Now that I've had time to think about it for a while, there's got to be something to it other than heat reduction. Each liter of air going through the intake spends a total of maybe a couple of hundredths of a second in the manifold. During this time, ideally, the airflow exhibits either laminar flow or laminar flow with a very small amount of boundary layer turbulence. (BTW this turbulence is GOOD and is the reason why you don't polish your intakes). So the volume of air that actually gets heated by the manifold is very small (because of aforementioned short time in manifold accompanied by low mixing rate in the gas charge). So if 1 percent of the intake charge gets heated by 100 degrees C, (which is 180 degrees F; quite a large increase) then the intake charge temperature goes up one degree C. This is insignificant compared with variations in ambient air temperature. Again, some real analysis combined with empirical data would tell the tale. I didn't see all that much difference in the dyno curves that couldn't be accounted for by different conditions on different days, or hood open vs. closed. As for what else could be happening, it's hard to say. Maybe some CFD work would be able to reveal that, but from what I've heard you rarely gain anything by moving the injector further upstream. But just because you've moved the manifold (on other cars) doesn't mean you have moved the injector. My Volvo had its injector ports in the cylinder head; you could move the manifold a foot away and it would make no difference aside from any velocity stack effect. Not saying I know the answer, but it's fun to think about. Oh by the way there's an online Otto cycle calculator at http://members.aol.com/engware/calc3.htm that you can use to see the effects of compression ratio, etc on efficiency. It's too bad you can't put in more parameters and get hp and torque vs rpm. That should be possible, even though it's not very accurate. At least you would know the BEST you could ever do. Dave -----Original Message----- From: Richard Cranium [mailto:[EMAIL PROTECTED]] Sent: Tuesday, March 06, 2001 2:44 AM To: Sentra Mailing List Subject: SML: Re: Phenolic Spacers >The only way to show for certain whether these spacers are actually doing >what you think they are is to put a thermocouple (or other comparable >instrument) out into the airstream in the intake (right at the manifold >gasket) and measure air temperature under the same ambient conditions, with >and without the spacer. True, testing with a some sort of measuring device will probably give the best results. >At any reasonable engine speed, there are tens of liters per >second moving through EACH intake passage; it's hard to imagine that this >amount of air could be heated to any degree by the intake manifold. > The air flow through the intake passage at steady state (forgetting about the flow pulses as the valves open and close) could be considered a control volume. The energy rate balance for steady state control volumes states that 0=Qcv/m-Wcv/m+(h1-h2)+(v1-v2)/2+g(z1-z2). Where Qcv is the heat transfer rate. The heat transer rate in the equation goes to zero if: 1. The surface area is to small for effective heat transfer 2. The temp difference between the cv and its surrounding is so small that Qcv is ignored 3. The air flows so quickly that there isnt enough time for Qcv to occur 4. The outer surface of the cv is well insulated I dont know how much air flows through, but if there is enough then there isnt enough time for heat transfer to occur aka #3. Correct me if im wrong, i forgot some of my thermo. So why the added HP? Anyone else have ideas. His website states hp gains. Javier got a B in thermo >It's possible that this mod is doing something other than what you think it >is. It'd take a much smarter guy than me (automotive-wise, anyways) to >figure it out. I'd also want to see a thermodynamic explanation rather >than >hand-waving. Unfortunately I bagged thermo in favor of statics/dynamics. >And I'm kicking myself right now. > _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com +----------------------------------------------------------------------+ List archives ==> http://www.escribe.com/automotive/sml Have a question? Try the archives first. +----------------------------------------------------------------------+ List archives ==> http://www.escribe.com/automotive/sml Have a question? Try the archives first.
