Ally radiator............

[steveww]

While I've seen the circa 70 deg C = more power claims in numerous racing oriented texts, in all the technical texts regarding engine design that I've read I've not found one single reference to back up the low temperature coolant = increased power claims.

The way a lower temp works is by allowing a bit more ignition advance is how it was explained to me. Whether this actually works or not I have no idea.

Keith,

The comments about the electric chair were a bit strong and not really called for.

[type26owner]

Steve,
My apology. Please don't represent someone's opinion as an irrefutable fact anymore though. Without some data to support what they claim they have as much validity as my wife.

When I'm not absolutely certain something is true I indicate that in someway in the same paragraph. When I state a fact you can be sure I already have a reference(s) to support my contention. Bullshitting doesn't get you very far in an academic research laboratory environment. I try not to do it here either.

We share a common love of the car afterall. Reducing the pain factor by solving technical issues is the theme of this polite forum.

[M100]

Had a quick glance at a few of my reference books and there is a brief mention in Heywood of the effects on internal metal temperatures for the cylinders and valves by changing water temperature.



COOLANT TEMPERATURE AND COMPOSITION.

Increasing liquid coolant temperature increases the temperatute of components directly cooled by the liquid coolant. Figure 12-28 shows the result of a 50-K rise in coolant temperature in a spark-ignition engine. The exhaust valve and spark plug temperaturesare unchanged. The smaller response of the metal temperatures to coolant temperature change occurs at higher heat flux locations (such as the valve bridge), and indicates that heat transfer to the coolant has entered the nucleate-boiling regime in that region. The response is greater where heat fluxes are lower (e.g., the cylinder liner), indicating that there heat transfer to the coolant is largely by forced convection. When nucleate boiling occurs (i.e., when steam bubbles are formed in the liquid at the metal surface, although the bulk temperature of the coolant is below the saturation temperature), the metal temperature is almost independent of coolant temperature and velocity. Addition of antifreeze (ethylene glycol) to coolant water changes the thermodynamic properties of the coolant.

[type26owner]

Martin,
I'd have thought the temperature of the exhaust valve seat and the stem of the valve would be the other way around. That does not make sense to me. The seat would melt the aluminum head at that highest temperature. That I've never seen. I'll bet this a cast iron head engine. Then those numbers would be reasonable.

Rohan, have you ever seen a seat come loose before associated with an overheating event? What has happened several times to our BRM race engine was the piston skirts scuffed badly and started to sieze. Nothing else bad happened.

There are pros and cons to an aluminum head. The thermal properties are in the pros column.

[rgh0]

Keith

I have seen loose seats in a couple of abused engines. Hard to tell the orginal cause but probably all related to overheating events.

I have only had one valve seat ever come loose in my engines. However the cause was not overheating but when I dropped a valve. The valve head destroyed the combustion chamber leaving nothing to hold the valve seat in place!

Rohan

[type26owner]

Yup, I've got three more BRM heads under the workbench that have been welded up already to repair those kind of surprises. We robbed a valve from some other engine and finally cured that problem but I can't remember the details from 30 years ago. Have to get around and finish machining them to press them back into service someday.

[bengalcharlie]

Hi,

I have a narrow 2 core radiator fitted to my plus two with the standard electric fan in front of the radiator.
At present I keep the temperature at about 85 degrees celsuis and I am happy with that.
This is after having fitted a 72 degree celsuis thermostat.
Initially I did have a 82 degree thermostat fitted but the temperature would rise to well above 90 degree.
I asked a long time lotus elan owner locally and according to him a twincam should ideally run at about 75 degrees.
Does that sound right?
However I think that during our winter time I will replace the current thermostat with the 82 degree oen

cheers

Robin

69 elan plus two
60 alfa giulietta spider

[bengalcharlie]

Soory guys,

I did not see that there were already three pages posted when I posted my question about the right engine operating temperature.
I see there is no right answer and that there are some different opinions about this subject.
All I can say is that my engine runs great except that it sometimes keeps runningafter having switched off the ignition ( detonation) although it never detonates driving the car.
I suspect the sparkplugs being to Hot? NGK 7BPES
Another lotus owner recommended I should try NGK 8BPES

Cheers

Robin

[type26owner]

Hey Robin,
The higher the number, the colder the NGK plug. Your plug choice is already really colder then the normal one by about 180C. A plug which is at the desired self-cleaning temp keeps it's insulator greyish/white but not brown. If you've got dieseling after the ignition is shutoff then your AFR is not okay inspite of it running decently. You likely have carbon builtup in the combustion chamber. Time for you to treat it with ChemTool. If that won't do it then a small amount of water sprayed into the carbie will.

[M100]

Martin,
I'd have thought the temperature of the exhaust valve seat and the stem of the valve would be the other way around. That does not make sense to me. The seat would melt the aluminum head at that highest temperature. That I've never seen. I'll bet this a cast iron head engine. Then those numbers would be reasonable.

The original source paper quoted by Heywood was "French and Atkins Thermal loading of a Petrol Engine, Proceeding of Institute of Mechanical Engineers Vol 187, 49/73, pp 561-573, 1973" - I don't have easy access to this but I would guess from the publishing date it would be a CI head.

Not sure where you can see the valve stem temperatures ?? although measurement points 15 and 17 seem a bit ambiguous.

[Dave-M]

More fuel to the fire regarding high or low running temps.
Have a look at the following (about half way down) regarding temp vs oil film thickness.
This is part of a series on valve train design and makes very interesting reading

http://www.profblairandassociates.com/p ... %20010.pdf

Regards
Dave-M

[Dave-M]

Sorry for double post

[type26owner]

Not sure where you can see the valve stem temperatures ?? although measurement points 15 and 17 seem a bit ambiguous.

Not knowing where the thermocouples were actually attached makes one guess at the location. It usually all goes wrong at that point. This data does not really help answer the main question.

The only conclusive evidence I'd love to see a dyno sheet that shows the torque peak when the twinkcam engine is operating at 72C. The few ones I've seen for other types of engine are all around 100C.

[type26owner]

Hi Dave-M
I would read it if it would not hangup my Firefox browser. I can't bring it up. What does it say?

[Dave-M]

Kieth, Just type it into the address box and press go.
Dave