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Thread: 2.0 Pinto spec carbs

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    2.0 Pinto spec carbs

    I'm refreshing a spare motor for a friend who is racing with the SCCA. The rules are very strange, and different for various cars in his class.

    For a 2.0 Pinto in "Production" class he can do essentially anything he wants inside the engine, but he's restricted to one 40mm downdraft Weber DCNF with 34mm chokes on a stock Ford intake manifold or two 40mm DCOE Webers on an independent runner side-draft manifold, also with 34mm chokes. Adding a plenum or cross-connecting the runners is forbidden. Modifying the carburetors is forbidden; annular discharge venturis are doubleplus forbidden.

    From what I've been able to figure, the 34mm-choked DCOEs he's running now are the main restriction on his power output.

    So... I've been looking at the single DCNF. The stock manifold doesn't look *that* bad, and while there are some overlapping intake events, each cylinder would see most of two 34mm chokes instead of all of one.

    Has anyone done any testing between a single downdraft vs. sidedrafts, with such small carburetors?

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    Re: 2.0 Pinto spec carbs

    Do I have it right? You may use twin 40 mm Webers setup, one butterfly for each cylinder? If so, you do not have to compare with original manifold and 1 carburetor. It does not even matter what carburetor you fit on this original manifold, I don't think you can get much more as 150 Bhp. With the original carb max output is round 145 Bhp, no torque. Twin 40 mm Webers with 34 mm chokes can make a lot more power and at least a lot more torque.

    The original inlet manyfold may look good but it can not stand pulse tuning as twin Webers can. Adding a plenum or cross-connections on you twin Webers would not be an advance. Lucky you may not do this.

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    Re: 2.0 Pinto spec carbs

    We can use sidedraft 40s, but only with 34mm chokes. The engine flattens out at 6000 RPM or so.

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    Re: 2.0 Pinto spec carbs

    You may need a better cylinder head or different camshaft to exceed 6000 RPM barrier. In no way a single inlet manifold with whatever carburetor fitted can out performance a twin 40 mm DCOE with 34 mm chokes at 6000 RPM or higher. The Twin carb setup will ALWAYS win and miles ahead.

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    Re: 2.0 Pinto spec carbs

    What camshaft are you using?

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    Re: 2.0 Pinto spec carbs

    I don't know. Both engines were built by a shop that's experienced with the rules; they just don't seem to have much oomph. The engine in the car has a flat follower cam; the backup engine, which I have apart at the moment, has a roller cam. I haven't measured the lift and duration yet.

    The two engines are supposed to perform the same; the one in the car flattens out at 6000-6200 and then the Miatas and Porsches in the same class just wave as they drive by. There's probably some power to be had by tuning, but the car is over 700 miles away, and unless the owner can find someone local, I'm going to have to do the best I can over the phone.

    The rules are: the carb and intake restrictions noted earlier, maximum .047" overbore, no welding in the combustion chambers or ports, a valve size limit, stock length connecting rods, valvetrain bits "must be made of metal", and some handwavery stuff about "spirit of the rules."

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    Re: 2.0 Pinto spec carbs

    The fact the engine "stalls" at approx 6000 RPM can be anything but let assume the engine was setup correct, ignition in working order, cam correct timed, etc... the cam will be responsible for the RPM range. OK, you need a working cylinder head. The carb's can't be the issue.

    I have no real experiences with these roller or flat follower cams but rollers should be able to do at least what or even better what "normal" cams can do.

    Can Porsches 911 6 cylinders in the same class use 34 mm chokes in there triple 40 mm carburetors? That's should be bad news because with 34 mm chokes these 2 ltr Porsches can develop max power, they are not restricted.

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