Nicholbry

For those purists, let me apologize in advance for even considering actually cutting into my beautifully factory-designed '90 S4 . At this point, I'm just thinking.

I have thought for some time now that the 928 might look nice with a couple hood vent openings closer to the windshield than the nose. For those of you who have ventured into Jacquemond's website you might understand. This is a recessed design.

Consider, also the flat Aston Martin Vanquish hood vents.

Here are my questions: Someone suggested that the openings might negatively affect the engine's air intake by de-compressing under-hood air-flow; thus, inadvertently altering the dynamics of the existing air induction. Is that something that would likely result? Which brings up another consideration: Should I, therefore, relocate the 2 existing air induction hoses to these openings for better air volume? Given the recessed design (jacquemond) or flat opening design (Vanquish) of these proposed hood vents, my concern is that it might not render adequate air volume to maintain the current volume of air flow or better? Does the existing system on my car rely on the outward force of air inward, or does the motor vacuum the air in?

Some of you might suggest the Callaway-style induction that some 928 owners have used in the past which are placed forward, right where the intake hoses gather the air on the existing arrangement. This design isn't appealing to my taste, however, and I am looking for something more contemporary.

Thanks in advance for your consideration!

Nicholas
'90 S4, Auto, Stone Grey Met./Linen

ibkevin

This has been covered extensively, try the search function.

hacker-pschorr

The Aston Martin has a ducting system to pull heat off the headers & out the vents on the hood.

If this is 100% for looks I say go ahead, hoods are cheap. If you are trying to gain some performance with the vents, I doubt you will find any.

944 guy

We're thinking about this ourselves for performance reasons:
Our engine management system gives us readouts on all engine parameters: manifold pressure, engine temp, water temp, intake temp, etc.
Especially the last one is reason for concern: even on the highway intake temperature is a whopping 15 degrees C (27 degrees F) higher than ambient. If you're in traffic it's over 20 degrees C higher. We also noticed the AC has a significant effect on intake temp (it raises it by 4, maybe 5 degrees C). Clearly the intake design could be a lot better. We figure the air coming in below the bumper picks up a lot of radiation from the radiator and AC condenser (perhaps even air that has passed through the upper portion of the condenser, making it HOT).
Second: the throttlebody and our portion of pipe between the filterhousing and the throttle body (we don't have a barndoor in the S) may also transfer some heat. Under hood temps can also be greatly improved.
So far we've only been brainstorming, but the most viable concept is making two air intakes on top of the hood, just ahead of either airfilter intake opening.
If we succeed in dropping the intake temp to ambient it should add almost 5% more power (colder, denser air). Second, this will make it something of a ram air intake, adding even more oompf.
But before we do anything, we'll need a few thermocouples to probe the airtemp at various locations, as our engine management system gives us the temp from where the barndoor used to be (and if that's already 15C above ambient... OUCH).

Fabio421

Search for "fat bully's thread" and see what Pierre did to help this problem. He installed a CF "plate" at the top of the radiator to split the air coming into the engine bay. The air below the plate goes through the radiator and the air above gets sucked into the intake.

As for air vents in the hood. Mark Kibort says that his hood vent on his racer allows more downforce on the front of the car. PM him for more details.

944 guy

Fabio, after posting that msg I started searching as well. There's quite a bit of info on the site here. Guess we'll be studying everybody's results before chopping hoods...
Our main interest is lower enginebay temps and lower intake temps, if Mark's info concerns that as well, I'd like to hear about it.

SharkSkin

Mark K. cut his hood vent to increase downforce IIRC. There may be some added benefits re: cooling but 928's already suck in pretty cold air, and I don't think any benefits in this area were expected/realized. Since the nose sees the highest pressure at speed, and intake air is drawn directly from the nose(stock), changes to under-hood pressure should have negligible effect so long as your intake tubes/airbox are tight. I'm assuming you would only cut the hood aft of the radiator -- cutting in front of the rad might create a vacuum in the intake area which would affect power, since most of the hood is a low-pressure area:

Nicholbry

Thanks much for the comments regarding this. After posting my question I did find much information about this hood vent scenario here on Rennlist. You guys will have to forgive me as I am new (first week) and I am still trying to find my way around. Glad to be a part of the 928 (Winning) Team!
Nicholas

mark kibort

i put the pressure sensors all over the front of the car, even up to the base of the windshield. every thing the pressure graph says, is true. put some vents near the front of the hood, and air is going to be coming out of it! (so this would not be good for ram effect, however the nose is in its stock config)

I have not seen any lower operational temps. i figure instead of the air venting under the car, it is now venting though the hood vent. between the splitter and the hood vent, i have a lot more downforce in the front to the point where the handling is much better and a push created by the new rear wing is now balanced.

if you want ram effects, use the stock intake around the radiator, and / or vent the intake to the rear of the firewall venting to the base of the windshield

MK