Hood Mods
12-30-2010, 03:08 PM
#61
By 123Quattro
I think they tune them for certain speeds, Toyota F1 which was the biggest team in F1 had a very advanced dyno, they said the got an extra 1% engine power from the intake. But given drag at high speeds is such a concern you need to factor that in. Maybe they could have gotten more power but the drag would be too high.
Greg
There really is no such thing as ram air. Engines ingest massive amounts of air. For a scoop to generate positive pressure into the intake, it would have to have several square feet of surface area.
I saw an internal document once referencing a Ram Air hood. It was only for perceived customer benefit.
I saw an internal document once referencing a Ram Air hood. It was only for perceived customer benefit.
Greg
12-30-2010, 03:36 PM
#62
Almost Deleted
Rennlist Member
Rennlist Member
I have to agree with Greg on this one. In what little studying I've done ["study" used loosely... grad school], the benefits are two fold: cleaner air & reduce the effects of under-hood heating.
In reducing the under-hood air flow, you reduce the drag & turbulence produced within a long down tube [see Boundary Layer Theory by Schlichting]. You can reduce the time at which the air runs in a heated environment under the hood... thus slightly improving the volumetric efficiency per intake unit.
That being said... simple physics tells us that this really only delivers noticeable benefits in optimal conditions [race setups]. It can also be done very very poorly, thus eliminating any positive effects.
In reducing the under-hood air flow, you reduce the drag & turbulence produced within a long down tube [see Boundary Layer Theory by Schlichting]. You can reduce the time at which the air runs in a heated environment under the hood... thus slightly improving the volumetric efficiency per intake unit.
That being said... simple physics tells us that this really only delivers noticeable benefits in optimal conditions [race setups]. It can also be done very very poorly, thus eliminating any positive effects.
By 123Quattro
I think they tune them for certain speeds, Toyota F1 which was the biggest team in F1 had a very advanced dyno, they said the got an extra 1% engine power from the intake. But given drag at high speeds is such a concern you need to factor that in. Maybe they could have gotten more power but the drag would be too high.
Greg
I think they tune them for certain speeds, Toyota F1 which was the biggest team in F1 had a very advanced dyno, they said the got an extra 1% engine power from the intake. But given drag at high speeds is such a concern you need to factor that in. Maybe they could have gotten more power but the drag would be too high.
Greg
01-01-2011, 02:29 AM
#63
Rennlist Member
you better go back to the "internet" to understand this a little better. 
pressure is what you need to look at. if you have a ram scoop in a low pressure zone, its ram pressure might be larger with a scoop, but its going to be FAR below "normal" pressure, if "normal" is ambient. in fact, you might actually see a reverse flow out of the intakek even though it is facing the "kinetic" flow of air. why? because air moves to differential pressure. higher pressure underhood vs "ram pressure" at vent, and the air will exit the inlet. dont confuse the direction of the ram duct, with the ram pressure.
pressure is what you need to look at. if you have a ram scoop in a low pressure zone, its ram pressure might be larger with a scoop, but its going to be FAR below "normal" pressure, if "normal" is ambient. in fact, you might actually see a reverse flow out of the intakek even though it is facing the "kinetic" flow of air.
why? because air moves to differential pressure. higher pressure underhood vs "ram pressure" at vent, and the air will exit the inlet. dont confuse the direction of the ram duct, with the ram pressure. Of course the Ferrari scoop generates a high-pressure "ram" air intake.
That part of the hood may be a low pressure zone absent the massive scoop when measured normal to the flow, but immediately when you put the directed scoop facing the flow there you get a above average pressure at speed. The direction in which the opening points is so important for the kinetic pressure. That's why the rearward-pointing openings see below-average pressure and forward-pointing openings see above-average pressure.
Every internet engineer should know this after years of education by google.
That part of the hood may be a low pressure zone absent the massive scoop when measured normal to the flow, but immediately when you put the directed scoop facing the flow there you get a above average pressure at speed. The direction in which the opening points is so important for the kinetic pressure. That's why the rearward-pointing openings see below-average pressure and forward-pointing openings see above-average pressure.
Every internet engineer should know this after years of education by google.
01-01-2011, 02:35 AM
#64
Rennlist Member
This is not exactly true. there is ram effct, and it has little or nothing to do with the inlet size, as long as the inlet can support the pressure gain compared to loses through it.
In other words, at 80mph, a 75% effecient ram scoop, (out of boundary layer, like up high, or in the nose of the car) will generate about .08PSI and at 160mph that would go up to about .36psi. (very very small gains with very efficient scoops). base of windshield inlets are efficiet and have some of the highest pressure available for the intake, very close to the "nose" pressure.
that why I take air from both.
In other words, at 80mph, a 75% effecient ram scoop, (out of boundary layer, like up high, or in the nose of the car) will generate about .08PSI and at 160mph that would go up to about .36psi. (very very small gains with very efficient scoops). base of windshield inlets are efficiet and have some of the highest pressure available for the intake, very close to the "nose" pressure.
that why I take air from both.
There really is no such thing as ram air. Engines ingest massive amounts of air. For a scoop to generate positive pressure into the intake, it would have to have several square feet of surface area.
I saw an internal document once referencing a Ram Air hood. It was only for perceived customer benefit.
I saw an internal document once referencing a Ram Air hood. It was only for perceived customer benefit.
08-31-2011, 09:08 AM
#67
Craic Head
Lifetime Rennlist
Member
Lifetime Rennlist
Member
01-16-2012, 12:10 AM
#69
Drifting
01-16-2012, 12:21 AM
#70
Rennlist Member
just do what i did, but make it more refined! its the way all the top brands are going wtih thier mods for obvious reasons. things that are functional, seem to look best too. take lessons from porsche, ferarri and aston Marton. dont bolt on some ricer vent. mine looks good because it doesnt change the lines or form of the car. but, it would be nicer if my vent had the structure of the aston Marton vents, which are little more than fancy screens.
01-17-2012, 01:19 PM
#72
Advanced
Join Date: Apr 2009
Location: Southern Maryland, sometimes...
Posts: 54
Likes: 0
Received 0 Likes
on
0 Posts
Could a circular hood bulge possibly create enough extra room for the ITB's? (sorry, i have no idea exactly how much space is required)
I imagine that something like the rounded bulge on an m3's hood would well match with the non-linear curves of the 928... especially with those beautifully flared hips.
I suppose the m3-ish bulge may be too small, but if a larger one could accomodate the ITB's while still matching the overall form of the vehicle, this might be ideal.
Sterling, to my eye your car has the best shape of any of the widebodies out there, by far! Very tastefully done and totally keeping in line with the original form of the car, but just improving on it. But to be honest, the previous hood mod (or at least what i saw in the photos) hurt my eyes... I kept getting flashes of trans-am in there... Of course the eyes that matter most are your own.
Good luck finding a solution.
I imagine that something like the rounded bulge on an m3's hood would well match with the non-linear curves of the 928... especially with those beautifully flared hips.
I suppose the m3-ish bulge may be too small, but if a larger one could accomodate the ITB's while still matching the overall form of the vehicle, this might be ideal.
Sterling, to my eye your car has the best shape of any of the widebodies out there, by far! Very tastefully done and totally keeping in line with the original form of the car, but just improving on it. But to be honest, the previous hood mod (or at least what i saw in the photos) hurt my eyes... I kept getting flashes of trans-am in there... Of course the eyes that matter most are your own.
Good luck finding a solution.
