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Thread: High Compression 2.4 S Motors

  1. #1
    Senior Member
    Join Date
    Mar 2003
    Santa Monica

    High Compression 2.4 S Motors

    Hello there!

    Does anyone have experience fitting 2.2 S pistons in a 72-73 S to get a high compression motor?

    What would the compression be? Any valve clearance problems? Anyone ever dyno a motor to see what the horsepower gains are?

    I would think the (already mighty good) throttle response would be awesome!

  2. #2
    On the advice of my mechanic, who had built countless race engines, I decide to run 2.2S pistons with 2.4S motor. He says around 10.1 compression and 15 - 20 HP and no issues at all in building.

    Motor is finished but not yet installed or dyno'd so the proof will be in the driving I guess but I know it was done to lots of 2.4 race cars that raced successfully out here and I wantd a power upgrade that could be reversed easily if someone wanted to return the motor to stock 2.4S


  3. #3
    Senior Member
    Join Date
    Jun 2003
    Yes I have built one of these engines on a 7R case. I had clearance problems on the bottom of the stroke, the piston skirts just kissed the case at BDC so I had to remove a little material from the skirts. I have no valve to piston clearance problems as I am using "E" cams. Awesome engine!


  4. #4
    I just helped build a similar motor and will be building another similar motor soon. The just finnished T-E motor did have some piston-valve clearance issues but it wasn't bad and was more of a result of relieved 2.2T pistons combined with crane 288 cams (cross between S and solex). We did have to advance the cam timing a hair (still well within specs just not at the target timing) to get the required clearances.

    I will soon be building a 2.4E motor using 2.2E pistons and solex cams. I don't anticipate any problem with them. I'm hoping to make right around 180, 25 over a stock 2.4E. I would think that increasing your CR up the point, point and a half will definitly up your Horsepower throughout the entire rev range but I wouldn't expect a full 20 HP more though.

    According to Bruce 2.2S pistons in a 2.4S motor should bump the "book" compression value up 1 point or so over stock 2.2 compression, about 10.5 or so (don't remember the exact value here) but when measured out it will only be about 9.6:1 which is just perfect for a street car on pump gas.

    Just some thoughts from my research.
    1973 T

  5. #5
    In Wayne Dempsey's book on 911 engines, this set up is one of his 'favorite' mods for a 2.4L. I did the same on mine as Clyde, but mines not wired up yet. I'm running it with Elgin's 'mod-S' cam. Wish I could give you the results, as I'm anxious to see how it comes out myself.

    Also, since I doing the whole rebuild at the time, we had Ollie's machine the lower covers for twin-plugs (just in case the compression is too high for the crappy gas we get here in NCal). I've not sprung for the twin electronics yet (still researching t-plug dist system a la RSR vs the more modern set ups out there - subject of a forthcoming thread before I decide).

    ....patiently waiting.....
    Chris Purpura @civilizedmisfit
    Member #479
    Current Cars:
    1972 911T aka The "Civilized Misfit" Build
    Miss February - EarlySRegistry 2023 Calendar
    1968 911S Ossi Blau/Beige Corduroy

    Past Cars:
    2019 911 Carrera GTS (sold, no regrets)
    73S - #1100 (restored and now somewhere in Europe)
    1997 993 Carrera 4S Black on Black (sold)

  6. #6
    My motor is a stroked 2.2S with high compression pistons. It's about 10.5:1 and I can run 91 with no problems - she makes good power all the way to 7200. Good daily driver with the MFI ... any questions, just ask.
    SReg. #778 OGrp: #8 RGrp: #---
    TLG Auto: Website
    Searching for engine #907495 and gearbox 902/1 #229687

  7. #7
    I remember your car was in an accident but what's the current status of it?
    1973 T

  8. #8
    Can you raise the CR for a 2.7RS engine in the same way. Any relatively easy mods to improve power for this engine ?

    To ask is to seek denial

  9. #9
    Originally posted by l33t9eek
    I remember your car was in an accident but what's the current status of it?
    I spent a good portion of last night stripping the left front of the car ... we've acquired a donor/parts car and the patient is slated for surgery in the next week or so. The prognosis thus far is that the 914 will be making a return to the ring, maybe even by the Jan. 2? R Gruppe track day.

    However, nothing is set in stone.
    SReg. #778 OGrp: #8 RGrp: #---
    TLG Auto: Website
    Searching for engine #907495 and gearbox 902/1 #229687

  10. #10
    Senior Member
    Join Date
    Mar 2003
    Santa Monica
    Thanks for all the great answers and info.

    I talked to an well known parts supply house, and a fellow there said a good rule of thumb is an extra 10% power for every 0.5 point increase in compression ratio.

    Even if it's just a rule of thumb, that seems (wildly) optimistic to me. Any thoughts?
    Early 911S Registry #224
    911S Targa 1973
    356B Roadster 1962

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