Ideas for cutting down on hood movement at high speed?

Cobra4B · #1 10-20-2008, 08:26 AM

Even w/ the paltry 240 horses in the stock 5.0 the car attains enough speed on VIR's 2 main straights to make the hood flop around like a fish. Any ideas for venting the hood? Maybe cutout the two side "eyes" on the fenders?

eric1h · #2 10-20-2008, 08:36 AM

I am adding 3 things to help with the flop........

4 rubber "hood stops" inside the engine bay at the 4 corners to help distribute the load.

rubber spacers in the heat extractor vent to keep it from vibrating

hood pins

If that doesn't hold it still nothing will

Squerly · #3 10-20-2008, 09:01 AM

Yes, I would like to see this go away too. I don't know how your cars are set up, but mine has 4 clips (two in the front/two in the back) and then 2 twisty-bolts positioned uniformly across the upper top part of the hood. The back straight at Road Atlanta allows for some admirable speeds and I'm always saying a silent prayer that the hood stays on.

Cobra4B · #4 10-20-2008, 09:16 AM

Quote:

Originally Posted by eric1h

I am adding 3 things to help with the flop........

4 rubber "hood stops" inside the engine bay at the 4 corners to help distribute the load.

rubber spacers in the heat extractor vent to keep it from vibrating

hood pins

If that doesn't hold it still nothing will

Your car is fiberglass right? I'd assume it reacts differently than the plastic cars like mine. FYI mine has multiple hood support struts under the hood on the chassis. To connect it uses 4 latches (2 on each side and 2 on each front corner) and 2 turn screw things (like my trunk has) at the rear of the hood on top/cowl.

The "heat extractor vent" you speak of is cowl induction for a carb setup I believe. I think the hood just needs more areas for air to get out.

Quote:

Originally Posted by Squerly

Yes, I would like to see this go away too. I don't know how your cars are set up, but mine has 4 clips (two in the front/two in the back) and then 2 twisty-bolts positioned uniformly across the upper top part of the hood. The back straight at Road Atlanta allows for some admirable speeds and I'm always saying a silent prayer that the hood stays on.

Sounds like ours are held on in the same manner.... anyone cut any vents yet? I'm thinking cutting out the side "eyes" would give the air more of an exit. Might open up the cowl area at the back of the hood as we're moving to a carb setup anyway.

NZGTRA17 · #5 10-20-2008, 01:01 PM

I have just finished reworking the hood on my car in a bid to cure this problem. I have cut out the 2 eyes on the side of the hood and put metal gauze in them. Looks smart, will assist airflow and also help with underbonnet cooling.

To help keep the hood down I have modified the 2 support stays near the back of the hood (the ones that currently have rubber pads that the hood sits on) by converting them to pin type latches while retaining the rubber pad. This way they trap the hood at the height yoiu adjust them to.

I am also ditching the screw in type fasteners and converting to Dzus fasteners as I do not have a lot of faith that the screw ins will stay in for long periods.

I would be careful about modifying the back edge of the hood on your car Brian as the back lip of the hood provides a lot of rigidity to the hood structure (particularly when you are removing, fitting and handling the hood). Someone has cut a section out of the center of mine and this has caused some cracking issues. When I put an engine cold air tray in the car I will also reinforce the areas that had previously been cut out.

Cobra4B · #6 10-20-2008, 01:08 PM

^ Mine also hase about 2 feet cut out along the back for what looks like a cowl intake setup. I was considering enlarging it but will take a closer look at it.

Good call on converting the other hood supports and modifying the rear fasteners.

Panoz26 · #7 10-20-2008, 02:14 PM

I am also ditching the screw in type fasteners and converting to Dzus fasteners as I do not have a lot of faith that the screw ins will stay in for long periods.

are you thinking about going with these:
http://www.hrpworld.com/index.cfm?tp...action=product

eric1h · #8 10-20-2008, 02:21 PM

Quote:

Originally Posted by NZGTRA17

I have just finished reworking the hood on my car in a bid to cure this problem. I have cut out the 2 eyes on the side of the hood and put metal gauze in them. Looks smart, will assist airflow and also help with underbonnet cooling.

To help keep the hood down I have modified the 2 support stays near the back of the hood (the ones that currently have rubber pads that the hood sits on) by converting them to pin type latches while retaining the rubber pad. This way they trap the hood at the height yoiu adjust them to.

I am also ditching the screw in type fasteners and converting to Dzus fasteners as I do not have a lot of faith that the screw ins will stay in for long periods.

I would be careful about modifying the back edge of the hood on your car Brian as the back lip of the hood provides a lot of rigidity to the hood structure (particularly when you are removing, fitting and handling the hood). Someone has cut a section out of the center of mine and this has caused some cracking issues. When I put an engine cold air tray in the car I will also reinforce the areas that had previously been cut out.

Mine has the entire area under the hood bump and the rear section cut out to vent air.

NZGTRA17 · #9 10-20-2008, 02:45 PM

are you thinking about going with these:
http://www.hrpworld.com/index.cfm?tp... ction=product

I like the look of those fasteners but for the application I have in mind (front edge of boot lid x 4 and back edge of bonnet x 2) was going to use steel Dzus buttons (also listed on the same site). The Dzus buttons are cheap, light and I like them as I have worked with them a lot during my years working on aircraft.

As I have already had the boot fly up on me at speed (no damage other than greyer hair) I will change out those screw type fasteners as well. My theory on the boot is that this flys off due to aerodynamic pressure within the boot area which works the screw fasteners loose. I have put a bunch of pressure relief holes across the bottom edge of the back of the car to reduce any pressure in the boot space and am also changing the fasteners on the leading edge of the boot. Other thing I have done is to put aluminium support stays up to the back edge of the panel that the leading edge of the boot lid fastens to (as well as a few other places). This really helps to stiffen up the structure that the boot lid attaches to.

NZGTRA17 · #10 10-20-2008, 02:52 PM

"Mine has the entire area under the hood bump and the rear section cut out to vent air."

I am not convinced that this is a good thing structurally (as discussed earlier) as it leads to flexing of the bonnet and cracking. There is already a good sized opening for air to get out already so I am not sure that cutting this off will fix the bonnet bulging issue. I guess taking some pressure readings before and after modifying would tell us.

Other thing to consider if modifying this area to fit a cold air system is that all the air rushing out of this cavity has been heated by the engine. I wonder if this is this the best place to terminate a cold air system (as per a number of the GTS cars), unless you are able to pick up the cold air stream above the bonnet. I have been thinking on this but have not decided what system design I will use as yet.

Any ideas/designs for this one?

eric1h · #11 10-20-2008, 02:57 PM

Quote:

Originally Posted by NZGTRA17

"Mine has the entire area under the hood bump and the rear section cut out to vent air."

I am not convinced that this is a good thing structurally (as discussed earlier) as it leads to flexing of the bonnet and cracking. There is already a good sized opening for air to get out already so I am not sure that cutting this off will fix the bonnet bulging issue. I guess taking some pressure readings before and after modifying would tell us.

Other thing to consider if modifying this area to fit a cold air system is that all the air rushing out of this cavity has been heated by the engine. I wonder if this is this the best place to terminate a cold air system (as per a number of the GTS cars), unless you are able to pick up the cold air stream above the bonnet. I have been thinking on this but have not decided what system design I will use as yet.

Any ideas/designs for this one?

I personally don't think that that would be a great place to terminate a CAI setup, as you stated, most of the air coming out that area will be heated, and its a low pressure area anyway, maybe a better idea, and something I have been thinking about, would be to add a NACA duct type setup offset tothe right of the hood down towards the bumper to feed the intake system. Similiar to the system on the viper, only offset to the right.

I still have the old airbox from my Viper and it would make an easy project I think.

Cobra4B · #12 10-20-2008, 03:06 PM

FYI the cowl area is used to suck outside air back in to feed a carb'd setup. Not to vent hot air.

NZGTRA17 · #13 10-20-2008, 03:31 PM

Quote:

Originally Posted by Cobra4B

FYI the cowl area is used to suck outside air back in to feed a carb'd setup. Not to vent hot air.

Brian, traditionally you would be right about this. The plenum area on most cars is used to suck in cold air for heating/circulation in the car and is used as it is in a high pressure area created by the airflow hitting the base of the windscreen. I used this area on my last race car for drawing cold air, via a reverse scoop, but that car had a bonnet that sealed heated engine compartment air within the engine compartment.

In our cars cars though, I suspect that we have heated air coming out of this area due to the escape route provided by the gap between the bonnet and the windscreen. This seems the likely scenario given the bulging we see in the bonnets caused by underhood air pressure. If the pressure under the hood is higher than the pressure at the base of the windscreen, we will have heated air coming out of this area which will impact gains of drawing intake air from this area.

Again some aero & pressure testing required to answer. I am not far away from running the car so may test some of these aero conundrums prior to modifying.

Cobra4B · #14 10-20-2008, 04:17 PM

^ Very true... my only real experience with this is with my C5 Z06. Back when I used to track it I removed the weatherstripping at the rear of the hood (remember they open reverse) thinking it'd let the hot air flow out and create a proper path for the air comming in the front air screens in the bumper. To my surprise it resulted in hood buffeting much like the Panoz. The removal of the gasket created a lower pressure area and was drawing air in which iwas fighting w/ the air comming in the front of the nose. I put the gasket back in and solved that issue.

I guess we can let you do all the real testing for us

I won't be hitting the track until next February at the earliest. Time to do the motor and suspension setup.

NZGTRA17 · #15 10-20-2008, 05:12 PM

[I guess we can let you do all the real testing for us

I won't be hitting the track until next February at the earliest. Time to do the motor and suspension setup.[/quote]

Your right Brian that testing is the only way to confirm this one. One of the good things is that with our seasons being opposite times of the year, I can read up on the Stateside practical experiences and mod my car accordingly (which I have been doing) in the offseason and vice versa.

POST REPLY TO THIS THREAD