Does a cold engine make more power?

Avery4

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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?
 
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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.
 

Avery4

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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.
 
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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?
 
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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
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.
 
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