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Old 03-28-2008, 11:00 AM   #28 (permalink)
Join Date: Dec 2007
Location: Bay Area
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The Miata - '01 Mazda MX-5 Miata
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Originally Posted by tjts1 View Post
The pumping losses you describe exist when there is a difference in air pressure between the intake manifold and the and the bottom side of the piston (AKA crankcase). The simple solution if you want to eliminate pumping loss isn't to heat up the intake air but to apply a vacuum to the crank case. A lot or racers do this. I tried it years ago and it work but its too much of a hassle to maintain.

Pumping losses also occur during the actual intake down stroke - as there's a pressure gradient between the cylinder and intake manifold. It doesn't help that it's pulling against a vacuum (which in turn was created by that same action - making a vacuum isn't free, unfortunately). This is one benefit diesels have fundamentally - no throttle.

But even if you apply vacuum to the crank case - now you've got pumping losses while traveling up as opposed to traveling down. But that said, the reason as far as I know, for racing applications applying vacuum is to remove blow by. First because that pressure can build up quickly in their application and second because it's not a good thing to have such gases in there. I've seen setups with limit switches/valves to pull full vacuum during peak power and then limit the vacuum when not under heavy load - to reduce parasitic losses from their vac pump....

Originally Posted by tjts1 View Post
I'll give you that, but I haven't seen one warm air intake that doesn't lose more power and efficiency because timing is being retarder than it gains from any pumping loss decrease.
Where do you live? I can show you mine - and you can peek at the SG to see the timing... My timing hasn't changed and my intake temps are around 120 once fully warmed up (which, just so happens to be close to the temp of my intake while driving through the sierra Nevada last summer - without the WAI ). I got the best economy on that stretch - except during the long downhill periods

But yes, this is a case where one must go with what works... There's no rule of thumb - there's a theory (as defined as well substantiated explanation) - but it's largely dependent on engine management - which of course varies from make to make and even model to model. Oh feedback control
Cars have not created a new problem. They merely made more urgent the necessity to solve existing ones.
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