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  #21  
Old 01-08-2012, 10:12 PM
yakdriver yakdriver is offline
 
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I did one on my 7 about 3 years ago with AFP. He only had a scoop for the 8 at the time and I modified it to fit the 7. That was quite a bit of work but it turned out nice. I get at least an 1" or more MP over my friend's 8 with stock Vans intake. I just finished putting a system on a friend's 7 with Silver Hawk servo and the 7 scoop. Scoop fits great and it was a real easy install. Don
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  #22  
Old 01-09-2012, 05:56 AM
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Quote:
I get at least an 1" or more MP over my friend's 8 with stock Vans intake.
Typical quote, but again, a comparison of filtered (stock Vans) to unfiltered (Bower with butterfly open). Take the filter out of a stock snorkel and compare, or compare filtered performance for both.
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  #23  
Old 01-09-2012, 06:31 AM
N184JG N184JG is offline
 
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Thanks for all the feedback. My problem is that I have a horz. cold air induction and a cowl with a scoop so I am looking for a simple fix.
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  #24  
Old 01-09-2012, 07:04 AM
yakdriver yakdriver is offline
 
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Quote:
Originally Posted by DanH View Post
Typical quote, but again, a comparison of filtered (stock Vans) to unfiltered (Bower with butterfly open). Take the filter out of a stock snorkel and compare, or compare filtered performance for both.
That's the whole idea of ram air induction, you can switch it to unfiltered ram air at altitude. You might get more MP taking the filter out of the Van's snorkel but you can't do it in the air. The Mooney 201 had the same type of system.
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  #25  
Old 01-09-2012, 07:28 AM
David-aviator David-aviator is offline
 
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Default 2 cents worth on ram air induction....

There is no question best manifold pressure is achieved with direct ram air. The unanswered question is how much better is it than filtered air.

That depends on the efficiency of the filter system. Seems to me Dan Checkoway did some experimenting in this area and found with his system the difference was minimal, like about a half inch. He had the standard filter connected to the left intake baffle area which also benefits somewhat from ram pressure.

With the 7A I had an internal K&N cone filter and it cost some rpm drop and 1 inch of MP until opening direct ram after take off. I could feel a surge when opening the valve and liked it a lot.

The prime advantage of the internal filter is it provides for more air across the top of the left side of the engine and for oil cooling.
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  #26  
Old 02-15-2014, 12:41 PM
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NDrv8r NDrv8r is offline
 
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Default Bower Ram Air

A question for those of you with glassed non removable on Bower scoops.
How do you remove and install the cowl? I have a snorkel and have issues removing the cowl relating to the air seals in front. It has to drop straight down to clear the spinner. So if it has to drop straight down, how do you attach the connector between scoop and filter housing? Can you reach through the inlet to work the connecting tube in place?
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  #27  
Old 02-15-2014, 05:36 PM
yakdriver yakdriver is offline
 
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I have about 1/2" space between the intake and the air cleaner. I attach the neoprene sleeve to the air cleaner. When you get the lower cowl up in position you can just work the sleeve around the intake with your finger.
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  #28  
Old 02-15-2014, 09:13 PM
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DanH DanH is offline
 
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Larry, don't buy into the "1 inch more" fantasy, in particular if it makes your airplane harder to service.

They're either talking about (1) a comparison between two different airplanes with uncalibrated MP gauges, or (2) the difference between sucking open the plastic reed valves on the Bower canister to tap low pressure lower cowl air, vs filterless outside ram air. No doubt there's an inch difference in the second case, but it's because the filtered performance is so bad. To make it worse, the lower cowl air is hot.

Apples-to apples: An ordinary Vans filtered snorkel from the left cowl intake will provide higher MP on takeoff than the Bower running filtered (probably 0.5" Hg). Install a larger filter media to feed the snorkel and the gap becomes even greater. The custom work to install a Vans snorkel with a bigger filter will be less than the custom work to install a Bower, and there is no cowl fitment issue.

In cruise, with the Bower butterfly open (unfiltered) you might get 0.2"~0.3 Hg more than you will with the standard filtered snorkel. The difference will decrease with increased media area feeding the snorkel.

As for a dedicated front intakes, filtered vs unfiltered, again it's mostly a matter of media area. By measurement, the filter drop across a big K&N (#33-2124) is, at worst, about the same as Rod reported for his intake with the butterfly wide open. Put another way, it's possible to fly filtered all the time and lose nothing.

BTW, when you hear claims of 1" or more, consider the hard physical facts. Around 175 knots true at 8000 feet is a typical cruise for a clean RV with an IO360. Assuming a standard day atmosphere, the absolute maximum available ram is 1.15" Hg. That's pitot pressure, 100% conversion of dynamic to static pressure. Capturing 100% is physically impossible in the case of an engine intake, as it is not a pitot, i.e. it has an open exit. To get 1" more MP than your friend's RV would require that he is taking his intake air from someplace with less than static pressure. It's clearly nonsense, even if he was sucking it from inside the lower cowl...you know, like a Bower running filtered.
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Last edited by DanH : 02-15-2014 at 09:25 PM.
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  #29  
Old 02-16-2014, 12:07 AM
scsmith scsmith is offline
 
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Default A more relevant data point

This will help give apples to apples data along the line that Dan Horton is suggesting.

I have a ram intake similar to a Rod Bower system, in fact I use his ram-air shut-off butterfly valve and his conical K&N filter. But instead of pulling air in through the reed valves from the lower cowl, I have a sealed can that transitions smoothly to a 3" scat tube that runs up to an intake in the middle of the intake baffle 'ramp' in the cooling air intake on the left side, in about the same location that Van's filter would go.

So, I can tell the difference between ram air and filtered air through the cooling intake.

At cruise power (24" 2400 rpm) the difference is 0.25" hg.

At take-off power at sea level, the difference is about 0.3" hg.

My ram inlet is a crescent shape under the spinner, kinda like a P-51, and it has fairly generous lip radius so it does not separate on the intake side when there are large flow angles from prop swirl (many Bower intakes have too sharp a lip in my opinion).

Anyway, I think it is as good as it can be, and it is only 1/4 inch of MAP better than pulling filtered air in through the cooling intake.

If I had it to do again, I think I would opt for the Van's snorkel, enjoy the smooth cowl aesthetics and concentrate on putting radiused edges on the filter intake in the cooling ramp to maximize flow through the big rectangular filter ( Like Dan C. did some time ago).
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Last edited by scsmith : 02-16-2014 at 12:10 AM.
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  #30  
Old 02-16-2014, 06:22 AM
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Kevin Horton Kevin Horton is offline
 
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I've got the standard Van's snorkel, and I am extremely impressed with the MPs that it provides.

Looking at the recorded engine monitor and EFIS data, I see that the MP increases during the take-off roll. The MP reaches the value seen before engine start about the time the IAS hits 60 kt. The MP is about 0.2" above the pre-start value by the time the IAS hits 85 kt. At 185 kt IAS, the MP is about 0.9" higher than the ambient pressure (based on comparing MP against pressure altitude, after correcting the MP for the known 0.2" error). My data suggests that Van's snorkel is recovering roughly 50% of the available ram pressure rise. That is excellent, considering that there has to be some pressure drop over the filter, and it takes a delta pressure to push air through the induction tract (i.e. the pressure at the start of the snorkel must be higher than the MP, or the air wouldn't flow).

I know that my MP indication reads about 0.2" high at high MP, based on comparison of the MP with engine stopped on the ground to the pressure altitude. I'm not sure what my MP calibration is at lower MP, so I've only looked at data from close to 30" MP. The data at higher altitudes give similar results, but I don't know the MP gauge calibration that those lower MPs, so I've ignored those data points.
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