Vented hood thread

[Chuck33079]

Someone with a vented hood needs to tape a bunch of short pieces of yarn around the vents and go for a drive. That way we can see if the vents are working. I'm concerned that some of the vents on the hood are too close to the windshield and outside air is getting forced in rather than the other way around.

[wstar]

Originally Posted by takjak2

Vents won't do a whole lot to cool the intake tubes, but the hot metal everyone with G3s runs robs power.

That's why mine are wrapped in heat shielding

[EZT]

Just reporting no issues with my vis and no problems in the rain. Not sure how they are at taking in cold air but you can see hot air escaping

[wstar]

Originally Posted by EZT

Just reporting no issues with my vis and no problems in the rain. Not sure how they are at taking in cold air but you can see hot air escaping

Well, hot air escaping is the only goal here. The "cold" air intake for the engine bay is through the nose and radiator. We just want to give the air coming out the backside of the radiator (out of the fans) a place to vent/suck out of the bay on the hood somewhere. It improves the overall flow rate through the radiator because you're relieving that buildup of high pressure when it all hits the bay and has nowhere good to vent to.

The general "makes basic sense on most cars" point of view is that the best place to vent it is as near as possible to the front/center of the hood right behind the radiator fans, because up high in the rear there's usually a reverse flow of air pushing back forward down the hood (it rolls over at the base of the windshield). Without real data on this exact car, though, it's hard to know for sure. Any kind of venting probably helps, but it would be nice to find a design we know is optimal before cutting up hoods.

[theDreamer]

Wstar, if I pick up the Seibon TS hood I will make some time to come by and we can do some testing. Be it crude paper & tape or other stuff, plus you know my engine bay makes plenty of heat so will be a good test.

[DIGItonium]

My car is still at the body shop, but hopefully it'll be done tomorrow. Here's the Aero Jacket one off OEM hood modification. The shop is going to look for an aluminum mesh grill, so the car will go back to get the grill cut and put on at a later date.

[cooltoy]

Looks good.

[synolimit]

Originally Posted by Chuck33079

Someone with a vented hood needs to tape a bunch of short pieces of yarn around the vents and go for a drive. That way we can see if the vents are working. I'm concerned that some of the vents on the hood are too close to the windshield and outside air is getting forced in rather than the other way around.

Lets say this happens. The hot air doesn't come out but it never did before either. But if you're pushing ambient temp air down into the engine bay then engine bay temps should drop! Whether the hot airs pulled out, or ambients pushed in, we still are achieve a desired goal of getting a lower temp.

[Chuck33079]

The problem is when you have high pressure air coming in from the back side of the hood, it can stall the air coming in through the grill, reducing airflow through the radiator.

That's at speed, though. At a stop, it'll still vent hot air. That's why we need to check which direction air is moving at speed.

[wstar]

Originally Posted by synolimit

Lets say this happens. The hot air doesn't come out but it never did before either. But if you're pushing ambient temp air down into the engine bay then engine bay temps should drop! Whether the hot airs pulled out, or ambients pushed in, we still are achieve a desired goal of getting a lower temp.

The goal is increasing the airflow through the radiator by giving the hot air coming out of the radiator somewhere to go. With no hood vents you tend to just build up pressure in the engine bay and that restricts radiator flow. If you install hood vents in the most wrong way possible, you'll end up pushing cold air *into* the hood through those vents, which will counterintuitively make the car run hotter because you're making the pressure situation worse (because radiator airflow is vastly more important than just stuffing cold air randomly into the bay). A rearward-facing vent that's too close to the windshield can be bad that way, because there's usually a flow of air that rolls under at the base of the windshield and moves forward along the upper part of the hood. Each car is a little different though, and it's hard to say without careful analysis.

[synolimit]

Originally Posted by wstar

The goal is increasing the airflow through the radiator by giving the hot air coming out of the radiator somewhere to go. With no hood vents you tend to just build up pressure in the engine bay and that restricts radiator flow. If you install hood vents in the most wrong way possible, you'll end up pushing cold air *into* the hood through those vents, which will counterintuitively make the car run hotter because you're making the pressure situation worse (because radiator airflow is vastly more important than just stuffing cold air randomly into the bay). A rearward-facing vent that's too close to the windshield can be bad that way, because there's usually a flow of air that rolls under at the base of the windshield and moves forward along the upper part of the hood. Each car is a little different though, and it's hard to say without careful analysis.

Well I've seen a few gtr vents and custom vents and no reports of horrible coolant temp issues so I think we're all good. I mean has anyone here even got their coolant dots over half way? Only thing I've noticed about our car in respect to you saying about the window and air is our car is pretty sealed up. I've never owned a car (which is about 30) that's had so much rubber sealing all the way around it.

[Chuck33079]

Originally Posted by synolimit

Well I've seen a few gtr vents and custom vents and no reports of horrible coolant temp issues so I think we're all good. I mean has anyone here even got their coolant dots over half way?

Stock or NA cars aren't really in dire need of this, it's more for the FI guys since we've got a big *** intercooler stuffed in front of the radiator. We don't need to hamper airflow any more than we already have. If it's over 100 and I've been beating on the car and then get stuck in traffic with the ac on full blast, I can get the temp gauge to move a couple of dots. The OEM gauge isn't going to be accurate enough to show anything but a drastic difference. We really need someone with a water temp gauge. DIGI's vents look like they're in the area where I'd think you'd get the most hot air being extracted at speed. He's got access to a thermal cam, so that should let us see airflow at idle. Unfortunately we don't have many options to test airflow at speed other than short pieces of string all over the hood. It works, but it's a pain in the ***.

[DEpointfive0]

Originally Posted by DIGItonium

My car is still at the body shop, but hopefully it'll be done tomorrow. Here's the Aero Jacket one off OEM hood modification. The shop is going to look for an aluminum mesh grill, so the car will go back to get the grill cut and put on at a later date.

( Click to show/hide )

Can we get pics from the underside of the hood?

[DIGItonium]

Originally Posted by DEpointfive0

Can we get pics from the underside of the hood?

I'll take some pics after getting the car back. The tech definitely cleaned it up nicely.

[Rusty]

The base of the windshield is a high pressure area. That's why the old cowl induction hoods, the L88 hoods, the Z28 hoods and the Trans Am hoods, just to name a few, all had their cold air intakes there. Using that high pressure area to push cold air into the carb. If you're thinking of using that area to vent a hood to release heat. It won't work.