Temperatures - a log

[Boink]

AKA "Experiments in Operating Temps" or "No no no, don't touch that."

Having fooled with a possible vapor lock problem, and not found that to be the issue, I became side-tracked with an amusing study. Using my trusty laser-guided infra-red thermometer gun, I thought I'd record some temps related to my 1275 (with dual HS2s). Curious? Of course you are. :cooler:

So, I let the engine reach normal operating temperature (though it was cold outside - maybe 45F), and then I collected the following values for a stationary car in the garage. Most values varied a bit (but the range wasn't significant), and all are Fahrenheit... and I probably could have let the car warm up a tad more (though I believe the temp gauge read about 175).

Exhaust header pipes = 530 (though at the head closer to 550)
Exhaust pipe = 260, half way back (under driver seat)
Muffler = 285
Tail-pipe = 60 (it was cold outside)
Engine Block = 167 header side, 144 passenger side
Sump = 148
Rocker Cover = 93
Carb Heat Shield = 123 (with header below it)
Carbs = 90s?... but variable depending on where
Radiator Top = 126

Useful? Absolutely not, but fun. So, for all the kids out there, don't touch the exhaust system.

 

[Spridget64SC]

Very interesting information. Typically on the 1275 race engines, we'll see 400-800 degrees F at idle depending upon needle used in the HS2's. This jumps to 1300 - 1400 degrees F at full song at the end of the long straights. This is measured via a Type K thermocouple located in #1 and #4 pipes a couple inches from the exhaust manifold to cylinder head junction and indicated on an EGT gauge in the cockpit.

What I find interesting was the comparison of the sump temperature to the water/radiator temperature. Both seemed low, but the water being lower than the oil is what is interesting. Must have been a cool day indeed with the radiator doing its job very well.

Thanks for posting the information,
Mike Miller

 

[Boink]

Interesing info on the race engine. I had know idea that they were monitored so closely (though, duh, it certainly makes sense). Those are amazing temps!

I suppose we could look up the specific heat (or heat potential) of a gas/air mixture to establish a high end, but I'm guessing the exhaust ports are the hotest (given the head is surely kept cool enough). I also read that exhaust gases are around 1100-1200F. Beats me.

I think I'll repeat all this after a drive (when I know it's fully warmed up) and not so cool outside. I'll also try to do a sampling around, say, the sump. There is considerable variability to be found in some locations. I was just glad that the fuel systems had reasonable temps (given my earlier concern about vapor-locking).

Adding: I think you're right about the cool day effect. The fan had the radiator fin section at about ambient temp (around 45). So, I think that does explain the rad being so low.

 

[jlaird]

You have just proven my contention that the BE cooling system really works and works well.

If your engine overheats you have a problem that can be fixed with cleaning and restoration.

 

[Boink]

LOL Amazing what heat-holding potential there is in grime. Maybe that's why I always feel hot.

 

[jlaird]

BOINK

 

[racingenglishcars]

Specific energy for fuel 42000 kJ/kg

The cool part is that the combustion cools off as it decompresses. First decompressing as the piston travels down the bore, secondly decompressing as it passes the exhaust valve.

Cars with higher compression, arbitrarily also tend to have more decompression. The combustion cools more towards the bottom of the stroke than an engine with lower compression.

This is compounded by the air/fuel ratio. More fuel burns longer and can produce higher EGT. Unless it's too much and it cools the EG. Proper amount of fuel theoretically burns more completely but in practice doesn't since combustion happens so fast. Too little will combust more completely than stochiometric and therefore burn hotter, but will in no way produce the power that a rich mixture will.

So Mark, Just for fun try adjusting your carbs a bit and measure it again under identical conditions.

 

[Boink]

Good one, Donn. Yes, tweak the carbs and check the temps. Kinda of a new version of Colortune. Not sure my stoichiometry is spot on... otherwise, surely I'd have just carbon dioxide and water out the tailpipe.

 

[Spridget64SC]

The dyno runs performed so far have us chasing a Air/Fuel ratio of ~12.5. That seems to be where these 5-ported 1275 engines with our sanctioning body's (SCCA here in the states) limitations on the engine configuration work best. Making betwe 100-105 BHP at the flywheel on the good ones at the moment. One weekend in South Carolina, we'll be adjusting trying to get up to 1350, and the next month in Georgia, we'll be adjusting trying to get down to 1350 on the EGT's. Always chasing the right tune. We'll look at the ambient temperature, relative humidity and barometric pressures trying to make an educated guess as to where to start out the weekend. Then use the EGT readings to determine if the choice was correct or we need to go in another direction.

Like Donn says, a richer mixture will produce more power, but for the street, its better chemistry equals better mileage. In these days, the better the mileage, the more $'s for other things for the car.

Take care and have a great weekend.
Mike

 

[Boink]

This is fascinating, Mike. I can well imagine how all these atmospheric variables come into play, and yet your main control is the simple mixture. Can you alter all this with supercharging pressure?
- Mark