333pg333

So as we're all told that the more hp you induce from your car, the stock cooling system can begin to struggle and we have things like steam vent kits and alternative water pumps suggested. My question is why does extra hp / tq make such a difference to the water temps IF you don't increase your rpms by much or any? So let's imagine that the hp increase is gained through a larger turbo, bigger cam, modified head, bigger headers and exhaust etc...you know the usual suspects, let's also assume we're going to run E85 (which burns cooler). So can we assume that the combustion temps change any? If so, why? You can monitor temps and tune with EGTs too.
Let's use 15psi as a reference boost level. Let's also assume we've got say a VR stage 3 kit and all the increases to our Volumetric efficiency via the other mods listed above. So we're running same boost but have gained eg 100whp. Let's also take 200lbs off the car and reduce the load.
Why would we see the temps rise?

Perhaps this isn't enough of a hike in power. So using E85 and the flexi fuel setup let's raise the boost to 24psi assuming all the components are up to it. Ok so how much hp do we have now? Can we say 450whp? Are we starting to boil the water yet? Do we need a larger radiator, bigger pump, steam venting etc? Have our combustion temps increased? If so, why? What am I missing?

Van

Simple:

power = energy

energy = heat

increase power increases heat

Another way to look at it... a candle is your engine at a low RPM. A blow torch would be your engine at a higher RPM. Obviously, a blow torch makes more heat than a candle. But, if you increases your power at the low RPM, that's the equivalent to putting lots of candles together - and again, it will make more heat.

anders44

correct, generating X KW, generates X heat, when you up it, more heat is generated.

stock radiator should be capeable of a lot imho, its quite big. but yes of course, you can't have a to cold engine.. you have thermostat, you can have it to warm

my new oil cooler is a setrab 650, aka 39x33cm covers 80% of radiator surface.. yay for no IC or ac condenser there.

btw, the candle/blow torch thing was a way more practical approach to it, and quite good

Willard Bridgham 3

The efficiency of Otto cycle engines (what we have) determines how much heat is wasted. Stock engines are designed to maximize efficiency for any given power.

As you increase the specific hp of a stock Otto cycle (more Hp), efficiency decreases and waste heat increases.

That plus what Van said......

adrian1

Just think of all the compression your running when under boost. I think its like 17:1 when 18 psi of boost. You'll ofcourse run hotter. I just been figuring an overheating problem on my car for the last fews weeks.
1. New coolant
2. New thermostat
3. low fan temp
And its almost there lol. Actually its good.

333pg333

OK but in this hypothetical we have increased all the parts to improve efficiency markedly. So this allows us to make more power much easier. Let's say that we don't increase boost or rpm but we just have 100whp more. Our combustion temps should be the same shouldn't they?

LUCKY DAVE

Here's the thing about the combustion process in your engine. It's an exothermic chemical reaction, and like (almost) all chemical reactions, it happens faster when you raise the temperature and/or pressure (put simply, the molecules bang into each other faster, so the reaction happens faster).
Since the reaction is (in this case) exothermic, the faster it happens the more heat is released in a given time.
In english, the higher the pre-combustion pressure, the hotter the burn, and the greater the amount of heat transferred to the surfaces that contact the burning gasses.
Remember, Otto cycle engines are HEAT ENGINES.

goldminer

I would have thought that if you are burning the same amount of fuel at the same compression ratio the heat generated would be the same. The increase in hp (at the wheels) would have to be coming from reductions in friction in the engine and drive train to get more power with less heat.
As an aside my car never runs hot, even on hot days at the track, maybe I'm not trying hard enough??

Van

Hypothetically, if you use a super oil, roller crank and cam bearings, delete the balance shafts, lighten the valves, crank, rods and pistons, lighten the flywheel, and remove all those pesky friction robbing gears in the transmission - but run your engine management exactly the same, I think you're right, you'd see a power increase measured at the wheels (or the one wheel bolted right to the drive shaft in my example) without a heat increase. But, on our engines, it wouldn't be 100HP it might not be over 25 (10% on a 250 HP engine).

For most people, though, to gain an extra 100 HP is going to require some means of consuming more fuel... which will make more heat.

Trucho-951

My $0.02..

With higher Volumetric Efficiency mods, one is simply stuffing a higher air mass flow rate into the engine, and along with the added fuel, the engine is now producing a greater amount of combustion energy.

Some of this energy is converted to mechanical energy (i.e. a better torque curve), and the remainder of this energy is converted in heat.

Although the mods mentioned above improved the engine’s volumetric efficiency (i.e., how much air it can process), what has not changed is the engine’s “energy conversion efficiency” , therefore a lot of combustion energy will be wasted as heat absorbed by the cooling fluids.

However, this is by design in order to allow the cooling fluids to survive.

If we wanted to improve the engine’s THERMAL efficiency so that our engine does not “waste” so much combustion energy, we would need to introduce thermal efficiency mods.

However thermal efficiency mods are not practical nor economical.

A higher operating temperature is necessary in order to reduce the temperature gradient between the combustion chamber and the operating fluids. This temperature gradient is the driving force transferring heat from the combustion chamber , through the cylinder walls, and onto the cooling fluids.

Again, thermal efficiency mods are not practical nor economical.


For example, some necessary mods would include things like: engine redesign to operate at a higher temperature, this would involve using different materials, for the pistons, rings, bearings, engine cylinders and block, and of course different clearances to accommodate the higher thermal expansion, also different types of operating fluids.


It is more practical to accept the thermal efficiency designed in by the engineers, and deal with the greater combustion heat output by improving the cooling air throughput, e.g., use better ducting into and out of radiators and oil coolers, and better venting to get rid of the heated air, e.g. using louvered hoods.

333pg333

Well we will definitely need more fuel as the E85 requires approx 25% more than the equivalent amount of pump....but it does burn cooler...so...
I was really just thinking out loud and trying to understand just how limiting our stock cooling system is. I guess there is the school of thought that may suggest preventative measures be taken before the event (overheating) takes place on some of these higher hp applications.
It would be interesting to see just what measures all the guys running say higher than 400whp have taken, if at all, and get their opinions. I know Corleone who possibly has the most powerful 951 on the 'list did mention he had cooling and/or pressurization issues.
See last page in this thread.
https://rennlist.com/forums/944-turb...light=corleone

I have wondered about just adding an extra pump to supplement the stock one, but I would be concerned about causing some imbalance or turbulence in the flow? Isn't this possible?

goldminer

Circulating the water faster is unlikely to fix the problem it's just moving the thermal energy around. You need to get rid of the thermal enegy form the system ie larger or more efficient radiator or more air flow through the radiator.

TurboTommy

You guys have to remember, though, that the theory of producing more heat with higher hp engines is only true if you are actually constantly using that extra horsepower. On a street engine, even if highly modified to twice the stock power, you are using more than the stock 220-250 hp for only a small fraction of the actual running time.
Also, as somebody already said, by modding via increase in thermal efficiency, you can increase the hp and actually produce less heat. Higher compression engines, for example, waste less heat into the cooling system.

blown 944

the real problem IMO is that you are confined to the engine block and heads that are only designed to remove so much heat ie; thermal transfer.

The only thing you can do is to improve apon them with more efficient coolant routing and oil cooling. Just adding a larger radiator is not going to be an easy fix if the coolant that is in the block at the time is overwhelmed and cannot be relieved fast enough in all areas.

The design of the front to rear of the std WP makes it hard for the rear cylinder to cool quick enough causing an imbalance in cylinder temps.

This is why I went to routing a coolant line to the rear of the head and use the electric WP to get it there. Now I just need to get nice cross flow coolant inlet and outlets by all cylinders.

Of course you need a decent radiator to remove the heat once it gets there too.

SOON...

333pg333

So Sid, have you just mounted the electric pump and just tapped it into the rear of the block? Have you been running this config for long? Do you see any issues with having the pressure of the other pump coming into the existing flow from the OEM pump? Have you been able to quantifiably measure any temp differences now with this setup or was it merely a mod based on suspicion? I'd be interested in seeing any pics of your setup if you have some saved.