Group,
I have done much experimenting with air scoops, not very scientific
though I might add. I know some things that don't work, at least not for
me.
I had the idea that if a small scoop was good, then a big one would be
better. Wrong! As Bill Hurt, (Herbert Streamliner Engineer) explained to
me, there are two kinds of pressure involve with a scoop, velocity
pressure (gets the air into the scoop) and static pressure (the needed
pressure to keep the air in the scoop. With a large scoop lots of air
gets in the scoop, but only that which the static pressure captures
stays. Results, turbulence!
I had a couple of problems with the large scoop. First, the pressure
build up pushes fuel out the idle air bleeds onto the manifold. I think
that any scoop that is working will give you this problem, so plug the
air bleeds if you have them. I replaced the injector nozzle lines a
couple of times because of small fires in the shutdown process. The
second problem was aerodynamic disturbance that caused ill handling and
spins.
I now have a scoop that is calculated to flow the amount of air needed
to supply the engine at the speed I expect to run. Tom Burkland
suggested this scoop design. Calculate the amount of air that the engine
displaces at your expected RPM over a mile of distance. What you want to
end up with is an opening in the scoop that will equal a column of air a
mile long that provides the air needed.
If you want the formula, I can provide it.
Tom, Redding CA #216 D/CC
John Beckett wrote:
>
> Kvach
>
> My experience is all non-supercharged so far. But I can tell you that
> there is a 'lot' of air being stuffed into a hood scoop, depending on
> design, at 200 MPH, and very hard to equalize air flow, inside the scoop,
> with an individual port Hilborn type injection. I didn't need a high speed
> by-pass, heck I couldn't get it rich enough and maintain consistent plug
> reading throughout the cylinders. Anyway I have the burned rear pistons to
> back up my theories.
>
> John Beckett, LSR #79
>
> ----- Original Message -----
> From: "Butters Family" <bbutters@dmi.net>
> To: <ardunbill@webtv.net>; <land-speed@autox.team.net>
> Sent: Thursday, February 10, 2000 1:42 AM
> Subject: Re: Tuning Mechanical Fuel Injection
>
> > I have some questions on mech. FUEL INJECTION is there any
> > relationship to high speed lean out and the forward faceing hat stuffing
> air
> > into the blower at 200+ mph. I guess you should know the answer to that
> > question if it becomes more of a problem or only shows up on the track and
> > not in the dyno room??? Has anyone used the conventional Hilborn type
> > injection on thier blower to do say 90% of the fuel requirement and make
> up
> > the remaining 10% with electronic down injectors that is regulated wih
> > O2 and EGT sensors. Seems like you woouldn't need those expensive high
> flow
> > electronic injectors and they could cycle better. Kvach
> > ----- Original Message -----
> > From: <ardunbill@webtv.net>
> > To: <land-speed@autox.team.net>
> > Sent: Tuesday, February 08, 2000 11:45 AM
> > Subject: Tuning Mechanical Fuel Injection
> >
> >
> > > Group, in looking more closely at the "Hemi Head Chevy Engine" article I
> > > told you about earlier today, there is an illuminating technical tidbit
> > > expressed for those like myself trying to get mechanical fuel injection
> > > working properly.
> > >
> > > That's a sidebar in the article entitled "Iskenderian Dyno Report". The
> > > chart under it reads in part as follows:
> > >
> > > RPM HP TORQUE BOOST BYPASS(jet)
> > >
> > > 5500 539 490 16# .105
> > > 6000 578 482 17# .105
> > > 6000 514 462 17# .090
> > > 6000 590 492 17# .110
> > > 6500 624 480 17# .110
> > > 7200 638 440 19# .110
> > >
> > > All the above involves this hemi-head 301 Chev running on alcohol with a
> > > 6-71 blower driven 1-1 with a Hilborn injector on top of it. With the
> > > Hilborn bypass jet system, a smaller (numerical) jet size means a richer
> > > mixture.
> > >
> > > Several interesting things here:
> > >
> > > l. The engine needed different bypass jet sizes to give max power at
> > > different RPM ranges. Something about the cam timing, etc., was letting
> > > more or less fuel escape out the exhaust at different rpms. Assuming the
> > > Hilborn pump delivers a constant increase in flow directly proportional
> > > to increase in rpm(does it?).
> > >
> > > 2. When running mechanical fuel injection, you can only run one bypass
> > > jet during a pass on a speed trials course (despite availability of 'jet
> > > selectors' etc., no time to turn 'em). One bypass jet size is not going
> > > to give you full power at all rpm ranges, blown or unblown, so you will
> > > have to focus on the top end and hope it doesn't hurt the mid-range too
> > > much.
> > >
> > > 3. The blower's manifold pressure increased at the top end because the
> > > gas-flow through the heads could not keep up with the increased output
> > > of the blower. At 7200, even though the manifold pressure went up to
> > > 19, the engine torque was dropping down sharply.
> > >
> > > The spark lead was 34 for all the above tests on this hemi-Chevy. The
> > > heads had the plug electrodes at the combustion chamber surface(no
> > > cartridge fire setup like the original Arduns).
> > >
> > > Any comment from veterans with mechanical fuel injection experience??
> > > ArdunBill
> > >
> > >
> >
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