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Old 10-14-2012, 09:45 AM   #29
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American Coach uses a roof mounted air intake with a air scoop very similar to the Kenworth design.
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Old 10-14-2012, 11:43 AM   #30
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watch your boost gauge. turbo boost goes with fuel and work load. pulling a hill with your foot in the throttle is one place you're going to pull max boost. but cruising on the flats, barley in the throttle, boost presure should be low if any. and this is where i'd look for increases. other wise i think the scoop would only help direct air to the intake track. this discussion is similar to everyone's idea on how to build small block cheys. rule of thumb was 1.5 or 1.6 rocker arms. then a fellow built a 350 running on gas and put in 1.8 rocker arms everyone said he's combination would not work. long story short he pulled 750hp on gas. now they make 2.1 rockers. iskenderian said their hydraulic cams were as agressive as one could go. comp cams kept bumping the designs up and iski bumped theirs. now we have the super mega cams.
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Old 10-14-2012, 12:43 PM   #31
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Originally Posted by VanDiemen23 View Post
If the intent of the scoop is to get cooler, more dense air, then OK, but a WELL DESIGNED scoop doesn't see any positive pressure until about 50mph, and with a 70mph top end, the juice just isn't worth the squeeze from a "poor mans turbo" standpoint.

They work on racecars, 1/4 mile and otherwise, because the majority of the time is spent well above 50mph, and everything under the engine cover is hot as hell.

Sometime the scoop is just an efficient way to get the air turned 90 degrees into the induction system, and it doesn't provide pressure recovery at all.
Since I started this crazy thread, I guess I should chime back in.

My original thinking when I first postulated the idea of adding a scoop on my side intake was simply to insure there was always positive pressure at the filter intake. I guess, as Van Diemen wrote, I was thinking of it as "an efficient way to turn the air 90 degrees", thus avoiding a potential low pressure area around the intake vent slipstream (Bernoulli's principle). Maybe at our speeds Bernoulli doesn't apply, but I can demonstrate Bernoulli by gently blowing over the top of a piece of paper, far below a 60mph airstream.

I never invisioned a "ram air" scenario where the scoop actually added enough head pressure to affect the inductions system, too many restrictions between the atmosphere and the cylinder for a few extra pounds of pressure to make any difference. I actually hadn't thought of the air being any cooler or denser or whatever either, but since the intake is still on the side of the coach where it has always been I don't suppose the state of the ambient air would change.

I did like the idea of moving the intake to the roof area, and using that same system to vent heat after you stop. That seems clever. You get a cleaner air supply than the dusty road environment, and venting the heat past my bedroom is something I could fall in love with. On the downside there would also likely be more moisture available on the roof that could sneak into the intake, so one would need to watch out for that.

Great conversation, lots of good thoughts. Don't know that I will ever get to this project, but winter is coming uphere in the frozen tundra, so who knows
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Old 10-14-2012, 12:57 PM   #32
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Originally Posted by wonderer1 View Post
watch your boost gauge. turbo boost goes with fuel and work load. pulling a hill with your foot in the throttle is one place you're going to pull max boost. but cruising on the flats, barley in the throttle, boost presure should be low if any.
I'd love to watch my boost guage but the damn thing quit working. A brand new ISSA Turbocator too (re:EXPENSIVE!). Just put it in this spring, lasted one trip. The pyro works fine but the boost, which I used to be able to bury at 30psi, now might move to 5psi under full throttle

I checked the plastic tube connections on both ends, they seem fine, so I've either got a nicked in the tube somewhere or a bad guage. Arghhh...
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Old 10-14-2012, 01:38 PM   #33
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I'd love to watch my boost guage but the damn thing quit working. A brand new ISSA Turbocator too (re:EXPENSIVE!). Just put it in this spring, lasted one trip. The pyro works fine but the boost, which I used to be able to bury at 30psi, now might move to 5psi under full throttle
Maybe you should have gotten a Banks.
Mine will hit 32-33 PSI when needed.
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Old 10-14-2012, 01:47 PM   #34
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Faster air is lower pressure air.. you want to build pressure and lower the speed. As I said before, scoops dont work the way people in this thread are thinking.
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Old 10-14-2012, 02:14 PM   #35
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My '98 Monaco Exec has the scoop on the roof moulded into the rear cap. Also has a side discharge fan on the right rear to vent hot air. Not sure if they still use this system anymore. Would be interested to see why, why not though.
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Old 10-14-2012, 02:17 PM   #36
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Unless you have some kind of a performance programmer you are not going to have much luck trying to raise the boost. My Cat C-7 for example will get a maximum of 27 psi of boost. If I try to give it more-disable the wastegate-the ECM will just defuel it. I can watch the pyrometer and see it happen. EGT will climb as the boost and RPM increases and when it hits 27 psi the EGT drops. It will also defuel above 2200 rpm where maximum horsepower is rated. If I turn my MP-8 all the way up the boost will go to 30-31 psi before it defuels.

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Old 10-14-2012, 06:17 PM   #37
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picking up air flow below 50mph is not exactually true. if you used a 4 ft dia. scoop feeding a 6" intake your going to increase flow a lot. but obviously you couldn't run one that big. lots of hp to pull one that big. but where is the line big enough to do some good and small enough not to cost hp. and yes look at some of the city busses. some have scoops on the roof. so i would check out the busses to see how they deal with the rain issue.
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Old 10-14-2012, 07:43 PM   #38
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You'll only flow as much as the 6", maybe even less. You need to slow the air down. the 4' scoop to 6" pipe would speed it up.
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Old 10-23-2012, 07:27 AM   #39
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I have never noticed anyone mention air temperature when reporting their MPG. Is there a difference between driving a desert highway on a summer day at 110F and driving the same road on a winter night at 40F? The engine intake air is colder and therefore more dense, but you are also trying to push the bus through denser air. Comments?

In practice, I assume many would also have their generator/AC running at 110F, thereby dropping the MPG.
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Old 10-23-2012, 08:06 AM   #40
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The trick is to achieve cooler air, ie denser charge, in the intake system. If I remember, a 3 degree c reduction will yield nearly 1% increase in power. That is the purpose of the cooler in the turbo system. Tricks to do this are legendary, but that is a source of cheap power. The turbo heats the charge greatly, but a 1 degree decrease in air temp results in about the same reduction through the system including the EGT.
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