Technical Effect of engine size on cooling

Question about cooling as related to engine size. I would like to hear of some actual examples if there are any out there. Here is the hypothetical setup:
406 ci Chevy with adequate radiator cooling capacity, good water pump, 160F thermostat, and fan/shroud all correct. Under normal highway driving, the engine runs at 200F.
Assuming no other changes to the variables, except engine size, what would be the operating temperature be for a:
350ci
327ci
301ci
283ci
Maybe there would be notable differences...don't know.
Thanks

 

This is a little backward to your question...but. Yea, It might run a "little" cooler, depending on how low you go in inches, and how modified the new engine is.

In my old, first car...56 Chevy 210 sedan, with the stock 265 and powerglide, OEM radiator...
The last engine was a fairly hot 350, with a 4 spd. and much more rear gear, SAME...OEM radiator.

Ran...as I recall 165° (ish) with a 160° thermostat with the 265. Four bladed fan.
It ran a very reliable 185°/190° with a 180° thermostat with the 350. Six blade fan.

Mike

 

I think the question is flawed, if you had an adequate cooling system, the 406 should run at or near the T-stat rating on the highway, certainly not 40*'s higher.

 

Should not make that much difference in a light vehicle. If its a really heavy vehicle used for towing, or something similar with prolonged full throttle, then you need more cooling.
Big heavy vehicles need big heavy radiators.

If you have a LOT more power, you can only use it for less time anyway. How fast will you be going after twenty seconds at full throttle anyway ?

Its why guys can fit turbos or blowers and end up having two to three times the original power, and the stock radiator and cooling system works just fine.

 

Operating temp will be the same with same thermostat. Anything with more HP will produce more heat into cooling system but should operate about the same temp.

 

Heat rejection is a function of fuel rate. If the amount of fuel burned is also a function of power required to move the car down the road, engine size, within reason, shouldn’t change much, all other things being equal.

Realistic though, the larger engine has more pumping losses, and flows more fuels while idling or running at a given speed at a given air/fuel ratio, so the smaller engine will reject more heat to the cooling system.

Also, the more powerful engine is more apt to be driven in an aggressive manner, increasing fuel consumption and heat rejection.

As long as the cooling system has the ability to reject the heat generated by th burning fuel, though, the engine will run at the thermostat opening point or band.

 

I think the heat produced by an engine also depends on the efficiency of the engine and other design features not just C.I.D. I run a 292 Y block in my Model A with a stock Model A radiator, it runs cool even the hottest of days. The stock Model A engine was 200 cid and the Y block cid 50% larger at close to 300cid. Lets looks at the Ford flathead with the exhaust going through the cooling system, I would think it would be harder to cool that than an engine without that feature. My '37 Cadillac with a 346 ci flathead V8 has a very large radiator, holds about 5 or 6 gallons and is not a cool running car, does not over heat but it takes all of the cooling system to keep the temp down.
I know in your question you are talking about similar designed engines so they would have less of these variables but I would think cylinder wall thickness, compression ratio and other things would be a factor as much or almost as much as displacement.

 

Given the information in the OP, there would be no change in operating temperature by simply changing engine displacement.

As posted above, there are many things that will affect cooling, but not in this case with the limited info.

 

Let’s just watch what happens here, it should be good

 

I'm seriously considering putting the 396 back in my old truck, because the 454 just runs a tad too warm. I had the same issue with another similar truck when I went from a 402 to a 454.

There's no way to give you numbers, too many variables...but I think you'll notice a significant change going to the 350, and the difference will taper off as you make your way down to the 283.

Give it a try, publish the results here, then we'll all know!

 

Any expected difference for same engines running different compression ratios.
I would expect a low compression engine may have a chance of running cooler than its high compression buddy.
Just speculation, can anybody support or condemn my theory???

 

I have the same radiator and thermostat in two vehicles.
1 - 36 Chevy truck, mild 350, 700r4, electric fan and AC, it runs at 180* up to 195* with ac on in traffic, takes a while to warm up.
2 - 1940 Chevy Coupe, 632", 900+hp, engine driven fan, it runs at 180* up to 200* in the staging lanes. it warms up quickly.
Amazing these have a cheap vertical aluminum radiator from speedy. something like 19" x 26". I was shocked it keeps the big block almost as cool as the little 350.

 

Someone earlier said it. The amount of heat CREATED is due to the amount of fuel burned. I will add, the amount of fuel burned in a given amount of time. What most of us cal "overheating" is in reality, under cooling.

Thermostats have nothing to do with max temp. Only minium.
An engine runs and performs better at a higher temperature. Not to mean an excessive temp. 200 is better than 160. Not being able to control at 200 can be bad.

Don't know if this is on topic or no. Hell, don't even know where I was headed.

Ben

 

@finn and @46international are on the right track. What causes heat anyway? It is the energy in the fuel being released in the combustion chamber. Roughly 33% of that energy (and that's on the high end of the scale, some are less efficient) is used to propel the car down the road, another 33% is lost as heat out the exhaust system, and another 33% is lost as heat into the cooling system. Heat lost via the exhaust and the cooling system is due to inefficiency of the engine, a 100% efficient engine would lose no energy as heat at all, but as we all know, that is impossible. But the heat generated depends on the amount of fuel consumed and the efficiency of the engine. In the example in the OP a smaller engine would not necessarily run any cooler in the same vehicle under the same conditions, except for improved efficiency, less fuel consumption. If it takes 50 horsepower to move a car at X mph down the road, it doesn't matter the size of the engine doing the work, 50 hp is 50 hp. Engine efficiency will determine how much fuel is required to create the 50 hp, and how much heat is created in the process. A less efficient engine burning twice as much fuel to do the same job will also create twice as much heat. I'm sure there is an equation engineers in the auto industry use to determine the cooling system capacity requirements for a car that takes into consideration fuel consumption rates and efficiency.

 

It is a pretty simple deal on cooling....Works out to BTU's in verses BTU's out...Larger engines can be harder to cool because of more cast iron that heats up....Lot of veriables in this...

 

What’s the compression ratio on each engine? A 283 works harder to do the same work as a 406.

 

Increasing compression ratio increases engine efficiency, because more of the heat produced by burning fuel is turned into useful work (the important thing is that the expansion ratio also increases). So as long as it's not getting it's timing retarded to prevent detonation, a higher compression engine should run a bit cooler....don't know if it's enough to see on the temp gauge, though.

 

I think you have to consider a couple of things. First a larger engine (built to same specs) is capable of consuming more fuel than a smaller engine and that fuel produces heat. More fuel consumption (properly burned) produces more heat. While it may or may not be a linear increase as the engine size increases is open for debate.
Next you have to consider that you most likely can't/won't build all of these engines to the same spec because because a cam that works well in a 400 may be too much for a 283......so you have to do something different. Same thing with valve size...whats perfect for a 400 may be too much for a 283. Then, in the case of the 400 you have a difference in the block casting itself. The cylinders have to be siamised in order to make the bores larger. There is a "steam hole" to move coolant but its not as effective as normal coolant passages.
In any engine the hottest part is the cylinder head. 500 Cadillacs often have a heat problem when installed in hot rods.There have been enormous radiators hooked to them without noticible difference in temperature. Some of the more involved builders are enlarging and adding additional coolant holes to increase flow to the heads. The LT1 Chevrolet made in the early ninties used a reverse flow where the coolant went thru the heads before it circulated thru the block. It worked very well with the factory aluminum heads. When Chevy stepped up to a more modern design using aluminum heads AND block, they went back to conventional cooling. The point here is that it doesn't matter how big a radiator someone has if they can't get sufficient flow thru the heads and also vent any air pockets in the heads. If your siamesed 400 block runs hot I would at least invest in some aluminum heads and someway to vent trapped air back to the radiator.

 

The magic number is 28 to 32 BTT/HP/Min for a Diesel engine. Can’t remember for Otto cycle. You can do a lot of engineering on things like ceramic coating of pistons and exhaust ports, but, in the end, the heat rejection will be in that range.

 

Thanks. The question may be a bit flawed, but I am not making any assumption about cooling system adequacy. If the system is inadequate, it could easy run 200 with a 160 stat.

 

Thanks, but not following how the temp would necessarily be the same with the same stat? It has been my experience that larger engines require more cooling capacity.

 

Yes, I agree that the factors you mention can affect temperature. Just trying to see if there is any consensus about temp variations in similar engines.

 

Assume 9.0-1 CR for all, just for grins.

 

Thanks. I have aluminum heads with steam holes drilled. As you have spelled out, there are a ton of variables which affect engine temperature. I was just trying to ballpark some numbers, on engines built as similar as possible.

 

Thanks, but that is over my ability to use.

 

Thanks, you are on topic...didn't even wander off any! Agree on thermostat comment. Lots of folks thin they can change their 180 stat for a 160 and drop their operating temp accordingly.

 

Thanks, that is an interesting comment on the similar temps of mild 350 vs 632. Never would have thought it.

 

Thanks, Squirrel. Good comments there, based on actual outcomes, not theory. Just what I am looking for. Your experience lines up with some of my swaps in the past. With very minimal differences in the builds, the larger CI engines I swapped in have always been harder to cool than the smaller ci ones i took out. Also agree with your thought there will be a noticeable drop from 406 to 350, then tapering off after that.

 

Good stuff, thanks.

 

@txcr13

You did say somthing along he lines of "adequate radiator...."

So, instead of beating around the bush, why not just tell the good folks on the HAMB, what the heck is your issue?