The throat is where you’d get significant gains, but the best I could do was just to move this bit around back and forth by hand. The result was a tiny bit smoother surface as I knocked off some high nuggets in the casting.
The purposes of the Swain Tech coating and the hand smoothing of the flow passages are to improve performance and reduce heat rejection from the turbine housing into surrounding parts. My goal was to gain back a bit of spool that is inevitably lost going to a bigger turbo.
I got my turbo back from RaggDoll Motorsport, now built to RENNEN spec. Of course, when I see a rough surface that’s in a flow passage, I can’t leave it alone.
I stuffed a rag as far down as I could as I didn’t want aluminum powder getting down into the volute of the housing. Then I took the flap wheel to it. Aluminum dust came off, so I wore a mask. Does this improve performance? Maybe 0.001%, but it looks and feels a bit nicer.
There are all sorts of objects in the way to getting the turbo back in. I zip-tied the coolant line as far out of the way as possible.
After a lot of struggling, I finally got the turbo back in by supporting it with a floor jack to act as another set of hands. There were two major difficulties in getting the turbo up into position: working the turbo around the coolant hardline and getting the two studs on the turbine housing bracket through the mating holes on a heat shield. I recall doing some prying on the heat shield to get the holes to line up with the studs. Then I installed this brace going between the turbine housing and engine block. The purpose of the brace is to help support the weight of the turbo to take the load off of the header to prevent cracking of the header.
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I personally think you can actually hear those minute surface flow improvements in the exhaust note. At this level, you’re not chasing performance gains, but rather aural pleasure, instead.
Way back in the day, I did gas stand testing to quantify the turbine efficiency improvement due to extrude honing a turbine housing. The gain was measurable and worthwhile for those seeking maximum turbine efficiency. The two major areas where surface smoothness mattered were the turbine inlet section and at the narrow throat section where the flow exists the housing volute and enters the turbine wheel. Basically, wherever flow velocity was highest. I couldn’t smooth out the throat section on this turbine housing, but I got the entrance section done and I bet the difference is measurable on the gas stand. The compressor side, not so much. I also like to call it arts and crafts time and it’s relaxing. Sure, the hand smoothing of the turbine housing is a small incremental improvement, but so is a drop-in air filter, thermal barrier coating, compressor inlet, or my x-pipe exhaust tip. Keep on adding them all up though and it comes meaningful 🙂
Awesome and thorough write-up! After a bunch of 4 cylinder miatas, I don’t think I could upgrade to a Porsche with a 4 cylinder though lol
I had glanced at the GT4, but it was essentially a $50k premium taking into account the ADM dealers were asking. The 4.0l GTS was roughly a $25k premium over my T. But in the end, I still really like turbo-4s.
Initial engineering meeting for the 718 6 cylinder : “What would be the best engine layout and displacement to give customer’s high levels of power with a linear powerband?”
Initial engineering meeting for the 718 4 cylinder: “Who has a copy of China’s engine displacement tax regulations?”
For the higher trim GTS, I don’t disagree. For the base trim, the 2.0l turbo stomps all over the 981 base 6-cylinder in torque, power, and fuel efficiency.
That said, the 2.0l with this turbo upgrade, good fuel, and some exhaust mods is 350wtq and 400whp capable which puts it in the range of a bolt-on and tune 4.0l 6-cylinder. I’m straddled with Cali 91 octane and keeping the stock cat. The 2.5l engine with larger upgraded VGT turbo is 500-550whp+ capable, over 400wtq, and still good response to boot because of the VGT. No NA modded 4.0L can touch that.
Not that everyone cares about fuel economy, but I can get 32-34mpg highway no problem. The 4.0l can’t touch that.
“The 2.5l engine with larger upgraded VGT turbo is 500-550whp+ capable, over 400wtq, and still good response to boot because of the VGT. No NA modded 4.0L can touch that.”
565>500-550 https://demanmotorsport.com/4-5l-cayman/
“I’m straddled with Cali 91 octane and keeping the stock cat.” –> We forge the chains we wear in life.
Mmm… A bit extreme as that’s well past bolt-ons and a $50k+ engine package. But it’s possible. RaggDoll is also working on a non-VGT big turbo package that will be good for 600-650whp on the 2.5l. A built bottom-end is recommended at that point. Of course, it’ll have some lag that the NA engine won’t.
Did you cerakote the compressor housing? Also, since the boost was holding with higher flowing wheels, did you notice a mass flow change in the data logs?