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Extremely tight fitments there, lot's of measurements, patience and skills needed, good work!!
Not related to this project but may be interesting in generally, Mountune makes one of the most competitive Rallycross engines, lot's of details revealed on following article, enjoy.
As you can see these engines are made to take huge mechanical stress. Also the anti-lag is so strong that it will create extra boost and therefore need to be tuned for different driving conditions.
The coordinate measuring machine, CAD of the manifolds, and CAM in the casting and machining processes are paying off. The first time in, everything is exactly in the right spot. In terms of the flow path radii and the merge angles, this is about as well you can do without modifying the frame. Also see how good (within reason, what I really mean is look at how much less it sucks) the access is to the exhaust manifold studs.
This is all very cool. You've said several times that the goal is to find the upper limit on how much hp a turbocharged 928 engine will produce. Question: How much of what you're learning will end up in John's twin-turbo kit? This larger version you're working on isn't practical for the street (I don't think). Is the idea to have a kit that can produce close to 1,000 hp and just turn down the boost for street use, or will these larger components be inefficient if the goal is to produce a more "reasonable" 500 hp?
This is all very cool. You've said several times that the goal is to find the upper limit on how much hp a turbocharged 928 engine will produce. Question: How much of what you're learning will end up in John's twin-turbo kit? This larger version you're working on isn't practical for the street (I don't think). Is the idea to have a kit that can produce close to 1,000 hp and just turn down the boost for street use, or will these larger components be inefficient if the goal is to produce a more "reasonable" 500 hp?
The goal, to the extent there is a goal, is to find out how much a turbo 928 S4 can produce on pump gas, with acceptable reliability, and with reasonable amount of modifications. With stock '87 S4, and I mean don't-even-open-the-valve-covers stock, 700 rwhp is hard to get past on pump gas. This next experiment is to see how much more one can do with a thoughtfully hot-rodded but still basically very stock-like low-compression engine.
All of the information that we will produce will end up benefiting John's twin-turbo kit. In terms of efficiency, the system on my car is so far being designed in a way that the only thing that needs to be changed between the most efficient 500 rwhp car and the most efficient 900 rwhp car is the turbo. It's so space constrained in there that we'd go larger diameter with almost everything ***except the exhaust manifold*** if we could, given the packaging.
Everything else other than the turbo itself is going to be about as efficient (or inefficient) at 500 rwhp as it is at 900 rwhp and pretty much in the corner solution anyway in terms of the sizing. Now, it may not be the most cost effective system if you're only looking for 500 rwhp with no need/ability to turn it up when the urge arises, but in my opinion you aren't giving up anything in terms of efficiency loss to use this system on that lower powered car. With a smaller turbo in this system, you can get close to a twin screw compressor experience; with a larger turbo, you'll get car that can be tuned to drive much like a really large normally aspirated engine. It may be that just changing the exhaust housing will accomplish this.
In fact, my car will run a different boost profile and different power in that range depending on the conditions, so it has to work well throughout the range even with these same turbos (2 x GTX3576R with 0.82 turbine A/R).
Certainly there was a lot of attention paid to detail on this exhaust side.
The manifold, like all manifolds, is a compromise. I think this will run the best (i.e., highest efficiency) at about 5250 rpm, which is fine given that high rpms are the Achilles heel of the 928 motor. In addition, the manifolds can be installed without removing the engine, they pass the analysis on durability in the intended environment, with heat shielding don't damage other components, and will clear everything even when the engine rocks on the motor mounts. The sand molds are designed such that they could be pressed with steel dies and don't have to be 3D printed if a larger series is desired. All machining operations are controlled by a computer program and can therefore be replicated accurately. It's actually quite impressive when you write it all down and read it out loud -- I should start writing product releases for Comp Cams! ;-)
There are sensor bosses cast in such that each exhaust port can be instrumented. If the engine runs in a way that somehow differs from what we've modeled, those will be drilled and tapped and instrumented. The bosses are suitable for pressure sensors, unlike the existing ports in the heads, because the pressure sensors need to be placed at a normal angle relative to the flow. A heat sink needs to be installed between the sensor body and the exhaust manifold because of the temperatures that the turbo exhaust manifold sees are so high.
Any idea when the next iteration will be done? It'll give us something to work towards.
Que sera, sera... I don't know. My guess is it'll be broken in this fall/winter and then dynoed to submission. Since it's an R&D project, you never know what, when, and where you'll find.
Just to be clear, that's for my little-bag-of-weird-tricks car. John will have a new version of his kit available way earlier than we'll see how deep that rabbit hole really goes. He's done with the revised exhaust side and all that needs to be done is the revised intake side. But you should email him and ask.
We're going to need bigger pipes, and here they are.
What do you think, are these pipes big enough? Will they flow enough compressed air for this engine? (That was what they call "a rhetorical question".)
The pressurized plenum box is solidly bolted to the engine with thick water jet cut bracket plates. At 2 bar boost, there's about 300 lbs force pulling the air box away from the engine. For those of you who frequent the bench press at the gym, it's about as much as a bar and three plates in both ends.
Since the engine moves on its Genuine Porsche motor mounts and the intercoolers are solidly fixed to the body, there needs to be compliance built into the piping system. You can see two points where that happens here. The silicone couplers will provide compliance both at the box inlet and in the middle of the pipe.
In terms of the pipe sizes, we're running 2.5" OD SS pipe from the intercooler to the engine bay. We have to make a relatively tight turn into the air box and there's then pressure recovery challenge in the air box. Therefore, the pipe gets larger before the turn with a conical diffuser, gradually increasing to 2.75" OD before the turn.
In terms of the aesthetics, this engine bay will look nice. The silicone couplers in the pipes are in the middle of the intake manifold lettering. Although many people like stainless without paint, these pipes will likely be painted to match the intake manifold color.
There air filtering setup for this new system is going to be pretty interesting. It will be a little bit harder for others to knock off than the old system. The bypass valves will be integrated to the air filtering system and connect to the first bend coming out of the intercoolers. The cutouts for the compressor bypass valves are larger now at 1.25" and they will slice off the outside of the 2.5" tube and then curve straight forward to hit the compressor bypass valves in the filter body. The flow capacity of the filter system will be massive, something that can't run thru the stock radiator shroud element.
A little compare and contrast below. Which pipe do you think will cause a higher pressure loss? ;-)
11-02-2015, 10:40 AM
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