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I've noticed several members have installed vents in the hoods of their C3's, like the one pictured below.
I am thinking of installing a hood vent in the new Tall L88 hood I purchased for the restomod of my 73.
My questions are:
1. Did you notice any increased cooling of the engine compartment?
2. Did you notice any performance gains?
3. Was it worth the expense
4. Would you do it again knowing what you know now?
Thanks
Dont think it would make it any faster (unless you were trying to break 180?)
But could relieve some underhood pressure and draw hot air out at any speed.
Want to fab a hood up on my A body just for that purpose, experiment with heat management.
I've been running this vented hood for years. really don't think it makes it any faster. Definitely has to let some hot air out. But never measured it in any way. Just liked the look and wanted more room for my RPM manifold and 3 inch tall air filter. (Not a drop base).
O.K. probably not all that helpful.
But the point is. If you like the look it certainly isn't going to hurt anything.
Last edited by 4-vettes; Oct 22, 2020 at 10:13 PM.
I have looked for the best way- and an educated guess- the new cars have it a little more figured out!!!
Using the electric fans- to actually help the air move out of the engine compartment looks to me would be the best.
Can't see just an open hole in the hood would make a substantial difference
Another heat issue would be shielding the exhaust...
Performance increase? IIRC dropping the air intake 10° will give about 1% increase in HP- not linear because it’s the ratio of the absolute temperatures.
Thanks Richard,
My thinking is the vent, when properly placed would provide some negative pressure behind the radiator and will allow more air to be pulled through the radiator at low speeds.
I will be running dual spal fans behind a DeWitts.
Plus if there is more air circulating though the engine compartment it will also provide cooler air into the open air cleaner.
It may be slightly cooler, but anything may be an improvement.
I also plan to keep the rear of the L-88 tall hood open to allow hot air to escape and remove any restrictions in front of the side fender vents.
I know I won’t see any noticeable performance gains and I’m looking more at air circulation.
Another plus is it may allow heat to escape when parked.
Putting the last post into context.
yes it certainly helps move more air. I am certain at ldle it's made a difference. At idle sitting at a light. I can watch the temp guage drop.
didn't happen with stock hood.
Also running twin electric fans.
Just to butt in here, I have a high rise hood, no vents. I left open the hood seals at the radiator support so air would flow over the radiator. With it slanted like it is, there is plenty of cool air flowing over the support. To verify that I put two temperature monitors on the car, one to get ambient and one to get air temps at, in my case, the carburetor which is where any significant HP is to be gained. I posted on this a while back with pictures and data.
At even modest road speeds I had plenty of cool engine air. Only when I stopped at a light would my electric fans come on to keep the motor cool. HP sitting at the light, well unless I want to light things up, I don't need it.
Personally, the more doodads and holes in things here and there, the sillier these cars look. If you like the look, and many do, that is a personal thing. I do not believe the return on investment is there for you Greg. I forget what motor you have, but either carbureted or fuel injected, cooler ambient air pushed up and over the radiator should be all you need.
Those cowl hoods are supposed to be sealed to an airbox so at speed the pressure pushes air in the opening...
have one myself..at idle sure the fans push hot air out (and right into the air cleaner, notsealed). At speed Im guessing it cant get drawn out.
Ideally use the cowl induction bit to get cool air for the air cleaner and 2 other openings where the air flowing acoss the hood could pull hot air out or release pressure.
Guess thats what the gills were for. Who knows.
I do like that scoop that comes off the fan in the pic above.
Lots of C1/2 and musclecar owners used to space the hood up about an inch in the rear to let hot air out.
Putting the last post into context.
yes it certainly helps move more air. I am certain at ldle it's made a difference. At idle sitting at a light. I can watch the temp guage drop.
didn't happen with stock hood.
Also running twin electric fans.
Just to butt in here, I have a high rise hood, no vents. I left open the hood seals at the radiator support so air would flow over the radiator. With it slanted like it is, there is plenty of cool air flowing over the support. To verify that I put two temperature monitors on the car, one to get ambient and one to get air temps at, in my case, the carburetor which is where any significant HP is to be gained. I posted on this a while back with pictures and data.
At even modest road speeds I had plenty of cool engine air. Only when I stopped at a light would my electric fans come on to keep the motor cool. HP sitting at the light, well unless I want to light things up, I don't need it.
Personally, the more doodads and holes in things here and there, the sillier these cars look. If you like the look, and many do, that is a personal thing. I do not believe the return on investment is there for you Greg. I forget what motor you have, but either carbureted or fuel injected, cooler ambient air pushed up and over the radiator should be all you need.
I get and understand what you did and the concept that removing the seal over the top of the radiator will allow air to flow over the radiator, which I would love to do as I agree with it totally.
BUT isn't that one of the big no no's for keeping air flow through the radiator and prevent overheating?
I'll be running a 496 BB and I'm looking at the vent to aid in cooling.
Have you had any issues not having the top radiator seal in place?
Those cowl hoods are supposed to be sealed to an airbox so at speed the pressure pushes air in the opening...
have one myself..at idle sure the fans push hot air out (and right into the air cleaner, notsealed). At speed Im guessing it cant get drawn out.
Ideally use the cowl induction bit to get cool air for the air cleaner and 2 other openings where the air flowing acoss the hood could pull hot air out or release pressure.
Guess thats what the gills were for. Who knows.
I do like that scoop that comes off the fan in the pic above.
Lots of C1/2 and musclecar owners used to space the hood up about an inch in the rear to let hot air out.
Have you had any issues not having the top radiator seal in place?
No I haven't. I have a deWitts with electric fans and it never comes on on the road. The motor is an LS376/515. The caveat is with no A/C I never take the car out on really really hot days, so I can't claim being completely free of heating issues.
BB's in my experience do put out amazing amount of heat. I'm thinking I shouldn't have butted in after all as I can't say one way or another what you should do if you have a stock cooling system. With me it was all about getting cooler air to the air filter. The deWitts with the electric fans handled the engine temps just fine.
I may be wrong but the only way the hood inserts help is if there is enough of a Bernoulli effect, or enough underhood pressure to exhaust under hood air out the top of the hood. So your hope is any additional cooler "makeup air" comes from under the car and up through the hood. I am doubtful that would do much.
Sounds like a "science project" as my old boss would say. He didn't look kindly on such.
From: Las Vegas - Just stop perpetuating myths please.
IMHO I think the vents belong over the exhaust manifolds. And that's where you find them on many of the new muscle cars - except chevy. Chevy puts them over the center of the motor which I'll guess still works but not where I want the air to flow out the top.
With my car I needed to stop up every, and I mean every path air could take around the Radiator. The more power you make. The more heat you make. After I got absolutely every path around the Radiator sealed. Then and only then would my car tolerate the Queensland heat. With my high rise hood there was a huge gap above the Radiator top seal and air could easily flow over the top. So it did and my engine ran HOT. so I did this.
I purchased a second rad top seal. Cut a section out and glued it into the hood so when the hood closes the 2 seals meet up and close the gap. That and a few other creative solutions down at the bottom and lower sides. ALL the air has to go through my Aluminium Radiator now. And my fans don't run all the time anymore. It gets bloody Hot here in Australia. Point is. I disagree with the gentleman who wants air to go over the top of the radiator. Sealing everything, and I mean everything is what finally worked for me.
I might add, when the car was box stock many years ago, and I lived in Wisconsin. It never had any overheating issues. However. Double the power....
I understand that the L88 hood offers more room under it. I have a factory L88 hood on my 1968 C3 and I used the hood because of the intake air system under the hood. I am running a very hot High Compression 427 and the intake air it gets is always very close to ambient. This makes power and helps deter my 427 and it's 12.25-1 compression ratio from detonating or pinging. In my opinion the cool air function of the L88 hood is the greatest and it makes power for a engine like mine.
The Under hood heat of a High Compression Engine with headers get really hot after shutdown. My hood has heat damage over the headers and that is the only place. I switched to a larger Deep Cycle FLA battery to allow the cooling system to run after shut down to cool things off a bit. I have been tempted to have fans mounted behind the gills to help blow the heat out of the engine area.
The hood I have is an original Factory L88 hood and that eliminates cutting holes in it. If I had a replica hood then I would get out the saw and cut out two vents over the headers to get rid of the excess heat.
I too want all the air to go thru the radiator and not over or around it. The air will follow the path of least resistanceand your radiator will get hotter. You need to make the air go thru the radiator to make the cooling system work it's very best.
No I haven't. I have a deWitts with electric fans and it never comes on on the road. The motor is an LS376/515. The caveat is with no A/C I never take the car out on really really hot days, so I can't claim being completely free of heating issues.
BB's in my experience do put out amazing amount of heat. I'm thinking I shouldn't have butted in after all as I can't say one way or another what you should do if you have a stock cooling system. With me it was all about getting cooler air to the air filter. The deWitts with the electric fans handled the engine temps just fine.
I may be wrong but the only way the hood inserts help is if there is enough of a Bernoulli effect, or enough underhood pressure to exhaust under hood air out the top of the hood. So your hope is any additional cooler "makeup air" comes from under the car and up through the hood. I am doubtful that would do much.
Sounds like a "science project" as my old boss would say. He didn't look kindly on such.
Your butting in is exactly what I’m looking for so please do so anytime.
I’ll be running a DeWitts with dual spal fans as well.
My thoughts are that, any additional movement of air and more air being allowed in and able to escape the engine compartment should help with the heat trapped under the hood.
My thought is that the hood vent may create a flow through effect and allow air to pass from the front of the engine compartment and exit out though the cowl and side gills, rather than having air flow being forced in at the rear of the cowl and trapping it in the engine compartment.
I am hoping that someone who has installed the vent will respond with their results so I don’t have to slip into my lab coat.
I think it is really difficult to know what the airflow is in an engine compartment. A factory equipped car with all the junk, i.e. AC compressors, AIR pumps, brake power boosters, vacuum reservoirs, etc are going to be much different than a car stripped of all that stuff. And often times, the flow is not what to be expected. Remember, its not a sealed compartment,.....the entire floor of the engine compartment is OPEN! Aerodynamics around a moving object is not always what it seams to be. High pressures, low pressures, are formed by the shapes of all components and shapes that exist. SO, my point is, its not as simple as cutting some vents into a hood.
What I do know, is my 77, with Dewitts radiator, kept my engine gage solid at 180-190 all day long, every day, in the heat of the summer. And I actually don't have either of the vertical sides of the radiator sealed. I also have a very basic engine compartment,....i.e. none of the mentioned junk. So, I suspect I have pretty good airflow into and out of the engine compartment. AND, I have uncoated stainless steel headers. In the heat of the summer, my car is as cool inside as it is outside,.....with no AC. I think I succeeded.
Last edited by Shovels and Vettes; Oct 24, 2020 at 12:03 PM.
In response to the last couple posts.
I do plan to keep all the seals over and around the radiator in place as I live in an area where the temperature can be over 100 any day during the summer and I want to be ale to drive my Corvette with the air on when it is hot.
I will have ac, but I am stripping anything un needed from the engine compartment so it will have more open area.
I have also thought about installing some small puller fans in front of the fender vents to pull out hot air when stopped and also about some type of air dam mounted behind the radiator that would force air up through the engine compartment at slow speeds.
I might just be over thinking the whole under hood heat as an issue, but the under hood temps I have now with a stock 454 is extreme and I’m trying to plan ahead.
Last edited by OldCarBum; Oct 24, 2020 at 12:11 PM.
Wondering the same thing for my stinger hood.
Hood Vent ?'s
