Quote:
Originally Posted by Isaac Zachary
I generally disagree with intake pumping loss statements. Things like lean AFR, EGR, pulse and gliding, higher gearing and different cam profiles can reduce pumping losses. But an engine cruising at a steady speed needing x amount of fuel and therefore air cannot have greater or worse pumping losses from the type and size of the intake. If the intake really does have greater pumping losses then less air and fuel enter the engine, the engine produces less power and the end result is that the car slows down or can't maintain the target speed.
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I disagree to an extent. Pumping losses can be realized purely by intake design. Take the tesla one way valve design for example, if the intake was designed like this, it would have a very hard time getting much air even with the carb wide open.
How much of a restriction is it for the little carb vs the stock carb at the equivalent power output level, that's a hard one to answer. I'm sure it's measurable, but I don't know the math myself to give hard numbers.
My dad's told me long ago people racing would always swap 2 barrel carbs on their engines. If I remember right the concept was more for the fuel economy and have similar power levels. The larger carbs were oversized for the power output, I suspect accelerator pump generally is oversized, and the 2 barrel of a 4 barrel is smaller so the 2 barrel carb to start with was more of an ideal size. It's just hearsay but a lot of stuff he's told me over the years similar to that seem to be valid.
I suspect there's 2 major things at play for better econ on the lawnmower carb, his self adjusting carb setup is actually a very good idea for carb'ed engines. It's a self adjusting carb that doesn't suck. The secondary effect is I think floored he might be dumping the same amount of fuel as 1/4 throttle on the stock carb. I think since he's under a power restriction, it's forcing him to drive more ideal for mpg. It sounds like his shift points aren't half bad for mpg to my ears at least.
I suspect if that engine was converted to EFI and had a similar throttle limit imposed on it, he would see similar mpg. Either case It's a neat project, not too many people would think of running a tiny carb on a v8. I've wished my Lexus LS400 had finer control for the throttle at times so I could better control the engine for mpg. Almost need 2 throttles, one for 0-25% throttle, and the other that works like normal.