Temperature management questions for a turbo engine

[peejay]

So we have this pump gas turbo engine that is now making enough power. The fueling and ignition are also controllable, so it can be tuned. Finally, oiling system is adequate for the intended use.

Next question: Any good ideas about tricks and techniques to make the engine robust to temperatures that would come with high duty cycles. For example, suppose I’d run the car in a fast hill climb event on a hot day. Or a full tank on a jet boat. It’s a car engine, which is just like to make as robust as possible for temperature issues if run very long and very hard.

Add more fuel as temps rise. Period.

I laugh when people say "Oh you can make 400hp from (stock 1.6l engine) all day". Oh yeah? Bring the coolant temps up to 100-110c, oil temps 10c higher, put it on an engine dyno at max power, and hold it there for a half hour. Then we will see who can make power "all day" and who is pouring their pistons out of the oil drain plug if held to that power for longer than a 10 second dragstrip pass, half of which is spent feathering the throttle for lack of grip.

[gruntguru]

Add more fuel as temps rise. Period.

Better still - add water.

Beyond about 14:1 the extra fuel is doing nothing except evaporative cooling. A litre of water provides 10 times the cooling of a litre of gasoline.

[Caprimaniac]

Lots of good hi ts here.

We found adding a electric waterpump helping.

You avoid cavitation on higher rpms, but maybe more important- when you’re out of boost- at lower rpm’s- the pump will run at max steam helping engine cool down quicker between the boost- shocks. Like in a turn or in the return lane.

[n2xlr8n]

Before I saw David's post, I liked the idea of hood vents and piston cooling.

[ptuomov]

So we have this pump gas turbo engine that is now making enough power. The fueling and ignition are also controllable, so it can be tuned. Finally, oiling system is adequate for the intended use.

Next question: Any good ideas about tricks and techniques to make the engine robust to temperatures that would come with high duty cycles. For example, suppose I’d run the car in a fast hill climb event on a hot day. Or a full tank on a jet boat. It’s a car engine, which is just like to make as robust as possible for temperature issues if run very long and very hard.

Add more fuel as temps rise. Period.

I laugh when people say "Oh you can make 400hp from (stock 1.6l engine) all day". Oh yeah? Bring the coolant temps up to 100-110c, oil temps 10c higher, put it on an engine dyno at max power, and hold it there for a half hour. Then we will see who can make power "all day" and who is pouring their pistons out of the oil drain plug if held to that power for longer than a 10 second dragstrip pass, half of which is spent feathering the throttle for lack of grip.

Interestingly, you mention piston temperatures. I was just studying Mahle’s piston temperature results in their knock detection study. This is a chapter in the piston book.

What they found is that holding ignition timing constant, richer mixture lowered the piston temperature. If they however then advanced the ignition timing back to the knock limit, the piston temperature actually went up while the engine didn’t make any more power. Their conclusion from this test was that fuel cooling doesn’t help pistons run cooler, holding the power produced constant. So running rich and advancing ignition doesn’t make pistons any safer.

The exhaust gas temperatures do go down with rich mixture regardless of the ignition timing (within reason), so the exhaust valves, exhaust port, exhaust manifold, and turbo all run cooler with rich mixture. So fuel cooling does work for the engine overall, just not for the pistons.

[peejay]

That IS interesting!

[gruntguru]

Interestingly, you mention piston temperatures. I was just studying Mahle’s piston temperature results in their knock detection study. This is a chapter in the piston book.

What they found is that holding ignition timing constant, richer mixture lowered the piston temperature. If they however then advanced the ignition timing back to the knock limit, the piston temperature actually went up while the engine didn’t make any more power. Their conclusion from this test was that fuel cooling doesn’t help pistons run cooler, holding the power produced constant. So running rich and advancing ignition doesn’t make pistons any safer.

Doesn't make sense. If advancing the timing didn't increase the power, they have advanced past MBT. Why would you do that?

[Kevin Johnson]

Try to tap into the main oiling circuit immediately prior to the branch that preferentially receives the more aerated fraction (2,6) in the bedplate using the same orientation (so it instead becomes the defacto deaeration circuit). Use that for piston oiling.

It has been so long since I have worked on the 928 -- I am assuming you spaced your pick-up by the same amount as the pan spacer?

[cjperformance]

Lots of good hi ts here.

We found adding a electric waterpump helping.

You avoid cavitation on higher rpms, but maybe more important- when you’re out of boost- at lower rpm’s- the pump will run at max steam helping engine cool down quicker between the boost- shocks. Like in a turn or in the return lane.

Good idea ^^
Also a basic but sometimes beneficial addition is a small steam relief tube/hose in any area of the cylinder head or block that looks like it could hold an air/steam pocket. Return this to a header/deairator tank.

[ptuomov]

Also a basic but sometimes beneficial addition is a small steam relief tube/hose in any area of the cylinder head or block that looks like it could hold an air/steam pocket. Return this to a header/deairator tank.

Porsche added those to later heads. There were likely small steam pockets forming under the exhaust ports, and added holes relieve the steam to the heads and from there back to the system.

We've already drilled these to the earlier heads that are currently in the car:

CoolingMod1.jpg

CoolingMod2.jpg

[ptuomov]

Try to tap into the main oiling circuit immediately prior to the branch that preferentially receives the more aerated fraction (2,6) in the bedplate using the same orientation (so it instead becomes the defacto deaeration circuit). Use that for piston oiling.

It has been so long since I have worked on the 928 -- I am assuming you spaced your pick-up by the same amount as the pan spacer?

That's not practical, but we've got another way to make the #2 main junction not an air oil separator. Then, we can probalby install the squirters in the main saddles in a way that the air goes to squirters and the oil goes to mains and rods, when oil is badly aerated.

Pickup is also spaced, yes. It's very close, but not too close, to the cast pan bottom.

[David Redszus]

Here are some interesting engine temperature changes based on various engine operating parameters:

Engine speed change per 1000 rpm = +54F deg
Engine load change in BMEP per 1.0 bar = +18F deg
Trapped CR change per 1.0.CR point = +18 Fdeg
Coolant temperature change per 10C=1 +6F deg
Oil temperature change per 10C at sump = +5F deg
Ignition advance change per 1o = +3.6F deg

Piston cooling oil spray..... -27.F deg
Pre-ignition.................. +180F deg

The gorilla in the room is the temperature effect of pre-ignition.

The temperatures were measured at the upper ring land.
The temperature increases are additive.

Here is what a typical race engine might use:
rpm +3000
load +2 bmep
TCR +2
Coolant +30
Oil temp +40
Ign adv +5

Total temp increase = 322F deg at piston ring land.

[ptuomov]

David, those numbers are for the top piston ring groove temps, right? Not the whole engine temps (which would be ambiguous anyway, as it depends so much on the cooling system).

[ptuomov]

Here's something from Mahle, this is for diesel but much of what is not injection related should apply to gasoline:

PistonBook.jpg

[Atom]

- Additional vents in the hood to cool down the area around the exhaust manifolds

Here is Aston's solution on the 90's Vanquish.
See the 4 rectangular chimneys.