The highly lame: Hood "Risers"
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Joined: Mar 2011
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From: North of Pittsburgh - PA
Nope. Simply wanted a discussion, which I feel was successful after the first few immature posts, because some people swear "by the science" that it goes both ways...
and at the latter discussion of drifters..
I hang out with drifters, I don't mind them, I feel like sometimes they simply ruin nice cars with their habbits, the zipties, the barrel smashing. On otherhand, theyre ballsy, and they do what they love, and ya can't say they park their cars, for most part theyre beat.
*No i don't drift my car, I just hang with some, fun nissan guys, a few rx7 guys* and I never will drift it.
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sure it'll cool the engine bay, it's easy to figure out. But at what cost? sub-par cooling system? the engineers designed all the airflow from the rad to expel under the trans tunnel at a very low pressure zone...opening up the hood disrupts the pressure system. you start to draw air from the cowl back through the tranny tunnel and this causes less airflow through the radiator. If you already have a large IC in front of the rad, the negative effects on the cooling system is worsened.
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Not really.
You have a high pressure zone at the inlet to your radiator. You also have a high pressure zone at the spot where your windshield meets your hood.
You have a low pressure zone back and underneath the car.
Nearly (if not all) cars are like this. It's why you don't see radiators in the hood of a car (don't get me started on top-mount interwarmers)
SO:
You run an undertray and seal the rad inlet to ensure that you get maximum pressure at the inlet to your radiator with minimal seepage while avoiding higher pressure in the engine bay. You seal the hood off so that no other high pressure zones cause higher pressure in the engine bay**. Then you make sure that that undertray you are running exits towards the rear of the motor since the underside of a car is generally a low pressure zone.
In the end, the high pressure at the radiator inlet is forced through the radiator into an area of lower pressure. The lower the pressure, the more efficient this process will be.
I think the logic that most people would cite would be along the lines of "heat rises, therefore giving it a spot to escape at the back of the hood is good, since air enters in through the front, and therefore can exit from the back."
Much like a turbo though, it is a combination of pressure AND flow.
** You CAN run a hood vent just behind the radiator as long as it is in a lower pressure zone on the hood.
You have a high pressure zone at the inlet to your radiator. You also have a high pressure zone at the spot where your windshield meets your hood.
You have a low pressure zone back and underneath the car.
Nearly (if not all) cars are like this. It's why you don't see radiators in the hood of a car (don't get me started on top-mount interwarmers)
SO:
You run an undertray and seal the rad inlet to ensure that you get maximum pressure at the inlet to your radiator with minimal seepage while avoiding higher pressure in the engine bay. You seal the hood off so that no other high pressure zones cause higher pressure in the engine bay**. Then you make sure that that undertray you are running exits towards the rear of the motor since the underside of a car is generally a low pressure zone.
In the end, the high pressure at the radiator inlet is forced through the radiator into an area of lower pressure. The lower the pressure, the more efficient this process will be.
I think the logic that most people would cite would be along the lines of "heat rises, therefore giving it a spot to escape at the back of the hood is good, since air enters in through the front, and therefore can exit from the back."
Much like a turbo though, it is a combination of pressure AND flow.
** You CAN run a hood vent just behind the radiator as long as it is in a lower pressure zone on the hood.
Last edited by Jeff_Ciesielski; Aug 9, 2011 at 02:21 AM. Reason: I no good at teh grammar
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If you want to reduce underhood temperatures, remove the heat source, the engine.
Per this discussion on CR and the fact that someone said Import Tuner did a test about hood risers on a Miata.
You're not getting many serious replies because we've been through this discussion 72.5 times already.
Per this discussion on CR and the fact that someone said Import Tuner did a test about hood risers on a Miata.
Originally Posted by Doppelganger
Yeah, read that article and it was rather really inconclusive. Randomly measured underhood temps. are no indication of airflow across the radiator. They also didn't say if it's venting or pulling heat out (given the physics of airflow, it would be pulling air into the engine bay). Lower underhood temps don't mean **** in all honesty...all engines care about is if the cooling system can properly transfer heat away. So intake temps in their test with their intake next to the hot manifold and near the firewall were reduced because air was coming into the engine bay at the firewall. Guess what? That is all air that could have passed over the radiator instead...which is slightly more important. Intake temps high? Try isolating the intake away from the damn header. Years ago, on my NA, I moved the intake ina box behind a TSI, put some extra shielding over the manifold, removed the coolant lines from the TB and I could put my hand on the IM at any time because intake temps were that cool (ambient).
So where did Import Tuner state any power gains or drop in coolant temperatures? Clearly that is what matters...not just underhood temps and slightly lower intake temps. Clearly the chickenheads running that "test" aren't to be trusted. "And keep in mind that these benefits were found by propping the hood of our naturally aspirated 1.6L Miata-we can only imaging how doing so (or adding a properly engineered, vented hood, for that matter) would benefit a more powerful turbocharged car, or an engine that runs hotter altogether, like a turbo rotary.".....really? So take a car that is now challenged at getting air across the radiator because there is now an intercooler blocking it and reduce the low pressure behind the heat exchangers by adding a lower path of resistance at the back of the firewall and I'm sure coolant temps will love you.....but hey, the useless AIR under the hood will be cooler!!!!
So where did Import Tuner state any power gains or drop in coolant temperatures? Clearly that is what matters...not just underhood temps and slightly lower intake temps. Clearly the chickenheads running that "test" aren't to be trusted. "And keep in mind that these benefits were found by propping the hood of our naturally aspirated 1.6L Miata-we can only imaging how doing so (or adding a properly engineered, vented hood, for that matter) would benefit a more powerful turbocharged car, or an engine that runs hotter altogether, like a turbo rotary.".....really? So take a car that is now challenged at getting air across the radiator because there is now an intercooler blocking it and reduce the low pressure behind the heat exchangers by adding a lower path of resistance at the back of the firewall and I'm sure coolant temps will love you.....but hey, the useless AIR under the hood will be cooler!!!!
You're not getting many serious replies because we've been through this discussion 72.5 times already.
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I'd like to remind everyone that my Professional Datalogging Set already contains a convenient string dispenser. No need to buy this low-quality yarn, instead use pre-waxed, high-strength woven datalogging thread that is easily dispensed from a convenient carrying case.
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I'd like to remind everyone that my Professional Datalogging Set already contains a convenient string dispenser. No need to buy this low-quality yarn, instead use pre-waxed, high-strength woven datalogging thread that is easily dispensed from a convenient carrying case.
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I'm Miserable!
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I'd like to remind everyone that my Professional Datalogging Set already contains a convenient string dispenser. No need to buy this low-quality yarn, instead use pre-waxed, high-strength woven datalogging thread that is easily dispensed from a convenient carrying case.
It sounds like there may be some brainy video data soon enough.
Make sure you dismiss it immediately!
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Identify, Quantify, and Modify, that's my motto.
Last edited by SJPatMarcy90RMcCartin; Aug 9, 2011 at 03:03 PM. Reason: Datalogged my typo.
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I feel like under certain circumstances a decrease in airflow over the radiator is not necessarily a bad thing, while reduction in underhood temperatures could prove to have a marginal benefit. My last 2 dynos saw a 20whp gain on my car almost exclusively resulting from lower ambient temperatures. Isn't it reasonable to think that a street driven miata that has no cooling issues may actually see a power gain from installing hood risers and thus lowering intake temps?
I'm half tempted to go take my hood off and drive around to prove (or disprove) that, in some instances, less airflow across the radiator is not necessarily going to send coolant temps out of control. Not saying we should all go install hood risers, but I'm not entirely convinced that these things are actually the devil either.
*Please don't ban me, lol*
I'm half tempted to go take my hood off and drive around to prove (or disprove) that, in some instances, less airflow across the radiator is not necessarily going to send coolant temps out of control. Not saying we should all go install hood risers, but I'm not entirely convinced that these things are actually the devil either.
*Please don't ban me, lol*
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I would question whether one can apply results from a dyno run directly to real-world situations, particularly the (in)ability of even the biggest floor fans to replicate airflow over the car at speed.
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