Cylinder Head Temps, My Experience + lessons learned Options

[rwilner]

I drove down to Chris Foley's shop to get his shift linkage installed this weekend. At the charlton plaza on I-90, I stopped to fill up. I usually put premium in the 914 but this time put regular in because it's what I put in my other cars and I was on autopilot. Oh well, I thought...let's see how she runs on 87, maybe I'm wasting my $$ on the good stuff.

Before the fillup, I was running between 300 and 325 F in 5th gear around 70-75 mph.

After the fillup, I was running between 380 and 400! (IMG:style_emoticons/default/ohmy.gif)

I spent the rest of the trip in 4th gear at no less than 3500 rpm to try and keep the head temps down. When I got to Chris' shop, we put the car in the air and drained out 5 gallons. I replaced them with 93 octane before getting on the highway for the ride home. My cyl head temps were back down to 310-350 for the return trip.

Here's what I learned:

• A cylinder head temp sensor and gauge are critical to know what's happening in your engine and should be on everyone's short list. Without it I would never have known of the dangerous operating conditions for the engine. The aircraft spruce gauge/probe are short $$ and a quick install.
• The state of tune has a major impact on running temps (duh). I am still tuning my car with the microsquirt and it's clear I have work to do.
• Higher octane gas makes your car run cooler.

As always YMMV but thought I'd share my experience.
Rich

[VaccaRabite]

Oh well, I thought...let's see how she runs on 87, maybe I'm wasting my $$ on the good stuff.

Before the fillup, I was running between 300 and 325 F in 5th gear around 70-75 mph.

After the fillup, I was running between 380 and 400! (IMG:style_emoticons/default/ohmy.gif)

What kind of compression are you running, and what engine size?

On 93octane with 9.2:1 compression in my 2056 I'm always in the 370-400 range in 5th, and so am always driving in 4th on the freeway to keep temps down. Works, but not where I want to be. My area has long hills and that is part of the issue, but I still think I can tune it cooler.

Part of the reason I am going to megasquirt is to try and better tune my engine out of the red zone in 5th.

A good head temp gauge is CRITICAL if you are modifying these engines in any way away from stock. Without the gauge, there is no way I can tell from the drivers seat that my engine is getting hot.

Zach

[rwilner]

What kind of compression are you running, and what engine size?

I have a stock GA 2.0L except for european Ps and Cs, so that puts my CR at around 8.5:1 I think.

I think a CHT is essential even for stock engines because as the FI parts age the mixture will change which will have a major impact on running temps. My car was giving me no indication of poor running except for the high CHT.