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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