TB vs TB Spacer?

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"TBone" wrote:


That is where you have it wrong. A larger phlenum has long been a trick to enhance flow from the old carb days at midrange on upper RPMs. It works on the theory of increased airmass and better fuel mixing and how it interacts with the suction pulses as the base of the carb or TBI unit and increases the flow efficency so that less "flow" is needed (throttle plate does not need to be open as much) to fill cylinders properly at the desired intake pressure in cylinders. (there is less over all pressure drop between base of TBI and intake port so overall flow is improved) Spacers are worthless on multi point injection becauce they truely have nothing more than a air valvle on their intake and most multi point system have pretty well tuned intakes as well unlike most TBI engines that are not tuned properly.
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We shall see.....

Not exactly..... Larger plenum made the runners appear longer and thus improved performance due to increased signal in a low vacuum environment.

Which is where you go into the woods. A larger airmass below the TB or carb kills the sharpness of "signal" (in reality its the accuracy of the vacuum drop). If its muted (as it would be wih a large airmass), the carb is slow to respond in allowing more fuel into the stream, a throttle body system doesn't have this sensitivity because you are no longer depending on vacuum alone to induce fuel flow.

And you are completely wrong here. Better flow depends on two things: 1) smooth passageways, and 2) larger pressure/vacuum differential between orifice (TB) and container (cylinder). If you drop the difference to nil, NO flow is the result, and the engine will stall. (Hint: vacuum leaks are a bad thing)

Yup, thats because TBI is a carb in disguise.
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Max

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"Max Dodge" wrote:

THe spacer increases the phlenum effect under the TB which can improve throttle responce and power some and the theory is that you want to also stir the mixture up more (more turbulance or swirl) to increase atomization of fuel mixture for better power and burn.
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True. In theory.

Wrong. You don't want turbulance in the intake manifold. You DO want a swirl effect in the > cylinder <. Fuel injection occurs just above the valve, so smooth, laminar airflow is an advantage in the manifold.
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Max

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engine. It should become obvious to even the most opinionated or just plain friggin' stupid folks (figure out which label fit's who) around here that if the turbulence was an issue to squeezing out a couple of HP the big 3 would have done it. For an exercise go lift the hood of your truck. On mine, a 05 325HP Cummins, from the airbox there air travels through a ribbed hose through a 90 and down into another 90 to the turbo. Doesn't really seem to be a concern about smooth airflow there. The wife's 05 GMC 255HP l6 Has pretty much the same no, turbo of course. Oh, no spacer on either of them. I'd submit that both DC&GM have engineers who probably spend months watching air flow, that's what they come up with. Further they probably know a hell of a lot more than most of the folks here about getting HP and economy out of a stock engine.
Roy
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