Does a cold engine make more power?

Originally Posted by Rhymingmechanic
When I drag raced, it seemed like my first run of the day was always the best, whether I drove the car 40-45 minutes to the strip or trailered it. Maybe cooler air earlier in the day accounted for some of that, but I also noticed better ETs with coolant temps at 180 or lower compared to 185 or higher. This was with a fairly mild Pontiac 400.

That's interesting, thanks for sharing. Maybe trans temp could have something to do with why your first run is the fastest? Presuming you had an auto, if your trans was heating up the torque converter could be slipping more and wasting more power?
 
The temperature thing is interesting. If anyone has the Motor Trend app, Engine Masters did a show on this. They found there was a significant gain in power when the fuel was cooled, more than the intake or the coolant in the engine. One of my friends has a 360 sprint car and when I showed him the episode he smiled adn said that was what he found during his many hours at a engine dyno.
 
Originally Posted by bdcardinal
The temperature thing is interesting. If anyone has the Motor Trend app, Engine Masters did a show on this. They found there was a significant gain in power when the fuel was cooled, more than the intake or the coolant in the engine. One of my friends has a 360 sprint car and when I showed him the episode he smiled adn said that was what he found during his many hours at a engine dyno.

I saw that, both their video on how heat kills power and iron vs aluminium heads. However, what they found regarding coolant temp doesn't seem to apply to all engines since other people have done the same test on other engines and found that hot coolant made more power with all else being equal, so I guess it really depends on the specific engine.
 
A lot of this uncertainty is directly related to emissions control. The computer can do all sorts of trickery depending on coolant temps and Intake air temperature. And you're right... any engine allowed to idle will heat soak and have reduced power. Intake air temperature can get pretty alarming on a summers day if you let an engine idle for a while. It takes driving to bring it down. IAT has a significant effect on engine power.
Also, when cold, the computer runs the engine rich to act as a choke would on a carbureted car. Cold engines require a richer air/fuel ratio. Conversely, the EPA wants leaner mixtures for pollution control. I don't know about newer exotic tech but most of the old fuel injected cars I had from the 80s-2000 you could FEEL more power when the engine was warming up because of the richer ratio more conducive to power. It seemed like 15 more HP on one of the old 5.0L fox bodys. In fact one of the old racer's tricks was to fool the coolant temp sensor so it thought it was always cold to gain a few hp, but I sware some of my old 5.0s felt noticeably faster as it was warming up. Like feeling like 15 hp or something. But that was seat of the pants.
All of this goes out the window on a race engine that is designed for maximum power and no regard for emissions. I don't know all the answers, but I do know you want hot oil and the coldest intake air temp possible. Kind of a mutually exclusive endeavor. Not sure on coolant temp. That has something to do with the thermodynamics in the combustion chamber and cylinder that any Mechanical Engineer worth his salt can easily explain. Any takers?
 
Originally Posted by Avery4


Years ago I read an article where someone dyno tested apparently otherwise identical iron and aluminium heads to see which made more power and with everything else the same the iron head made more power, which made sense to me since the iron head holds more heat in the combustion chamber and absorb heat slower. However, I saw an Engine Masters episode yesterday where they did the same test and with everything else the same the otherwise identical aluminium heads made more power because they kept the cylinders cooler. I'm so confused
confused.gif



There's also a chance that one or the other will let them bump the timing up without pre-ignition. Ergo the quantifier "everything else the same".

As said above, there are gains to "reverse flow" water pumps and other design decisions.
 
from purely theoretical thermodynamics, the hotter the engine, the more efficient it is. Efficiency is not power. Gas mileage drops in the winter, but power increases (ignoring ethanol mixtures). My physics class taught us that a Ceramic engine block could achieve much higher efficiency than metal blocks because Ceramics can achieve much higher temperatures without melting. But no manufacturer has made a ceramic engine without cracking and other brittle issues.

“ The efficiency of ordinary heat engines also generally increases with operating temperature, and advanced structural materials that allow engines to operate at higher temperatures is an active area of research.”


you can produce a lot of power without being efficient at all, maybe using 10% of heat energy to make 1000hp
 
You can make more horsepower with a cold engine as evidenced by Nascar qualifying. This is a moot point on modern engines with fuel injection and closed loop oxygen monitoring computations. The computer controlled stoichiometric ratio insures the best efficiency will also pretty much insure the most horsepower at the same time without harming the engine.


A interesting side story, when I ran the USCG 44 footers in Oregon there were times that we had to go full throttle right from the dock. Those engines were not putting out the power needed till about five minutes along the way. That cold water really affected the performance until they got to operating temperature.

I have used that same analogy for any engine. Maybe I’m wrong?
 
I have used that same analogy for any engine. Maybe I’m wrong?
What about the expansion of metals inside the engine? Having a cool, oxygen-rich combustion chamber is not the same thing as having a cold engine. You will not get proper compression from a cold engine, amongst other things.
 
A warmed up engine with cold air coming in is what you want. Some engines heat up the intake tract with sustained running which hurts power, heck some engines used to run coolant around the intake manifold to boost intake temps for mileage efficiency, but I think most now have a plastic intake with reduces heat soak quite a bit if the engine is pulling some air through. The scangauge in my Focus shows air intake temps at ambient when running on hwy. The intake temp will creep up quite a bit if the car is just sitting idling though as the intake is right behind the rad.
what if i wrapped ac coils on the air intake? That would result in some good results
 
What about the expansion of metals inside the engine? Having a cool, oxygen-rich combustion chamber is not the same thing as having a cold engine. You will not get proper compression from a cold engine, amongst other things.

That’s where I have to defer to the engineers. I was on the throttle and wheel and not in the engine compartment.

These were Detroit diesels. They were plugged in at the dock to keep the water jackets and I think the oil warm all the time. In normal situations we would idle away and increase speed slowly to let things warm up properly. In those few cases it was full throttle right off the bat. You could tell the performance suffered.

These engines didn’t have long lives and needed constant maintenance and repair.
 
That’s where I have to defer to the engineers. I was on the throttle and wheel and not in the engine compartment.

These were Detroit diesels. They were plugged in at the dock to keep the water jackets and I think the oil warm all the time. In normal situations we would idle away and increase speed slowly to let things warm up properly. In those few cases it was full throttle right off the bat. You could tell the performance suffered.

These engines didn’t have long lives and needed constant maintenance and repair.
I almost forgot to reply to this one. I am not an auto engineer. However, I believe that the issues that you guys were experienced were due to metal expansion. The coolant and motor oil might be kept warm. However, even then, you need to give the metals inside the engine a bit of time to warm up and expand. When you leave full throttle with a vehicle from a cold start, the metals expand too fast and at different rates. Maybe I'm wrong. However, this would explain the reliability issues and constant repairs, along with the short live spans that these engines experienced.
 
Its air inlet temp that makes the difference.
A denser cooler charge can pack more in the cylinders making more power.

You need a warmed up engine to seal properly but the colder the inlet air the more power it will make- as the whole holistic assembly heat soaks this gets hard to do later in the day.
 
Its air inlet temp that makes the difference.
A denser cooler charge can pack more in the cylinders making more power.

You need a warmed up engine to seal properly but the colder the inlet air the more power it will make- as the whole holistic assembly heat soaks this gets hard to do later in the day.
Nailed it!
 
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