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Author Topic: Hood scoops  (Read 1601 times)
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wheelrdealer
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« on: February 01, 2013, 09:06:45 AM »

After reading 38 flatties thread on the definition of a cowl and hood scoops on blown flatties, I started thinking. I went to the link and worked the hood scoop volume formula for my scoop. 7.5" X 8" for a 302 cu in motor. It is about 3 to 4 times larger than it needs to be. With that said, I am looking at options for a smaller air intake opening. I am sure these questions have been answered before but I cannot find them. I have a D/CGALT the grill and headlights are covered but the car came with a prostock style hood scoop over the tunnel ram intake. We ran it in 2011 as built to get a baseline.

I would like opinions on switching to a cowl hood and plumbing air intake from the headlight bucket area. Not sure if that is legal but I cannot see where it is not.

I had some hemi cross ram style velocity stakes at the shop and taped it in the headight bucket. It could be trimed to the shape of the opening and plumbed to an airbox for the carbs.

Would this work better than a scoop? It has to take some HP to push that big mailbox scoop.

Please let me know your thoughts.

Thanks,

Bill




* Rebuild 156.JPG (96.35 KB, 640x480 - viewed 129 times.)

* Rebuild 155.JPG (88.04 KB, 640x480 - viewed 134 times.)
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Tman
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« Reply #1 on: February 01, 2013, 09:39:19 AM »

Shouldn't this be moved to the tech section and not here in diaries? huh
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« Reply #2 on: February 01, 2013, 11:59:24 AM »

Page 69 says "engine intake air may be ducted from these openings (headlights)".
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wheelrdealer
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« Reply #3 on: February 01, 2013, 02:07:01 PM »

Shouldn't this be moved to the tech section and not here in diaries? huh

Tman:

Perhaps so, but since I don't have a build diary thread. I am rebuilding my car so I thought I would ask the questions hear. If Jon or Bob want to move it to technical thread that will be fine.

Stan, thanks not sure why I missed that but I did.

Now that it is legal... is it a better way to go than a scoop for a small displacement motor?

Thanks in advance for the resopnse.

Bill
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Rex Schimmer
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« Reply #4 on: February 02, 2013, 12:00:41 AM »

Bill,
You need to size the opening to the required engine air flow at your maximum speed and then I would make it about 10-15% larger then you need to expand the volume of the inlet tract after the inlet to reduce the speed of the incoming air. By reducing the air velocity you will increase the pressure at the engine inlet, which is just what you want. By doing this you can take advantage of the "ram effect" of the high speed, and don't believe anyone that says it is worth 3-4 psi at 200 mph, properly done it may be 1 psi but that is still a 6% improvement.

Rex
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« Reply #5 on: February 02, 2013, 07:30:17 AM »

Bill,
You need to size the opening to the required engine air flow at your maximum speed and then I would make it about 10-15% larger then you need to expand the volume of the inlet tract after the inlet to reduce the speed of the incoming air. By reducing the air velocity you will increase the pressure at the engine inlet, which is just what you want. By doing this you can take advantage of the "ram effect" of the high speed, and don't believe anyone that says it is worth 3-4 psi at 200 mph, properly done it may be 1 psi but that is still a 6% improvement.

Rex

Rex:
Thank you, that is what I wanted to know. I don't have the D motor or the car to mount a threat to Jucewik's 234.+ record but I do have enough to go a little faster than my current personal best. That is the goal for now.

Thanks again

BR
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Rex Schimmer
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« Reply #6 on: February 02, 2013, 01:30:07 PM »

Bill,
There is one other thing that you might want to consider, the rice burner motorcycle mfgs use it on the inlets of their high performance 4 cylinders and it should work on your D motor also and that is designing the air box as a "Helmholtz volume". This is the sizing of the air box volume and the engine displacement such that the inlet box will go into a high frequency pulsation which can be matched to your engines maximum hp rpm. I have never done this but if you search this site you can find a thread that discussed this and also a link to a sight that can help you calculate the size. I am sure you have driven down the road with one window open and you start getting a pulsation inside the car, that is a Helmholtz pulsation, and it can be helpful.

Rex
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« Reply #7 on: February 03, 2013, 10:10:07 PM »

Rex:
Thanks, great information.
Bill
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