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Is anyone reproducing these bellypans?
Mine is ok but I am temted to frame it and hang it on the wall while driving with a repro one fitted (have to make one still)
Isn't the cover under the radiators/front of the engine designed in such a way that it creates a slight underpressure behind the radiator while driving. And if it is not fitted, hot air will stay in the enginebay?
no, that is strictly for drag reduction and dirt avoidance. actually, it creates a slightly higher pressure in the rear of the radiator. (where is the air going to go? it has to find its way out the vents and toward the rear of the car)
I did the pressure measurements on the stock 928S4 and thats what we found. however, a great match with the hood vent, if you needed more downforce and better flow through the radiator with the bottom covers
Originally Posted by jeff spahn
My thoughts exactly. That's why I put belly pans back on.
I too open hood when parking for the end of day.
Originally Posted by Hacker-Pschorr
On modern day Aston Martins with hood vents this is what they are for. If you look down the side of the engine are heat shields with ducts / chimney's leading up to the vents.
You can see the four "chimney's" on each side of the engine flanking the throttle bodies in this photo:
But again....what is happening with stock 928's after all these years that leads anyone to think we need such heat dispersion? Todd did a lot of data modeling with his twin turbo design and marveled at the way a 928 is designed to direct air leaving the radiator over the manifolds and down under the car (.....another important reason to have belly bans installed). Trying to "fix" this could actually create a new problem.
Yes, the current design does take some of the heat of the manifolds and route it to the rear of the car. a hood vent would take some of that air, (not all) and route it to the low pressure area of the hood.
the aston martin vents are not the same as the vents we are talking about here. (and those aston hood vents look to be on the older version too. Pre -2002) that is a ambient pressure vent, for the chimney outlets. the any pressure that builds from the air inlet via the radiator, vents out here and to the rear of the car.
on the 928 with the hood vents as discussed. we are venting to a low pressure zone that creates more pressure differential, which provides more flow through the radiator and increases downforce in the front of the car for racing.
mainly more flow for street cars and a way to keep engine temps down a little.
Originally Posted by antlee928
I'm thinking that, if indeed, we need to add more cooling to under-bonnet temps, what would be the most effective yet aesthetically pleasing way to do this. Will bonnet vents such as that proposed or any other necessarily reduce under bonnet temps. I am also wondering is the under bonnet temp issues are when the car, after a run, is then parked. I normally open the bonnet after parking my car in the driveway or in the garage to allow for faster cooling and to reduce any "baking" effects. Good question though to explore. How would Porsche address this problem today??
the engine components can handle the heat, but any reduction of heat does reduce the heat effect of their aging. by how much is unknown.
on a street car i would be more worried about water entering the car, where none normally is ever seen.
Last edited by mark kibort; 02-12-2016 at 02:51 PM.
When college my house mate had a Cutlass F-85 with cowl induction. He had to put sponges in the hood vents any time it was wet or raining out to keep the water from choking out and killing the car. And they were on either side just forward of the middle of the hood.
When college my house mate had a Cutlass F-85 with cowl induction. He had to put sponges in the hood vents any time it was wet or raining out to keep the water from choking out and killing the car. And they were on either side just forward of the middle of the hood.
cowl intake is where the high pressure is found at the base of the windshield. has to be well designed to not have the issues you saw.
On modern day Aston Martins with hood vents this is what they are for. If you look down the side of the engine are heat shields with ducts / chimney's leading up to the vents.
You can see the four "chimney's" on each side of the engine flanking the throttle bodies in this photo:
.
Here is what the "modern" astons have as far as hood vents. no chimnies
your pic was probably a 2001 aston
Here is the race car and the street car. notice how the venting works for downforce and better radiator cooling in the race car. the vents are just vents on the aston street car.
Here are also an example of both hood vents for heat and hood vent for flow optimization using the lower pressure zone i speak of . thats the last picture below on the aston DBS.
I have often wondered about the merit of the belly pans as my car, when purchased, came without them. So not trying to second guess the Porsche analytics of this aspect of the 928 and seems like I should be sourcing replacement pans to provide the additional assistive airflow for cooling.
I am guessing originals are probably NLA and even if they were would be quiet expensive. Who supplies aftermarket pans that deliver similar airflow results??
i had used this carbon fiber duct for the removal of that extra heat when we were stationed in Albuquerque. the vent was placed right behind the radiator, worked like a champ. that being said i have a stock hood now. the rivets made it look a little riceish to me
I have often wondered about the merit of the belly pans as my car, when purchased, came without them. So not trying to second guess the Porsche analytics of this aspect of the 928 and seems like I should be sourcing replacement pans to provide the additional assistive airflow for cooling.
I am guessing originals are probably NLA and even if they were would be quiet expensive. Who supplies aftermarket pans that deliver similar airflow results??
Cheers
We did a lot of pressure measuring around the nose, inlets, radiator,(front and back) and in the engine bay and under and over the car. the main thing the underbelly pans due is going to direct flow over the headers and out the back. (better colling of the ex manifolds) there is no change in pressure drop with and without the belly pans, so dont get excited about additional flow. its really about where the flow goes.
If you do a hood vent, you get additional pressure differential with the hood outlet being in a lower pressure zone. (basic flow 101). unless you change the pressure differential, or remove pressure drops, flow volume will not change
Originally Posted by Ducman82
i had used this carbon fiber duct for the removal of that extra heat when we were stationed in Albuquerque. the vent was placed right behind the radiator, worked like a champ. that being said i have a stock hood now. the rivets made it look a little riceish to me
RL]
that wasnt that bad of a duct.. yes the rivets are not that great, but if you did body work around it,...... maybe??
anyway, ,there is no real removal of extra heat via flow, but certainly venting out of the engine is a way for the engine heat to escape
Originally Posted by Mongo
There has to be a better way to blend these ducts into the factory hood. Something a bit more natural...
I think the new gt3 cup car vents look pretty nice. im sure there is a way to get that kind of look if someone had the time and body shop tools.
HI all made my own Strosek style bonnet. With NACA ducts at the front just before the air tubes and a bonnet vent/bulge above the inlet plenum with hole cut in bonnet negative resistance there been told.Lets hot air out when stood and car runs cooler.
02-12-2016, 12:30 PM
