Hood scoop questions

[Tharon]

Hi all, new to Landracing.com and first time forum user, so please be gentle. I have some questions on forward facing hood scoops.
I run a Holden commodore (Caprice in USA) at Lake Gairdner in Australia.
E/Pro, 260 ci V8, 1000cfm throttle body, EFI (MoTec M48)
I have read the article in Hotrod magazine regarding the results on this subject and I am looking at using the Harwood #3182 which was one that they tested. The manufacturer list these scoops as an "open back".
If this literally is an open back, what would be the advantage, I thought the high speed of the air into the scoop at the front would negate the purpose of having the back open a,s it would be a greater force than the low pressure at the base of the windshield.
Yes, I am hoping to benefit from ramming the the air
Sorry if this is a repost of an older subject, I am just after info before I make a purchase and I thought you guys would be best on the subject.
Thanks in advance for any input.
Tharon.

[Stainless1]

If you want the benefit of ram air at speed you need a sealed system... If the air is just passing through a scoop it is not sealed.  If it has a pick up at both the front and the back it seems to me that the one with most pressure would just push the air out the other side. 
We used to pick up air from both sides of the Lakester, but our data showed we were not increasing the air pressure in the air box.  We changed to just one source and air pressure was developed in the box. 
I am not familiar with sedan hood scoops, but I would only pick from the front or the back.... just my opinion.

[WOODY@DDLLC]

My 2 cents: http://www.engineprofessional.com/

[Milwaukee Midget]

Scoops are Simple? 

Good read, Woody.

[Sumner]

.........Yes, I am hoping to benefit from ramming the the air..

Besides picking up some rammed air effect, if the back is closed and the scoop is sealed as mentioned by SS, you can pickup better aero by having the right size scoop opening.

If the scoops frontal area is sized so that most of the air hitting the opening is going into the engine then the air flow around the opening will give you better Cd there.  If the opening is too large, as that one probably is, the air the engine can't use is piling up at the entrance to the scoop and becoming turbulent there and then going past the scoop in a manner that is making the Cd worst.

Drag cars can produce a lot of power at low speeds and get it to the ground with their tire/track combination so they need a larger opening to get the air for the power at low speeds.  We can't use high power usually at lower speeds so don't need that large opening in general.  At high speeds where we can use the power the small scoop opening can 'scoop up' a lot of air in the distance the car travels for each 2 revolutions of the engine's crank.

I have more info here and it is these guys, John Burk and Tom Burkland, that turned on the light for me  ....

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

I also have a spreadsheet for figuring the scoop inlet size here...

http://purplesagetradingpost.com/sumner/bvillecar/bville-spreadsheet-index.html

As a couple examples here is the old scoop on Hooley's Stude that worked very well and got him a record at 249+ with a roots blown 400 ci SBC...



Notice the size of the scoop on Rick and Jack's 360+ mph streamliner below...





http://yacoucci.com./gallery/v/Neb/album84/103_0305_IMG.jpg.html

Sumner

[Tharon]

Thanks for your thoughts guys.
Stainless i had exactly the same thoughts about "open back"and one cancelling the other out.
I just didn't know if i may have been missing something or maybe they are just sold with open front and back so the purchaser can do as they wish.
I will get to study everyone's links in the coming days.
Thanks heaps..

[wheelrdealer]

I don't get to say this much but... Mine is too big! My scoop that is. I did the math on Sumner's formula and for a D engine my scoop is way oversize. Will be thinking about a good way to extend the current scoop while reducing the inlet like I see on Hooley's Studebaker. Another project.

BR

[SPARKY]

I started with one of Harwood's old Formula scoop  we ended up  whacking it all up ---- what used to be the rear became the front---( we just came forward on the taper until we liked the diameter, radiused  the inside and tapered the top and sides to fair as we wanted--- but we were on a lakester did not have to deal with bothersome things like windshields and such

[jl222]

.........Yes, I am hoping to benefit from ramming the the air..

Besides picking up some rammed air effect, if the back is closed and the scoop is sealed as mentioned by SS, you can pickup better aero by having the right size scoop opening.

If the scoops frontal area is sized so that most of the air hitting the opening is going into the engine then the air flow around the opening will give you better Cd there.  If the opening is too large, as that one probably is, the air the engine can't use is piling up at the entrance to the scoop and becoming turbulent there and then going past the scoop in a manner that is making the Cd worst.

Drag cars can produce a lot of power at low speeds and get it to the ground with their tire/track combination so they need a larger opening to get the air for the power at low speeds.  We can't use high power usually at lower speeds so don't need that large opening in general.  At high speeds where we can use the power the small scoop opening can 'scoop up' a lot of air in the distance the car travels for each 2 revolutions of the engine's crank.

I have more info here and it is these guys, John Burk and Tom Burkland, that turned on the light for me  ....

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

I also have a spreadsheet for figuring the scoop inlet size here...

http://purplesagetradingpost.com/sumner/bvillecar/bville-spreadsheet-index.html

As a couple examples here is the old scoop on Hooley's Stude that worked very well and got him a record at 249+ with a roots blown 400 ci SBC...



Notice the size of the scoop on Rick and Jack's 360+ mph streamliner below...





http://yacoucci.com./gallery/v/Neb/album84/103_0305_IMG.jpg.html

Sumner

   Sumner...Not sure what your comparing, Jacks 122.99 max G motor 360 mph hood scoop looks bigger than Hooley's 400 cu.in. scoop.

   I would never put that small a scoop on the 222 Camaro.

               JL222

[Sumner]

.... Sumner...Not sure what your comparing, Jacks 122.99 max G motor 360 mph hood scoop looks bigger than Hooley's 400 cu.in. scoop.

His is smaller, it was the perspective of the picture.  Here is a better one of his scoop...

.....I would never put that small a scoop on the 222 Camaro.

               JL222

Nor would I recommend one that size.  Not sure if you ran through the formula or not but besides how far the car travels in 2 engine revolutions (figured by gearing and tire size) the other two factors are displacement and if it is naturally aspirated or blown.  A motor running 14-15 lbs. of boost compared to na is going to need about twice the scoop opening and if you were running 18-30 #'s 3 times the scoop opening.

For instance with Hooley's old motor, 400 ci, with 28 inch tires and 2.47 rear the scoop size with a 10% oversize would be:

na = 6.5 sq. in.
8# boost = 10 sq. in.
15# boost = 13 sq. in.
28# boost = 19 sq. in.

Since we ran an overdrive 4th gear our real final ratio was about 2.22.  That would of resulted in openings smaller than above since the car went further each 2 revolutions but I used the 2.47 which also oversize the scoop some.  We also never had much luck with the roots blower over about 8-10 #'s since the air got too hot with no intercooler and I think we made less HP down at the 4-5 as a result vs. running less boost.  We also ran the car extremely rich, in the low 10's which I felt kept the motor together.  Other than forgetting to turn the cooling water on never hurt the motor on a lot of runs to the 5 mile and even then no piston damage.

The 572 that is in the car now won't be run over 14-15 #'s with the present turbos so the opening for it is sized at about 24 sq. in. (3 X 8 inches) even though the formula says 17 sq. in..  This gives us some leeway if we got better turbos at some point.

Sparky makes a good point in that this is more critical with a streamliner or lakester if there is nothing behind the scoop except hopefully clean air.  Our present scoop...



... has the whole car behind it sitting down there at the front of the car .

Good luck to you guys this year,

Sum

[tauruck]

This must be one of the most interesting threads.

I need to ask a question.

A turbo charger spinning at full boost will take in a certain amount of air but will a scoop increase that volume?.

What I'm getting at is will more air forced in just stack up at the intake?.

[WOODY@DDLLC]

The pressure inside the scoop rises with forward speed. This increase in pressure raises the air density. More air molecules + more fuel molecules = more HP. When you add the engine it becomes a flow limiter. It can only move so many CFM. Turbos just move more and stuff it inside the engine. What you are really interested in is the mass flow - more molecules! When you size the scoop inlet to CFM with the column of air hypothesis what happens is the engine will reduce the air pressure inside the scoop, you will have a lower air density and you WILL lose HP especially at lower mph! The CFM matches just fine [at the design speed only] but you will have less molecules of air in each cubic foot. If the opening is too big then the engine can't keep up and you get spillage out of the scoop and higher drag. Several other interacting factors come into play! Scoops are Simple - NOT! In some cases the lower HP may have aided traction in the launch but it will cost mph on the far end. Most scoops tend to increase HP some but do you want 50%, 75% or 100% of the potential?  That's just my three cents! 

[Seldom Seen Slim]

Woody and the rest of you:  It's a hypothetical question from a novice in this stuff, but how 'bout a scoop with variable bits?  Like the scoop's open front could change for different speeds, or maybe a spill/waste gate at the rear to let out excess air (out the back?) when the scoop is bringing in too much air and creating the spill drag? 

Has it been done - or at least studied?

[TheBaron]

Yes, it has been studied and applied....

Check out the inlets of a lot of jet fighters...

The inlets have to manage any  supersonic shock waves that could get into the compressor section.

[Seldom Seen Slim]

Okay - the technology exists.  Has it been tried on race cars and bikes?  Has it been tried on land speed vehicles?