Turbo Boost and FE

[GasSavers_Hal9000]

Originally Posted by Gollum

Oh, and just because a turbo increases thermal efficiency doesn't mean better FE. Thermal Efficiency is about how much power an engine is making for the given heat generated by the engine. This has nothing to do with fuel usage under a cruise or around town condition.

I've got disagree with you here. If engine heat can be equated to wasted fuel energy (which it can), then increased thermal efficiency will mean that you're extracting more energy per lb of fuel burned and converting it to mechanical energy. Wether you use that to accelerate faster, or cruise a greater distance at low throttle openings is primarily up to the driver. Engine design can also affect this but for a given combination, you have a lot of choices (The force is within you.... you must use it wisely... )

What IS true is that a turbo may only increase the thermal efficiency of the engine at certain rpm/throttle openings. The goal is to get the increases in the area where they will be most useful for FE fans. That's a different goal than HP fans.

On another (although similar) note, I've had an idea rattling around in my head for years now.... It's for a true tunnel ram intake that might produce a small amount of positive pressure at highway speeds. It would have to incorporate a turbo style BOV to avoid pressure waves, and would need a long straight stretch to work (my original idea was for a rear-engined VW), but it would probably have the same effect on the highway as a Low pressure turbo would.... If there are any VW owners around who want to do some fabrication, I'll be happy to share my thoughts.

[itjstagame]

I've thought about the ram air idea too. It definately has been known to add a couple HP to racing motorcycles, at the HP they were running it was about 5% increase and only from a fairly quick speed.

I'm sure I could look up the equations, but what kind of pressure could you really expect to see at 55MPH as most of us go. I agree it might help offset the losses associated with going at an increased speed a little, like if you got 65MPH you'll get 4x increase of pressure on the front of your car so now you'll have a bit more boost to your intake, but overall I'd be a loss.

Of course you could always completely seal the entire engine bay off and get a gigantic radiator openning and then all air would have to either be forced into the engine or slow you down as drag. Actually now that I think about that, the more pressure you have from a RAM intake setup the more drag you neccissarily have to be inducing on your car. The drag of course is worse for a giant radiator hole than for a small intake hole (based on openning area). Also would a smaller openning be better because of less drag, or would a larger openning that tappers waaay down to a small intake be better because it increased intake PSI?