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From: "Jack Ford" <jackoford@theofficenet.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-1008286@logan.com>
Subject: Re: [FlyRotary] Re: Fuel Injector Position 
Date: Mon, 20 Jun 2005 17:57:22 -0700
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Yo, Bill,

Those crossover manifolds were on the less old 440 engines. OLD 300s had
392" Hemis.

The idea of a dashpot for gentle throttle closure MIGHT not be a bad thing -
not very heavy, not critical to operation, maybe in some situations and
designs, could perform a useful function in fire and noise
prevention............ Slamming a throttle closed is not a good thing for a
lot of reasons.

Jack Ford

Original Message ----- 
From: "Bill Dube" <bdube@al.noaa.gov>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Monday, June 20, 2005 5:22 PM
Subject: [FlyRotary] Re: Fuel Injector Position


> When you have long manifold runs, the accelerator pump volume becomes
HUGE.
> Perhaps I am dating myself, but the old Chrysler 300 had four-barrels
> outboard of the valve covers and the manifold runs crossed the entire
> engine. The accelerator pumps on those carbs were enormous. Blipping the
> throttle was like flushing a toilet.
>
>          The reason this is so is because you must instantly provide the
> fuel for a whole manifold full of air. You go from a pretty good vacuum to
> a full atmosphere in the time it takes for the butterfly to open. As this
> initial slug of air is flying past the butterfly, you must quickly dump
> fuel into it.
>
>          On the quickly closing side of the problem, the fuel wetting the
> walls of the manifold is, indeed, a serious issue. Fuel doesn't evaporate
> that well at room temperature and pressure. Thus, the less volitile
> fraction of the gasoline wets the manifold walls. When you suddenly shut
> the throttle, you get a big dip in pressure. The surface area of the
wetted
> walls is quite large and the fuel layer is thin, so when the pressure
> drops, all the fuel flashes into vapor.
>
>          If the manifold is very long, you can get enough fuel to cause a
> few misfires which fill the exhaust with fuel/air mixture. Then as the
> mixture becomes leaner, the engine fires, touching off the mixture in the
> exhaust system. Ka-bang.
>
>          On cars with carburetors and long manifolds (like air-cooled VWs)
> they put a throttle position damper to prevent the throttle from closing
> too quickly.
>
>          Bill Dube'
>
>
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