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Thread: 911S race motor

  1. #1

    911S race motor

    i am looking at purchasing a '67 911S that has been set up for vintage racing. it have a substantial amount of engine upgrades including 12:1 compression pistons and an aggressive race cam. suspension mod's and safety mod's have also been done.

    my desired use of the car is time trials, vintage racing (when i've acquired all the appropriate licenses) AND street use of the vehicle. by street use, i mean weekend driving, mainly short trips.

    my questions to the anyone interested in offering an opinion are:

    1). is it realistic to expect that a 911S with aggressive race upgrades can be used for street purposes?

    2). if so, what steps must one take to "detune" the motor for the street?

  2. #2
    IMHO, if this is a dedicated track car now, as it sounds, there is no way to cost-effectively "detune" it for the street. You would be better off buying a stock car and mildly preparing it for vintage racing in the "stock" class, if you want a dual-purpose car. Or better yet, buy TWO Porsches (and a trailer and tow vehicle) and have the best of both worlds!

    A fully race prepared car is not going to be appropriate for street use for a number of reasons:

    1. 12/1 compression ratio means you will have to run race gas at all times to prevent detonation, even if it's twin-plugged. At $4.50/gal., your trips will need to be VERY short, or your wallet VERY fat. You can't just "fill 'er up" at any gas station.

    2. Big cam (large overlap, lift and duration) means high RPMs to make big power. If it is a 906 grind, you will be coming into the power band at about 6,000 RPM, and it will be weak coming off the line at every stop light. This is not what you want on the street. Also, longevity on such a high-strung motor is not going to be great. High RPMs mean high wear, and you're going to be freshening that motor in a matter of a hundred hours of use, not hundreds of thousands of miles, like a street motor. You're going to want to make those hours count (on the track).

    3. Ride height and suspension stiffness will make your street driving a nightmare. You will grind your valences and tub going over every drainage swale and driveway if it is lowered properly for the track. If it has high spring rates and solid pickup points, motor mounts and bushings (monoball/heim-joint/polygraphite) appropriate for track usage, it will rattle the fillings out of your teeth on the street. Tracks are generally much smoother than our pot-holed city paving.

    4. Does it have a full cage as part of the safety prep? This makes it much more difficult to enter and exit the car, especially with door bars, and even with padding, represents a safety hazard for street driving when you aren't wearing a helmet.

    5. Noise will be a problem. Does it have headers and an open exhaust? Besides no heat in the cabin, you will be swapping out mufflers every time you want to drive it on the street, and the intake noise alone of a high RPM race motor may be enough to get you busted on the street if you wind it out. When you change back pressure on the exhaust, the air flow through the engine will be diminished, losing power, and you are going to have to change your jetting or fuel mixture to match the reduced flow or run too rich. Do you really want to spend an hour or two in the garage every time you switch from street to track configuration?

    HTH, and is not too much of a "wet blanket".


  3. #3
    Chuck Miller

    911S race motor

    Man, ttweed's info. is so sound, practical, and right-on ... it almost sounds like he tried to put one on the street like that himself ... in weak moments, we all think about it ...

    Great response

  4. #4


    thanks for your feedback. i called several porsche shops that i trust (andial, hergesheimer, racer's group) and they said many of the same things the "amateurs" did. (just a little message board humor)

    as much as i want to be optimistic about a car i'm looking at purchasing, i'm getting enough feedback to keep myself grounded in reality. as much as i would like to jump right into vintage racing, i may have to re-evaluate my options and look for a car that is more suited to street/track.

    i suppose a good test drive will tell all. thanks for your ideas.

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