couver

Hello all! I recently purchased a 718 Cayman base model from a dealer. I happened to add the boost gauge to the multi-display, and what I noticed is that it is almost always zero. I did some experimenting, and the only condition that appears to cause boost is throttle position. In other words, if I drive the car with low to medium throttle, but increasing enough to stay with traffic, go uphill, etc.., then the boost is zero, even at high engine rpms. But, if I tip the throttle in hard (I'm going to say maybe 75%), it will boost. In contrast, my other car, a 2017 Subaru Forester XT, which is also 2.0L boxer turbo (LOL), will start boosting immediately on any throttle input. I asked the Porsche dealer if the boost is strictly tied to throttle position, and they didn't know, and couldn't tell me if my car is normal or not. Anyone have any knowledge about the boost characteristic on the base car? Thanks!

Edit: After reading the first couple of responses, can anyone confirm that they are able to accelerate from say, 0-60, shifting 1-2-3 (forgot to mention that I have a manual), at a reasonable pace--maybe slightly faster than typical traffic acceleration--and not induce any boost? I know it is pretty subjective, but might be interesting.

iliveoncaffiene

Mathematically, it boost is tied to rate of change of acceleration, or "jerk". Constant acceleration (constant throttle position) doesn't require much boost. If you quickly move the throttle down, it's going to spool up more.
Also, change the drive mode: Sport Plus pre-spools the turbo and even at 2000rpms in 7th gear you will have ~1psi of boost, Sport is much more turbo happy, and Normal is the most tame.

L Tigre

Part of that description sounds legit: it requires some throttle input to get the turbo rolling. If the pedal is not depressed, or depressed only lightly, boost will stay at zero. I am not surprised this is the case even at high RPMs. If the engine is spinning fast but no torque (or little torque) is being requested, then the boost will stay at zero.
But: the boost should start to rise well before you get to 75% of throttle pedal position; I would say something in the range of 20-30% depending on various factors. That is the experience on my base 718 and it 'feels' correct to me.
I know that, even without variable vanes (as the 718 base does not have; nor the subaru I think), there are a lot of set-up factors that impact turbo behaviors; they get configured very differently depending on the car. I would not worry about it being quite different from the Subaru. But I would worry about throttle pedal in the 30%+ range, and boost stuck at zero (which I would view as truly 'stuck' and worth checking out).
My two cents, hope it is useful-

couver

While I get the "more you push the peddle, the more boost you will get," I'm looking for specific input on the behavior of the base 718--i can literally drive in all kinds of conditions, without inducing ANY boost--that just seems odd to me. I read somewhere that the base model is supposed to start boosting at 2,000 rpms, which may be true, but I'm wondering if it should really take 75% throttle to get ANY boost. By the way, I also owned a WRX for 5 years, and heck, going back a ways, even a Saab 900 turbo, so I've got some experience with turbo cars, and the zero boost unless throttle is smashed is unique, but may also be a fuel savings approach by Porsche. My car doesn't have Sport+, but I don't see a lot of difference between normal and Sport, but I really only did the testing in normal mode--will try Sport when I get my car back (dealer has it for a separate issue with battery) and see if it boosts with less throttle.

Edit: Just saw the response from L Tigre as well... okay, yes, some boost at 30% tip in seems like it would be more normal. I'm going to ask the dealer to look at it closer. I found another thread on here about a bad wastegate--not sure if that would cause the lack of boost, but something to consider.

L Tigre

If the wastegate is sticky or gets stuck open, then yes would cause the boost to stay low or zero even when the engine's operation would call for boost. The wastegate is something like an internal bypass. The other data point might be: if you hit it hard, where does the boost reading max out?... what's the highest boost it'll get to under hard operation? (I do not know the answer to that on my own car, but look forward to finding out!... and will let you know-)

couver

I read that it is rated for 20. I observed 18. But, it takes full pedal mash to get it, and the space between some boost and all the boost seems narrow--so narrow that it is gone and over before I have to shift.

worf928

Turbochargers require exhaust gas energy to spin the 'hot side' impeller that is shaft-connected to the 'cold side' impeller that compresses the intake charge (i.e. 'the boost.') Exhaust gas energy is a function of the mass of the moving gas and its velocity. The mass of exhaust gas is proportional to the position of the 'go pedal.' The velocity of the exhaust gas is proportional to engine rpm. So, at low rpm you need a wide-open throttle to get mass. At high rpm you need less throttle opening because the pistons are moving faster thus imparting more velocity to the gas.

The 'bigger' the turbocharger the more exhaust gas energy is required to get the impeller spinning. This is the first-order definition of "Turbo Lag." The 2.0 flat-four turbo has a big turbocharger. It needs a lot of exhaust gas energy.

That's the basic theory.

Next, while turbochargers are the most efficient form of forced induction they do require a bit more fuel for each horsepower produced under boost than a normally aspirated engine. And when 'boosting' the engine the air fuel ratio is often rich for various reasons.

Thus, in general, under boost, a turbocharged engine requires more fuel per horsepower produced than a normally aspirated engine. And as a result also produced more pollution.

Next, let's factor into this, EPA/EU economy and emission test requirements.

And, factor in electronic control of the waste gate which allows exhaust gas to bypass the hot side impeller thereby preventing the turbo from 'spooling up' to make boost. (The waste gate is required in order to limit boost and to bypass boost completely under certain conditions.)

Net result: in "normal" mode at low-to-moderate 'go pedal' conditions the engine management system is trying to 'pass the tests' (DieselGate notwithstanding) and is thus limiting boost unless you 'really mean it.'

OP, try again in Sport mode and see what you get.

Lukejt

I have a Cayman S and the boost gauge is about the same as you’re observing. I agree the waste gate is probably responsible for controlling the amount of boost. Nothing is wrong with your car, enjoy the ride.

couver

Got my car back from the dealer a few hours ago (separate issue), and did a little testing.... I think there is some fuel-economy logic built into the system that closes the wastegate based on the RATE of thottle application, which then induces boost, and it will stay in boost until you back off the pedal, which must open the wastegate again. I did my normal driving, which is fast, but very smooth application of pedal, and... no boost under any conditions. But, even at low rpms, if I "goose" the pedal, then the car will boost. So, the answer to inducing boost is to tip in hard enough for the computer to close the wastegate. Maybe there are other factors, but considering that this seems to work consistently and all different rpms, it seems to be the primary factor. Pressing the Sport button seemed to require less throttle tip-in to induce boost.

This is basically what iliveoncaffeine said, so gold star to him/her .

GregWormald

One thing I've noticed in 2+ years is that the throttle response is very linear.
Little throttle--little acceleration--no boost. Lots of throttle--lots of acceleration--lots of boost. And everything in-between.
Unless I floor it suddenly I rarely notice any increase in acceleration from the boost coming on (except below 2000 rpm).

fueledbymetal

Sounds normal for Porsche. My old WRX would go into boost with any throttle application, but my Porsche in "normal" mode on the sport chrono only boosts with extreme throttle application. Once I switch it to sport or sport+ it's an entirely different animial - it goes into boost with the slightest throttle application. For that reason alone I will always spec SC on a turbo Porsche going forward.

matmanx1

Having just bought my 718 Cayman base less than a week ago this is exactly what I have discovered and I am driving with a little more pedal pressure as a result. It's different than a normally aspirated car but I am finding it to be fun. Push the go pedal a little harder than I am used to when starting off or going around a corner and that builds boost and results in a pleasing push back into the seat with zippy acceleration. It's a really fun (but not the most efficient) way to drive these cars!

Fume

This is the same on my GTS as well. Normal mode almost never uses boost without quickly going to wide open throttle. Sports mode, it's possible that it might get on boost quicker than normal but I haven't noticed it all that much in this mode either. Sports+ it seems like it's always on at least 1psi boost, even if I'm off the pedal, and very quickly adds boost as I press the pedal down. This mode definitely feels the most responsive.

couver

I'll definitely be using the Sport button!

It really seems to be the rate of pedal tip-in--once it triggers the wastegate, it can be modulated, even at lower pressure (still need to play with it some more). It is definitely an interesting implementation, and I, like you, will be changing my driving inputs approach to realize the performance. I guess it does explain why I have been getting 30 mpg --that won't last long, LOL!

spdracerut

With modern ecus and electronic throttles, throttle/boost response can be easily tuned. Just vary throttle blade position vs. gas pedal position. In 'normal' mode, can limit throttle blade movement vs. throttle to save gas. For sport mode, ramp up the throttle movement quickly with initial throttle input.

But compared to the Subaru FA20DIT engine, there are two main differences: the 718 has a larger turbo and it's also single scroll instead of twin-scroll. So those two differences will create a laggier turbo setup.