[shappy]

I happen to really enjoy listening to the sound of the motor on deceleration and love to downshift my current vehicle to hear the exhaust as I slow down.

I have yet to drive an S or GTS, but when I test drove a base Boxster (manual trannny) I noticed that there was very little engine braking when downshifting to slow down.

I don't want this to turn into a debate as to whether using engine vacuum to slow a car down is good or bad for the drivetrain, but I was curious if the 2.5L motor offers better engine braking than the 2.0L?

Thanks!

 

[Wine.O]

I happen to really enjoy listening to the sound of the motor on deceleration and love to downshift my current vehicle to hear the exhaust as I slow down.

I have yet to drive an S or GTS, but when I test drove a base Boxster (manual trannny) I noticed that there was very little engine braking when downshifting to slow down.

I don't want this to turn into a debate as to whether using engine vacuum to slow a car down is good or bad for the drivetrain, but I was curious if the 2.5L motor offers better engine braking than the 2.0L?

Thanks!

Good chance the car you drove was equipped w/ the Sport Chrono option. For an M/T, this package includes automatic rev matching. Took a good bit of getting used to in the car I test drove. Like you, when I'm driving twisty roads aggressively, I like the option for rear wheel braking that downshifts can provide (yes, insert your "you should be driving differently" editorials here). When I ordered my car, I left the SC package off. Suspect my downshifts feel very much like you're accustomed to.

 

[ZuffenHouseRules]

I'm with you, enjoy downshifting (with manual throttle blips) together with some engine braking for the tactile feel as well as sound. Engine braking effect with the 2.5 has never impressed me as notably different from the several n/a F6 engines preceding. However it *is* a quieter engine, in all phases of operation, esp. in Normal mode. Could that account for your impression of less engine braking?

I suppose in concept the engine braking effect is proportionate to its displacement, since it effectively becomes a pump driven by the crank. Bigger pump > more resistance? So maybe the 2.5 offers slightly more braking than the 2.0, though I wouldn't expect you could notice. Are you comparing to a 6.6 V8 perhaps?

 

[shappy]

I'm with you, enjoy downshifting (with manual throttle blips) for the tactile feel as well as sound. Engine braking effect with the 2.5 has never impressed me as notably different from the several n/a F6 engines preceding. However it *is* a quieter engine, in all phases of operation, esp. in Normal mode. Could that account for your impression of less engine braking?

I suppose in concept the engine braking effect is proportionate to its displacement, since it effectively becomes a pump driven by the crank. Bigger pump > more resistance? So maybe the 2.5 offers slightly more braking than the 2.0, though I wouldn't expect you could notice. Are you comparing to a 6.6 V8 perhaps?

Believe it or not, I am comparing it to the 2.0L in my ND Miata. However, I think what may be one of the big differences is gearing. The Miata is geared very short, 6th gear is a 1:1, so it may be that when I downshift, the gearing may be having a larger influence.

I actually think my Miata offers more engine braking than my S4 before it and the Golf R I had before that. I mention those since one was a supercharged V6 and the other a turbo inline four.

I just noticed that the base Boxster I test drove had almost zero engine braking when downshifting and I wasn't sure why that would be the case.

 

[Wine.O]

Believe it or not, I am comparing it to the 2.0L in my ND Miata. However, I think what may be one of the big differences is gearing. The Miata is geared very short, 6th gear is a 1:1, so it may be that when I downshift, the gearing may be having a larger influence.

I actually think my Miata offers more engine braking than my S4 before it and the Golf R I had before that. I mention those since one was a supercharged V6 and the other a turbo inline four.

I just noticed that the base Boxster I test drove had almost zero engine braking when downshifting and I wasn't sure why that would be the case.

Yes, related to displacement, but as you note, perhaps more so by gearing ratio as well as vehicle weight. I had an NC Miata and yes, it was amazing how you could get the back wheels to pull. My new 718 does pretty well though in the lower gears when I need it. I still suspect the car you drove was rev matching (SC package). Hard to feel braking when the car spins the engine up for you as you drop gears. Probably makes for smoother rides to the store, but for me at least, defeats the purpose a little when on a more spirited drive.

 

[ZuffenHouseRules]

the gearing may be having a larger influence.

That makes sense. I definitely feel engine braking in the 4>3 and 3>2 shifts (but also some in the higher ratios when coming off the freeway at speed and blipping/downshifting through a long sweeping exit ramp).

My occasional route home takes me to a stop sign at the top of very steep hill. I leave the car in 1st and let the engine alone brake its descent. Revs climb to 4000rpm with zero throttle, while speed held in check with zero brake-pedal, so there is engine braking!

 

[GGG]

I happen to really enjoy listening to the sound of the motor on deceleration and love to downshift my current vehicle to hear the exhaust as I slow down.

I have yet to drive an S or GTS, but when I test drove a base Boxster (manual trannny) I noticed that there was very little engine braking when downshifting to slow down.

I don't want this to turn into a debate as to whether using engine vacuum to slow a car down is good or bad for the drivetrain, but I was curious if the 2.5L motor offers better engine braking than the 2.0L?

Thanks!

Throttle valve stays open for 2 seconds if you release the throttle. That's what gives the feeling of a lack of engine braking.

 

[My718isPorsche#5]

Turbocharged engines have less compression. Where I find this most noticeable is going down steep hills.

 

[ZuffenHouseRules]

Turbocharged engines have less compression.

Good point! But I wonder....if Sport mode is keeping the turbo spinning on trailing throttle, then even with ignition retarded (and no combustion cycle) wouldn't the pressurized intake cycle mean that the 'pump' is still pushing as much air as a larger n/a engine with higher compression ratio (as compression ratio for both engines is calculated solely on cylinder volume BDC:TDC irrespective of boost I think)?

Although 9A2B4 has a quite high-for-turbo 9.5:1 compression ratio in both 2.0 and 2.5 -- as high as fairly recent n/a engines I think. For current Porsche comparison:

911 Turbo: 9.8
911 Carrera: 10
GT2 RS: 9.0
GT3 RS: 13.3

 

[shappy]

In addition, perhaps the 13:1 compression ratio on my Miata, coupled with the short gearing is amplifying the compression braking effect, making the difference seem that much more stark.

I plan to test drive a 2.5L Boxster in the next few weeks, so I will see if there is much difference between the two 718 motors with respect to compression braking.

 

[Michael1]

Throttle valve stays open for 2 seconds if you release the throttle. That's what gives the feeling of a lack of engine braking.

Is it the throttle valve or the fuel shutoff?

 

[GGG]

Is it the throttle valve or the fuel shutoff?

Injection and ignition is cut, but the air is still flowing into the chambers as if the throttle is open.


edit: video explaining what I mean

 

[shappy]

Drove another base model today and I did notice that when it was in sport mode there was definitely less engine braking than when in normal mode. This suggests that the throttle is indeed staying open a bit so that you get the backfires in the exhaust, which would have an impact on engine braking.

 

[GregW]

I know that cruise control uses both engine and brake to maintain the speed, and it stays on until you use the brake pedal. What that would do overall I don't know. It could be worth a try with the control set very low.

 

[Bob D.]

Very Helpful

Injection and ignition is cut, but the air is still flowing into the chambers as if the throttle is open.


edit: video explaining what I mean


GGG, really appreciate your pointing this out and love the linked video which explains it well.