly where to put the cylinder head temp gauge. My first thought was to put it where I have noted in the picture a few posts above. But now I'm also thinking about adding a volt meter and/or an ammeter. If I do... I'd want to cluster them together. I doubt there is an aftermarket A Pillar mount such as posted HERE . OR... I could go with a "pod" mounting system as seen in the top picture shown HERE ... And mount them somewhere on the top of the dashboard.

I'd love to be able to mount to the A Pillar... But it is so thin I think the gauges would stick too far out and possible obscure forward vision. I'd also have to make my own. (Which would be kind of fun.)

Any suggestions?