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Thanks for keeping us updated on the progress with this build. In the video, John says this is the culmination of 10 years of development effort. I'm grateful the 928 community can benefit from the dedication from people such as John, Greg, and the rest (I shouldn't have started listing them.).
Intake maifold studs, spacers, and fuel rail versions
The blue engine has an intake manifold with different length studs than the original '87 engine in the car had. That means the fuel rails aren't going to be easily interchangeable. Likely next step is to take some long mounting tab fuel rail cores and clean, test, modify, and retest them.
The difference easily visible here:
Cosmetically, the difference between raw cores and the reworked fuel rails is about as significant as the difference between these people before and after the make-up artist:
This isn't about my car or engine, but you might nevertheless find this informative, and more importantly, entertaining. John's having a conversation about engines with a toy donkey:
The jackass will probably actually talk in the subsequent videos, should there be enough mental energy in the system to operate a video editing software.
This isn't about my car or engine, but you might nevertheless find this informative, and more importantly, entertaining. John's having a conversation about engines with a toy donkey:
I thought it was an interesting video. I hope he keeps his promise to document the build process in more videos.
I thought it was interesting that he's installing a spacer to increase the size of the plenum, but he's doing that on just the driver's side, not both sides. He said that tests had shown the 5th cylinder was starved of air and that the spacer would allow more room for that cylinder to breathe. (There's not a lot of room between the top of the bell mouth for the tube feeding the 5th cylinder and the driver's side intake cover. I thought the two sides were basically mirror images of each other. If so, isn't there another cylinder on the other side that's equally starved for breathing room?
If you've got the manifold in hand, you'll note that the passenger side short runners are quite straight. The driver side short runners are the problem, because they feed right in top of the port, requiring and awkward ?-shape runner. Runner #5 is the worst because it is in the front and therefore has the least amount of hood clearance and thus the shortest radius turns. Controlling for everything else, most importantly 90-degree and 180-degree exhaust interference, the cylinder #5 is down by about 5% in cylinder filling compared to the better runners. This is not new information, Dennis Kao's motor had the same arrangement as did Todd Tremel's supercharged car.
Thank you for the explanation of why the flow to #5 is worse than the rest of the cylinders. I'm sure the subject is old hat to many Rennlisters, but some of us are relatively new to the 928. While I dreamed of owning one as a boy, that dream had faded from memory long ago. It was only reawakened by chance about 3 years ago. I was searching for a classic car on an internet used car lot. The car next to the one I was looking for was a white 928. After a year of searching, I bought my 1990 S4.
Now I have a problem. Thanks to the work that some in the 928 community are doing, I find I need to buy at least two more 928s. One that I can keep basically stock (with which to enjoy the true 928 experience). Another to have Greg perform his stroker magic and the last to have John trick out with his twin turbo. In both cases, not because I'm a good enough driver to be able to use gobs of power from one Greg's or John's power plants, but because they're both works of automotive art. Entirely different and, at the same time, eerily similar in their appeal.
Now I have a problem. Thanks to the work that some in the 928 community are doing, I find I need to buy at least two more 928s. One that I can keep basically stock (with which to enjoy the true 928 experience). Another to have Greg perform his stroker magic and the last to have John trick out with his twin turbo. In both cases, not because I'm a good enough driver to be able to use gobs of power from one Greg's or John's power plants, but because they're both works of automotive art. Entirely different and, at the same time, eerily similar in their appeal.
Although this is a turbo thread, I think you shouldn't discount mild hot rodding of the 5.0L engine along the lines of what Jim Morton and Dennis Kao did. DK may want to weigh in, but those were some very nice results they got with simple but very thoughtfully matched modifications (intake manifold porting, higher compression, custom camshafts, and headers). At the same time, you'd have the opportunity to make the engine more reliable by fixing some known potential problems. That won't take you to 650hp at the wheels like the turbo system does, but you'll retain the looks and the character of the car and make it noticeably faster. Another example of a motor that does similar things is Jim Corenman's GT.
The pitfall and the fun with hot rodding the normally-aspirated stock engine is that one has to understand how an internal combustion engine works to modify it in a way that makes more power. In my opinion, mostly that's just shifting and/or extending the torque curve to higher rpms for a normally aspirated engine. If you install bigger cams, that'll shift your torque curve to the right to higher rpms. Then, with the dynamic compression now lower because of the later IVC, you can regain almost (all but not quite all) lost low-end torque by increasing the static compression ratio. The headers are IMO needed above 6000 rpm because the 90-degree exhaust blowdown interference will start interfering with cylinder #1 with stock exhaust manifolds above that rpm point. Good headers will then allow the cams to have more overlap, which will boost the mid-range torque without the 180-degree exhaust blowdown interference destroying the low-rpm operation or the 90-degree exhaust blowdown interference destroying the high rpm-operation. And so on.
High rpm operation of the 928 engine can cause reliability problems, however. One of the reasons why I think turbo conversion is so well suited to the 928 engine is that you don't have to rev the engine higher than stock S4 redline to make all the power in the world you can practically use on the street with street tires.
The next thing on the agenda is designing new anchoring brackets for the shorter plenum box. At 15 psi, one can reasonably use the stock like clamping mechanism of the box to MAF to MAF boot to throttle body and support it with some brackets. At 30 psi and o-ring seal of the box to MAF, the requirements on the bracket are more severe. Take area of the plenum box opening and multiply that by boost pressure, and you'll get the force pulling the brackets. At 30 psi, 10 square inches or so of area means 300 pound force trying to pop the MAF out of the box and the boot out of the MAF. Them brackets better be sturdy...
This is where they have to be fitted:
The shorter plenum box moves the bracket connection points somewhat. Ideally, the brackets would have mostly tension load and the lifting force, if any, would be taken care of the wide dimension of the bracket. The block heat expansion would easily be accommodated by the narrow dimension of the bracket. Thus, a flat steel plate bracket would work very well here, provided John can anchor it securely to the block at a location that gives favorable force vectors.
Paper mockup:
After the paper mockup, the next mockup is made from aluminum sheet that is easy to work with:
The final brakes will be water jet cut from steel plate and bent to shape.
Other brackets are being made as well. The system has a lot of stainless steel braided hoses because of the heat that the turbo exhaust manifold radiates. Those lines need to be fastened securely because otherwise they vibrate and shave off metal from surrounding components like files. As an example, here's the bracket that holds the main fuel line next to the passenger side fuel rail cover:
Oh yeah and here's a frivolously added unrelated shot of my current hottie:
We need to get some data on the torque curve as a function of ignition advance in each LH and EZ-K cell. To estimate those curves, we need to take knock off the table as well as disable the knock retard temporarily in the name of science. They requires high octane gasoline fuel for the experiment. The first option is this unleaded, the second option is the leaded one in case we need even more octane. This is just for data collection, the car will actually be tuned for 93 octane pump gas.
Fuel is the most important thing to pick for a dyno session. The close second is what music to play while the car runs. It's gotta be something with an electric guitar to be drowned down and totally overwhelmed by the exhaust roar. Some ideas we're working on:
My 7-year-old daughter was watching that video on airplay with me and started asking questions about it. She's smart, so I didn't want to sugarcoat it. I said "Those people are singing about killing people like you and me". She was somewhat concerned, so I told her that "So far they are just singing." I'll have to teach her about the French Revolution later tonight.
On a positive note, it's fortunate that I don't have to explain to her what Weeknd's "Can't feel my face" is about...
A quick update about John's near-term to-do list:
- There's a new chin spoiler coming that replaces the cracked old one. Arrived...
- A custom oil cooler needs to be fabricated from a Setrab element.
- The oil cooler will also need custom lines, brackets, and shroud
- The fuel line and plenum box brackets should be done by the end of the week
- The fluorosilicone boots are being made in Mexico
- Intercoolers need to be hung and the pipework fabricated
That's a start...
Here's the new chin spoiler and the large Setrab cooler to be fitted.
04-29-2016, 01:31 AM
