I hope things work out. I guess it would be more satisfying if we knew why the turbos failed.

 

Oil temps of 250-260 are unusual in the 997tt. I have run 45min continuously at a very aggressive pace on track and won't see higher than 220-230 on my gauge - not the most accurate but I never get close to 260 and track temps here are routinely over 100F.

Fuel starvation can lead to a momentary lean-out condition which will shoot EGT very high. I try never to run under 1/4 tank for that very reason of avoiding fuel starvation mid corner.

Some of the things I recommend for the track users:

1)go with a low restriction exhaust - not only does it sound cool but it allows the engine and turbos to run cooler

2)I always drop in a couple gallons of 104 octane unleaded race fuel. You can't always trust the octane of gas station pumps and a couple gallons of 104 will give you more breathing room from possible detonation/heat issues

3)if there is ever a momentary miss or loss of power, I go into the pits and check everything. I have developed boost leaks/popped hoses mid session. I also will add some 104 octane then for added safety

 

RE: Oil temps: I glanced at the temp gauges while running and noted oil was 250+'ish which was higher than the 220-230 I normally experience too. Coolent temp was 175 where it always is. I wasn't particularly concerned (perhaps I should have been) given the hot ambient temps - it was really cooking - probably much higher than 101 degrees on the track! Oil temp dropped to 220'ish within 1/2 lap after taking the checkered and was sub 200 after a couple of miles of cruising down the highway at 65 mph. Before starting the day's event, I noticed the oil level was down 1 bar (~1/3 litre) on the electronic gauge but those more mechanically inclined than I who were wandering around the paddock recommended not topping it off because of the high expected temperatures.

I think we can get 100 octane unleaded at the track for $8 or $9 a gallon. Would you consider an octane booster additive in lieu of that in hot conditions (or in all conditions for that matter)? Thanks for your insights.

 

I think most tests of the octane boosters I have seen only raise the octane rating by 0.x with "X" being the advertised boost (6 points). So a gallon or two of 100 octane is much, much, much better. Some here have experimented with Xylene or Toluene but the simplicity and safety of race fuel at the track can't be beat.

FWIW I have tracked my car as:

1)stock
2)stock ecu + AWE exhaust
3)flashed ecu + AWE exhaust
4)AWE 750 package (modified VTG turbos, intercoolers, headers, intake, exhaust, ecu)

and never have experienced temp or heat induced problems. My plugs looked a little worn but without any detonation signs at ~15k miles. My opinion has always been running more boost without less backpressure was a risk.

You now are in a position where you might as well go to a 700hp+ level. My suggestion would be to do an entire package from one of our reputable tuners here - not to cobble something together. Cheers!

 

Steamboat, sorry to hear of your troubles. Glad you see the upside of this - you get new turbos, i/cs etc....

I would suggest speaking with one of the board sponsors (Switzer, Proto, etc...) about getting Alpha turbos on there. I think a used pair of stock vtg turbos goes for about $2500, and a modded pair would probably cost more. For a little more money you could get into alpha 28s which sound like they are very good for the track, but there are plenty of other options.

Gene, you indicated that more boost leads to higher egts. If you had a turbo like Champions 68mm vtg or alpha 3076 which produces lots of power with lowish boost(such as 1.3bar) would that mean lower egts for say 700 crank hp compared to getting upgraded vtgs with 700 crank hp requiring 1.5 bar? In other words, the power is the same but the amount of boost is less.

 

Thanks everyone! Can someone run down the acronyms in play......lambda, IAT, EGT, please. Sorry to be such a dolt....... Best,

 

Well the EGT is affected by a myriad of factors. In Steamboat's car though since he only changed the ecu tune I'd have to assume that boost and ignition timing is more aggressive and would raise the EGT. I might also guess that the factory thresholds for IAT and EGT could have been altered to allow for more sustained boost and timing and thus more power.

But I think it is safe to generalize that running turbos which are more efficient that can generate more power with less boost should run with safer EGT's (so long as the tune is safe) - you aren't overspinning the turbine wheels for power. Lastly, VTG turbo designs are reportedly inherently less tolerant of high EGT's versus non-VTG designs, so the alphas should be safer than the modded VTG's..

 

Sure. Lambda is referring to the air/fuel mixture ratio or AFR, or how lean or rich the motor is running. Running too lean or too rich can lead to higher EGT's. EGT is exhaust gas temperature. The temps get high enough to make the turbos glow red like branding irons. When they get too high the turbo explodes like yours did. IAT is intake air temperature. On a factory turbo when the IAT gets over 50C the ecu will reduce engine power to prevent higher EGT among other bad things

 

Great explanation! Rep point for you!

 

91 octane..260 oil temps..1.3BAR boost..600 cpsi cats..40w weight oil...5,500 elevation and 100+ degree F (38C) temps..translates to

engine knock timing and misfire, burning oil at low viscosity, high exhaust gas temps due to increased (constant) turbo boost and back pressure, and raising boost psi at consistent elevated levels running which also means ECU conformed to constant pressure for compensating the altitude elevation.

91 octane was only the start of trouble in this preparation.

Sorry to hear it.

 

Thats quite a sad story but lets face it there really wasn't much working in the engines favour. Eclou's 6 pointer spells out the recipe for disaster.... All that white smoke was purely unburned fuel mixed with a bit of oil that ignited in the exhaust, hence the flames. Woah....I can just imagine the level of heat exposure imposed on the piston crowns in the lead up to that disaster. You may well be looking at more than 10K if you dare open the motor. What about the induction of particle contamination from the disintegrated turbos? It's highly unlikely the intercoolers filtered it all. Anyways....

 

That makes sense. I was looking at my turbos (off the car) and it was interesting to see the "turbo anatomy" up close. I didn't realize that ALL of the exhaust passes through the turbine on the way to the muffler. That means it's always spinning. Presumably there is a way (?wastegate) to modulate it's speed in addition to just exhaust flow. Must be one durable piece of spinning metal! Although obviously not indestructible.

 

the turbine wheels are pretty tough but the thing is spinning at some ridiculous rpms - 100,000 is pretty normal. On the VTG add the moving vanes and you have more parts that can lead to failure:

 

Not to take away from the OP's topic, but a very good primer on turbocharging can be found here:

http://www.turbobygarrett.com/turbob...ch_center.html

In a traditional turbocharged engine, a BOV is a pressure relief device on the intake side...it prevents the turbo’s compressor from going into surge. It is installed somewhere between the compressor discharge of the turbo and the throttle body, usually after the intercooler. If the throttle let off rapidly, airflow is quickly reduced leading to flow and pressure fluctuations - surge. BOVs use a combination of manifold pressure signal and a spring to detect when the throttle is closed...when the throttle is let off rapidly, the BOV vents remaining air pressure in the intact tract to atmostphere.

On the exhaust side, a wastegate controls the boost pressure. There are applications with no wastegates, some with internal wastegates, and some external. They allow exhaust flow from the turbine wheel to escape, allowing it to match the required pressure needed for a given boost level. It too is calibrated with a spring.

Ultimately the goal of a regulated turbine is to expand the usable flow rate range in practical applications while maintaining a high level of efficiency. With VTG turbos, turbine output is regulated by changing the inflow angle and inflow speed at the turbine wheel inlet using vanes located in front of the turbine wheel. This replaces a typical wastegate. When the guide vanes are closed, higher flow velocity lead to high turbine output, hence a high charging pressure. As the vanes open, the turbine reaches its maximum flow rate. The advantage of this type of setup is output control over bypass control. The entire exhaust mass flow is always directed through the turbine and can be converted to output - supposed "greater efficiency." The guide vanes adjustments are electrically controlled by the ECU programming.

Many members here prefer the use of VTGs in our cars. We are already setup electronically with an ECU that controls the wastegate - to go back to traditional internal or external wastegated turbos requires some plumbing as well well as a boost controller, as well as programming to shut off the ECU's typical controls. Remember the long arguments about APR's tune, and why they were producing significant torque and power? One of the arguments being made was that the tuners at APR were manipulating the VTG vanes in ways that other tuners can't? My above explanation should help explain why this can't be the case.

Going back on topic, I found that BorgWarner reports that their gasoline VTG turbochargers are tolerant of tempreatures to 850C. It would have been interesting to see what the EGTs were with Steamboat's EVOMSit tune, in high ambient temps, 600 cell exhaust, and 91 octane.

 

Thanks Bob, that was quite informative.