Water temp and it's effects on power and emissions

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Just reading an interesting book on the Rover V8 by Des Hamill. How to power tune Rover V8's.

He raises an interesting point that the maximum power for the Rover V8 is produced when the water temperature is 75 degrees but does not go further to substanciate the claim only to say that much higher temps result in a 10 bhp drop.

And yet for Emissions - the best temperature seems to be 98 degrees - I guess this is just so the Cat is as hot as possible. With the fans being set to come on at 95 ~ 98 degrees.

From talking with people like Vixpy - he says that TVR's often seem to always produce their best power figures on the second dyno run - which seems to contradict the lower temp theory - in that latent heat would have been built up in the engine water system..

What do you guys think is the ideal engine temp for bhp and do you have any knowledge to substanciate this ?

Edited by rev-erend on Thursday 6th November 09:11

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Boosted LS1 said:

I think higher temps reduce friction due to the block expanding. High oil temps may also be a factor in reducing resistance. The lsx's frequently convert to a higher temp thermostat.

Interesting point - probably less pumping losses as the oil being thinner would take less effort to pump, although I think that would be a very small amount.

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spend said:

The classic Vizzard "Get it in, keep it cool, squeeze it tight, aggressively light it off, burn it well, expand it with minimum loss and dump it." is enough for me

OK - the area's in the engine that are cooled are :

Around the bores (first), then around the cylinderheads (last).

The piston engine is a heat expansion engine (basically.. I think) if the cylinder walls and head are too cool then the heat will soak into them and this heat will effectively be wasted. The objective in the cooling is to stop the block and heads from getting too hot and twist / buckle ..

Now the hotter this can be must be better for the thermal efficency ..

So for instance - I would think it was more thermally efficent at :

98 degress than 75 degrees

But due to the block design and specifically the liners the ideal temp must be somewhere in between.

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GreenV8S said:

If you're concerned about the hot gasses losing heat to the chamber walls after burning I think you can forget about any changes in engine temperature. The combustion gasses are over 1000C hotter than the metal around them and changing this by a few degrees either way is not going to make any difference.

Changing the temperature (and hence density) of the incoming charge on the other hand is very important.

Good point - hence why it's best to remove any heating pipes possible from the inlet system to help it run cooler.

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spend said:

If I remember correctly Rob has been an advocate of running cooler water temps, and I would have thought the data he has from the engine dyno might be more appropriate to evaluate your hypothesis?

That would be very interesting..