cowl inducion scoop /how close to windshield?

Tobbe1 · Post by **Tobbe1** » Sun Sep 20, 2009 1:51 pm

how close to the windshield should you put an cowl inducion scoop for best results ?

maybe the wrong forum ..body ? or should it be in engine tech?

a pic ...(not my car)

cjperformance · Post by **cjperformance** » Sun Sep 20, 2009 8:59 pm

How long is a piece of string? dont laugh, someone came up with an equation for this!
Anyway, it really depends on the use as to how exacting you need to be.
For a street/strip car as long as you have enough clearance to allow enough air flow for the engine, what looks good with the shap/profile of the car will work ok.
For a more serious race effort some basic trials with a manometer will tell you how much scoop pressure you are getting, move the scoop aroung a bit to get best results., this will be different for each type of car as frontal area and widscreen angle play a big part in how much pressure is a vailable and in what position.
Some little blobs of Blu Tack of some othe skicky stuff, even play dough, modeling clay with 3" of string stuck to it will help show you the direction of the air at any given point along the bonnett/windscreen whil you drive thru some different speed ranges, this can give a good idea of where the opening needs to be, combine this with the manometer to experiment for the best posi.
If you have big money to spend you could go for wind tunnel testing but this is really 'high level' race efort stuff and is not needed for most applications.
Most people just put them where they look good, if you spend some string/manometer time you will be infront of most.

idoxlr8 · Post by **idoxlr8** » Mon Sep 21, 2009 2:52 pm

I'll save ya some time, already done the manometer thing. It won't matter how close it is to the base of the windshield. If you're wanting cool air, what you have is fine. If you're wanting pressurized air, get a forward facing scoop or rig up something that draws from the grill.

Tobbe1 · Post by **Tobbe1** » Mon Sep 21, 2009 3:23 pm

back when my car was street driven i notice tha i have a lot of air going true the air vents up front ...would that show that a cowl scoop should work?
how mutch pressure do you have in your manometer tests...front/cowl/ scoop etc ?

idoxlr8 · Post by **idoxlr8** » Tue Sep 22, 2009 3:38 pm

The pressure diff between the cowl area and engine compartment = not much (open cowl). Difference between engine compartment and grill? Enough to blow all the colored water out of the manometer.

Tobbe1 · Post by **Tobbe1** » Tue Sep 22, 2009 4:01 pm

idoxlr8 wrote:The pressure diff between the cowl area and engine compartment = not much (open cowl). Difference between engine compartment and grill? Enough to blow all the colored water out of the manometer.

i should run a well sealed off cowl scoop no air from the engine bay should enter the trottle/intake did you test that to?

idoxlr8 · Post by **idoxlr8** » Fri Sep 25, 2009 8:55 am

The car we were testing it on did not have a sealed cowl scoop unfortunately. That would have been interesting to test.

Tobbe1 · Post by **Tobbe1** » Sat Sep 26, 2009 2:53 am

idoxlr8 wrote:The car we were testing it on did not have a sealed cowl scoop unfortunately. That would have been interesting to test.

thanks for make that clear

anyone else that have info in this matter ?

MadBill · Post by **MadBill** » Sat Sep 26, 2009 9:08 pm

I Almost have the data you need!
I ran similar tests last week on an SCCA GT1/Trans Am Corvette. Unfortunately we were short on time, so rather than the gauge pressure at each location, I measured just the pressure difference between the two legal intake locations: a.) a rectangular opening on the top rear of the hood bulge, about 3" forward of the windshield and b.) the radiator air box. In this case at 180 MPH it was about one measly inch of water pressure (~ one quarter of a percent) higher at the cowl!

The big difference though was that first, the car's cooling is so good that it needs 2" of tape across the grill to get water temp, which reduces the box pressure. Two, the strong flow through the rad also greatly reduces it and three, a pair of 4" brake cooling hoses deplete much of what remains.

The pressure available at the grill increases as the square of the speed and at 150 MPH is theoretically plus 2.7%. The pressure at the grill is bound to be less and is influenced by the windshield slope, hood contour, etc.

BTW, rather than a messy tube full of food-dyed water, invisible to to the in-car video, (been there, done that) I used a Dwyer Magnehelic 25" H20 gauge: http://www.dwyer-inst.com/Products/Product.cfm

BirdMan · Post by **BirdMan** » Sat Sep 26, 2009 9:17 pm

I put a cowl hood on my son's '64 Falcon because that is what he wanted. It is blended in a front face of hood and extends to rear of hood and we cut the angle to clear cowl/windshield when hood is opened. No testing or anything. We did make an air pan with non-flammable pillow/cushion material we got from fabric store.

us7race · Post by **us7race** » Mon Oct 12, 2009 6:30 pm

I have A 6" Cowl on my S10 and it is against the windsheild. I have ran it back to back with it and with No hood and there was No ET difference in the 1/8th mile. But that is with a 1100 Dominator. Before when I ran an 830 Holley it would pick up almost a full tenth automatically... Just some personal experience..

MadBill · Post by **MadBill** » Thu Oct 22, 2009 10:46 pm

cjperformance wrote:How long is a piece of string? dont laugh, someone came up with an equation for this!...

To solve for 'L', the length of a string, Let 'A' be one end and 'B' the center point.
L = 2AB
Q.E.D.

cjperformance · Post by **cjperformance** » Sun Oct 25, 2009 8:41 am

yes Bill, thats the one ! Just got to dig out my telescopic tape measure to find that dam center point !