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Is yours a one off from Kuhn or is he selling this as a product yet, ie larger turbo with exhaust manifold and tuning software....I will contact Kuhn....very cool
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....
Originally Posted by andy-gts
Is yours a one off from Kuhn or is he selling this as a product yet, ie larger turbo with exhaust manifold and tuning software....I will contact Kuhn....very cool
The blue engine has a lot of modifications to make it more reliable. In addition, it has a mildly ported intake, mildly ported heads, Elgin 65-6 cams, and pistons dished to about 8.5:1 compression. In my opinion, it's punching above its weight based on the VE measurements.
I don't know what John's plans are for making more of these cars. I'm just enjoying mine as a science project.
Here's the balance of the mass flow from the two sides. This is without any fine tuning yet, just hooking up everything symmetrically. We could balance the flow with either closed loop control or tuning the open loop control with a restrictor pill, but it's probably not worth the time as the flow is so close to balanced without any further tuning:
Post intercooler in a very straight pipe section with a honeycomb flow straightener ahead of the sensor and the sensor element smack right in the middle of the 2.5" ID pipe per spec. It should be very accurate as everything about the environment is within the brand-new sensor's spec. There's an identical sensor on both sides. There's also the stock-style 928 MAF in the stock location, which has allowed us to get realistic flow mapping of the stock-style sensor. See below:
Then, there's the question how this relates to the exhaust manifold pressures, wastegate bypass mass fraction, etc. It turns out that the compressor side mass flow gives you an unambiguous picture of what's happening on the exhaust side balance if both compressors push into the same pressure, as they do in John's plenum box.
A digression: The only exception to the rule that you can infer turbo exhaust side from the compressor intake side mass flow (and pressure and temp) would be under surge conditions, in particular, the co-surge between the compressors. Co-surge is defined as a condition under which one turbo's compressor pushes charge air thru the other turbo's compressor in the wrong direction. This could happen at very high pressures and low mass flow, for example, when closing the throttle after high load and high rpm. The whole piping on my car is designed to minimize the chance of co-surge. You get co-surge risk when you have a single restrictive intercooler and combine the compressor outlets before the intercooler, especially if you don't have good bypass valve circuits. John's got none of those design errors built into the system, so there's little to no risk of co-surge. We have also empirically verified that there's no surge or co-surge in the engine using the dual turbocharger speed sensors. I've got 99 problems but co-surge isn't one of them.
If I were to build something 928ish for higher rpm use with twin turbos, I’d probably use Mahle or Manley Subaru pistons. For 100mm Nikasil bore. Manley for higher boost, lower (but still high) rpm, Mahle for lower (but still high) boost and higher rpm.
The stock S4 piston is 765 grams. Installing these low weight pistons means rebalancing the crankshaft.
Åke
Yes, and custom long rods with 23mm small ends. The rods would also be a lot lighter than stock rods, so even more would need to come off the counterweights.
Tuomo, in order to optimize the wrist pin weight you can turn them out conically internally at the ends. Should save appr. 10-20 grams. Åke
Personally, I wouldn't touch a new Mahle wrist pin with the hope of making it better. I don't have the understanding. They have made the pin shorter and designed the wrist pin bore to work with this specific pin. There isn't a single perfectly round shape in that bare piston anywhere, everything is biased one way or another to match the other parts and the operating environment. Even if I think that a wave-shaped pin inside bore (thickest at the two points that have the piston pin boss end and the rod small end begin, and thinner at the ends and in the middle) how do I know that the piston itself isn't designed of straight short pin?
One thing that I found surprising is that the gap (for the rod small end) between the wrist pin bosses of the piston is about 29.5mm (sloppy caliper measurement). The wrist pin length is about 57mm. That leaves only 13.75mm or 0.54" of the wrist pin inside the piston pin boss per side when the pin is perfectly centered! That sounds awfully little to me. There's some slack relative to the lock grooves, too. I wonder how they can get away with such a short distance?
I think it's a separate question if there's an old engine from a whole different era of engineering standards and a lot of hot-rodding experiment with the stock parts. There, I can see how trying out things like tapering the wrist pin and lightening the rods and pistons would be a worthwhile experiment. I would be quite comfortable with minor, well thought out modifications to the stock 1987 S4 original parts, like changing the piston dish or reshaping the intake valve back.
The other thing is this "2618" low-silicon vs. "4032" high-silicon alloy debate. I'm using quotes there because I don't think any of the major piston manufacturers use any of those alloys. Many US aftermarket piston manufacturers used to only have the capability to do "2618" style low-silicon alloy pistons, so they marketed the living daylight out of the "2618" as somehow better for high performance than "4032". They were extremely successful, so now even major piston manufacturers sometimes make aftermarket "2618" pistons, like Mahle does. If you read their internal documentation and books published by the engineers/scientists working for major piston manufacturers, it's pretty clear that they consider "2618" pistons in a street driven car engine a foolish choice.
06-18-2018, 12:00 AM
