Udo,
I'm no expert, but could it be that you need more fuel because
the engine is getting additional air via a ram air effect?
A 490 Cu in engine at 7500 RPM needs about 1060 CFM
of air (assuming no pumping losses). If an inlet duct opening,
pointing forward, is 4x6 (24 sq inches) the air passing through
it goes something like. (hope this table comes out)
MPH CFM Factor of air needed
10 146.67 0.14
20 293.33 0.28
30 440.00 0.41
40 586.67 0.55
50 733.33 0.69
60 880.00 0.83
70 1026.67 0.97
80 1173.33 1.10
90 1320.00 1.24
100 1466.67 1.38
110 1613.33 1.52
120 1760.00 1.66
130 1906.67 1.79
140 2053.33 1.93
150 2200.00 2.07
160 2346.67 2.21
170 2493.33 2.34
180 2640.00 2.48
190 2786.67 2.62
200 2933.33 2.76
210 3080.00 2.90
220 3226.67 3.03
Up to about 70 MPH the engine is having to suck air through
the duct. At about 80 the air you are running into supplies
what the engine needs. Above 80 you would be ramming
excess air into the engine, requiring more fuel at higher
speeds.
Am I off in the weeds someplace?
Thanks,
Jim W.
>Snip
>----- Original Message -----
>From: "Udo Horn" <vintagethunder@hotmail.com>
>To: <jwaldron47@earthlink.net>; <land-speed@autox.team.net>
>Subject: Engine Air Inlets - definite improvement
>
> If anyone can explain why the jetting would be contrary to normal tuning
> changes, I'd be interested in hearing it. Is B'ville unique, does the
salt
> and or altitude effect the mixture differently than one might expect? Here
> in the east we do have some dragstrips, even at altitude, where we tune
for
> sea level. (Definition of east coast mountain 2500 ft.)
>
> Regards,
> Udo Horn
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