Refueling turbocharged cars (Page 1 of 2)

Every car should take a cool down lap before coming in - not just turbo cars.

I agree on the easy lap before you come in, especially for brakes.  A turbo will not cool of while you are driving it.  I had an egt in a blocked off wastegate port (used an external wastegate) and the difference between driving really hard and normal wasnt much.  Idling is the only way to let the turbo cool off.  Thats not gonna happen on a racetrack.  A trick is to have the turbo plumbed far away from the head, they run much cooler far away.  Not always possible.

Use a good synthetic oil.  We accidently tested mobil 1 2 years ago.  We had no gauges and had no idea we had no coolant after it boiled away.  We got black flagged for smoking.  The cylinder head and oil filter read 405' F with an IR gun.  Plastic windage tray in the oil pan melted but we still had oil pressure (the one light we had.)

  I'd say if you are worried, make sure the turbo oil drain has no carbon build up so the oil can flow down and out.  Take an easy lap, drive the pit speed limit idling in 2nd.  If you need more its up to you if you want to wait or shut it off so you can get back out there.

I have a 1.5 quart oil pressure accumulator in my daily driver.  It maintains a little oil pressure for about a minute after shutdown.  Its not the piston & spring type, just an aluminum can.  The time the oil pressure accumulator can supply oil depends on how tight your bearings are and how big of a restriction the oil inlet in the turbo is.
    Im not sure the possible BS over the oil accumulator would be worth it.  If you are having oil pressure issues accelerating/cornering then an oil accumulator is probably a good idea.

Some guys run the car extra rich when cooling them off but it doesnt do the plugs any favors.

I think if you can fill it up fairly quickly and get back out there the oil after startup will wash the hot stuff down and mix with the rest of the oil.  If you are that worried about it take the turbo and oil drain off after each race and clean them out.  I think you will see the coking doesnt grow as quickly as you might think it does.

Ford 2.3T's have water running through the turbo housing, like the powerstrokes.

I have been told by a Turbo Guru that the water cooled turbo's are because the average driver is too negligent to properly shut a std turbo.
~we qualify in that to average negligent person label in that we want to come in very hot and shut down the engine~
The better systems pump water w/ an electric pump for a few minutes after the engine is shut down.
~if you were to mimic this system you could pretty much do what you want.

Most turbo's are oil cooled. When making boost (under heavy throttle) turbo's spin upwards of 100,000 RPM. When you shut them down suddenly after heavy load, residue oil in the center housing (the CHRA) overheats and turns into coke. The shaft and bearing can overheat and fail.. i just don't know if it fails over the long term, or fails suddenly, potentially during the race...

I was thinking about placing an old oil cooler inline upstream of the oil inlet and mounted slightly higher to "drip" the reminder of the oil in the cooler into the turbo. A really cheap unpressurized version of the canton turbo after-oiler.

We always sailed past BS inspections with no problem. With more serious mods, do the judges really pick on stuff like new AN fittings and such?

thanks,
olaaf

Problem is here in Lemons where during pitting (hot pit or paddock style) the car must be completely off... kill-switch and all. sometime you can get away with having it on but if caught you can get trouble for it. So that electronic system that keeps oil/coolant flowing to prevent premature turbo failure is nill. Supercharged cars like Punisherbass' are a little less finicky about cool down but a s/c car put down as much heat if not slightly more directly to the motor then a turbo does which makes the independent oil reservoir nice.

I have a Subaru turbo that may not be able to be rebuilt  from where I work and it isn't pretty and those are oil/coolant jacketed. An oil starved turbo will fail hands down thus why people are suggesting a cool down lap.

I would reccomend a cool down lap(s) also but more in the sense of drive less aggressive/race like on your final lap out. Although if you are about due to pit in and a full course yellow pops up that'll be easy peasy to accomplish.

How about a manifold sprayer? A push-button switch to spray water mist on your center section/turbine housing as you're coming in for the pit stop. You can use a junkyard washer tank with an in-tank pump, and a spray nozzle off of a 90's Buick. If you spray it slowly enough you can cool the housing down to manageable temperatures in less than a minute.

We haven't seen many turbochargers fail in Lemons racing (unless you count the Sharks and their three-turbos-eaten-per-race ghettocharged 5 Series, but that was because they were running geological boost pressures due to wastegate misunderstandings). Mostly we see turbochargers assisting head gaskets in their failures.

A couple easy suggestions:
1.  After pouring a jug or two of fuel; stop fueling and start the car up and let it run for a second or 2 to pump fresh oil.  Then shut it off again and resume fueling.  The 5-10 seconds that takes should be less than a cool-down lap would cost you.

2. Rig up a manual override for the wastegate. Then when you're ready to come in you can trip it so the exhaust bypasses the turbo and it cools quicker.  A CO2 cartridge hooked to the wastegate with a valve is a quick and dirty way to do this.

Do you have any testing to prove this?  Egt's dont care if you are in boost or not, If theres hot exhaust going by the turbo will get hot.

Heat becomes an issue in turbo cars in boost when the ignition timing gets low to avoid ping.  This is from low octane gas, high compression, low ignition timing or combinations.  When you get to the limits of the compression and octane and the timing starts getting down to around 20' and lower there is a ton of heat going in the turbo from the combustion event happening late.  The heat/energy under better ignition timing instead gets used to push the pistons down. 

The testing I did was with standalone, EGT in the turbine housing, and a wideband 02 sensor.  There was about 16" between the turbo and exhaust valves.  You could argue ignition timing was too low.  I went from about 30' in light cruise up to 50' of timing (7.8:1 engine) through the light throttle maps.  EGTs didnt move much.  I build and tune turbo standalone cars for a living and have been tuning standalone for 15 years.

  I would coast home for 2 minutes to cool the turbo down even though it was water cooled to get the temp below 700'F (lowest idle temp the turbo would go without running it rich.)  When driving (light cruise, not trying to get around a track) the temp hovered around 1150'F.  At full spool it would go to 1400'F.

The closer a turbo is to the valves the more heat that the turbo sees up to the current peak egt.  If you put an EGT in a turbo on a subaru for example (long distance from the valve to the turbo) you will see very low temps, highest i remember seeing on the last one I did was 900'f at the turbine housing.  If the EGT probe was at the egt peak temp point in the exhaust it would obviously show a much higher temp.

If you pop the hood on a 1.8t vw/audi you can see the turbo glow at idle.  Yes, it will get hotter while driving as theres more energy/heat in the exhaust.

The hotter the oil the thinner, it will mostly drip off the turbo bits and down the drain.  The thin layer left over that burns turns into carbon.  When this carbon builds up and eventually blocks the drain in the turbo the oil has nowhere to go so it goes out the seals.  The coking accumulates slowly.  If its clean and the turbo drain is clear theres no way the turbo will coke up and cause a failure during a race unless there is an oil supply issue.  Overspinning it, running it lean or rich, surging it, or overheating it with low timing can destroy it.

The oil supply line can get oil crud/sludge in it and end up blocking the turbo feed if a chunk gets dislodged.  Cleaning the oil supply line is a really good idea.

The only problem with the op's oil cooler above the turbo is the oil supply line is usually small, so filling up the oil cooler (forcing the air to drain out the turbo) means the turbo oil supply will have a delay.  This is no good for the dry turbo.  This can do bad things to the bearings until the oil supply gets there.  Its especially bad when the driver gets excited to race and spools up the dry turbo.

The highest rpm's i've seen on a turbo map were 250,000rpms.

BS inspectors will overlook an fittings for fuel and safety stuff.  For an oil feed you could argue its for safety.  Rubber hose will fail, possibly in a firey mess but a turbo didnt have to be added.  Pretty sure they will count it towards the $500.  If the engine came turbocharged and the line looked sketchy, bring pics they might let you get away with an fittings/hose.

Water cooled turbos can use convection after shutoff to help keep them cool.  Better OE systems use an auxiliary water pump and can run the radiator fan like crazymike said.  Water cooled turbos keep the bearing housing below the coolant boiling temp which depends on pressure but figure 260'F.  Good synthetic oil will have no problem with this.

If the oil drain line, oil feed line, and center section are all clean i really doubt you will have an issue caused by coking.  If it was ready to fail it could fail during the race.  The g's could break a chunk of coking loose and block the drain or feed.  Clean hot oil could start breaking down sludge/coking and cause an issue too.

jrbe, thanks very much for the data and advice. excellent post.

olaaf