Raising the bonnet.

[GU357]

Im sure this has been covered before and it looks rice and whatever else but does it actually make for an increased air flow under the hood? so that the engine is cooler?

u would figure hot air rises so making a small gap for it to vent would be beneficial.

but theres also that old trick of lifting the bonnet at the front which proved to be non-beneficial as it didnt improve engine temperatures.

so has anyone got any proper physics into the equation?
or any recording of engine temperature differences.
simply putting a a thermo in there isnt the same because it just proves that more hot air is moving in that area not so much that the engine bay is hotter.

[dougie_504]

I doubt it keeps the engine that much cooler. Air rushes in the front where the bonnet meets the bumper anyway, pushing out some of the hot air.

I think it's more for clearance issues.

[GU357]

ahh i heard some stuff about low n high pressure like a spoiler kinda where the air would have to rush through faster to match the speed like a spoiler

[TbM]

Are you talking about raising the rear of the bonnet? from my understanding there will be high pressure at the base of the windscreen where the bonnet will be open which wont allow it to remove much/if any heat while in motion, under the carr will have lower pressure so the air will tend to flow there.

[Jccck]

Are you talking about raising the rear of the bonnet? from my understanding there will be high pressure at the base of the windscreen where the bonnet will be open which wont allow it to remove much/if any heat while in motion, under the carr will have lower pressure so the air will tend to flow there.

Sounds about right.

Raising the back of the bonnet (Below the windscreen) will not suck any heat from your engine bay, nor blow any cool into it either.
And it looks terrible.
As goes for those 'Headlight Intakes' where you cut your High Beam out and have a neat hole to your airbox.. They don't really do anything at high speeds.

[GU357]

yeh, figured as much, so its reallly best for turbo aplications where the car is hotter and to prevent over heating at idol.

[connorling]

I did it once, only because I took the headlight out as intake in my eg, air has to go somewhere, so I lift the rear section of the bonnet, I think it helps.

Now I got turbo, i will try it next time on the track, monitor the temp using power fc controller to see if water temp drops

[curtis265]

in regards to raising the bonnet at the mounts (i.e. hood spacers), read this



UPDATE: Test of rubber insulator removed from plastic cowl, no hood spacer vs stock setup!

So I've heard so many friggin' things about hood spacers. Some love them, most hate them, some swear by their effectiveness, others throw around physics and logic, but I couldn't find any REAL DATA. Hence, I went out and I tried to collect some of my own. For all you guys to know, performance mods I have include injen sri, ws2 exhaust, nst pulleys, hondata IMG and of course the wonderful Cobb accessport that made this possible!

It isn't perfect but I compared before and after on the same night within an hour of each other at 67 F. Temperature stayed constant here throughout.

The test was done to test the max temperature of the Intake Air Temp (IAT) at idle and how long it took to get there and the average IAT at 80mph (cruise control on flat ground on the freeway for around 5 minutes). The reason for this is because some people have said this vent method might actually hurt effectiveness of airflow out of the engine bay by messing with proper air flow AT SPEED (low pressure, high pressure and all that jazz that I won't pretend like I completely understand).

So, I have the excels sheet that I gathered from my Cobb Accessport , but I'm too lazy because I have nothing to gain by lying since I'm not selling anything.

Caveat: I did the DIY hood spacer from 0720steve (thanks btw) because really, there's no difference between it and the ones corsport is selling. I used 3/8 nylon spacers, but with the washers I also added in, it's about a fingernail's difference from corsport's 1/2 inch spacers as far as gap.

My results:

At idle, the stock hood without spacers took approximately ~20 minutes to move from 95-156 degrees. I messed up my timing so I didn't get the exact minutes and seconds, but it definitely wasn't less than 15 minutes or more than 25.

At idle, the stock hood WITH spacers took 21 minutes to move from 96-156 degrees.

BOTH topped out at 156 degrees after the test. Maybe they could have climbed a couple more degrees, but I wasn't going to sit and waste gas for another 10 minutes, it's not practical anyway since you'll never be stopped in traffic half that long. And any movement quickly lowers and stagnates your IAT.

I have data across speeds, but I decided to take average IAT at 80mph since most people drive around that speed or slower on freeways. At 67F outside, my average IAT was 95.6 WITHOUT hood spacers.

Average IAT was 98.141 at WITH hood spacers!

Yes that's right, hood spacers actually measured nearly 3 degrees hotter!

ALSO, I took the average grams of air per second (g/s) the intake was bringing in when I was cruise controlling at 80mph.

Without spacers=33.43g/s (average)
With spacers=25.60g/s (average)
Hence, at idle, the the spacers were providing less grams of air per second to my intake at 80mph.

Apply whatever margin of error you want, but honestly, I felt that if my IAT wasn't at least 10 degrees cooler at either idle or at speed, I couldn't justify this mod. It's ugly (at least to most), likely slightly more dangerous (it isn't OEM fit and messes with the car's intended aerodynamics), causes more drag, costs you money (no matter how cheap), and allows more water into the car. And frankly, even if I did realize 10 degrees lower with the spacers, that's only, in theory, 1 hp. I was hoping to see at least a significant slowdown in heating up or a lower max temperature at idle.

Maybe the results would have been different if it wasn't so cold out (it was night time), but either way, I've tried it and trying to pass on what I've learned.

Also another caveat nobody has talked about, when removing one of my stock bolts, the female thread part in the actual hood came off! It's weird but I guess they welded in the threaded part of the hood into the hood (since the sheet metal itself is so thin). Long story short, I'm back to stock but my hood's only being held on with 3 bolts now. Grrr. Anyway, you run that risk if you mess with the OEM hood.

Hence, according to my admittedly simple test (although really time consuming!), hood spacers DO NOT WORK and in fact, made things worse. For those who say they feel the heat coming out, I'm sure they do, but if you've ever felt the hood around there without the spacers, you feel a lot of heat coming out anyway. I really don't know how to explain the no-duh logic that a vent should allow lower temps. This is my data and that's all I can bring to the table.

UPDATE: Now, moving onto testing the stock hood vs. removing the rubber insulator on the plastic cowl
The test was done at 64 degrees.

Stock Hood it took 26.25 minutes to rise at idle from 109-156 degrees.
IAT at 75mph=88.6 degrees (average)
mass airflow at 75mph=28.36g/s (average)

VS
Removed rubber insulator on stock hood took 25.93 minutes to rise from 109-156
IAT at 75mph=88.3 degrees (average)
mass airflow at 75mph=28.36

Hence, removing that weather stripping/insulator didn't do squat. Especially because I did it second and it only got colder as the night went on (between 12:30 and 3am).

FINAL NOTE: I can't say corsport's spacers are useless/detrimental. My test was on what's theoretically pretty much the same thing. Still, I'm not here to bash their product or people who want to go with this mod. This is just my opinion. Also if you have any complaints that I didn't do something right and my results make no sense, you may be right, but honestly, I can't imagine my errors could equal significantly slower heating up of the engine, significantly lower max temperature, significantly higher airflow, or anything else to justify this mod to me. Not at this point anyhow. Maybe somebody else will post up their data and correct me, but until then, I'm happy with my properly aligned hood and smooth body lines!

Hope you all benefit from my experience! and Special thanks to my girl, who stuck with me all night and helped me with the spacers! Love you babe!
http://www.8thcivic.com/forums/garage/167276-do-hood-spacers-work-answer-here.html

[EKVTIR-T]

Sounds about right.

As goes for those 'Headlight Intakes' where you cut your High Beam out and have a neat hole to your airbox.. They don't really do anything at high speeds.
Do you have any data to back this up or just sprouting hearsay

[curtis265]

Do you have any data to back this up or just sprouting hearsay

there's strong logic behind it

[curtis265]

although that experiment shows otherwise, there is definitely method behind the madness - cowls are regions of high pressure so you would expect some air to enter the bonnet from that region... Just that it probably mucks around with the manufacturer's intended airflow

[TbM]

there's strong logic behind it

i would of thought a headlight intake would help depending on the normal intake location, taking air from a higher pressure zone logicly should aid the intake, hence them using those front open intakes on supersports bikes n drag cars ect.

[curtis265]

i would of thought a headlight intake would help depending on the normal intake location, taking air from a higher pressure zone logicly should aid the intake, hence them using those front open intakes on supersports bikes n drag cars ect.

whoops misread it!

Would be keen to see some raw data in the form of MAP sensor readings

Would depend a lot on the loss coefficent of the nominal orifice size and shape

[Indie]

From what I've read, it depends on the car and its individual set-up. Sometimes it will divert the wrong air to the wrong place, and actually cause an increase in temperatures where you don't want it.

Considering the fact that I think it looks crap, I wouldn't bother, personally.

[eeko]

I personally think it doesnt look too bad. Depends on the rest of the car too.. not fussed about benefits or not, just a nice addition to put a unique touch on a car.

Will post a picture of my car running hood spacers in a bit.

[TbM]

I personally think it doesnt look too bad. Depends on the rest of the car too.. not fussed about benefits or not, just a nice addition to put a unique touch on a car.

Will post a picture of my car running hood spacers in a bit.

Its not legal and its quite dangerous, i suggest you rethink what your doing.

[Jccck]

i would of thought a headlight intake would help depending on the normal intake location, taking air from a higher pressure zone logicly should aid the intake, hence them using those front open intakes on supersports bikes n drag cars ect.

Well think about it this way;
If you place the hole in an area of large wind resistance (Lower in your front bumper, obnoxiously large hood/roof scoop, etc) then it will tunnel air into your intake.
But if placed on an aerodynamic surface (Say an Evo-like hood vent, or a headlight intake on a sleek and sporty car) the air is supposed to flow right past it normally, but since you've put a hole there all that's going to happen is cause low pressure just inside the entrance of this hole.

I've read a couple of articles on this 'Headlight Intake' business, feel free to hunt around.. But they all seemed to have reasonble proof as to why if they were affective to your Engine, they'd be detrimental to your Aerodynamics.. And it would outweigh the benefit in most applications.

[curtis265]

Well think about it this way;
If you place the hole in an area of large wind resistance (Lower in your front bumper, obnoxiously large hood/roof scoop, etc) then it will tunnel air into your intake.
But if placed on an aerodynamic surface (Say an Evo-like hood vent, or a headlight intake on a sleek and sporty car) the air is supposed to flow right past it normally, but since you've put a hole there all that's going to happen is cause low pressure just inside the entrance of this hole.

I've read a couple of articles on this 'Headlight Intake' business, feel free to hunt around.. But they all seemed to have reasonble proof as to why if they were affective to your Engine, they'd be detrimental to your Aerodynamics.. And it would outweigh the benefit in most applications.

in that case a headlight intake's effectiveness depends heavily on the angle of the headlight

I found this years ago, was an interesting read if any of you are curious. Anyone got any CFD software? We could try modelling our own cars


Software Used: CFDesign V10 by Blueridge Numerics
Model analyzed: 2009 Honda Civic Si Sedan

Overview:

I have been very fond of Bill (NitrousG35) and his cowl induction idea. The ingenuity of it was mesmerizing and while I had heard of the technology, I had never thought to implement it myself on our vehicles.

Now...while the science is very sound, I was a bit skeptical of the actual performance of the system due to the shape of our vehicle. I figured I would run my own simulation to see how well this idea would actually work.

Problem Definition


This program unlike many others generates its own mesh-tetrahydral type
Input conditions: Velocity = 100 km/h
Output conditions: Pressure = 0 Pa (while I know ambient pressure is usually 101.3 kPa, the pressure differential between the input and output is assumed to be 0)
The model was traced from a picture of a stock FA5 and then scaled appropriately
The model is 3D, however a 2D analysis was conducted due to the inaccuracy of the 3D model. The 2D model retains geometric accuracy over the midplane of the model


Sources of Error


Underbody is perfectly flat. This does not explicitly affect the region of flow being analyzed. If you look closely at the pictures however, you will see that this reduces the overall amount of drag on the vehicle just aft of the model. (interesting by product to consider if our bottom panels were completely flat)
The boundary layer over the surface of the vehicle was not defined by me. Rather, I relied on the program to generate it's own boundary layer mesh.


Analysis

I chose the input velocity of 100 km/h due to the fact that

1) Metric measurements are the way of the future (only you U.S people still work in imperial...lol)
2) It is only over 80 km/h that aerodynamic benefits can be felt on a vehicle.

---

The first picture shows the meshing process I used. I let the program generate it's own mesh over the length of the volume being analyzed. I then defined a fine mesh where I wanted to accurately simulate the flow over that region. The fluid used was air (obviously) and an ambient temperature of 24 deg. C was used.

Without getting into the math of this too much, let me say that velocity and pressure are inversly proportional. This means that lower velocity regions will exhibit higher static pressure than higher higher velocity regions.

If we take a look at the velocity profile picture first: we can note there are two regions that demonstrate the extremity of velocity drop.

1) The bumper
2) Between the hood and the windshield - where the proposed cowl induction system would go

Now...the bluer the region, the slower the air. Comparing just the colours its very apperant that we have a slower region of air at the bumper than between the hood and the windshield.

We can attribute this to the stagnation point of the vehicle - the point at which the steam line of an air particle hits zero velocity.

---

Now taking the Pressure profile picture into consideration: we can see that the static pressure is very high at the bumper and less so between the hood and the windshield. What this means is simply that while the cowl induction idea is very good....the area between the hood and the windshield (while relatively high in stative pressure) is not the primary region of high static pressure.

In order to gain maximum benefits of a ram air system, something like an M&M scoop would be much more useful because it is placed much closer to the primary region of high static pressure. This will in affect draw in the most amount of air, the quickest.

http://farm5.static.flickr.com/4003/5075020666_751e7b72a3_b.jpg

I realize this explanation was very quick and did not adequately explain the fundementals but if I get time when I am at home, I hope to do a better write up then (currently I am at work).

One thing I must mention is that Bill stated that our HVAC system draws air in from the region between the hood and the windshield...making use of this pressure zone. While this is true, I think that this is more a case of simplicity of ducting (being so close to the dash) and packaging of the system, rather than optimal performance of the HVAC system on our cars.

Also...the simulation also seems to prove why major aerodynamic companies like M&M have designed their intake ducts as such...and why cowl air induction is not as readily used on our vehicles. The scoop on the gruppe M induction system faces the front and not the rear because (in my opinion) there is still not great enough of a pressure differential created to produce a maximed state of ram air.

Just some thoughts...

From the results it seems as if the highest pressure region is low in the bumper

[dougie_504]

Build a shroud around headlight intake hole maybe?

[GU357]

Mighty car mods tested the headlight intake on a dyno using a massive fan to try blow cold air at the headlight, made no effect.

and the highest pressure is close to the bottom of the car, which is part of why ground effects is most effective when low to the ground.