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Author Topic: NACA vents vs. Hood Scoop question  (Read 3010 times)
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Lemming Motors
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« Reply #30 on: September 21, 2018, 04:26:04 AM »

Not all those throats are inhaling at the same time which is why the air requirement calculation divides the revs by 2.

My Euro version of the calculation is litres x (revs/2) = litres / min and then convert litres x 0.035315 to cu ft and I get 293 cu ft min.

The Jenvey throttle body air box only has a 3.5" intake and they were more than happy to supply that knowing a 122ci capable of pulling up to 9,000 rpm.

Rik I am assuming your are talking an S2000 motor as your spec and shift points are remarkably identical to my calculations or is that just a weird coincidence (cue doo doo doo doo music).
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A Bonneville Lakester please barman.
Certainly sir; a lick of salt, a sip of gas and a twist of Lemming. More Lemming sir?
Just a squeeze.

A Squeeze of Lemming it is sir.
QikNip
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« Reply #31 on: September 21, 2018, 09:28:05 AM »

Not all those throats are inhaling at the same time which is why the air requirement calculation divides the revs by 2.

My Euro version of the calculation is litres x (revs/2) = litres / min and then convert litres x 0.035315 to cu ft and I get 293 cu ft min.

The Jenvey throttle body air box only has a 3.5" intake and they were more than happy to supply that knowing a 122ci capable of pulling up to 9,000 rpm.

Rik I am assuming your are talking an S2000 motor as your spec and shift points are remarkably identical to my calculations or is that just a weird coincidence (cue doo doo doo doo music).

Your air requirement observation is brilliant. cheers As I was laying in bed last night this same thought occurred to me (only half of the cylinders on the intake cycle per revolution). As for the motor, it's a 1979 Porsche two liter single overhead cam 924 block and head.
Rick
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QikNip
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« Reply #32 on: September 23, 2018, 12:05:41 PM »

NACA ducts work as long as you use the correct formula....

Won't name names but someone real famous with a big world record that uses them told me he wouldn't use one on a NA vehicle, they run blown.  A blown engine can suck in the air it needs if you give it a place for that to happen. Not that a NACA duct wouldn't work, but a lot of variables that would almost dictate wind tunnel testing to make sure in your situation that it would work.

This might possibly help with scoop design that wouldn't hurt drag too much....

http://purplesagetradingpost.com/sumner/bvillecar/bville-scoop%20info-1.html

Sumner:
Somehow I overlooked the link you included and only noticed them this afternoon. They were quite useful-particularly the John Burk / Tom Burkland write ups. Thanks!
Rick


« Last Edit: September 23, 2018, 01:25:06 PM by Sumner » Logged

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Rex Schimmer
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« Reply #33 on: September 23, 2018, 02:05:47 PM »

Here is a big "IF" but if we are not chasing ignition gremlins next year and are able to get multiple runs in I have a part that I have made that will fit onto the present position of our inlet scoop and will allow me to use a NACA duct for the inlet. I will try to not compromise in the adaption of the inlet from our scoop to the NACA configuration and maybe we will be able to see if there is enough difference to warrant using a NACA duct.

It is a year away and many things can change and Duke and I have a pretty long list of things we want to change but I would really love to try this.

Rex
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QikNip
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« Reply #34 on: September 25, 2018, 02:21:13 PM »

Here is a big "IF" but if we are not chasing ignition gremlins next year and are able to get multiple runs in I have a part that I have made that will fit onto the present position of our inlet scoop and will allow me to use a NACA duct for the inlet. I will try to not compromise in the adaption of the inlet from our scoop to the NACA configuration and maybe we will be able to see if there is enough difference to warrant using a NACA duct.

It is a year away and many things can change and Duke and I have a pretty long list of things we want to change but I would really love to try this.

Rex

Rex:
Since we have the same displacement, I'm curious as to where you're getting that NACA duct and it's size.
Rick
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145.632 G/CPRO 8/17 Bonneville Record
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Rex Schimmer
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« Reply #35 on: September 25, 2018, 05:53:55 PM »

"Getting the NACA duct"!!! The ones that you can buy are junk, I have lots of 3003, tin snips, hammers, TIG welder and the chart of dimensional relationships required to build a NACA duct with the right dimensions, screw buying a piece of junk when I can build my own!!!!! I will size the opening based upon 220 mph, my motor at 12,000 rpm and a fudge factor that will be determined when I start the project.

Rex
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Stainless1
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« Reply #36 on: September 25, 2018, 10:33:39 PM »

Rex, if you want the size and pics of ours just let me know what I can tell you.   
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Stainless
Red Hat 228.039, 2001, 65ci, MSA Bockscar Lakester with a little N20 
MSA Bockscar Lakester #1000 my fastest mile 245 and change, 84 ci turbobusa motor... but Corey's 233 MPH H/BFL record is still 3MPH faster than mine.
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« Reply #37 on: September 25, 2018, 11:39:30 PM »

"Getting the NACA duct"!!! The ones that you can buy are junk, I have lots of 3003, tin snips, hammers, TIG welder and the chart of dimensional relationships required to build a NACA duct with the right dimensions, screw buying a piece of junk when I can build my own!!!!! I will size the opening based upon 220 mph, my motor at 12,000 rpm and a fudge factor that will be determined when I start the project.

Rex

 cheers cheers cheers cheers cheers
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Lemming Motors
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« Reply #38 on: September 26, 2018, 04:03:51 AM »

I have just created a NACA duct calculator spread sheet from the Staniforth text, graphs and charts, and some basic formula from the interweb. Email me if you want me to send it - you're welcome to QC the math and compare it to other sources - might be useful, might be a rabbit hole, might amuse. jmellelieu@yahoo.com
John
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A Bonneville Lakester please barman.
Certainly sir; a lick of salt, a sip of gas and a twist of Lemming. More Lemming sir?
Just a squeeze.

A Squeeze of Lemming it is sir.
tauruck
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« Reply #39 on: September 26, 2018, 04:41:53 AM »

That basic formula works. I went NACA crazy and built moulds from 2" in length to about 12".
No shortage of accurate genuine aviation ducts here.

Thanks for sharing. You'll help a lot of guys with that. cheers cheers cheers cheers

Mike.
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Lemming Motors
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« Reply #40 on: September 26, 2018, 05:03:02 AM »

Mike. You have had way too much fun with knackered ducts if you've made molds over a range of sizes  grin

What surprised me, using a 4:1 opening and a 7 or 8 degree ramp angle (and I haven't even heard the term cotan since high school in the '70's) is how long the duct is compared to its width i.e. the body / surface opening. Many of the after market ones seem much 'chunkier' - they appear to be about 2 times length to width whereas my calculations were more like 3 times.

Maybe they have much steeper ramp angles or maybe not. Perhaps they are performance bolt on's like fluffy dice. Dodge - I will have to make a much taller screen to see past the dice - that's something else I didn't include in the Lakester design!
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A Bonneville Lakester please barman.
Certainly sir; a lick of salt, a sip of gas and a twist of Lemming. More Lemming sir?
Just a squeeze.

A Squeeze of Lemming it is sir.
QikNip
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« Reply #41 on: September 26, 2018, 07:55:07 AM »

I have just created a NACA duct calculator spread sheet from the Staniforth text, graphs and charts, and some basic formula from the interweb. Email me if you want me to send it - you're welcome to QC the math and compare it to other sources - might be useful, might be a rabbit hole, might amuse. jmellelieu@yahoo.com
John

email on the way Smiley
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145.632 G/CPRO 8/17 Bonneville Record
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tauruck
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« Reply #42 on: September 26, 2018, 11:23:17 AM »

Mike. You have had way too much fun with knackered ducts if you've made molds over a range of sizes  grin

What surprised me, using a 4:1 opening and a 7 or 8 degree ramp angle (and I haven't even heard the term cotan since high school in the '70's) is how long the duct is compared to its width i.e. the body / surface opening. Many of the after market ones seem much 'chunkier' - they appear to be about 2 times length to width whereas my calculations were more like 3 times.

Maybe they have much steeper ramp angles or maybe not. Perhaps they are performance bolt on's like fluffy dice. Dodge - I will have to make a much taller screen to see past the dice - that's something else I didn't include in the Lakester design!

I'm still knackered. grin
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