Scottie-GNZ Posted August 9, 2006 Share Posted August 9, 2006 This is a continuation of the cooling discussion in the Gabe's thread "Pics from a small car meet". Quicker240 said "I thought the air at the base of the windshield in a moving car was LOW pressure(I.E. would SUCK air out of the engine compartment) ,and was easier for an intake to get at.Now I'm confused again dang it! Your diagnosis seems backwards to me." I thought the same thing as you which is why I positioned the scoop that way (I certainly do not need ram air ). However, someone pointed out to me that the idea of the mucle car cowl hood back in the 70s was so the pressure at the base of the windshield force air into the cowl induction. The top of my radiator angles back towards the front so the air from the fan is being directed towards the back of the hood and that is why I did what I did. If that person's theory is right, that explains what we believe is happening to me. I could probably prove it by blocking off the hole in the scoop but my thinking is that holes on the side would relive all pressure from under the hood even if it came in from the back. Any experts out have an opinion? Quote Link to comment Share on other sites More sharing options...
Twoeightnine Posted August 9, 2006 Share Posted August 9, 2006 Im no expert, but Wayne Guinn is. Check out this excellent read. http://www.camaro-untoldsecrets.com/articles/rpo_zl2.htm Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted August 9, 2006 Share Posted August 9, 2006 You probably should have reposted your symptoms from that first post. Do you have the factory chin pan installed? The early Z's had a turbulence problem underneath the vehicle that disrupted the airflow through the radiator and caused them to overheat at speed. I put one on my otherwise stock Z and it made a difference. My understanding of the cowl hoods is exactly as you say. The base of the windsheild is a high pressure area and will force air into the engine compartment at speed. The middle of the hood should have some nice, smooth airflow which I would think will cause a low pressure region to extract air from the engine compartment. If I were you I would not put holes in both places. Other wise couldn't it just recirc the air? The last HybridZ word of warning is to make sure your lower radiator hose has the spring inside of it so it doesn't collapse with engine speed. Quote Link to comment Share on other sites More sharing options...
Twoeightnine Posted August 9, 2006 Share Posted August 9, 2006 As one can see by reading the article on cowl induction, The induction system creates some positive pressure. Its greatest benefit is in inducing "cold" air into the engine. It must have the plennum sealed to the cowl however to perform it's designed function. As far as heat issues, I would look up front to gain flow. Underpaning of the air dam will provide forced flow. Sealing the plennum will reduce the cowl induction back pressure and gain you HP. Lets not forget the fan as well for low speed cooling. Quote Link to comment Share on other sites More sharing options...
Ivan280zt Posted August 9, 2006 Share Posted August 9, 2006 Scottie, With my setup on highway my car is running so cool that sometimes I think that its little too cool. When I am driving in city if I am cruising more that 20mph my fan never comes on and temp stays about 185-190. I also have 3.5" I/C from James T. that blocks WHOLE radiator. I really belive that those cutouts on the side of cowl are more than capable of keeping my car cool. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 9, 2006 Share Posted August 9, 2006 You could easily do a yarn test to check this out. Just tape 2" pieces of yarn around the opening and see where the yarn goes. I bet the yarn goes into the engine compartment. Another way to look at it is like this: the air comes up over the hood and hits the windshield. The windshield is a major obstacle, and the air is forced to change directions to get around. When the air hits the obstruction, pressure is created (stick your hand out the window on the freeway and feel the pressure). You've got an open hole right there, so the pressure is going to force the air down into the engine compartment. I think you're right about the cowl induction hood being a problem Scottie. If you have a cowl hood it is pushing air into the engine compartment from the cowl, while the car driving forwards is pushing air in from the front. If there isn't a good place for the air to go, it's going to get stuck there, as it has to take a convoluted path out the transmission tunnel or under the sides of the car to get out. The shape of your RX7 is similar to the Z. A vent in the middle of the hood should suck air out of the engine compartment, as this area has a lot of flow and no obstructions and is just aft of the bumper and grill and should be a low pressure area. If you have the stock hood you could use a hole saw and just drill a couple holes in the hood and put yarn around the holes and see if it looks like the yarn is getting blown up and away or if it is getting sucked into the engine compartment, then you could cover the holes later with a louvered vent or something like that. Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted August 9, 2006 Author Share Posted August 9, 2006 You probably should have reposted your symptoms from that first post. Here is the story. I am using a Capri hood scoop turned backwards so the original opening in the front now faces the windshield. Around town I have no cooling issues despite a 4" thick FMIC, B&M Supercooler and OEM RX7 oil cooler all in front of the radiator (AFCO 24x19 w/Taurus fan). However, as soon as I get on the highway for a little distance, the temperature creeps up to 205+. Once I get off the highway, even if I end up stuck in traffic, the temp will start coming down. My conclusion is that pressure from the base of the windshield is being forced into the scoop at speed and actually prevents hot air from escaping. If I had those openings on the side of the hood, they might help the hot air escape even at speed. I wonder how that scoop would look with round holes running down the side of it? While 205* does not concern me much, on a long trip like to the SEZ, that means my Taurus fan will not turn off for the whole trip. Recently I had the fuse get so hot that it melted the plastic fuse holder and the fan quit working and badly overheated the engine. Do not want that to happen again. Quote Link to comment Share on other sites More sharing options...
Mike kZ Posted August 10, 2006 Share Posted August 10, 2006 Did you try blocking the hole in the scoop, and try it that way on the highway? Quote Link to comment Share on other sites More sharing options...
deMideon Posted August 10, 2006 Share Posted August 10, 2006 I have a 280 with the vents in the hood and I took the metal off so they are completely open. I really believe they are allowing at least some air out since my vents inside the car are almost unusable as all I get is really hot air blowing into the car! Quote Link to comment Share on other sites More sharing options...
johnc Posted August 10, 2006 Share Posted August 10, 2006 Rule number 1: Air flows from a high pressure area to a low pressure area. Rule number 2: Air needs an entrance, a path, and an exit for the flow to occur between high and low pressure. Rule number 3: Air will always take the path of least resistance to flow from a high to a low pressure area. The front of a car and the area in front of a windshied are both high pressure. Trying to flow air between the two won't work very well because it relies on the pressure differential between two (relatively) high pressures. Its better to look for low pressure areas to direct the air entering the radiator: Front wheel wells. Front part of the hood. Underneath the car. Its very important to make sure the air coming in the front of the car has to flow through the radiator. Make sure the radiator is completely sealed, ducted to the incoming airflow. Any gaps around the raditor allows air to escape. Its very important to make sure the air exiting the radiator has a low pressure are to go to and a nice path to follow. The engine compartment itself is considered a high pressure area because of the incoming air from the radiator. Adding additional pressure from an unshrouded cowl scoop makes things worse. Some things you can do: Get rid of the scoop. Open up the inner fenders so that air can flow into the front wheel wells. Shorten any belly pans. Cut a hole in the hood behind the radiator and put a small lip on the front edge of the hole. Quote Link to comment Share on other sites More sharing options...
BayAreaZT Posted August 10, 2006 Share Posted August 10, 2006 John - could you clarify what you mean by a small lip on the front edge. Wouldn't you want a lip on the back edge like a reverse scoop to allow air to escape? Quote Link to comment Share on other sites More sharing options...
johnc Posted August 10, 2006 Share Posted August 10, 2006 Nope, front edge lip creates turbulence just like the air behind a car with a small spoiler. Turbulence is low pressure. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 10, 2006 Share Posted August 10, 2006 Take a look at the GT40. Right in front of the hole that exhausts the air that goes through the radiator they put a lip. On the GT40 I think it was a little piece of angle aluminum. This helps to further reduce the pressure and increase the suction on the hole at speed. http://www.me.mtu.edu/~prater/carpics/fords/GT40/gt40_2.jpg Quote Link to comment Share on other sites More sharing options...
BayAreaZT Posted August 10, 2006 Share Posted August 10, 2006 Ok, makes sense. I was confusing the lip with the scoop that guides the air out. Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted August 11, 2006 Author Share Posted August 11, 2006 Good feedback. Thanks, all. I am stuck with this hood for now as it is aluminum and I also cannot remove the scoop because it has a big hole in it. Quote Link to comment Share on other sites More sharing options...
deja Posted August 12, 2006 Share Posted August 12, 2006 I have a 280 with the vents in the hood and I took the metal off so they are completely open. I really believe they are allowing at least some air out since my vents inside the car are almost unusable as all I get is really hot air blowing into the car! My vents are open too, you can see the valve cover in the pict. I think it helps with air flow though the engine compartment. Quote Link to comment Share on other sites More sharing options...
HeatRaveR Posted August 12, 2006 Share Posted August 12, 2006 Cut a hole in the hood behind the radiator and put a small lip on the front edge of the hole. I've always read so many discussions about the ideal place to put a vent to have the hot engine bay air escape, but it seems to hard to get a conclusion from them. Is the concensus that the ideal place to put a vent is actually near the front, just behind the radiator? (which would be approximately just before the beginning of the power bulge) Or is it better to have it more towards the rear so that any heat generated by the engine itself can also escape? Quote Link to comment Share on other sites More sharing options...
Synlubes Posted August 14, 2006 Share Posted August 14, 2006 Behind the radiator back to about the strut towers is what I have heard most on an S30. Unsure about the stock hood vents as far as exhausting air??? They are between a low and high pressure area. Not sure what they do other than let hot air exit the engine compartment after you have stopped. If only someone would do the string test on the hood (and get video) it would answer this nagging question. Mine is in pieces and wont see road for a while. Quote Link to comment Share on other sites More sharing options...
Tim240z Posted August 14, 2006 Share Posted August 14, 2006 A bit of real world experience: When I replaced the hood on my 71 C20 truck (rust issues), I decided to use a cowl induction hood instead of a plain one. One Saturday I spent all day washing, polishing, waxing and buffing the truck...looked great (but I digress).... The next morning I went for a drive on the freeway. There was a bunch of water droplets all over the truck (overnight dew). As I drove, I noticed that the water from the hood, and the windshield cowl was actually getting 'sucked' into the opening of the cowl induction of the hood. This began happening at about 35-40mph, and became more vigorous as speeds increased (got up to 80MPH before backing out). That made me a believer. Tim Quote Link to comment Share on other sites More sharing options...
Twoeightnine Posted August 14, 2006 Share Posted August 14, 2006 There was a bunch of water droplets all over the truck (overnight dew). As I drove' date=' I noticed that the water from the hood, and the windshield cowl was actually getting 'sucked' into the opening of the cowl induction of the hood. Tim[/quote'] Drawn perhaps, not "sucked". Thats where the tread started was the high or low pressure discussion. Heres a quote for ya. "Chevy engineer Doug Roe, who worked with Product Promotions chief Vince Piggins, found a dramatic performance gain by taking the cool dense air at the high pressure area near the base of the windshield. Ducting pressurized fresh cold air from this area to the carburetor creates a more dense fuel charge with increased volumetric efficiency resulting in more horsepower." I know.....Im being picky. Quote Link to comment Share on other sites More sharing options...
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