Steady state fuel economy...carbed V8

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PackardV8
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Re: Steady state fuel economy...carbed V8

Post by PackardV8 »

dannobee wrote: Tue Jun 21, 2022 8:15 am Like Tom said, get the intake vacuum as close to atmospheric as possible to avoid pumping losses.
One more time, the OP said "carb"; carburetors and distributors are not at their best at near-WOT at low RPM in a hard pull. Without vacuum advance, cruise efficiency suffers. As previously mentioned at low vacuum, most carburetors are designed to open the power valve.
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Re: Steady state fuel economy...carbed V8

Post by dannobee »

Manifold vacuum is not the only source for vacuum. You can also run the advance can (and egr valve) off of ported vacuum.

EGR is nothing new; it's been on cars in one form or another for over 50 years now. I think the oems pretty much have if figured out by now.
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Re: Steady state fuel economy...carbed V8

Post by HQM383 »

travis wrote: Sun Jun 19, 2022 7:42 pm One of my recent ponderings on my new 91 mile a day round trip commute...

If you have 2 engines built appropriately for good fuel economy at a low cruise rpm (1700 rpm@75 mph in this case...OD and 2.73 gears), one a 302 and the other a 393w, would you expect to see a significant difference in steady state fuel economy? My thoughts are that the low torque 302, besides being smaller and lighter, would have lower internal friction and would require more throttle input to maintain steady speed which would reduce pumping losses. The 393 on the other hand would make significantly more low rpm torque and require less throttle to maintain speed. Thoughts?
If both were factory stock for a reference point of “built appropriately for good fuel economy at a low cruise rpm” and both were tuned for the same AFR (let’s say 14.7:1 just for the sake of a number) at your steady state cruise then the larger engine has the potential for ingesting a greater quantity of the 14.7:1 air fuel mix per revolution. Rpm is a constant as vehicle weight and gearing remain unchanged, and so would be tq to maintain speed. Less throttle angle for the larger engine to achieve required tq but still operating under 14.7:1 the same as the smaller engine that has a more open throttle blade. Which engine could maintain steady speed set the leanest AFR? Not sure but that could be your winner.
I’m a Street/Strip guy..... like to think outside the quadrilateral parallelogram.
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