The 4-banger turbo 718s haven’t gotten much love from the aftermarket because they are just the lowly 4-cylinder engines instead of the all-mighty 6-cylinders in the Porsche lineup. Those of us who grew up tuning turbo-4s from the 1990s and 2000s know how much potential they have. Enter RaggDoll Motorsport.
RaggDoll has a shop 718 GTS with the 2.5L engine. As no one else was really making high quality performance turbocharger upgrades for the 4-cylinder family of engines, RaggDoll decided to go at it themselves. I have typically shied away from hybrid turbos as many companies just do them wrong, but I’m comfortable with what RaggDoll has done in creating their RENNEN turbocharger upgrade for the 718 Cayman 2.0L base engine. For one, they rebuild with new OEM Borg Warner bearings. They also don’t hog out the turbine housing to stuff in a too-big diameter turbine wheel which can cause numerous issues.
From my estimations, the stock 2.0L engine turbocharger is good for about 39 lbs/min. The RENNEN gets a compressor wheel upgrade capable of about 53 lbs/min which is basically what the 2.5L GTS turbocharger compressor flows. So, the factory compressor housing is already well-sized to the new bigger compressor wheel of the RENNEN. To go with the higher flow compressor is a higher-flow design of turbine wheel. The RENNEN is sized to be a modest upgrade in order to retain good response characteristics. The goal with the turbo upgrade is to be able to make good power while only using 91 octane fuel. The Race Gas Concentrate is great stuff, but I don’t want to have to depend on it.
I’m just going to highlight some of the tips and tricks of the install because there are a bazillion steps. To swap out the turbo on the 718, you need access from both above and below. Removing the bulkhead panel behind the seats gets you access to the compressor outlet tube.
With the compressor outlet tube removed, you need a long and straight T30 driver to loosen the screw holding the oil feed line in place. Later, I found out that it’s easier to pry the oil feed line off the turbo after the turbo has been unfastened from the header giving a bit of free play; I wasted about an hour trying to pry out the oil feed line before I figured out the trick to loosen the turbo from the header. You will need a very short and very thin pry tool; I used feeler gauges to start. After I took this picture, I did stuff rags in the two open pipes. It would be very bad to drop a fastener into the turbo.
To keep from dropping the oil feed line screw multiple times and having to crawl under the car multiple times when reinstalling, I had the bright idea of using a little bearing grease to hold the screw to the torx driver. This was after crawling under the car multiple times due to dropping the screw. The tub of motorcycle bearing grease is the same one I’ve had for almost twenty years. Considering I don’t even have a motorcycle anymore, the tub of lube will probably outlive me. Hey, that’s a nice grade 8.8 stainless steel screw.
I found an 8mm ratcheting close-ended wrench came in handy in a number of tight spots. These two oil lines need to be removed from the turbo oil drain reservoir.
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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.
Bench racing through the keyboard is always fun. So the 4.5 is down on tq by quite a bit against the 2.5 RaggDoll VGT set up. On pump gas there are a dozen cars putting out over 500 wheel hp (not crank like the 4.5L numbers) and 500 wheel TQ. And I should add these are cars they aren’t even set up like Raggdoll’s Farrah (her 718.) https://www.instagram.com/raggdolls_718?igsh=MW45ZzI3b3R6N2t1Zw%3D%3D&utm_source=qr Those running all of her stuff are running even stronger. The irony is there are 2.0s out there with Dyno jet dynos’ laying down 450 hp and 400 tq (to the wheels) on 93/94 pump fuel . Not one or two but dozens. The 2.5 VGT turbo is a great turbo the problem is many people don’t know how to tune VGT’s so they get a bad name. But the RaggDoll Six-66 turbocharger has put down 610 wheel on pump and water meth it could do the same on E85 (which the 718’s can now run with Raggdoll’s flew fuel system.) I’m sure reliability is gonna be brought up so let’s cover that now. RaggDoll has put 20,000 miles on her 550 plus wheel motor with only one issue and that was lifting the heads. For those that don’t know what that is it’s when the cylinder pressure gets so high (from lots of boost) so much so that the factory head bolts stretch and the head literally lifts from the block … so think about that for a min. The stock rods don’t bend or break and the stock forged Mahle pistons hold together. If that don’t shows us all how amazing and strong these motors truly are. I don’t know what would. By the way we installed ARP head studs and 30 plus psi with no more head lifting. The 4.5L is definitely cool but you can buy a 2.0 718 for $40k or less and drop less than $10k in RaggDoll mods and put down about as much as the 4.5 so $10k vs $50k upgrade over the big difference in platform cost also. .. im betting the 2.0 4cyl base is lighter too. A d to add here is the thing… I own a company called Executive Auto Service in Las Vegas we specialize in McLaren , Ferrari, Porsche ..etc. I been in this buisness my entire life and I can tell you it’s likely not $50k and your done and again how long does it take? And is it something you can do in your garage over a weekend yourself? Because with all the RaggDoll series of products these are DIY install friendly and those DIY guys are breaking dragy records daily. (While so and so is waiting 6 months to get his 4.5 car back probably ) And the 4.5 your done that’s it for power. And for any true car enthusiasts (most atleast) doing mods and making your car that much faster and feel that much better is what it’s all about. Let’s talk about big power. For less than $20k in DIY bolt on’s on a 2.5 you can run 5.5 second 100-200 kph’s and 136 mph through the 1/4 mile . That’s at 90 plus degrees out and a 2500 D.A by the way. There are RaggDoll Series Two turbo upgrade cars with nothing but her pump, her inlet, and some RaggDoll tuning that are in the low 6s 100-200 running high 10 second 1/4 miles (on pump fuel ) And yes this can be done 💯 reliably. At the end of the day to each their own but I can tell you the 2.5 with RaggDoll bolt on’s will destroy the 4.5 and I will stress yes this can be done and is being done on pump gas. If you run E85 or meth with her Six-66 turbocharger we have seen 610 wheel and 580 wheel tq. Ya these cars and her upgrades are that serious. That’s 720s power and currently RaggDoll has the fastest trap speed record . So fast that if she had done it on a track with traction she would be low 20s some have said her dragys are 9.9’s .. that’s on stock motor and pdk with a stock but hybrid turbo . If that’s not impressive I dont know what is. So sorry the 4.5 is a beautiful machine I love it! But the type of brutal power that these 718’s are now starting to put down the 4.5 is not even in the same power class anymore,.. it’s just not. Is the 4.5 a cool car? sure! it’s more than cool! But is it something just anyone can go out and buy and build over the coarse of a few days? Nope! But you can go buy a 2.0 or 2.5 718 and with less than $10,000 in RaggDoll bolt on’s put out the same if not more power down and that’s. without even getting started, Both the 4.0 and the turbo 4cyl s are great cars in their own right, but bang for your buck it’s the 4cyl all day hands down no question. And if someone reads this and says ya but the 4cyl sounds like a Boxster motor well that’s actually P cars roots for one so I guess it depends on how you look at it. Secondly RaggDoll has a true Equal length exhaust manifolds available that makes these 4 cylinders sound pretty amazing, and make even more power., especially with a RaggDoll 3.5” titanium exhaust. https://raggdollmotorsports.myshopify.com/
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?
The coating on the compressor housing is whatever RaggDoll uses. What I datalogged is an increase in calculated mass air flow from ~153g/s to ~165g/s. That calculation is based off some volumetric efficiency model in the ECU and that’s likely not true anymore as the bigger turbo and compressor inlet should have improved the VE. So the true mass flow gain I think is greater. From 7000-7500rpm, the ECU calculated average ‘Torque Actual’ value increased from ~310 lb-ft to ~328 lb-ft. I’ll have more data in the next article. IAT on the big turbo run was about 15F hotter too during this particular pull as I’d been driving on the highway a bit. Edit: I just looked at another log with comparable IAT between the stock turbo and RENNEN, and the RENNEN had an average of 335 lb-ft of torque this time. In both comparisons, the car accelerated from ~7000 to ~7400rpm in 2nd gear about 0.05-0.055 faster than the stock turbo. And this is the RENNEN on 91 oct vs the stock turbo on 93 oct.
Excited to see how this works out, specifically if there are any issues with thermal management on track at higher power levels. I’ve been resisting the urge to tune my T for that reason. It’s been fun to watch the build!
Engine coolant and oil temperatures are all well under control. The weakness of this engine setup is the intake air temps as the low-temp coolant system isn’t good enough for sustained track use. The bigger turbo will help here, being able to make the same power at lower boost. RaggDoll has a solution which are massive fans on the radiators for the low-temp circuit, but it’s an engine-out operation. The GT4 sides scoops do help, but we’re talking IATs of 60F-80F over ambient. Up in the canyons, not pushing as hard as on track, I was seeing IAT about 25F-30F over ambient. People have done water injection, meth injection, and I know of one person who is going to use a water sprayer on the side radiators. I’ll see where my car stands after the next track day. I would consider going the water sprayer on the radiator route.