Water temp and it's effects on power and emissions

[rev-erend]

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

[Boosted LS1]

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.

[rev-erend]

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.

[GreenV8S]

Thinner oil would reduce friction at all the bearing surfaces too - as long as the film doesn't break down. The effects surely wouldn't be much though. I think the mechanical expansion of the block and increased piston clearances are probably more significant effects.

[350Matt]

Oil temp does have quite a strong effect on power, if the sump temps are below 70°C the windage loss is pretty high, at 6000rpm I would guess about 6-7 bhp. Its diminishing returns after that point with most oils

Matt

[spend]

Theres also the lube, working clearances etc. in the box & diff.... Getting everything upto even operational running temps is a bit of a lack art IMHO. RR's are bursts of heat then 'standing/cooling' which is not quite 'road conditions' however you look at it. Even as guideline your temp sender is only measuring a single point, which may not be a true indicator of the range of temps round the block & manifold, never mind the rest of the car???

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

[GreenV8S]

350Matt said:

Oil temp does have quite a strong effect on power, if the sump temps are below 70°C the windage loss is pretty high, at 6000rpm I would guess about 6-7 bhp. Its diminishing returns after that point with most oils

Matt

Windage losses as in airo drag on the crank? How does that depend on oil temperature?

[rev-erend]

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.

[Boosted LS1]

GreenV8S said:

350Matt said:

Oil temp does have quite a strong effect on power, if the sump temps are below 70°C the windage loss is pretty high, at 6000rpm I would guess about 6-7 bhp. Its diminishing returns after that point with most oils

Matt

Windage losses as in airo drag on the crank? How does that depend on oil temperature?

Thick oil mist versus thin oil mist and counterweights passing through, maybe. Viscosity stability needs to be stable.

[GreenV8S]

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.

[spend]

Do the second and third runs have any differences then? I reckon getting the engine / drive train to its steady state condition might just be impossible on a RR (or at least not in the remit of the operator or the available ventilation ((wind tunnel + RR might be a bit expensive?). The longer / more often you run the more likely you are to get the bits heated through evenly, but then you hit the isolated overheating due to lack of cool air that you would get on the open road.

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?

[rev-erend]

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.

[GreenV8S]

Your point about transmission losses is a good one. I think it would be usual to do a coast down test after each power run which in an ideal world would compensate for this, but I don't know if actually does. I guess you also have warmer tyres which could reduce slip at the rollers?

[rev-erend]

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..

[Busa_Rush]

Most cars run at water temp of 90+ish C for lower emissions compared to 75-80 C for more power. You need to be up at 75C water temp for the oil to be doing any good in most cars as it will usually be 10-20 degrees hotter than the water and needs to be at 80C to 100C to operate in its designed range.

Most motorbike engines run at water temps of 70-80 C for max power.

[That Daddy]

Busa_Rush said:

Most cars run at water temp of 90+ish C for lower emissions compared to 75-80 C for more power. You need to be up at 75C water temp for the oil to be doing any good in most cars as it will usually be 10-20 degrees hotter than the water and needs to be at 80C to 100C to operate in its designed range.

Most motorbike engines run at water temps of 70-80 C for max power.

I would go with this one,i mean what can you tell the Japs about engines ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, nothing,bike engines are complete marvels of quality engineering at its best and at mass production levels

Edited by That Daddy on Friday 7th November 23:13

[spend]

brushsalesman said:

i mean what can you tell the Japs about engines ,,,,,,

Computer tells me "あなたのエンジンは流出する機械を食べる米である"

which if PH rendered it would obviously translate to 'your engines munch rice and make effluent'

Edited by spend on Saturday 8th November 01:20

[That Daddy]

spend said:

That Daddy said:

i mean what can you tell the Japs about engines ,,,,,,

Computer tells me "あなたのエンジンは流出する機械を食べる米である"

Spend as usual your out of your depth son dont start digging a hole for yourself,you know what happened last time leave this one to the posters who have already contributed good replies(your not one of them) so just stick with what you know,i would not doubt your knowledge of the TVR car for one second but dont start getting ambitious.

Edited by That Daddy on Saturday 8th November 00:27

[HiRich]

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.

Whilst I understand what you're saying, I believe there's still a lot still to do with cylinder wall temperatures. Energy loss via heat into the block is significant (around a third of the chemical energy), and there are a lot of effects (good & bad) from increasing wall temps. Working from memory, as it's a long time since I did engines:

• Warming the incoming charge (bad)
• In the micro-climate very close to the wall, leave too much energy in the unburnt charge, allwing the fuel to decompose, become volatile, and detonate (bad)
• Risk of higher peak temperatures & pressures (bad for NOx emissions, but potentially better for power)
• Conversely, in the same microclimate, not quenching the flame early. That's a little more power and better emissions (good). Incidentally it's a similar issue that causes the emissions problems for wankel engines - heat loss & incomplete combustion through the large cylinder surface area.
• Expansion phase will be closer to adiabatic - which should increase the amount of extractable power (good)

If, on a new design, you can extract the benefits whilst managing down the drawbacks, it looks like there's scope for improvement. Whilst more for the aero improvements from smaller radiators, the F1 engine manufacturers have certainly been investigating this area.
So not particularly relevant for a 40-year old design like the Rover, but in another twenty or so years I think we'll have seen some noticeable advances in this area.

[tvralfagtv6]

That Daddy said:

Busa_Rush said:

Most cars run at water temp of 90+ish C for lower emissions compared to 75-80 C for more power. You need to be up at 75C water temp for the oil to be doing any good in most cars as it will usually be 10-20 degrees hotter than the water and needs to be at 80C to 100C to operate in its designed range.

Most motorbike engines run at water temps of 70-80 C for max power.

I would go with this one,i mean what can you tell the Japs about engines ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, nothing,bike engines are complete marvels of quality engineering at its best and at mass production levels

Edited by That Daddy on Friday 7th November 23:13

Interesting point there was a chap tup north who built all the Honda winning superbike motors in his shed. Forget the guys name but all the honda works engines were built in the uk so don't underestimate British engineering excellence. but I get your point and agree re bike engines