Am I just going to ruin my airbox?
12-20-2007, 08:50 PM
#16
Rennlist Member
Your lower air filter housing has a great flow design. On my 84 I removed the trumpet and installed larger tubes. One purpose for the tube neck down was to create a venturi effect for better ventilation of timing belt area.
12-20-2007, 09:04 PM
#17
Rennlist Member
12-21-2007, 12:23 AM
#18
Three Wheelin'
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Your lower air filter housing has a great flow design. On my 84 I removed the trumpet and installed larger tubes. One purpose for the tube neck down was to create a venturi effect for better ventilation of timing belt area.
Your lower air filter housing has a great flow design. On my 84 I removed the trumpet and installed larger tubes. One purpose for the tube neck down was to create a venturi effect for better ventilation of timing belt area.
12-21-2007, 12:40 AM
#19
Rennlist Member
I had no driveability problems cold or warm. Dont know if I really gained anything. It appeared like there would be smoother airflow without it. A velocity stack raises the air filter several inches above a smooth unobstructed airway.
12-21-2007, 12:46 AM
#20
Three Wheelin'
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as I said before, there is some data suggesting that changing out the neck down tubes for straight tubes does gain hp---I can't remember how much or how little.
venturi affect, maybe. I remember it as being a noise reducer.
---Russ
venturi affect, maybe. I remember it as being a noise reducer.
---Russ
12-21-2007, 01:03 AM
#21
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as far as naca ducts on the hood or the low pressure areas at the bottom of the windshield, there are ways to improve the airflow to the intakes, but every one has their preferences.......
any hole in the hood must be matched up with where the air pressures are.
Bad example:
the hood scoop on the Subaru WRX---totally useless. not a pressure area, scoop not high enough off of the hood to do any good.
Good example:
any of the current hood scoops used on a Pro Stock drag car. (but you wouldn't want a 10 inch tall piece of "that" sitting in the middle of your 928 hood, would you?)
Good example:
Nascar cup cars where the air intake is at the bottom of the windshield--although there is no "scoop". (difficult to manage with 928 due to firewall/airbox location, but could be done on a "dry racing" track car---no windshield wipers frees up the area needed for the air intake.)
Good example:
route your current intake tube/scoops further to the grill opening, where they can ingest fresh air. This was used on early Ford Thunderbolts, some other early '60s drag cars.....be careful of bug/rock intake.
Fair example:
Viper and Z-06 Vette using naca duct varients. Opening is very far forward to the front to get the pressurized air from over the bumper......again, bugs, rocks, etc......
---Russ
any hole in the hood must be matched up with where the air pressures are.
Bad example:
the hood scoop on the Subaru WRX---totally useless. not a pressure area, scoop not high enough off of the hood to do any good.
Good example:
any of the current hood scoops used on a Pro Stock drag car. (but you wouldn't want a 10 inch tall piece of "that" sitting in the middle of your 928 hood, would you?)
Good example:
Nascar cup cars where the air intake is at the bottom of the windshield--although there is no "scoop". (difficult to manage with 928 due to firewall/airbox location, but could be done on a "dry racing" track car---no windshield wipers frees up the area needed for the air intake.)
Good example:
route your current intake tube/scoops further to the grill opening, where they can ingest fresh air. This was used on early Ford Thunderbolts, some other early '60s drag cars.....be careful of bug/rock intake.
Fair example:
Viper and Z-06 Vette using naca duct varients. Opening is very far forward to the front to get the pressurized air from over the bumper......again, bugs, rocks, etc......
---Russ
12-21-2007, 01:10 AM
#22
Rennlist Member
A quick refresher.
the stock air box, generally leaks, to the tune of .25" Hg vaccum. when sealed properly, you can get upwards of .5"Hg vacuum. (.25" with it in stock form) I also did ram pressure tests at all points of the front intake. there is gains to be made, as small as they are, to vent the air box to the HiVac area. this area gets greater pressure than the front tubes.
the venturi tubes are for noise, as the neck downs restrict flow, IF they were sealed. since they are not, some of the air comes from the leaky air box and the attachment points of the tubes.
venting the air box can help with restriction, if you seal up the air box. this means the air coming in is slightly hotter than the air that is drawn in from the tubes. you have to calculate whether the trade off in temperature is greater as far as density, than the vacuum it relieves. most likely, its a wash, unless you vent to the base of the windshield, then you get the best of both worlds!
mk
the stock air box, generally leaks, to the tune of .25" Hg vaccum. when sealed properly, you can get upwards of .5"Hg vacuum. (.25" with it in stock form) I also did ram pressure tests at all points of the front intake. there is gains to be made, as small as they are, to vent the air box to the HiVac area. this area gets greater pressure than the front tubes.
the venturi tubes are for noise, as the neck downs restrict flow, IF they were sealed. since they are not, some of the air comes from the leaky air box and the attachment points of the tubes.
venting the air box can help with restriction, if you seal up the air box. this means the air coming in is slightly hotter than the air that is drawn in from the tubes. you have to calculate whether the trade off in temperature is greater as far as density, than the vacuum it relieves. most likely, its a wash, unless you vent to the base of the windshield, then you get the best of both worlds!
mk
12-21-2007, 01:17 AM
#23
Rennlist Member
Nothing in the hood area is good for air intake pressure. it would actually become a vent, (opposite) as i use it for downforce!
the pressure sensor i use is very sensitive. the values ive measured equate to the diagram below. the nose is the best pressure area, base of windshield is near the same.
MK
the pressure sensor i use is very sensitive. the values ive measured equate to the diagram below. the nose is the best pressure area, base of windshield is near the same.
MK
as far as naca ducts on the hood or the low pressure areas at the bottom of the windshield, there are ways to improve the airflow to the intakes, but every one has their preferences.......
any hole in the hood must be matched up with where the air pressures are.
Bad example:
the hood scoop on the Subaru WRX---totally useless. not a pressure area, scoop not high enough off of the hood to do any good.
Good example:
any of the current hood scoops used on a Pro Stock drag car. (but you wouldn't want a 10 inch tall piece of "that" sitting in the middle of your 928 hood, would you?)
Good example:
Nascar cup cars where the air intake is at the bottom of the windshield--although there is no "scoop". (difficult to manage with 928 due to firewall/airbox location, but could be done on a "dry racing" track car---no windshield wipers frees up the area needed for the air intake.)
Good example:
route your current intake tube/scoops further to the grill opening, where they can ingest fresh air. This was used on early Ford Thunderbolts, some other early '60s drag cars.....be careful of bug/rock intake.
Fair example:
Viper and Z-06 Vette using naca duct varients. Opening is very far forward to the front to get the pressurized air from over the bumper......again, bugs, rocks, etc......
---Russ
any hole in the hood must be matched up with where the air pressures are.
Bad example:
the hood scoop on the Subaru WRX---totally useless. not a pressure area, scoop not high enough off of the hood to do any good.
Good example:
any of the current hood scoops used on a Pro Stock drag car. (but you wouldn't want a 10 inch tall piece of "that" sitting in the middle of your 928 hood, would you?)
Good example:
Nascar cup cars where the air intake is at the bottom of the windshield--although there is no "scoop". (difficult to manage with 928 due to firewall/airbox location, but could be done on a "dry racing" track car---no windshield wipers frees up the area needed for the air intake.)
Good example:
route your current intake tube/scoops further to the grill opening, where they can ingest fresh air. This was used on early Ford Thunderbolts, some other early '60s drag cars.....be careful of bug/rock intake.
Fair example:
Viper and Z-06 Vette using naca duct varients. Opening is very far forward to the front to get the pressurized air from over the bumper......again, bugs, rocks, etc......
---Russ
