928 RS Concept Sketch
08-27-2014 | 03:15 AM
#901
Thread Starter
Drifting
Joined: Dec 2012
Posts: 2,453
Likes: 6
From: Pennsyltucky
I was thinking since i've got a test hood to cut up why not.
I didn't want to change the intake runners. I simply wanted to experiment with a cold air intake design that utilized the high pressure area (loc. 10) directly above the air box on our hoods.
The stock air cleaner bottom and top half including filter will be used. The experimentation will only be in a different suction tube design that was short and basically went straight up thru the hood.
2006-on (IIRC) model 911 GT3s have an air collector below their rear spoilers that generate 10-15 HP at speeds above 65mph simply be taking advantage of the pressure build below that spoiler. I read this in Excellence i think.
So i was curious to try the same principle.
I didn't want to change the intake runners. I simply wanted to experiment with a cold air intake design that utilized the high pressure area (loc. 10) directly above the air box on our hoods.
The stock air cleaner bottom and top half including filter will be used. The experimentation will only be in a different suction tube design that was short and basically went straight up thru the hood.
2006-on (IIRC) model 911 GT3s have an air collector below their rear spoilers that generate 10-15 HP at speeds above 65mph simply be taking advantage of the pressure build below that spoiler. I read this in Excellence i think.
So i was curious to try the same principle.
08-27-2014 | 06:24 AM
#902
Nordschleife Master
Joined: Dec 2004
Posts: 6,164
Likes: 5
From: Guelph, Ontario, Canada
Heh, man yur kinda putting me on the spot a little bit here! I mean, on the one hand we've got Porsche with decades of design and performance engineering, and actual wind tunnels, and baro-graphs, and then me out here in the real world with no data at all to back stuff up.
Having said that, you and me, and many others have seen the empirical evidence that the intake geometry is pretty convoluted, if I may use some four dollar words. Mooney aircraft designed their intake on the small planes so that at cruise they get back about .7" of manifold pressure due to ram air effect. Pretty smart there.
There's a lot of physics involved with the airflow in conduit or chambered systems. You have laminar flow, boundary layer flow, eddie currents, stalled air, pockets, etc. To put it mildly, it's darn complicated. If you've ever seen the intake of an S4 after 150k miles, the air flow patterns are weird.
I guess I will say without being too committal that there's improvements to be made. We had some folks locally make some spacer plates for the sides of the S4 plenum, and the difference in flow rates was negligible as I recall.
There are two areas to improve, the first is temp input. Using PV=NRT as our base, we can postulate that Manifold Pressure is fixed(ambient), and the Volume of the chamber is fixed(non-S4), so that any reduction in T will require an increase in N(number of molecules) to balance the equation. This is of course, all in front of the throttle plate. So, any reduction in Temp is a good thing, and that's why the ricers have cold air intakes. The 928 could really benefit here because all of the air going into the engine sits up top where it heat soaks before reaching the throttle. one thing that helps is to remove that insulator blanket on the hood, and leave it bare so that heat will exit the hood radiantly. Since we're not dealing with steady-state air, but air flowing air, we discuss that next.
In a perfect system, we would have a smooth, continuous column of air reaching the throttle plate all in laminar, continuous rate speed delivery. Of course, we are far from a perfect system. We have a ton of bends, and different sizes plenums and ports, and also differing surface finishes along the way. The old hot rodders of the 60s used a simple velocity stack to straighten the air coming into the carb, and that worked quite well. Since were not tootling along in the air at 150 knots, we are on the ground with all the dust and grit, we gotta have a filter, and since it's a Porsche with a V8, we gotta have some bends.
Without going into a flow analysis, there seems to be some improvements that can be made before the throttle plate. I recall another 928 DIY guy that made up a huge plenum on top with individual throttle bodies leading directly to the intake valve. That seemed to flow really well, but I can't recall who it was. I guess I could search for it, but I'm not that invested.
All I can say is to maybe drill and tap a sensor port a few cm up from the head, and put a gauge on it, then start testing. Try to reduce the number of bends involved, and the increase the radius where possible. Try to keep it as cool as possible, and where you can't keep it cool, insulate the chamber. I think I remember seeing some of the air duct intakes that have an insulator on them, and that can help as long as the air inside is always moving. I won't get into intake reversion due to valve operation, but that's another area where things get a little cranky. This kind of stuff is so hard to measure without a magnehelic gauge, some flow gauges, temp gauges, and a dyno. It's basically modify and test, which gets costly. I don't think this helps, but maybe gives you some ideas. The old carbed Porsche had downdraft IDFs with the velocity stacks and they ran really, really well for what you got. Of course, back then it was state of the art. Good luck if you try something, maybe search for the guy that did the intake plenum, and copy that. As I recall it worked out pretty keenly.
Having said that, you and me, and many others have seen the empirical evidence that the intake geometry is pretty convoluted, if I may use some four dollar words. Mooney aircraft designed their intake on the small planes so that at cruise they get back about .7" of manifold pressure due to ram air effect. Pretty smart there.
There's a lot of physics involved with the airflow in conduit or chambered systems. You have laminar flow, boundary layer flow, eddie currents, stalled air, pockets, etc. To put it mildly, it's darn complicated. If you've ever seen the intake of an S4 after 150k miles, the air flow patterns are weird.
I guess I will say without being too committal that there's improvements to be made. We had some folks locally make some spacer plates for the sides of the S4 plenum, and the difference in flow rates was negligible as I recall.
There are two areas to improve, the first is temp input. Using PV=NRT as our base, we can postulate that Manifold Pressure is fixed(ambient), and the Volume of the chamber is fixed(non-S4), so that any reduction in T will require an increase in N(number of molecules) to balance the equation. This is of course, all in front of the throttle plate. So, any reduction in Temp is a good thing, and that's why the ricers have cold air intakes. The 928 could really benefit here because all of the air going into the engine sits up top where it heat soaks before reaching the throttle. one thing that helps is to remove that insulator blanket on the hood, and leave it bare so that heat will exit the hood radiantly. Since we're not dealing with steady-state air, but air flowing air, we discuss that next.
In a perfect system, we would have a smooth, continuous column of air reaching the throttle plate all in laminar, continuous rate speed delivery. Of course, we are far from a perfect system. We have a ton of bends, and different sizes plenums and ports, and also differing surface finishes along the way. The old hot rodders of the 60s used a simple velocity stack to straighten the air coming into the carb, and that worked quite well. Since were not tootling along in the air at 150 knots, we are on the ground with all the dust and grit, we gotta have a filter, and since it's a Porsche with a V8, we gotta have some bends.
Without going into a flow analysis, there seems to be some improvements that can be made before the throttle plate. I recall another 928 DIY guy that made up a huge plenum on top with individual throttle bodies leading directly to the intake valve. That seemed to flow really well, but I can't recall who it was. I guess I could search for it, but I'm not that invested.
All I can say is to maybe drill and tap a sensor port a few cm up from the head, and put a gauge on it, then start testing. Try to reduce the number of bends involved, and the increase the radius where possible. Try to keep it as cool as possible, and where you can't keep it cool, insulate the chamber. I think I remember seeing some of the air duct intakes that have an insulator on them, and that can help as long as the air inside is always moving. I won't get into intake reversion due to valve operation, but that's another area where things get a little cranky. This kind of stuff is so hard to measure without a magnehelic gauge, some flow gauges, temp gauges, and a dyno. It's basically modify and test, which gets costly. I don't think this helps, but maybe gives you some ideas. The old carbed Porsche had downdraft IDFs with the velocity stacks and they ran really, really well for what you got. Of course, back then it was state of the art. Good luck if you try something, maybe search for the guy that did the intake plenum, and copy that. As I recall it worked out pretty keenly.
I was thinking since i've got a test hood to cut up why not.
I didn't want to change the intake runners. I simply wanted to experiment with a cold air intake design that utilized the high pressure area (loc. 10) directly above the air box on our hoods.
The stock air cleaner bottom and top half including filter will be used. The experimentation will only be in a different suction tube design that was short and basically went straight up thru the hood.
2006-on (IIRC) model 911 GT3s have an air collector below their rear spoilers that generate 10-15 HP at speeds above 65mph simply be taking advantage of the pressure build below that spoiler. I read this in Excellence i think.
So i was curious to try the same principle.
I didn't want to change the intake runners. I simply wanted to experiment with a cold air intake design that utilized the high pressure area (loc. 10) directly above the air box on our hoods.
The stock air cleaner bottom and top half including filter will be used. The experimentation will only be in a different suction tube design that was short and basically went straight up thru the hood.
2006-on (IIRC) model 911 GT3s have an air collector below their rear spoilers that generate 10-15 HP at speeds above 65mph simply be taking advantage of the pressure build below that spoiler. I read this in Excellence i think.
So i was curious to try the same principle.
When you use the high pressure location to draw in air be prepared to deal with all the rain that will drop in there too. While it seems logical to draw intake air from this location, why did Porsche NOT do it? Noise is one reason, but there is much more to this than you think. In fact it is one of the most significant things after head design.
08-27-2014 | 12:19 PM
#903
Thread Starter
Drifting
Joined: Dec 2012
Posts: 2,453
Likes: 6
From: Pennsyltucky
So you want to be smarter than the Porsche engineers, huh? You have to understand that a significant amount of engineering energy was used in designing that intake system. You are NOT going to improve it. Do a temperature rise test at the intake point and at the filter. The amount of heat absorbed through this system is negligible. This has been discussed here before quite a bit. Save your energy.
When you use the high pressure location to draw in air be prepared to deal with all the rain that will drop in there too. While it seems logical to draw intake air from this location, why did Porsche NOT do it? Noise is one reason, but there is much more to this than you think. In fact it is one of the most significant things after head design.
When you use the high pressure location to draw in air be prepared to deal with all the rain that will drop in there too. While it seems logical to draw intake air from this location, why did Porsche NOT do it? Noise is one reason, but there is much more to this than you think. In fact it is one of the most significant things after head design.
IIRC you poo-poo'd me porting,polishing and adjusting the 'barn door' spring in my AFM, you even chased me over to the other forum to do so..
And there was and is a VERY noticeable gain there, it cost me nothing but an enjoyable afternoon milling and polishing.
Why didn't Porsche do this? you know the answer.
My US 928S wasn't engineered for all-out performance. It weighed over 3300 lbs when i brought it home.
So gaugeman, let me worry about my time being wasted, I'll let you worry about your's.
My 'RS' is not ever going to be my daily driver but rather a good weather/weekend/DE car. Not commuting with it in the rain.
I'm going to experiment with my trashed hood, i can't say it will offer a huge gain but i have nothing to lose.
08-27-2014 | 12:40 PM
#904
Instructor
Joined: Feb 2005
Posts: 209
Likes: 0
Manufacturers have to consider a lot of competing issues with air inlet designs. There's always power to be had for the enthusiast here if you don’t mind a little inlet noise, aren't concerned about low water crossings or following behind 18 wheelers in the snow etc.
08-27-2014 | 01:51 PM
#906
Shameful Thread Killer
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From: Rep of Texas, N NM, Rockies, SoCal
So you want to be smarter than the Porsche engineers, huh? You have to understand that a significant amount of engineering energy was used in designing that intake system. You are NOT going to improve it. Do a temperature rise test at the intake point and at the filter. The amount of heat absorbed through this system is negligible. This has been discussed here before quite a bit. Save your energy.
When you use the high pressure location to draw in air be prepared to deal with all the rain that will drop in there too. While it seems logical to draw intake air from this location, why did Porsche NOT do it? Noise is one reason, but there is much more to this than you think. In fact it is one of the most significant things after head design.
When you use the high pressure location to draw in air be prepared to deal with all the rain that will drop in there too. While it seems logical to draw intake air from this location, why did Porsche NOT do it? Noise is one reason, but there is much more to this than you think. In fact it is one of the most significant things after head design.
08-27-2014 | 02:19 PM
#907
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Joined: Aug 2004
Posts: 19,831
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From: Rep of Texas, N NM, Rockies, SoCal
I was thinking since i've got a test hood to cut up why not.
I didn't want to change the intake runners. I simply wanted to experiment with a cold air intake design that utilized the high pressure area (loc. 10) directly above the air box on our hoods.
The stock air cleaner bottom and top half including filter will be used. The experimentation will only be in a different suction tube design that was short and basically went straight up thru the hood.
2006-on (IIRC) model 911 GT3s have an air collector below their rear spoilers that generate 10-15 HP at speeds above 65mph simply be taking advantage of the pressure build below that spoiler. I read this in Excellence i think.
So i was curious to try the same principle.
I didn't want to change the intake runners. I simply wanted to experiment with a cold air intake design that utilized the high pressure area (loc. 10) directly above the air box on our hoods.
The stock air cleaner bottom and top half including filter will be used. The experimentation will only be in a different suction tube design that was short and basically went straight up thru the hood.
2006-on (IIRC) model 911 GT3s have an air collector below their rear spoilers that generate 10-15 HP at speeds above 65mph simply be taking advantage of the pressure build below that spoiler. I read this in Excellence i think.
So i was curious to try the same principle.
Suppose we make our test setup with the ports above and below the hood at sector 10.
http://www.oriflow.com/images/Magnehelic_Backside.jpg
http://www.uvm.edu/safety/sites/uvm....elic_gauge.jpg
We start driving, and watch the Magnehelic gauge as we speed up. At some point, there will be a differential reading, or the pointer will stick on 0, or possibly go down a bit. If it goes down, you need to reverse the tube sample ports. It's possible that you would find that there is an even HIGHER pressure at sector 10 under the hood than above. If this is the case, you would have a venturi effect http://4.bp.blogspot.com/-rBh6t5i9E2...uri+Effect.jpg with the differentiator being the hood(which looks surprisingly like the top surface of an airplane wing!). Now, in this case - if you were to pick off the air intake at sector 10 ABOVE the hood, you would be trying to force the air into an area of higher pressure below the hood from an area of lower(relative) pressure, which would be defeating the purpose of the process.
Now, you would want to also check the temps at the two stations because if you decide to have a radiator exhaust behind the radiator in the hood, it's very possible that you would be picking up even hotter air than the stock location!
Gah! Exactly opposite of our intentions.
Hotter, and lower pressure air intake. Like I said - weird, but true. What often looks simple, and logical just doesn't work in the real world without testing.<edited for clarity>
Last edited by docmirror; 08-27-2014 at 03:27 PM.
08-27-2014 | 04:58 PM
#908
Instructor
Joined: Jun 2014
Posts: 127
Likes: 0
From: A land of ice & snow .. mostly
There are ways of creating a usable differential air pressure gauge (a manometer, or liquid, type) with essentially home depot parts that could be used to compare the pressure differential between two different points on your car. The gauge could be used to measure a series of pressure differentials and help you determine if your change would be beneficial, as well as the preferred location(s), before cutting and fabrication.
Start by measuring the pressure differential between the new intake area and the area in front of the current intake openings. If the test looks favorable to moving the intake locations then it's time for more testing. Test two would be measuring the pressure differential between the area in front of the current intake openings and the pressure in the airbox either before or preferably after the air filter. Obviously all all future airbox readings would need to be taken from the same location. Test three would be taking a vacuum reading (non-differential, or differential to atmospheric pressure) of the vacuum in the airbox. Tests four and five would made after the new intake system has been installed. The goals would be the same as tests two and three, to measure the pressure differential between the inlet area and airbox, and to measure the level of vacuum in the airbox.
That data should be able to provide a basic understanding of why the changes were made (if test one was favorable), what the benefits are, and also indicate if there is a need to test with a wideband to measure changes to the car's air-fuel ratios. If the new intake location is even a moderately improvement, the AFRs will probably need to be checked. I'm not familiar enough with the Bosch mechanical fuel injection systems to know how they react to changes in the expected rate of air flow.
Actually you could skip the two point differentials and just collect a full set of absolutes or differential to atmosphere at all of these points. Bonus points for being able to collect each specific pressure at each location tied to a specific speed. That would give you some idea how changes in speed would impact the new design. Having an automated system to do all this data collection would be wonderful, but probably prohibitively expensive for hobbyists. An observer or in-car video camera and cruise control might actually be the easiest way to collect speed incremented measurements.
The difference between "I tried this, and think it feels better" and "the data shows we made this much of an improvement" is a functional system of metrics, and the tools to measure them. While the tools and time expended in gathering data add cost and complexity to a project, the observed consensus is that the benefits generally outweigh the costs.
Forgive the lengthy response. I found your idea interesting, and began to go though the process of figuring out how I would gather data. I figured I'd share my thoughts. Actually for me this is a bit timely, our Chump Car team is currently stripping down the remnants of a 928 parts car and is hoping to be racing it next season.
Start by measuring the pressure differential between the new intake area and the area in front of the current intake openings. If the test looks favorable to moving the intake locations then it's time for more testing. Test two would be measuring the pressure differential between the area in front of the current intake openings and the pressure in the airbox either before or preferably after the air filter. Obviously all all future airbox readings would need to be taken from the same location. Test three would be taking a vacuum reading (non-differential, or differential to atmospheric pressure) of the vacuum in the airbox. Tests four and five would made after the new intake system has been installed. The goals would be the same as tests two and three, to measure the pressure differential between the inlet area and airbox, and to measure the level of vacuum in the airbox.
That data should be able to provide a basic understanding of why the changes were made (if test one was favorable), what the benefits are, and also indicate if there is a need to test with a wideband to measure changes to the car's air-fuel ratios. If the new intake location is even a moderately improvement, the AFRs will probably need to be checked. I'm not familiar enough with the Bosch mechanical fuel injection systems to know how they react to changes in the expected rate of air flow.
Actually you could skip the two point differentials and just collect a full set of absolutes or differential to atmosphere at all of these points. Bonus points for being able to collect each specific pressure at each location tied to a specific speed. That would give you some idea how changes in speed would impact the new design. Having an automated system to do all this data collection would be wonderful, but probably prohibitively expensive for hobbyists. An observer or in-car video camera and cruise control might actually be the easiest way to collect speed incremented measurements.
The difference between "I tried this, and think it feels better" and "the data shows we made this much of an improvement" is a functional system of metrics, and the tools to measure them. While the tools and time expended in gathering data add cost and complexity to a project, the observed consensus is that the benefits generally outweigh the costs.
Forgive the lengthy response. I found your idea interesting, and began to go though the process of figuring out how I would gather data. I figured I'd share my thoughts. Actually for me this is a bit timely, our Chump Car team is currently stripping down the remnants of a 928 parts car and is hoping to be racing it next season.
08-28-2014 | 05:44 AM
#909
Nordschleife Master
Joined: Dec 2004
Posts: 6,164
Likes: 5
From: Guelph, Ontario, Canada
IIRC you poo-poo'd me porting,polishing and adjusting the 'barn door' spring in my AFM, you even chased me over to the other forum to do so..
And there was and is a VERY noticeable gain there, it cost me nothing but an enjoyable afternoon milling and polishing.
Why didn't Porsche do this? you know the answer.
My US 928S wasn't engineered for all-out performance. It weighed over 3300 lbs when i brought it home.
So gaugeman, let me worry about my time being wasted, I'll let you worry about your's.
My 'RS' is not ever going to be my daily driver but rather a good weather/weekend/DE car. Not commuting with it in the rain.
I'm going to experiment with my trashed hood, i can't say it will offer a huge gain but i have nothing to lose.
And there was and is a VERY noticeable gain there, it cost me nothing but an enjoyable afternoon milling and polishing.
Why didn't Porsche do this? you know the answer.
My US 928S wasn't engineered for all-out performance. It weighed over 3300 lbs when i brought it home.
So gaugeman, let me worry about my time being wasted, I'll let you worry about your's.
My 'RS' is not ever going to be my daily driver but rather a good weather/weekend/DE car. Not commuting with it in the rain.
I'm going to experiment with my trashed hood, i can't say it will offer a huge gain but i have nothing to lose.
Fact is I like almost all you have done on this car. I respect what you have done. It is well known that the limitations in this intake system is the 'U' under the spider and the cams. Been posted by people much smarter than either of us.
I'm not worried about your time. Was just trying to make a helpful hint. I like the idea of the hood vent behind the rad, so I am not doing this to try to anger you. Sorry if you took it that way.
I don't think it was blow back. I certainly didn't take you to task for saying the factory system was better, that's for sure.
08-28-2014 | 11:47 PM
#910
Rennlist Member
Joined: May 2004
Posts: 1,099
Likes: 270
From: Tampa, FL, USA
Mark Kibort Hood Mods on Race Car
Mark Kibort has a hood outlet in the location you are considering on his race car. You can come up with something similar to Mark's mesh to keep it more kid finger (and debris) friendly.
I am mocking up (not done, of course) some ideas of the same for my silver car. I am considering mimicking the curves from the hood and outer front headlight openings for the hood surface opening shape, and for the curve into the motor area using the smooth curves found on the Strosek hood holes. I am also considering using as much of the charted low pressure area as possible (#5-#9.5), using more than one of these vent openings, and including a shallow pan underneath the rearward ones to deflect rain (if it happens to ambush me) and also direct the under-hood heat out. The rain pan will be angled slightly off level with opposite slope of the hood. Not much room to work with, so I don't know if it will be worth it.
Kibort is also one that did a lot of experimentation with the stock S4 intake system prior to the plenum (and with the plenum too, but that is not applicable here). I could not find the thread, but as I recall, he did not gain, and maybe even lost HP by trying to take advantage of pressure area #10. More motor sound (not noise
) did come from his mod, which made it seem healthier, but the numbers said otherwise. He did find it very worthwhile to seal up the filter box as best as possible, as he found it leaked air quite a bit, meaning hot engine air would sneak in along with the long draw from the air tubes.
Others have commented that the air is not affected too adversely from the heat soaked tubes because it is constantly moving. Not sure if I agree with that - every little bit helps, in my opinion. I had insulated GTS intake tubes on my white car, but they have since deteriorated.
Here are some pictures of Kibort's hood mod and other referenced items:
I am mocking up (not done, of course) some ideas of the same for my silver car. I am considering mimicking the curves from the hood and outer front headlight openings for the hood surface opening shape, and for the curve into the motor area using the smooth curves found on the Strosek hood holes. I am also considering using as much of the charted low pressure area as possible (#5-#9.5), using more than one of these vent openings, and including a shallow pan underneath the rearward ones to deflect rain (if it happens to ambush me) and also direct the under-hood heat out. The rain pan will be angled slightly off level with opposite slope of the hood. Not much room to work with, so I don't know if it will be worth it.
Kibort is also one that did a lot of experimentation with the stock S4 intake system prior to the plenum (and with the plenum too, but that is not applicable here). I could not find the thread, but as I recall, he did not gain, and maybe even lost HP by trying to take advantage of pressure area #10. More motor sound (not noise
) did come from his mod, which made it seem healthier, but the numbers said otherwise. He did find it very worthwhile to seal up the filter box as best as possible, as he found it leaked air quite a bit, meaning hot engine air would sneak in along with the long draw from the air tubes. Others have commented that the air is not affected too adversely from the heat soaked tubes because it is constantly moving. Not sure if I agree with that - every little bit helps, in my opinion. I had insulated GTS intake tubes on my white car, but they have since deteriorated.
Here are some pictures of Kibort's hood mod and other referenced items:
08-30-2014 | 01:33 AM
#911
Thread Starter
Drifting
Joined: Dec 2012
Posts: 2,453
Likes: 6
From: Pennsyltucky
Thanks Carlos for the useful info.
Re Venting Hood:
I have done some thinking and i really want to leave the hood alone as in no cutting. I will trim the interior fender flange to allow more hot air out.
I just like the look of the stock hood too much to cut right now. I think my car will have a cleaner, smaller OB look.
If Mark Anderson,the LeMans entry cars back in '83 and '84 and the many other noted 928 racer's cars didn't and don't have hood vents,
i think i can live without them too.
On the other hand,
The only factory prepared racing 928 (Daytona Lightweight) does have its hood cut. But why?
there isn't information that i can find about this.
I figure these louvers are either for a special high speed cold air intake or
they were there to bring in cool air (where hot air sort of lingers)
and more effectively move the hot air out pushing it down and out the underside of the car as it normally does.
Cooling the intake temps a bit added a little extra power and efficiency. But that would seem to create unwanted lift.
Maybe high enough speeds weren't reached for the added lift to be an issue.
I don't think they were there to vent warm radiator air up and out, because of 1. the location and 2. the forward angle of the louvers
but their angle is hard to make out for sure from the photos i have seen.
They may do a combination of all three. I'd like to know though.
Re Intake mods:
Because i don't want to cut the hood (No naca ducts) and due to where the great pressure is, I have decided I want to try and bring the air through the front bumper cover. I think this is the best way to get additional ponies at speed.
I plan on removing the fogs and fabricate a duct opening there out of thin sheet metal and paint it. Simple VW style air duct from it to the stock tube ends.
I will seal and insulate this and the suction tubes and airbox well also.
I don't see this as presenting a water problem because the added suction tubing will go in and then up to meet the stock suction tube end. Any water would run back down and out i think.
I am not sure but the 'semi works' Max Moritz cars may have done this.
Then i will add a factory front 'S' spoiler.
So, I'm painting the hood and throwing it on, doing the simple intake mod (look how high pressures are there) and driving it til it gets too cold to.
Then i plan on pulling the motor for some real performance modifications.
Re Venting Hood:
I have done some thinking and i really want to leave the hood alone as in no cutting. I will trim the interior fender flange to allow more hot air out.
I just like the look of the stock hood too much to cut right now. I think my car will have a cleaner, smaller OB look.
If Mark Anderson,the LeMans entry cars back in '83 and '84 and the many other noted 928 racer's cars didn't and don't have hood vents,
i think i can live without them too.
On the other hand,
The only factory prepared racing 928 (Daytona Lightweight) does have its hood cut. But why?
there isn't information that i can find about this.
I figure these louvers are either for a special high speed cold air intake or
they were there to bring in cool air (where hot air sort of lingers)
and more effectively move the hot air out pushing it down and out the underside of the car as it normally does.
Cooling the intake temps a bit added a little extra power and efficiency. But that would seem to create unwanted lift.
Maybe high enough speeds weren't reached for the added lift to be an issue.
I don't think they were there to vent warm radiator air up and out, because of 1. the location and 2. the forward angle of the louvers
but their angle is hard to make out for sure from the photos i have seen.
They may do a combination of all three. I'd like to know though.
Re Intake mods:
Because i don't want to cut the hood (No naca ducts) and due to where the great pressure is, I have decided I want to try and bring the air through the front bumper cover. I think this is the best way to get additional ponies at speed.
I plan on removing the fogs and fabricate a duct opening there out of thin sheet metal and paint it. Simple VW style air duct from it to the stock tube ends.
I will seal and insulate this and the suction tubes and airbox well also.
I don't see this as presenting a water problem because the added suction tubing will go in and then up to meet the stock suction tube end. Any water would run back down and out i think.
I am not sure but the 'semi works' Max Moritz cars may have done this.
Then i will add a factory front 'S' spoiler.
So, I'm painting the hood and throwing it on, doing the simple intake mod (look how high pressures are there) and driving it til it gets too cold to.
Then i plan on pulling the motor for some real performance modifications.
08-30-2014 | 08:13 AM
#913
Former Vendor
Joined: Feb 2004
Posts: 2,139
Likes: 0
Hi Matthew,
Are you sure the Daytona racer had a cut/vented hood? I can't remember that mod from the research I did on it.
There have been 200 MPH 928 open road racers that really did not have much in body modifications to reach those speeds. You might want to look through Rennlist threads about those races to see what they did to prepare for running at those speeds.
Best regards,
Are you sure the Daytona racer had a cut/vented hood? I can't remember that mod from the research I did on it.
There have been 200 MPH 928 open road racers that really did not have much in body modifications to reach those speeds. You might want to look through Rennlist threads about those races to see what they did to prepare for running at those speeds.
Best regards,
08-30-2014 | 12:54 PM
#914
Thread Starter
Drifting
Joined: Dec 2012
Posts: 2,453
Likes: 6
From: Pennsyltucky
There are ways of creating a usable differential air pressure gauge (a manometer, or liquid, type) with essentially home depot parts that could be used to compare the pressure differential between two different points on your car.
Forgive the lengthy response. I found your idea interesting, and began to go though the process of figuring out how I would gather data. I figured I'd share my thoughts. Actually for me this is a bit timely, our Chump Car team is currently stripping down the remnants of a 928 parts car and is hoping to be racing it next season.
Forgive the lengthy response. I found your idea interesting, and began to go though the process of figuring out how I would gather data. I figured I'd share my thoughts. Actually for me this is a bit timely, our Chump Car team is currently stripping down the remnants of a 928 parts car and is hoping to be racing it next season.
New Garden Airport that may be the best test as the gains will be at higher speeds. I plan on being able to unplug my intake modification very easily for a number of reasons.
Hi Matthew,
Are you sure the Daytona racer had a cut/vented hood? I can't remember that mod from the research I did on it.
There have been 200 MPH 928 open road racers that really did not have much in body modifications to reach those speeds. You might want to look through Rennlist threads about those races to see what they did to prepare for running at those speeds.
Best regards,
Are you sure the Daytona racer had a cut/vented hood? I can't remember that mod from the research I did on it.
There have been 200 MPH 928 open road racers that really did not have much in body modifications to reach those speeds. You might want to look through Rennlist threads about those races to see what they did to prepare for running at those speeds.
Best regards,
It does look to be just be part of the graphic.
And again if these hard core 928 builders don't have em..I'll be OK.
I found a conversation regarding the Lightweight car on the early 911S registry..with link to my thread..https://www.google.com/url?sa=i&rct=...09496064017500
The previous owner is involved in this conversation and would know a lot about this car. He probably has many pictures.
08-30-2014 | 05:01 PM
#915
Former Vendor
Joined: Feb 2004
Posts: 2,139
Likes: 0
Hi Matt,
The previous and current owner of the Daytona 928 is Porsche.
I received pictures of it without an engine in the back of the old Porsche museum. Should still be somewhere in the back of their new museum.
The cuts you think you see are actually lines of the graphics.
I talked to Vic Elford about driving it during that 1984 Daytona race. He said Porsche would not allow any modifications to be done to that 928 and wanted it to look as stock as possible.
Hope this helps,
The previous and current owner of the Daytona 928 is Porsche.
I received pictures of it without an engine in the back of the old Porsche museum. Should still be somewhere in the back of their new museum.
The cuts you think you see are actually lines of the graphics.
I talked to Vic Elford about driving it during that 1984 Daytona race. He said Porsche would not allow any modifications to be done to that 928 and wanted it to look as stock as possible.
Hope this helps,