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6 years of racing from 2009 to 2015, including many road races (Road America, Gingerman, The Autobahn CC, etc) plus Pikes Peak and Bonneville. Videos of all of this is posted. I shouldn't have to tell you that racing is far more strenuous on a motor than street.
I wish you continued success with your project.
Thank you. I agree that racing hours are more consuming than street hours. How many hours and miles on your engine since the last rebuild? I recall vaguely an estimate from Porsche testing that race miles count with a multiplier of 5x compared to consumer street miles.
Tuomo, the optimum reliability test used to be starting in Hamburg and go WOT all the way down to Munic. The problem nowadays is the heavy traffic and you car being too fast in order to perform the test in full. I have heard of stock 928s especially GTSs failing from bearing failure.
Åke
I am not surprised to hear that GTS's are primarily the ones blowing given their oil-burning problem due to no oil-drain holes in their pistons. As we all know, oil-ingestion causes octane to go down, and pinging goes up.
Also, look at how many GTS' have a pinging problem on premium gas just running around town, there are plenty of threads on it. Perhaps this could be due to excessive carbon build-up due to the oil-burn listed above.
So combine these elements on a long, high-speed run. The engine will be pinging/detonating continuously, hammering on the bearings the entire time, which will eventually cause a spun bearing.
However, a 928 with proper oil-control as well as a tune with zero detonation, can run from one end of the Autobahn to the other indefinitely...
Mark Kibort's stock 5.0L as well as his current Green Bay stroker, both with 100+ hours on the race track, all while pulling 1.5g's in the corners, is proof of that. Because of the corners and the resultant oil sloshing, the track is a much tougher test on the bearings than the long, straight, Autobahn. Yet he has never had a spun bearing, and his 5.0 when pulled apart, its bearings still looked new. Zero detonation equals zero spun bearings. It is my opinion that MK's use of a rising-rate fuel pressure regulator from day-one has always kept his engines rich enough to avoid detonation on the leaner cylinders such as #6.
All that to say, not all 928's are the same.
A 928 in good mechanical condition, as well as having a proper tune preventing any detonation, can survive the Autobahn without engine damage, including a TT 928.
Last rebuild only just completed now. Partial tune went in and piston rings were bedded on the engine dyno. Got 897.7 HP so far on gas and 12.7 pounds of boost. Now the engine will go into the car and I will go to the chassis dyno to finish the tune.
When I first saw these numbers, I thought: "Holy Temperature Drop Batman!"
Then, I saw this,
Originally Posted by BC
Unless I am misreading or missed other info -
IATs post intercooler will pose problems with detonation if you look at similar platforms. On a road course those would rise possible (balancing more air flow, but also more heat) to 130. You would need meth there to cool post IC pre port.
and thought WTF is he talking about?
So, I did some non-exhaustive poking around.
From what I found - which is not everything, not conclusive, and nothing I'd bet a body part on, but is I think more-or-less correct to the extent that it backs-up the Tuomo/Kunn desgn - volume manufacturers of turbocharged cars (e.g. Porsche, etc.) are ok with IATs up to 20°C above ambient.
So, if Google does the math right, Tuomo's seeing ~11°C above ambient.
And that's standing still with only a couple of fans blowing air.
On the road, turning front wheels will help draw air through the intercoolers and with the road moving under the car and the undertray installed, ground effect will draw more hot air out of the engine bay than during a static test.
Obviously, only extensive on-road testing will show if these numbers are transient and what the steady-state heat-soaked thermal exchange numbers look like. But, so far so good.
Originally Posted by Hacker-Pschorr
Silliness aside, can we keep this thread on track please? ... lets not get stupid.
Also, look at how many GTS' have a pinging problem on premium gas just running around town, there are plenty of threads on it. Perhaps this could be due to excessive carbon build-up due to the oil-burn listed above.
As far as I am concerned there is no 'perhaps' about it. I have one data point, but under the circumstances it was enough for me to form a conclusion: GTS 5-speed with *everything* else perfect pinged like mad under almost all conditions. After removing the astonishingly-thick buildup on the pistons: zero ping under all street-obtainable conditions.
However, a 928 with proper oil-control as well as a tune with zero detonation, can run from one end of the Autobahn to the other indefinitely...
As long as 'proper oil-control' results in not emptying the sump during sustained high rpm running then I agree.
John is going to take some of these components to be flown in a highly precisely calibrated flow bench to get us complete documentation. There’s a firm that can flow this air box system at different manifold densities and boost levels, and those benches are rare.
Everything is getting documented. There’s a good chance that this will be the final design for the twin turbo system, which will then be frozen for production.
I am not surprised to hear that GTS's are primarily the ones blowing given their oil-burning problem due to no oil-drain holes in their pistons. As we all know, oil-ingestion causes octane to go down, and pinging goes up.
Also, look at how many GTS' have a pinging problem on premium gas just running around town, there are plenty of threads on it. Perhaps this could be due to excessive carbon build-up due to the oil-burn listed above.
So combine these elements on a long, high-speed run. The engine will be pinging/detonating continuously, hammering on the bearings the entire time, which will eventually cause a spun bearing.
However, a 928 with proper oil-control as well as a tune with zero detonation, can run from one end of the Autobahn to the other indefinitely...
Mark Kibort's stock 5.0L as well as his current Green Bay stroker, both with 100+ hours on the race track, all while pulling 1.5g's in the corners, is proof of that. Because of the corners and the resultant oil sloshing, the track is a much tougher test on the bearings than the long, straight, Autobahn. Yet he has never had a spun bearing, and his 5.0 when pulled apart, its bearings still looked new. Zero detonation equals zero spun bearings. It is my opinion that MK's use of a rising-rate fuel pressure regulator from day-one has always kept his engines rich enough to avoid detonation on the leaner cylinders such as #6.
All that to say, not all 928's are the same.
A 928 in good mechanical condition, as well as having a proper tune preventing any detonation, can survive the Autobahn without engine damage, including a TT 928.
I really would like to know if Tuomo´s twin-turbo car would stand WOT driving for an extended time of several hours. The problem is there is no place where such a test can be performed. Kibort´s stroker engine is running Clevite racing rod bearings which is quite an upgrade compared to the stock Glyco bearings.
Åke
I really would like to know if Tuomo´s twin-turbo car would stand WOT driving for an extended time of several hours. The problem is there is no place where such a test can be performed. Kibort´s stroker engine is running Clevite racing rod bearings which is quite an upgrade compared to the stock Glyco bearings. Åke
Horses for the courses.
I believe that Glycos and tight bearing clearances work well when the rod big end doesn't deform at all and stays round. The big end deforms when the piston and rod are too heavy for the rpms that the engine sees. When the big end deforms under tension, then the bearing grabs from the sides. This might lead one to contemplate increasing the bearing clearance, but now the local pressure on the bearing shell goes up too much for the soft bearings, and they fail. In contrast, if the big end stays in shape, the tight bearing clearance can hold up to very high loads even with soft bearings. The key, in the 928 context, is to limit the rpms with stock rotating assembly.
For high rpms that deform the rod big end under load, one would want harder bearings with more eccentricity. This would allow larger clearances, which are more forgiving to big end deforming. Hard bearings can take the higher local pressures caused by larger clearances. Fortunately, that's not what the engine in my car is seeing.
hmmm interesting , I bought some woven ceramic cloth for just that purpose, still have not made a heat barrier as I didnt want to mess up the air flow around the engine and make some heat issues worse , I am interested in knowing if this protects from heat but still allows appropriate air flow........!
hmmm interesting , I bought some woven ceramic cloth for just that purpose, still have not made a heat barrier as I didnt want to mess up the air flow around the engine and make some heat issues worse , I am interested in knowing if this protects from heat but still allows appropriate air flow........!
What's your specific concern? Is there an actual problem you're trying to solve?
The stock belly pans are designed to to smoothly diffuse the radiator exit air across the entire engine bay and to ingest some cold air to protect the motor mounts. This should work just fine in your normally aspirated car with headers. If you want to add some protections, I would consider small additional stainless steel heat shields around the valve-cover gaskets, oil pan gasket, and starter motor, but those would likely be a total overkill for your car. Those sort of small heat shields shouldn't adversely impact the air flow within the engine. Then there's of course the option of adding ceramic heat barrier coating on the headers, but that might cause a small change in how the headers work (might get better, might get worse) and aesthetics will also change.
I assume your headers aren’t like my turbo exhaust manifolds that glow in the dark like Challenger...
Here's the volumetric efficiency of the blue engine:
This was measured on the dyno using two new calibrated mass air flow sensors, intake manifold air temperature sensor, and intake manifold pressure sensor. This was at about 30 psia manifold pressure and about 100F intake air temperature, ingesting air at the peak rate of 1907 kg/h. The engine wasn't run above 5500 rpm for this calibration test, but the shape of the VE curve suggests that it's not going to nose over any time soon at higher rpms. We'll achieve 95-100% volumetric efficiency for the entire power band, even with 8.5 geometric compression ratio, cast-iron exhaust manifolds, and the stock S4 intake manifold.
So what to conclude from this? These Elgin 65-6 cams are the bomb. They'd carry the normally aspirated 928 S4 engine pretty damn far, especially with headers and higher compression. I'm not an expert, but the cams look just right to me for a 5.0L 928 S4 engine. The other conclusion is that the stock S4 intake manifold maybe isn't the worst thing in the world to put on a 5.0L engine.
hmmm I was wondering, what if anything special did you do to the engine......special valve train, lifters ,coatings, rods cranks, ......you state stock s4 engine , was it tore down and built new or just as is with xxxxxxx amt of miles on it I saw on a thread from 2010 or so where you were inquiring about crankshafts, did you put a taylor drilled style one in or just leave it stock, any change of bearings....????just curious, I got the bug again....
05-30-2018, 10:05 AM
