Hood vents question?
 

I'm thinking to cut holes in my hood and instal these hood vents https://cgi.ebay.com/ebaymotors/JDM-U...spagenameZWDVW. Where is the best spot on hood for these kind of vents? Is it worth to do this modification?
https://i17.ebayimg.com/02/i/05/82/96/59_1.JPG

By doing this, what do you hope to achieve?

I want to vent hot air under my hood since my temp went up after 80% grill block and full belly pan.

Is venting an engine undertray will do the same effect what venting the hood?

I would assume that it would be more cost effective to just take out part of your grill block. don't get me wrong, they look cool and if you want them for that then have at it. IMO, you would get the same results by taking out part of your grill block which would just take time and you may have some negative aero affects by those vents.

Ok, then I guess that they might help.

Since heat rises, I'd say that venting the undertray would only work while you're moving.

Is it causing a problem? Heat can be good.

the best place is there where the difference in pressure between the inside and outside is greatest, you can measure this with a pressure gauge, but generally this is halfway the hood at the sides. you want to make sure you stay ahead of the high pressure bubble in front of the windshield or you"ll have air going in the vents.

generally the air on the underside of a vehicle is moveing faster especially if you have an undertray so extraction there would be better, but there's a few drawbacks. if the underside of the car is less than optimal you'll likely have a lot of turbulence there, wich you don't want to add to that, and wich might prevent the extractors form working propperly. air that comes out at the top will move over the smooth car body.
also hot air, wich will be found in the engine bay, will rise... venting at the bottom will expell the coolest air but leave the hot air trapped at the top, hood vents will help here.

one car that comes to mind as a good examle of hood vents is the opel kadett E gsi (i owned the less sporty version without the vents)

here nicely highlighted in yellow
https://upload.wikimedia.org/wikipedi...tt_GSi_16V.jpg

No. Heat radiates evenly in all directions. Hot air, because it is less dense, will float on top of cooler air if any is around, since the cold air sinks to the bottom and displaces the hot air. However, in an enclosed engine compartment, there won't be any cold air displacing hot air, so no convection.

Got it! Thanx for the clarification.:thumbup:

Even a small amount of forced airflow, rolling at 5mph or having the fan on, will disrupt convection, it's relatively weak, which is why chimneys need to be tall to get good draft in still air. (They get a lot more in a slight breeze too)

Definitely a good mod, IMO. However, I believe you will find that those particular ones are fakers and will need to have holes cut in them to be actual vents.

To all those wondering why, this would redirect some of the air coming in through the grille up and over the car, instead of underneath it. That means cleaner aero and more stable at speed. Google pics of the Ford GT-40. They used a complete duct so all grille air went over the car. No need for grille block then, but it is not always easy to put such ducting in a production car.

Thank you, BluEyes. I left the Gt 40 out when mentioning the Lotus Elise and Exige in my thread. The Ford GT-40 has a better example of radiator out flow top slots in my view.
Richochet, 14/06/08

my car has hood vents right on top of the engine. hot air rises, so that's the best position for the vents in order to dissipate heat.

hood scoops are different. as the name implies, they scoop air into the engine compartment while you're driving and are not for venting heat (although they will vent heat when your idling). hood scoops are best placed near the engine's air intake to maximize cold air for power. these are mostly at the sides of the hood or at the front of the hood and the air will be "scooped" into the engine compartment and cool the area right where the intake is located. in general, hood scoops are placed where the air intake is located in order to scoop cold air into the intake.

while driving, hood scoops will create more drag, an actual hood vent (you see these types of hoods with holes behind a "bump" and has no scoops above the holes) would actually use the vaccum created by the airflow over the bumps to vaccum out heat.

I leave my hood vents open in the summer and block them during the winter.

I know this sounds odd, but if you want hot air to rise up and out, why not put them on backwards? Thus avoiding some of the aero drag. Air goes in at radiator, through engine compartment and up and out the vents.

I think that's a good idea. the scoops in turn become hood vents.

:thumbup: good plan make sure you get real vents

https://www.240sx.org/links/installs/hood/hood12.jpg
I think I go will this kind of hood vent. It will the the cheapest hood vent to make and the most effective. Check this out ...https://www.240sx.org/links/installs/hood/hood.htm

that works :thumbup:

You could also put some spacers where your hood attaches to your car. This will raise your hood near the windshield and allow some of the hot air to escape. I've seen drifters use this technique because of the extra heat from their turbos.
It's real cheap (just cost of spacers) and easy to do (& easily reversable if you don't like it).

true and some you can just remove the gasket

Not a good idea to raise the hood. The best air flow is when you have big difference is air flowing pressure. Area close to the windshield has high pressure almost same as is the front of the grill. Now area close to radiator has low pressure and that's the best spot for hood vent.
https://us1.webpublications.com.au/st...1/2162_6lo.jpg
BLUE-->LOW PRESSURE
GREEN-->HIGH PRESSURE
RED--> THE HIGHEST PRESSURE

Hood vents either bring cold air into the engine bay or intake, or the provide a vent for hot air in the engine bay, I have lined and insulated my hood with aluminium foil that is to 100mm of rock wool, I do like the heat, the hotter the engine the less fuel it takes, I would say remove part of your grille block.

I have yet to make my grille block so I can understand if your worried about to little cooling.

what wool and foil ???

Nope. When running hot, engines are calibrated to run rich to help avoid preignition and to help cool the engine. Insulation will help speed warm-up and keep the engine warm when running errands however and this improves economy by reducing warmup time.

Regarding lifting the back of the hood, that does not exhaust air, it pushes more air under the hood. Musclecars have used this since the 60's, called cowl induction, to bring in higher pressure, cool air to make more power. Often special intakes are used that seal to the raised cowl area forcing the air into the engine. From an aerodynamics perspective, lifting the rear of the hood is very "dirty" as it causes MORE airflow through the engine bay and underneath the car.

No, Paulie has the right idea. A grille block reduces airflow through the engine bay, while a well placed hood vent redirects some of the airflow that is there under the hood back above the car instead of underneath. Not only will this help reduce drag but also reduce front end lift for more stable handling at high speed. If the hood vent is sufficiently large, a duct could be made to seal the vent to the radiator and redirect ALL cooling airflow out the hood, avoiding airflow over the non-aerodynamic engine block entirely. At that point, a grille block may be superfluous.

Not on my engine, for example the hotter the coolant the leaner the fuel mixture gets as it uses a NTC sensor to monitor the warm up cycle, I have a knock sensor which retards boost using the waste gate, I have never had ping due to a hot engine, even when the coolant is at 98 degrees Celsius. If an engine is Pinging than something is wrong.

Shadowworks you see my question ??

Makes sense now. That's because 98c/208F isn't running hot, it's just on the high side of normal. After all, you could technically run straight water coolant at those temps. I would expect to see an efficiency gain at that temp if your OE spec thermostat is a cold one like 185 or even 175F.

Many cars don't even turn on the cooling fans until 220F/104.4c but you may see some pinging there on cars with no knock sensor depending on engine speed/load. You won't hear knock if there is a knock sensor, but the reduced timing will hurt efficiency. Stuff like hot enrichment and timing retard are really hitting when the engine gets hot like 230F/110c.

Sorry I missed that, it's not actually wool, Its thermal insulation called type 2 foil insulation in the house building trade, its basically super thick bubble wrap with two foil layers on each side, this has the same thermal value of 100mm of wool.

It reduces sound from the engine bay and helps the warm up time of the engine, it also helps the engine say warmer for longer after its been shut down.

thanks,,, I have some of that bubble foil :thumbup:

Flow through cooling to low pressure spot.
 

Keep the grille block, make sure that it is aerodynamically smooth and preferably directs air flow up over the front of the bonnet/hood. Then hoping there is room for the next bit, tilt the radiator forward on its mount, modifying any duct to the hood/bonnet vent that you have already put in, then, build another duct to take air from behind the front bumper/airdam to the radiator.

Now you will have a flow through system that takes cool air from under the front of the car, reducing uplift, through the radiator and out the top into the existing low pressure zone. Unless you do a lot of slow up hill heavy stuff, the low pressure zone will hopefully be enough to avoid having to fit a second fan.