Crown

Board: Porsche - Cayenne Language: English Region: Worldwide Share/Save/Bookmark Close

Forum - Thread


    Compression Ratio??

    The compression ratio on a Cayenne S is 11.5:1 while on the Cayenne Turbo is 9.5:1. So I imagine the Turbo's compression ratio is lower due to the Turbo's, which makes sense, But why exactly is it lower? Just a curious question.

    Re: Compression Ratio??

    Quote:
    Porsche930S said:
    The compression ratio on a Cayenne S is 11.5:1 while on the Cayenne Turbo is 9.5:1. So I imagine the Turbo's compression ratio is lower due to the Turbo's, which makes sense, But why exactly is it lower? Just a curious question.



    You've answered your own question. It's due to the turbos.

    A naturally aspirated engine will not be able suck more than the swept cyinder volume of air into the cylinder during each induction stroke.

    A turbocharged engine has the advantage of the air being compressed ahead of the induction valve, resulting in a larger mass of air (= larger "free volume") being pushed into the cylinder during each induction stroke.

    More air + more fuel = bigger bang = more power.

    The "effective" compression ratio of a turbo engine when the turbos have spooled up is higher than the geometric compression ratio, due to the fact that the induction air is compressed. This is not the case with a NA engine.

    Re: Compression Ratio??

    Oh okay. Ya I thought I might of answered my own question but your answer was exactly what I needed. So what would happen is the CT had the same compression ratio of the Cayenne S? Would the engine not last as long?

    Re: Compression Ratio??

    Quote:
    Porsche930S said:
    Oh okay. Ya I thought I might of answered my own question but your answer was exactly what I needed. So what would happen is the CT had the same compression ratio of the Cayenne S? Would the engine not last as long?



    First, you'd get pre-ignition of the fuel ("knocking"), because the effective compression ratio would be higher than the octane rating of the fuel would allow, then the engine wouldn't last as long.

    Re: Compression Ratio??

    Hmm. Sounds pretty interesting. Thanks for the info!

    One last question, and I should prob. know this stuff, but what does the number (we'll just say X in this situation) mean to 1----> X:1?

    Re: Compression Ratio??

    Quote:
    Porsche930S said:
    Hmm. Sounds pretty interesting. Thanks for the info!

    One last question, and I should prob. know this stuff, but what does the number (we'll just say X in this situation) mean to 1----> X:1?




    Compression ratio is the ratio of the volume of the air in a cylinder when piston is at bottom dead center (BDC) to the compressed volume of the air when piston is at top dead center (TDC).

    Say a cylnder has a "swept" volume of 600 cc, and the remaining combustion chamber volume at TDC is 60 cc, then the compression ratio would be:

    600 + 60 : 60, which is 11 : 1.

    Re: Compression Ratio??

    Alrighty. That actually makes a lot of sense. Thank you fritz!

    Re: Compression Ratio??

    Quote:
    fritz said:

    Compression ratio is the ratio of the volume of the air in a cylinder when piston is at bottom dead center (BDC) to the compressed volume of the air when piston is at top dead center (TDC).

    Say a cylnder has a "swept" volume of 600 cc, and the remaining combustion chamber volume at TDC is 60 cc, then the compression ratio would be:

    600 + 60 : 60, which is 11 : 1.



    What would we do without you?

    Re: Compression Ratio??

    Quote:
    RC said:
    Quote:
    fritz said:
    600 + 60 : 60, which is 11 : 1.



    What would we do without you?



    Use an electronic calculator?

     
    Edit

    Forum

    Board Subject Last post Rating Views Replies
    Porsche Sticky SUN'S LAST RUN TO WILSON, WY - 991 C2S CAB LIFE, END OF AN ERA 1/19/18 10:13 PM
    throt
    263655 1687
    Porsche Sticky OFFICIAL: New 991.2 GT3 (2017) 1/21/18 5:31 PM
    Boxster Coupe GTS
    260593 4018
    Porsche Sticky OFFICIAL: 911 GT2 RS (2017) 1/23/18 10:02 AM
    throt
    89759 1386
    Porsche Sticky 992 (Next 911 generation 2019/2020) 1/12/18 7:11 PM
    the-missile
    67527 673
    Porsche Sticky Porsche Mission E - the future of Porsche? 1/3/18 8:32 PM
    CGX car nut
    39875 468
    Porsche Sticky OFFICIAL: New 991.2 Turbo S Exclusive Series (2017) 11/28/17 12:15 AM
    EnglishManInNY
    23926 332
    Porsche Sticky OFFICIAL: New Porsche Carrera T 12/1/17 7:24 PM
    crayphile
    13729 243
    Porsche Sticky OFFICIAL: Porsche 718 GTS models (Oct. 2017) 10/24/17 12:19 PM
    amazon
    7291 19
    Porsche 918 latest news Thread Closed 11/6/17 10:43 AM
    RCA
    548417 5574
    Porsche 991 GT3 RS 1/9/18 1:43 PM
    Kimi
    456625 5816
    Porsche OFFICIAL: 991 Turbo and Turbo S 10/26/17 1:33 PM
    NSXER
    446383 4239
    Porsche OFFICIAL: 2016 Porsche Carrera 911 [991.2] Facelift 3/24/17 12:49 PM
    RCA
    254981 1382
    Porsche OFFICIAL: 911 R (2016) 1/4/18 9:14 PM
    wurlie
    247604 2558
    Porsche 997 GT3 RS 4.0 3/15/17 10:40 PM
    noone1
     
     
     
     
     
    231293 737
    Porsche Cayman GT4 12/30/17 11:07 AM
    Boxster Coupe GTS
    213276 2482
    Porsche 991 GT2 RS (2017) - Rumors, speculations and gossip Thread Closed 7/3/17 2:04 PM
    RCA
    175537 1699
    Porsche The moment I've been waiting for... 11/13/17 2:32 AM
    Pilot
     
     
     
     
     
    165152 874
    Porsche OFFICIAL: New 991.2 Turbo and Turbo S 1/23/18 12:27 AM
    RCA
    164506 1074
    Ferrari 488 GTB/GTS 1/21/18 10:49 AM
    RCA
    141394 1220
    McLaren McLaren on a winning streak 1/23/18 4:11 AM
    Whoopsy
    139016 2857
    Porsche 991.2 GT3 Thread Closed 3/7/17 11:47 AM
    RCA
    125036 1651
    Porsche Boxster Spyder (981) 12/29/17 8:31 AM
    dreamcar
    110809 692
    Porsche OFFICIAL: New Panamera (2016) 1/6/18 10:41 PM
    Wonderbar
    108111 1284
    Others Audi R8 V10 Plus (2016 model) - Review (updated Feb 13th 2017) 1/18/18 11:38 AM
    RCA
    105677 1869
    Ferrari Ferrari F12 Berlinetta / 599 GTO Successor 12/5/17 3:29 PM
    RCA
    87271 765
    Porsche OFFICIAL: 718 Boxster (2016) 10/20/17 11:17 AM
    DaveGordon
    81722 732
    Others VW caught cheating emissions tests 7/10/17 2:36 PM
    RCA
    81485 861
    Porsche 991 GTS 4/3/17 4:27 PM
    bluelines
    68500 247
    Porsche OFFICIAL: Cayenne (958) Facelift 2014 3/2/17 4:22 PM
    RCA
    67179 163
    Porsche OFFICIAL: New 991.2 (facelift) Carrera 4 and Carrera 4S 3/30/17 7:33 PM
    Carlos from SpainM
    60368 131
    371 items found, displaying 1 to 30.