AutoX hood alterations.

[spyderdrifter]

So this is to those of you who do take part in actual racing, please others don't take that the wrong way, your imputs are welcomed, this is just dirrected to them.

I was tinkering with my car today and put the hood back on, not bolted on, just on with it latched. Was wondering if any of you have adjusted your hoods to make the gap in the rear to allow hot under hood air to escape out the back. For those who have done this alteration, how well does it function during on track driving? Was toying with the idea of doing this for track duty if it's worth the effort.

[TSiAWD666]

It's a bad idea. That area at the bottom of the windshield is a high pressure zone which will force air into the engine bay increasing its pressure. This will then lessen the differential across the radiator reducing the overall efficiency of your cooling system.

[spyderdrifter]

Wow... Didn't know there was that much of a difference. That's a drastic one even. So that's all based on the cowling contours? Am I correct to assume that adding a vent on the rear of the hood instead for the same reason would have a positive result, or would it be doing the same thing?

[TSiAWD666]

Same thing really. You want an exhaust vent in an area of lower pressure to help whatever's inside the engine bay push out through the vent. This is why you see vents more towards the center of the oem hood.

Adding a small lip in front of the vent can help to induce a low pressure zone over the vent. Something similar in shape to a gurney flap on a wing.

[snowborder714]

The ideal location for a vent is over the exhaust manifold. Look up people who have installed the RRE vent and you'll see the most popular and effective location. Obviously you can go a different route and get an aftermarket hood, but you should evaluate how the ventilation is and whether it'll be effective or not.

[rlacasse1]

Or just look at TSiAWD66's profile picture. See how the vents are sitting further forward on the hood vs sitting right at the back.

There's an image on one of the 3s sites I frequent show the low and high pressure areas. I'll see if I can find it and I'll throw it on here for you.

[spyderdrifter]

I have seen the posts regarding RRE's ventalation from behind the radiator. I'm quite impressed with that setup and how well it works despite the lack of space. I'm a very firm believer of functional aerodynamics and don't want to add anything that'll break up the air flow. I'm already considering fabricating ventalation ducting to route air out from the engine bay, and under and out to the sides of the chassis. Only got the issue of adding more air under the car where I don't want it.

[rlacasse1]

3000GT / Stealth / GTO - seal cowl induction?

Look at post #6. It's BMW, but it gets the point across.

[spyderdrifter]

That's pretty informative. Good info.

[eclipsegsx1736]

Check out the thread below for the ducted radiator vent I did:

My ducted radiator setup - road racing

Originally Posted by spyderdrifter

I have seen the posts regarding RRE's ventalation from behind the radiator. I'm quite impressed with that setup and how well it works despite the lack of space. I'm a very firm believer of functional aerodynamics and don't want to add anything that'll break up the air flow. I'm already considering fabricating ventalation ducting to route air out from the engine bay, and under and out to the sides of the chassis. Only got the issue of adding more air under the car where I don't want it.

Venting the air under the engine bay is exactly what you don't want to do aerodynamically, unless you're trying to create an airplane. It'll cause a dramatic increase in front-end lift (negative downforce) and is a big contributor to front end lift that most stock road cars tend to have.

Beau

[Ludachris]

Originally Posted by eclipsegsx1736

Check out the thread below for the ducted radiator vent I did:

My ducted radiator setup - road racing



Venting the air under the engine bay is exactly what you don't want to do aerodynamically, unless you're trying to create an airplane. It'll cause a dramatic increase in front-end lift (negative downforce) and is a big contributor to front end lift that most stock road cars tend to have.

Beau

Beau, you really need to upload a bunch of photos of your car to your gallery so people can quickly view them for reference (like me).

[spyderdrifter]

Originally Posted by eclipsegsx1736

Check out the thread below for the ducted radiator vent I did:

My ducted radiator setup - road racing



Venting the air under the engine bay is exactly what you don't want to do aerodynamically, unless you're trying to create an airplane. It'll cause a dramatic increase in front-end lift (negative downforce) and is a big contributor to front end lift that most stock road cars tend to have.

Beau

I saw this thread of yours some time ago. Amazing work you did. Once I build my road race engine and start getting the body ready, I'll be looking to build one of these as well.

[jtmcinder]

Best shot I have to show where to put hood vent.

[spyderdrifter]

That's a beautiful shot.

How about the vent in the front of the hood bulge, does that have any positive effects?

[rlacasse1]

In front of it or on it? And I don't see why it would have any significant positive effect.

[Spoolin92GSX]

Where jtmcinder has it is spot on, same place I just installed my Carbontrix vent. Even farting around town I notice more consistent coolant temps, and with the vent in that location it helps pull the heat from the turbo and manifold in addition to promoting flow through the radiator.

[spyderdrifter]

Originally Posted by rlacasse1

In front of it or on it? And I don't see why it would have any significant positive effect.

On the front side of the bulge itself. I've seen it done, but figured it was more for show than a mod with real functionality.

I am looking into doing my setup like what Beau and jtmcinder have done there's. I love Beau's radiator duct setup. Looks amazing, like it came from the factory almost (my opinion).

[rlacasse1]

I think if you put it there it would actually bring air in. Someone can correct me if I'm wrong, but I'm pretty sure that's what it would be doing. Which is the opposite of what you want.

[LandoAWD]

Why do you need to cool the timing belt?

[black_gst]

Originally Posted by spyderdrifter

On the front side of the bulge itself. I've seen it done, but figured it was more for show than a mod with real functionality.

I am looking into doing my setup like what Beau and jtmcinder have done there's. I love Beau's radiator duct setup. Looks amazing, like it came from the factory almost (my opinion).

Originally Posted by LandoAWD

Why do you need to cool the timing belt?

that mod is for people with really high timing belt temps, or really low IQ's

[jtmcinder]

Originally Posted by rlacasse1

I think if you put it there it would actually bring air in. Someone can correct me if I'm wrong, but I'm pretty sure that's what it would be doing. Which is the opposite of what you want.

As requested: you're wrong. When the car is moving, air moving across the hood creates a low-pressure zone that pulls air out. (Reading up on the difference between static and dynamic air pressure is useful here.) Also, when the car is sitting still, that location is great for having the air pulled in by the fans and come out after crossing the turbo. I found that I didn't have to get out and open the hood between runs with this vent. After yanking the AC, it's very easy to get the fans to run on high when sitting in grid: just push the button that used to turn on the AC.

[Ludachris]

Best location for the vent, if you're not running ducting between the radiator and the hood, is just above the radiator fans/exhaust manifold. That's where the majority of the heat sits. Placing it on the hood doesn't seem like it would have the same effect. You can see where I have mine in my gallery.

[spyderdrifter]

Gotta love those high timing belt temps... I always kinda guessed a vent in that location would help circulate air under the hood, is that a correct assumption?

[jtmcinder]

Chris -

There are two main arguments for putting the vent further back and closer to the head on an autocross car. First, that location will extract more air because it's a lower pressure area than up nearer the nose. Second, an autocross car wants to vent heat when moving very slowly and/or sitting still, so moving it over the turbo, instead of in front of it, is better. Your vent seems more optimized for road-racing, instead.

[Ludachris]

I should also mention that I plan to run ducting between the radiator and the hood at some point, which means I'll need to add more venting if I want to allow heat to escape from under the hood since the ducting will be sealed.

[jtmcinder]

And before anyone brings it up, since the differences between Evo Xs and DSMs seems to be an issue these days, please note that Evo Xs use a completely different air-flow through the engine bay, so don't even think about adding a NACA duct anywhere on the hood (other than over the air-filter, maybe). The NACA duct on an Evo X is to drive air DOWN across the turbo (which is on the back of the engine on an Evo X) and then out the bottom of the car. A DSM really doesn't want any air coming in through the hood.

[black_gst]

Originally Posted by spyderdrifter

Gotta love those high timing belt temps... I always kinda guessed a vent in that location would held circulate air under the hood, is that a correct assumption?

you dont want to circulate air under the hood, you want to extract hot air.

lots of air comes through the radiator, redirecting that air through the hood and passing by the exhaust manifold is what you want to do.

directing more air in just creates more drag and even lift

[spyderdrifter]

Sweet. Got the direction I needed.

[eclipsegsx1736]

Originally Posted by Ludachris

Beau, you really need to upload a bunch of photos of your car to your gallery so people can quickly view them for reference (like me).

Originally Posted by spyderdrifter

I saw this thread of yours some time ago. Amazing work you did. Once I build my road race engine and start getting the body ready, I'll be looking to build one of these as well.

I am looking into doing my setup like what Beau and jtmcinder have done there's. I love Beau's radiator duct setup. Looks amazing, like it came from the factory almost (my opinion).

Thanks guys! I do need to take some better pictures soon. There are a few pictures and some more info in my build thread for this car:

http://www.dsmtuners.com/forums/dsm-...-tt-99-gsx.htm

As jtmcinder said, airflow over the vent extracts air. Also, adding a lip in front of the vent will help create a lower pressure zone directly behind the lip and greatly improve this effect. You'll see this on the OEM Evo hood vent, although their design is pretty conservative as anything more extreme would probably look ugly for an OEM car.

Beau

[snowborder714]

Here's my setup, which seems to be setup more for road racing than autox per jtoby's info.
Hood vent installation and CF hood painting