How much do more aggressive cams affect gas mileage ?

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Thread: How much do more aggressive cams affect gas mileage ?

  1. #1
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    How much do more aggressive cams affect gas mileage ?

    I have a 94 TT with stock twins, just BPU. Last summer I refreshed my engine to replace all the leaking hoses, gaskets etc. Valve stem seals were the biggie, but there were small leaks everywhere due to rubber hardening etc.

    While I was doing the valve stem seals, I also replaced the cams with Kelford T-202C (268/272) and the springs/retainers with Supertech TS1012 dual springs. Titan V2 adjustable cam gears, and they're degreed in just right.

    I used to get at least 240 miles to the tank of 93 octane, and sometimes a lot more with just easy highway driving. But now it's down around 200 or so with general around-town driving, short highway stints, and no really hard pulls or anything. At first I thought it was "just that tank" but it's been pretty consistent last few fill-ups. I'm hoping it's the crappy winter gas, but in general the car barely goes out in the cold.

    So, do cams have that much of an effect ?

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    More lift = more fuel. Yeah it will effect it. We donít buy these cars for gas mileage though lol


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    i recorded mark7m001.mp3 Mark 2JZ's Avatar
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    I would say yes as far as worse gas mileage. Also maybe since the cam overlap at lower rpms/low load it’s less efficient.

    I could be wrong but that’s my $0.02
    1994 Supra PT71GTQ

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    I kept rationalizing it as more lift = more fuel/air = more power, so less throttle needed for same power ==> same mileage.

    But nooooo, guess not

    Didn't think about the overlap. Last couple of tanks have been "regular" driving, not Supra pulls on the highway at higher rpm. Heading from CT down to Philadelphia for Northeast meet in a few weeks, 2.5 hours of highway. We'll see how that does for mileage.

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    Game Over Boost Wang's Avatar
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    Quote Originally Posted by Mark 2JZ View Post
    I would say yes as far as worse gas mileage. Also maybe since the cam overlap at lower rpms/low load itís less efficient.

    I could be wrong but thatís my $0.02
    Stock ecu playing things safe, paired with any big exhaust removing any remaining exhaust reversion with more overlap will do it.
    OP's gas mileage will likely be worst if he didn't degreed those cams.
    -Sam

    1993.5 White turbo hardtop. 1 of 26

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    Super Moderator Wreckless's Avatar
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    More lift by itself won't affect gas mileage nearly as much - the 'more air = less throttle needed' would mostly apply.

    The overlap and increased duration does lower overall efficiency at lower RPM's which means worse fuel mileage when idling and at light throttle vs stock cams. There's always a tradeoff, until we start talking VVTi which is awesome when it's tuned well because you can get a lot of the cake and eat it too.

    But no, most of us don't buy these cars for fuel milage
    Jeff
    "I spent a lot of money on booze, chicks and fast cars. The rest I just squandered." -- George Best
    Quote Originally Posted by KING View Post
    Who would have ever thought.....the impact an automobile can make.....

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    Heh, no, no I didn't get them for the mileage ... but I wasn't really expecting a hit unless I really got into it on the highway etc. Ah well.

    I do have a vvti head sitting in the garage, waiting to be installed. Well, that plus single, plus standalone, plus plus plus. Hrm, can I get an Aristo 2jzgte vvti ecu for now ? Until I can do the whole single upgrade that is ?

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    Super Moderator Wreckless's Avatar
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    Quote Originally Posted by Halfwalker View Post
    Heh, no, no I didn't get them for the mileage ... but I wasn't really expecting a hit unless I really got into it on the highway etc. Ah well.

    I do have a vvti head sitting in the garage, waiting to be installed. Well, that plus single, plus standalone, plus plus plus. Hrm, can I get an Aristo 2jzgte vvti ecu for now ? Until I can do the whole single upgrade that is ?
    That'd be a lot of work to do a VVTi swap with a VVTi ECU just to rip the VVTi ECU out and go standalone anyway. I'd recommend just doing the VVTi and standalone at the same time, and change fuel/turbos/etc as your build plans dictate.

    Just don't skimp on tuning costs. If there's a local guy that a lot of Supra people highly recommend, but he's not cheap, there's a good reason why he's not cheap and that is money well spent.

  11. #9
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    So, pick a standalone that can handle the twins and vvti ? I thought most of the standalones didn't handle the sequential twins, only in true-twin ? The main players seems to be ProEFI, Haltech and AEM, right ?

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