Air Intake tubes?
01-01-2005, 04:00 PM
#31
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John, The difference is dramatic. If I remove the hood the car does smoking burn outs even when the engine is hot.
Doug, I should probably qualify a few more items. The flaps have been removed. The AC is off during all of my testing since I normally run the car with the windows open. I have an external transmission cooler. The radiator is a Devek aluminum model. My thermostat is 75C. If I pop the hood open up to the safety catch my air box temperature drops down to 125F at idle, 70F ambient. Very interesting. The 928 design was not optimized for stop and go driving. An unfortunate reality is that much of LA driving is like this and ambient temperatures are greater than 70F much of the year.
The entire induction system on my car is being changed. The exhaust will be completed next week. All preparations focus on obtaining maximum power from a stroker motor. This is home work before the motor goes in.
Doug, I should probably qualify a few more items. The flaps have been removed. The AC is off during all of my testing since I normally run the car with the windows open. I have an external transmission cooler. The radiator is a Devek aluminum model. My thermostat is 75C. If I pop the hood open up to the safety catch my air box temperature drops down to 125F at idle, 70F ambient. Very interesting. The 928 design was not optimized for stop and go driving. An unfortunate reality is that much of LA driving is like this and ambient temperatures are greater than 70F much of the year.
The entire induction system on my car is being changed. The exhaust will be completed next week. All preparations focus on obtaining maximum power from a stroker motor. This is home work before the motor goes in.
01-01-2005, 05:53 PM
#32
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Hi,
thanks pappy.
We have been monitoring the operation of the flaps and when working correctly they do aid the flow of cool air to the intakes
In normal operation (for most owners) and using the OEM 83C-98C coolant thermostat they are obviously a real aid to engine warm up. At up to an ambient of about 33-35C they feed the coolest air directly to the intakes. This of course is more so in highway operation when the cooling fans may be inoperative for long periods
Regards
thanks pappy.
We have been monitoring the operation of the flaps and when working correctly they do aid the flow of cool air to the intakes
In normal operation (for most owners) and using the OEM 83C-98C coolant thermostat they are obviously a real aid to engine warm up. At up to an ambient of about 33-35C they feed the coolest air directly to the intakes. This of course is more so in highway operation when the cooling fans may be inoperative for long periods
Regards
Last edited by Doug Hillary; 01-01-2005 at 06:13 PM.
01-01-2005, 06:23 PM
#33
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Doug,
That is very interesting. I was going to run an experiment along similar lines. The top of the radiator would be insulated by a sheet of high temp plastic and a diverter would be added in the space where the flaps used to be.
That is very interesting. I was going to run an experiment along similar lines. The top of the radiator would be insulated by a sheet of high temp plastic and a diverter would be added in the space where the flaps used to be.
01-02-2005, 03:30 PM
#34
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New Data: If you insulate the top of the radiator and add a WRX style hood scoop just forward of the radiator the air box temperature drops by ~ 40F at idle. At 60 MPH the air box temp drops by ~ 10F. The car feels much different as in significantly quicker. Bog after sitting at a stop light is gone. Detonation is gone. I will post more pictures after the job is done correctly. The new configuration deals with water ingress by shunting it across the top of the radiator since the scoop is forward of the second hood brace. At high speeds I'm sure that some water will enter the air tubes, but that poses a question, why would you be driving at high speeds in the rain? The stock air tubes and air box are retained (in my case these have already been modified to reduce heat transfer). The new intake manifold will go on after I run temp profiles on the stock unit.
01-02-2005, 04:59 PM
#35
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OMG, Nooooooooooo 
Originally Posted by pappy92651
New Data: If you insulate the top of the radiator and add a WRX style hood scoop just forward of the radiator the air box temperature drops by ~ 40F at idle. At 60 MPH the air box temp drops by ~ 10F. The car feels much different as in significantly quicker. Bog after sitting at a stop light is gone. Detonation is gone. I will post more pictures after the job is done correctly. The new configuration deals with water ingress by shunting it across the top of the radiator since the scoop is forward of the second hood brace. At high speeds I'm sure that some water will enter the air tubes, but that poses a question, why would you be driving at high speeds in the rain? The stock air tubes and air box are retained (in my case these have already been modified to reduce heat transfer). The new intake manifold will go on after I run temp profiles on the stock unit.
01-02-2005, 05:13 PM
#36
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Yes, I know, adding WRX technology to a German car. It gets a bit less original every day. It all started with the GT cams. The new exhaust and engine will make it sound very non 928. This is just the beginning.
01-02-2005, 05:42 PM
#37
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A little lighting help...
thanks for sharing
01-02-2005, 08:39 PM
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Yes it is ugly. I only have 2 holes 4" in diameter so I will be exploring other options before I commit to permanent attachment. Louvers? Recessed vents? Carbon fiber hood? This scoop is doing what it should but others might also work. I abandoned the rear hood approach because others who tried this said that they had problems with wandering idle in their automatic cars. A 5 speed is not under load until you engage the clutch. If I pull the top half of the air box off my idle while in gear goes all to hell.
BTW, this is not the original hood, but it was in nice shape and matches my car. It is now a test mule.
BTW, this is not the original hood, but it was in nice shape and matches my car. It is now a test mule.
01-02-2005, 11:39 PM
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Wider & not as tall...
Originally Posted by pappy92651
Yes it is ugly. I only have 2 holes 4" in diameter so I will be exploring other options before I commit to permanent attachment. Louvers? Recessed vents? Carbon fiber hood? This scoop is doing what it should but others might also work. I abandoned the rear hood approach because others who tried this said that they had problems with wandering idle in their automatic cars. A 5 speed is not under load until you engage the clutch. If I pull the top half of the air box off my idle while in gear goes all to hell.
BTW, this is not the original hood, but it was in nice shape and matches my car. It is now a test mule.
BTW, this is not the original hood, but it was in nice shape and matches my car. It is now a test mule.
01-03-2005, 12:18 AM
#42
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Excellent experimentation Pappy. It sounds like your air flow augmentation reduces the idle temp and throttle delay, but since we all know Porsche engineers do not overlook anything and can never make any mistakes, I wonder why isn't there a "scoop" in front already?
Too much wind resistance for a 172mph run?
Looks?
The engineers didn't have lead feet at stop lights?
Too much wind resistance for a 172mph run?
Looks?
The engineers didn't have lead feet at stop lights?
01-03-2005, 01:59 AM
#44
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Originally Posted by pappy92651
The next step will be to determine what the temperature deltas are within the MAF, TB, and intake manifold. There is a vacuum port on the drivers side intake cover that will be used to place a thermocouple inside of a port.
http://www.omega.com/ppt/pptsc.asp?r...1DK&Nav=teml04
get one of these. Cheap and VERY handy. It will perform and display the delta T for you as you drive.
01-03-2005, 03:09 AM
#45
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Wait a min folks....." significant difference" ????? commmmmon!!!!!!!!
we are talking, even at its best case, less than 10 to 20 degrees. ( as was said) . Now, that is less than 2-3 %. on 240 rear wheel hp, thats around 5hp. you CANT feel 5hp!!!! Plus , all the tests are done in the engine bay at varying speeds. Folks, this data is meaningless, as the heatsoaked components have little to do with heat transfer at Wide Open Throttle. put it this way, when i come in to the pits after a hot lap in practice sesson, my intake manifolds are cold to the touch. when i come into the pits at the end of a race, it is much hotter, due to the fact that we have a cool down lap where the intake manifold is at vaccum for most of the 2-3 min of a cool down lap, and by the time we idle into the pits, the heat transfer is fast and obvious. Point is, just because the intake air is measured in the tubes has a value, it will be grossly different at WIDE OPEN THROTTLE. the only way to verify this is on the dyno. Your best bet is to insulate the tubes, use them in stock position, and vent the air box to the rear windshield area of the engine bay. hood scoops are fine for getting slightly cooler air, but the stock inlets are very well designed as some very good bell mouthed inlets. just because the air moves over a hot radiator, doesnt mean all that air is heated very much. the air moving over the radiator has a poor heat transfer. we are talking about 250cfm per tube (under WOT and 6000rpm) this means that at peak torque, CFM flow numbers are closer to 175cfm. thats the flow volume of a large 7" diameter computer fan! you think much of that air is heated, and going more than twice the speed due to the 3" intake tube, is going to transfer enough heat to change the air density??
easy experiment. get a electric stove set to a low simmer setting. put a fan near it and blow over the coils. see if there is a temp rise. Ive done the experiement, and there is very little heat transfered.
the key thing here is to relieve the restriction of the stock air box which has been verified at .5"Hg vaccum at WOT. with the box vented, the vacuum drops to under .2"Hg.
food for though. what do you think?
Mk
we are talking, even at its best case, less than 10 to 20 degrees. ( as was said) . Now, that is less than 2-3 %. on 240 rear wheel hp, thats around 5hp. you CANT feel 5hp!!!! Plus , all the tests are done in the engine bay at varying speeds. Folks, this data is meaningless, as the heatsoaked components have little to do with heat transfer at Wide Open Throttle. put it this way, when i come in to the pits after a hot lap in practice sesson, my intake manifolds are cold to the touch. when i come into the pits at the end of a race, it is much hotter, due to the fact that we have a cool down lap where the intake manifold is at vaccum for most of the 2-3 min of a cool down lap, and by the time we idle into the pits, the heat transfer is fast and obvious. Point is, just because the intake air is measured in the tubes has a value, it will be grossly different at WIDE OPEN THROTTLE. the only way to verify this is on the dyno. Your best bet is to insulate the tubes, use them in stock position, and vent the air box to the rear windshield area of the engine bay. hood scoops are fine for getting slightly cooler air, but the stock inlets are very well designed as some very good bell mouthed inlets. just because the air moves over a hot radiator, doesnt mean all that air is heated very much. the air moving over the radiator has a poor heat transfer. we are talking about 250cfm per tube (under WOT and 6000rpm) this means that at peak torque, CFM flow numbers are closer to 175cfm. thats the flow volume of a large 7" diameter computer fan! you think much of that air is heated, and going more than twice the speed due to the 3" intake tube, is going to transfer enough heat to change the air density??
easy experiment. get a electric stove set to a low simmer setting. put a fan near it and blow over the coils. see if there is a temp rise. Ive done the experiement, and there is very little heat transfered.
the key thing here is to relieve the restriction of the stock air box which has been verified at .5"Hg vaccum at WOT. with the box vented, the vacuum drops to under .2"Hg.
food for though. what do you think?
Mk