Temperature management questions for a turbo engine

[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.

[ptuomov]

Here are some practical ideas that I'm kicking around:
-Thermal barrier coating on piston tops, combustion chamber faces, valve faces, valve backs, exhaust port
- Addition of piston oil squirters
- Higher oil pressure with a shimmed spring of the oil pressure relief valve to increase oil flow
- Additional vents in the hood to cool down the area around the exhaust manifolds

Stuff that's already taken care off is big dual oil cooler, exhaust manifodl external TBC, low exhaust manifold back pressure, and sufficient exhaust flow capacity. The cams are mild, car idles super smooth, compression about 8.6:1, intercoolers aren't obstructing the radiator, etc.

[bentvalves]

care to share some under hood pics of this love affair?

[David Redszus]

Following are my opinions:

-Thermal barrier coating on piston tops, combustion chamber faces, valve faces, valve backs, exhaust port

If piston tops do not absorb heat and transfer to the cylinder walls via the rings, the chamber surfaces will run hotter and lead to aberrational combustion. If excess heat is anticipated, raise the oil viscosity.

- Addition of piston oil squirters

Very good idea. One of the few methods to reduce piston temps that really work.

- Higher oil pressure with a shimmed spring of the oil pressure relief valve to increase oil flow

Higher oil pressure can lead to excess pressure and oil aeration. A plot of oil pressure vs rpm will indicate the pressure curve peaks. There should be no curve flat tops.

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

Under hood air flow is quite important. We have used multiple pressure sensors to evaluate under hood flow areas.

Perhaps the most important is the cooling system: radiator, ducting, etc. and the inter cooler.

[ptuomov]

Following are my opinions:

-Thermal barrier coating on piston tops, combustion chamber faces, valve faces, valve backs, exhaust port

If piston tops do not absorb heat and transfer to the cylinder walls via the rings, the chamber surfaces will run hotter and lead to aberrational combustion. If excess heat is anticipated, raise the oil viscosity.

- Addition of piston oil squirters

Very good idea. One of the few methods to reduce piston temps that really work.

- Higher oil pressure with a shimmed spring of the oil pressure relief valve to increase oil flow

Higher oil pressure can lead to excess pressure and oil aeration. A plot of oil pressure vs rpm will indicate the pressure curve peaks. There should be no curve flat tops.

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

Under hood air flow is quite important. We have used multiple pressure sensors to evaluate under hood flow areas.

Perhaps the most important is the cooling system: radiator, ducting, etc. and the inter cooler.

The piston and combustion chamber coatings may limit the boost a little bit on pump gas, but the car's making hard-to-handle power already.

Oil viscosity is already higher than what the factory recommended for the normally aspirated engine.

I'm in the process of sizing the piston oil squirters, using oil flow rates recommended by Mahle's book and some computations about oil flow in the engine. The result seems to be that I could use as much oil flow to the piston squirters that's possible in light of pump supply and, more importantly, the ability to get the oil to return to the sump quickly enough.

Intercoolers are in the fenders with separate vents, working great.

The radiator is big.

Work to be done on sealing the ducts to the oil coolers and radiators. May also punch an additional air hole to the air cleaner so it's not competing with the radiator for air flow.

[David Redszus]

The piston and combustion chamber coatings may limit the boost a little bit on pump gas, but the car's making hard-to-handle power already.

Piston to wall clearance is more important to thermal transfer than coatings.

Oil viscosity is already higher than what the factory recommended for the normally aspirated engine.

And it should be. But SAE viscosity is irrelevant; actual viscosity at the point of lubrication temperature is what matters. Minimum cSt should not be less than 4.0.

I'm in the process of sizing the piston oil squirters, using oil flow rates recommended by Mahle's book and some computations about oil flow in the engine. The result seems to be that I could use as much oil flow to the piston squirters that's possible in light of pump supply and, more importantly, the ability to get the oil to return to the sump quickly enough.

Agreed.

The radiator is big.

Bigger is not always better. Fin count and air flow velocity are very important. We use a thermal imaging camera to look at radiator hot spots (and cold spots). Radiator shrouding to improve air pressure drop matters a lot. What are you using for coolant? It is common to install coolant pressure sensors in the cooling system to track local coolant pressures; quite often, local pressure blockages are found.

[Bradley67]

Don't dismiss valve spring oilers. A lot of heat is generated by valve springs. Seeing you already have an engine oil cooler this would definitely help lower internal engine temps and increase spring life.

[ptuomov]

Don't dismiss valve spring oilers. A lot of heat is generated by valve springs. Seeing you already have an engine oil cooler this would definitely help lower internal engine temps and increase spring life.

There's too much oil in the heads most of the time, with the by product of good valve spring cooling. I have beehives, relatively light components, and not crazy cams, so the seat closed force is like #80. 4V DOCH is easy on the springs. So I think I'm covered there.

[Calypso]

Perhaps a little simplistic add on to the list is increasing the oil capacity.

[ptuomov]

Perhaps a little simplistic add on to the list is increasing the oil capacity.

Got two turbo oil sumps and two big coolers, plus an oil pan spacer. The regular sump volume in the pan is hard to increase, but I can stash some oil in the turbo sumps, lines, and big external coolers. The only limit there is that one never wants the oil level in the main pan either too high or too low under any operating conditions, so those other rat holes in which oil can be stashed aren't ideal locations.

[Big Al]

If you can , cool the oil that goes to the squirters.

[ptuomov]

If you can, cool the oil that goes to the squirters.

It goes to from pump to coolers and then to main galleries, from which it divorces either into squirters or to main bearings (and rods). So it should be reasonably cool.

[Calypso]

Perhaps a little simplistic add on to the list is increasing the oil capacity.

Got two turbo oil sumps and two big coolers, plus an oil pan spacer. The regular sump volume in the pan is hard to increase, but I can stash some oil in the turbo sumps, lines, and big external coolers. The only limit there is that one never wants the oil level in the main pan either too high or too low under any operating conditions, so those other rat holes in which oil can be stashed aren't ideal locations.

Have followed the project time to time in its thoroughness, so didn’t really anticipate that being overlooked, but occasionally something like that may happen.

[ptuomov]

Perhaps a little simplistic add on to the list is increasing the oil capacity.

Got two turbo oil sumps and two big coolers, plus an oil pan spacer. The regular sump volume in the pan is hard to increase, but I can stash some oil in the turbo sumps, lines, and big external coolers. The only limit there is that one never wants the oil level in the main pan either too high or too low under any operating conditions, so those other rat holes in which oil can be stashed aren't ideal locations.

Have followed the project time to time in its thoroughness, so didn’t really anticipate that being overlooked, but occasionally something like that may happen.

Thanks for the suggestion, sometimes we overlook some simple stuff.

[MadBill]

At a glance, more oil capacity would seem logical, but in reality it just takes a little longer to peak.