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The turbos are just getting warmed up at 10 psi boost and mass flow to support about ball park 540 axle hp:
As expected, the motor runs about the best at the 4750-5750 rpm range. After 5750 rpm there's a dip in the torque curve, which for this engine is significantly smaller than for a stock engine in percentage terms. To get the torque curve as flat there for stock engine, we had ramp up the boost pretty aggressively above 5500 rpm. In contrast, this run is with constant boost.
The consensus seems to be that the dip in the stock engine torque curve above 5500 is due to the stock intake manifold. I disagree with this as my theory is that the 10% torque dip more about the stock cams and stock exhaust manifold in the stock S4 engine. In our case with bigger cams, the remaining 4% torque dip is in my opinion due to 90 degree exhaust blowdown interference causing first high pumping losses (and later at high boost knock) in cylinders 1 & 6.
...and the system is designed for 20+ psig? Assuming Boyle's law still holds I hope John's dyno is man enough when you turn the wick up! Rgds Fred
Too much uncertainty at this point, but it might go as high as 20 psig on pump gas and 30 psig on race gas. Who knows, though?
An even bigger uncertainty for this motor is how high it can go in terms of rpm. What's the max rpm before 1&6 start chocking and knocking, rings fluttering, heavy pistons and rods spanking the bearings, etc. As a reference, from memory I think that S4 rev limiter was set to 6300 and GT to 6600 rpm or something like that.
The turbos have a lot of headroom because we're only here on the compressor map right now:
Little more breaking in, still at or under 10psi boost.
It's making power as one would expect.
There's a green flat reference line in the graph that's just a horizontal reference line. It gives you a visual contrast of the wiggles of the torque curve (or lack thereoff).
The turbos are still not even at 100k rpm:
The 60lbs injectors are going to run out soon and need to be swapped to big ones. They are running at 75% duty cycle at the peak. The AFR is now a bit above 12 at high rpms and high load, and close to 14.7 at low rpms and low load. It'll neither be washing the bore walls nor knocking at those settings during the break in.
OK enough with the "running in" that is all done and dusted in the first 20 minutes, time to saddle up those horses and make tracks to where 'there be monsters' Thanks Guys...
Your Turbo's are just getting going according to your curves. If I read them correctly they should be able to deliver about 35 psig at full chat.
I am a bit surprised to read that you feel your 60lb injectors are near their limit. I would have thought such were capable of something close to 1000 bhp. Presumably your preference is to avoid switching over the duty cycle as per the stock injector programming at 5200 rpm.
Even so you should be able to get to about 760 bhp when you hit 100% at those AFR's.
Have you got any friends with a KC-135? At that burn rate you are going to need in-flight refuelling!
OK enough with the "running in" that is all done and dusted in the first 20 minutes, time to saddle up those horses and make tracks to where 'there be monsters' Thanks Guys...
Originally Posted by FredR
Your Turbo's are just getting going according to your curves. If I read them correctly they should be able to deliver about 35 psig at full chat.
I am a bit surprised to read that you feel your 60lb injectors are near their limit. I would have thought such were capable of something close to 1000 bhp. Presumably your preference is to avoid switching over the duty cycle as per the stock injector programming at 5200 rpm.
Even so you should be able to get to about 760 bhp when you hit 100% at those AFR's.
This project is moving forward according to a plan, and that plan doesn't call for a high boost run yet.
Our rough task list is the following:
- Using the current configuration on dyno, measure the exhaust back pressure and the blowby gas flow rate from the turbos to confirm that the breather system can be expected to work. If everything checks out, then button up the breather.
- Switch the injectors to larger ones, and tune the idle and the rest of the fuel map. This will likely involve increasing the idle speed somewhat and tweaking the ignition grid definitions and values to create a simple controller that forces the engine speed towards the target idle. Drive the car for a while to make sure that injectors work.
- Change oil to synthetic 10w60 oil. Send the break-in oil to be analyzed.
- Hook up the full set of pressure transducers and thermocouples onto the car and start the actual dyno tuning.
Turbo cars are to some extent fuel cooled at high load. When the previous iteration went to 700 axle hp, the 60 lbs injector duty cycle was something like 90% even when firing only every second revolution.
I have a hunch that the bearing loads may be higher and oil hotter in this engine than in the stock 928 S4 engine. Hence the scientific wild *** guess to go to more viscous oil.
Originally Posted by Hacker-Pschorr
"No Country For Old men"
Don't get that photo. Is that expressing displeasure of an oil argument potentially breaking out?
Originally Posted by V2Rocket
that's a bad b***h.
A bad batch of oil?
Originally Posted by Roy928tt
OK, Plan endorsed. Yep might as well change injectors now, no sense whatsoever running out of headroom on injectors. Cheers
Or spending time tuning the fuel tables for small 60 lbs injectors right before going to big injectors and redoing the whole task again.
This. For sure you want to have it working correctly before moving on. Some might find that 5 or 6 hundred HP is enough.... <points finger at himself>
Yes, there are enough changes in this iteration that it made sense to break the car in with the existing 60 lbs injectors and the fuel tables tuned for those injectors. It's safe, and then there would have been less trouble shooting complications if something wouldn't have been working. Now, going to the bigger injectors, we'll know that whatever problems we'll experience are due to those injectors and/or the LH attempting to control them.
In terms of HP, more is never enough and too much is just right. My black car was in that 5-6 hundred range in 2009, eboost2 took it to 7 where we hit the wall with completely stock '87 engine. Now we're trying to go above those levels with the blue engine and bigger everything.
01-29-2017, 07:51 AM
6250 rpm and 10 psi
