Recent posts have been made regarding the aerodynamics, cooling and lifting at speed of the stock and aftermarket hoods with some interesting information and photos.
Consensus seems that the C5 tends to build up air pressure under the cowl at speed.

Venting the hood is doable, but I worry about what effect the water coming in will have.

Has anyone done anything with a flapper type panel that would seal normaly but open under pressure/high heat conditions?

I tried an experiment with mine. I was having cooling issues with the stock radiator, especially in traffic in the central FL heat. Stuck in rush hour traffic I popped the hood just to see if it made a difference and found the coolant temp not only decreaed 10 degrees but the AC was blowing colder as well. [runs cooler with AC on and both fans generally] Once traffic opened up I drove it unlatched for a bit, but pulled over to latch it worrying that it might blow up at a certain point[ althogh no movement at 45-50]

I later tried leaving the hood unlatched but tethered with several HD zip ties, allowing slack to see if the hood would rise. The car seemed to like it, running at 197, or about 5 degrees below where it ran normally at 70mph.
I tried running it up and found the hood would begin to rise against the restraints ~80-85mph.
Obviously it isnt somethig you want to run around doing all the time, but it got me wondering about cowl type hoods. Another Idea that I havent tried is removing the seal and blocking up the hood mounting points about 1/2 - 1".I wonder if this would be a simple way to improve cooling and release some air pressure at speed?
I should mention that since I replaced the rad withan all aluminum unit the cooling is much better. Just wondering if anyone has tried anything similar.

 

Not much help with modding a hood. But Rain didn't bother anything with this setup (Halltech GT2 DRED). But only been driven in rain once, for a couple hours, lol. Seemed like when you were moving at highway speeds, airflow through it kept any rain from going into the hole.

 

The base of your windshield is a high pressure zone and the faster you go the more pressure will build. Nascar air cleaners are ducted at windshield base for cool pressurized air. As far as venting, removing the rubber seal where your hood closes will slightly benefit around down slow speed driving as your tests have shown but not going to help dissipate lift at high speed. As the guys stated above a heat extractor hood will benefit cooling and help eliminate aero lift.

 

Why are people so FREAKED out about engine temps on these cars. You think GM didn't test???

 

What are the reasons why you would not recommend your hood? I asked because I have been looking at that style hood for years.

 

I see people wanting to improve performance over factory especially in summer months of the hottest states....cooling plays a major role in how much ignition timing a Corvette can take without Knock Retard kicking in and limiting performance.

 

I always find it entertaining to read these pseudo engineering fantasies....
GM uses a 5 million dollar wind tunnel and 50,000 dollars worth of software and invested 80 hours in that tunnel to fine tune the aerodynamics of the C5, which includes a properly aligned hood and ground effects, to create 73lbs per square of down force before the cowl, and 175 lbs of down force off the rear hatch. My joy comes in viewing the conclusion of a guy unlatching the hood, changing its angle and using zip ties to engineer a better design. Want to cool down the engine bay? take the hood off, or use a design that was establish to extract heat using design savaging principles that actually work. if you notice all heat extraction hoods that are effective, use the same extraction point. Including the GM C5R race team.. and FYI MCM was the designer of the GM R race team hood design. they also did all the ground effects and hoods for the C4 R GM race team as well. Chief design engineer was Mike Mickoz, and a close friend of mine.
OH BTW.. you can rent the GM wind tunnel for 2000 dollars an hour.

 

...sorry, I couldn't hold back on that one

 

Well ...I am certainly happy to have provided you entertainment at least.

I think I can speak for a number of people here on the forum. I respect your knowlede and experiance. I also apreciate your ability to provide invaluable inside information on the design history. However What I do NOT apreciate is your repeatedly demonstrated habit of disparaging people on here or your arrogant attitude which has landed you on the S#&^list of more than a few members.

No, I am not an automotive engineer. Neither are most on the forum.I don't claim to be an engineer or an expert on C5 Corvettes. But I do have ~40 years of extensive [and expensive] experiance in this hobby and a reasonable degree of inteligence. The essence of hod rodding has always been backyard innovation, asking how something works, and if it can be done better.

As well designed as the C5 was [or most anything] there is room for improvement. Most of us are cannot afford the fee for a wind tunnel. After a ~23% reduction in net pay [thanks, Obamacare] a new extractor hood isn't in my budget either.

My post was for discussion in general and observed phenomena in followup to recent posts. I had cooling issues with the large intercooler, turbos and an original radiatior which have since been resolved with a larger new unit. Regarding the concern for temps, Yeah I got concerned when it hit 250, and noted an immediate improvement with the hood popped. I have seen cooling improvements on other vehicles w/ cowl hoods, which had me wondering about some of the cowl hoods on the market for the C5.

My admittedly non-windtunnel limited later experiment on the highway was to see if there was any benifit to cooling under those conditions. And there was, albeit marginally. I also wanted to see if there would be any lift at speed. And there was. It was tethered in that fashion to limit it.

You state the amount of downforce documented in the wind tunnel and I dont doubt that. However it seems that the pressure underneath exceeds that, at least at the speeds mentioned. At higher speeds perhaps the downforce could excede that pressure. It could also be I have extra underhood pressure from additional venting in the front end [which also improved cooling and IAT from the intercooler.

Bottom line is this. I come on here to learn, and share what I have learned and to discuss that with others. I have learned much from your past posts and value your input. If you want to discuss the topic and share your knowlege, then hey, I'm all ears.

On the other hand, if you just want to flame people or basicly insinuate we are idiots, I'd just as soon you STFU.

 

the people who I find on their **** list, are not worth my time of effort. my pount here as in all posts where some one claims to offer extensive testing on practical applications with no ability or pedigree to do so. I'm a professional and have " STOPPED " hundreds of new forum members who come here looking to gain knowledge and experience.. you claim to know a lot about automotive technology, but you fail to recognize that people who have developed this car have so much insider knowledge in the development than a guy like you to send people down the wrong path. Im here to add real input.. Did it ever occur to you that none of the Last 20 years of Corvette sponcered GM Corvette race teams use a cowl extraction point??? We know there is a Vortex at the base of the windshield that pushes air Down and not up or out from the cowl area. I've defused so many people who said they removed the cowl area gasket to remove heat, which is impossible on a C5. unless the force of air under the hood overcomes the vortex at the cowl.. I've saved hundreds of people from going the route that you want to go by opening the hood at the cowl... It doesn't work... BTW when have taken the C5 to 180+ in the tunnel, we did not have any hood problems with excessive lift or a compromised hood latching system.
Also I'm not trying to rain on your parade but rather trying to put your time and effort into another area that you might be able to improve.

Don't take my comments as personal insults. Everyone likes to play... what I've found here on this forum in my 13 + years here is too many bankers, lawyers, construction workers want to play engineer, or they want to be a hero with some magic that they say works in the hope that somehow someone would follow them down a path of poor testing and bad information.

The people who have me on their ignore list are the people that are too blind to see the real picture. If it wasn't for the thousand of people that Ive helped and the constant barrage of PM's from people who continue to be my friend in this forum for ten or 12 years, I would leave this forum. in fact I've done that three times in the past and only with PM's and emails did I come back.. there are a dozen or so threads on this forum that confirm that. and I have hundreds of emails

Many people don't like me because I can be arrogant. I don't know everything about a corvette but the things I do comment on, I am an absolute expert. When some guy who mixes cement for a living tells me he knows better than I do, what can you expect. I have every respect for a guy who mixes cement and I would not tell him how to do his job. it doesn't matter if you feed your family buy working in the service industry, trash and garbage, or you perform brain surgery, I respect all people until I loose respect for them and it usually comes at the hands of their disrespect for me and my profession.

I passionately defend the design, I defend the members here, who have been wronged in some way and the vendors who sometimes get a bad rap. I've never once said the design is perfect. In my 40 years of engineering design , the C5 was the best ( most rewarding ) project of my career, it came together better than any other project. The design stands on its own.

The nice thing about this forum is that if you don't like what I have to say, you can easily ignore me. it takes one click of the mouse.
The End

 

ET rules !

 

I've had this hood on my car for 12 years without any problems.

 

I wonder how many more hours of development was needed to prevent the C5's hood from flapping on the freeway.

 

The C5 was put to the test on the 4.8mile 30 % high bank track in Milford at 150 +mph, and also in the wind tunnel. The designed is certified by the Department of Transportation. Why do some Corvette Owners take every opportunity to trash this car with very poor information. Flexing of the hood is expected, " flapping " around suggests tis flapping all over the place. Its easy to point fingers when your finger is unloaded.

 

This hood (ACP) is the only hood I've found that improves the aero on a C5 and it doesn't really help the cooling that much.

 

all those vents and it doesn't help? That sucks

 

So ET, for those of us who have 200+ more hp than the car came with and want to run near 200mph in a sanctioned event, would you suggest there is any way to vent the stock hood to help with the air pressure under the hood as well as getting some of the heat of the additional hp out?

I have pretty good savvy when it comes to building a house, but I'm always open to suggestions on hot rodding issues.


And 8vette7...I love the look of your hood! If I need to help you get rid of it I can give it a shot. What area does it not deliver in?

 

I don't know the quality of the build in that beautiful hood. I have no way of testing it to failure. there are a few things you can do without destroying that hood.
I would close off the side vents of the hood ( you can make a temporary vent block . I would open up the front of the car around the fog lights. If that center section is not open, I would open it. The Idea, if I can explain this to you. is the heat rises in the center of the hood, air is forced through the front around the fog lights creating a slight push of cold air forcing hot air to the top of the hood . AS air passes over the hood, scavenging pulls hot air from the top of the hood in what GM use to call flow through ventilation.
I would do this.
open the front around the fog lights to add a cold push. Under hood temps 180/200 F cold air push at 90F



Open this area, to pull hot air out. The MCM is capable of 150 + but its not available but the structure is as sound as the factory
Its also very important to have a proper alignment of the hood with the front fascia and headlight doors

I don't know about the structure of this hood with the side vents.



open this area of your hood and make sure the cowl seal is in place



This is only a suggestion. without testing its only a suggestion. in testing like this, one of the things I try to do in a home modification is to make sure it is easily reversible. IN my suggestion this is the case. Its not as aggressive but the risk is minimal.

The factory hood is not easily modified for heat extraction. But its capable of 150 + mph

I cant find an after market hood that capable of 150+ MPH and designed to extract heat.

 

I never expected it to help with the cooling. This is the same hood the C5R ran and it's designed to reduce lift and cancel the two areas of negative air over the fenders. It does both in a noticeable way.

 

ET that sort of info is exactly why I wouldnt want to 'ignore' you or see you leave the the forum again.
Curious why you advise blocking the side vents though? I can see how it might weaken it, but if they are already there...would it lessen the extraction of the center vent?

I did open up the fog light and licence areas for more airflow to the intercooler. And since it doesnt have an extractor, is that why I was seeing hood lift at ~80?