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1970-72 Outside Air Induction Hood - K&N X-Stream Airflow Top Plate
On the 1970-72 W-25 hoods. Would the K&N X-Stream Airflow Top Plate air cleaner perform better than a solid top base?
What I noticed is that with a SOLID top base air cleaner and the W-25 hood. With the hood closed, the solid top blocks the OAI (outside air induction) air inlets. So the air cleaner will be pulling air from the sides of the air cleaner, which would mean hot engine bay temperatures. With the K&N Airflow Top late filter, it allows the airflow to come in through the top, which is a cooler air charge, especially with the vehicle moving at 30mph+.
Anyone have 1/4 mile or dyno testing that would prove my theory true?
The OEM factory air cleaner will NOT fit under the hood with the high rise intake.
Plus, the factory setup is very restrictive with airflow. It would make LESS power with the OEM air filter setup.
But the OEM factory air cleaner prevents hot air from being pulled in from the engine compartment, which is why I asked. Running an open element like that is pretty much useless with the OAI hood. You'll get a tiny bit of a temp reduction, but nothing close to what the factory system would provide as you're still pulling hot air in from the sides. If you aren't sealing off the flow path so that it ONLY pulls from the hood, I wouldn't bother worrying about it. If you do seal it off, and you can't run the factory flapper door setup, then I'd run the element top filter.
But the OEM factory air cleaner prevents hot air from being pulled in from the engine compartment, which is why I asked. Running an open element like that is pretty much useless with the OAI hood. You'll get a tiny bit of a temp reduction, but nothing close to what the factory system would provide as you're still pulling hot air in from the sides. If you aren't sealing off the flow path so that it ONLY pulls from the hood, I wouldn't bother worrying about it. If you do seal it off, and you can't run the factory flapper door setup, then I'd run the element top filter.
If you've sealed it off, why are you concerned about pulling in hot air? It'll work just like the factory system, with air pulling in from the area between the filter and your seal.
In theory, the element top plate will perform better, but if you're actually concerned about it - just test it. It isn't difficult at all to do. Next time you're at the track, run a pass with it, and run a pass with a solid top.
If you've sealed it off, why are you concerned about pulling in hot air? It'll work just like the factory system, with air pulling in from the area between the filter and your seal.
In theory, the element top plate will perform better, but if you're actually concerned about it - just test it. It isn't difficult at all to do. Next time you're at the track, run a pass with it, and run a pass with a solid top.
I know you can hear the extra cfm from the top element(I think it was rated for 900cfm or better)
If you've sealed it off, why are you concerned about pulling in hot air? It'll work just like the factory system, with air pulling in from the area between the filter and your seal.
In theory, the element top plate will perform better, but if you're actually concerned about it - just test it. It isn't difficult at all to do. Next time you're at the track, run a pass with it, and run a pass with a solid top.
Problem is car ran a 12.10 and if I run it at a track again, I will probably get booted. Unlike newer modern muscle cars that are safer and tech certified to 10.00 without a need for a cage.
So I wanted to see if someone else did a test of running with and then without the sealed air filter setup.
Problem is car ran a 12.10 and if I run it at a track again, I will probably get booted. Unlike newer modern muscle cars that are safer and tech certified to 10.00 without a need for a cage.
So I wanted to see if someone else did a test of running with and then without the sealed air filter setup.
break is 11.50 now! So no you will not get booted.
Problem is car ran a 12.10 and if I run it at a track again, I will probably get booted. Unlike newer modern muscle cars that are safer and tech certified to 10.00 without a need for a cage.
So I wanted to see if someone else did a test of running with and then without the sealed air filter setup.
You have a chassis dyno anywhere near you? That would be an option that wouldn't put you at jeopardy with your local track.
A stationary chassis dyno would be hard to replicate driving at 60mph+ down the road with the cooler air intake charge.
Couple of things.
First, the question you're asking is whether or not air having to move around the top plate is impacting power. Air has to make that turn regardless of any ram effect. If there is no difference in power with no ram air, there will be no difference in power with it.
Second, at 60 MPH, you aren't getting much benefit. Your stagnation pressure at that speed is only ~ 0.1 inHg. At 120 mph, you might see a small gain as your stagnation pressure increases to 0.5 inHg.
Thing is,
1) the scoops aren't in a position to receive that level of stagnation pressure. They're back away from the leading edge of the hood, and down low on it. So they're dealing with the boundary layer from air impacting the front of the car and making the turn to go over the hood. As Joe said in your other thread, you've got so much turbulent flow going through those scoops that there basically is no ram effect.
2) A low 12 second car like yours should be going through the traps at about 120 mph. So you wouldn't see any real benefit until the absolute end of your run.
The benefit to the scoops is pulling in cold air - not ram air.
First, the question you're asking is whether or not air having to move around the top plate is impacting power.
2) A low 12 second car like yours should be going through the traps at about 120 mph. So you wouldn't see any real benefit until the absolute end of your run.
The benefit to the scoops is pulling in cold air - not ram air.
The top plate allows more airflow. No doubt smaller air cleaner surface areas for a 468 cubic inch engine will hurt performance.
I agree on the RAM AIR not really doing anything but the COLD AIR will make a difference. Bringing in outside (let's say 75F) air versus 200F+ engine bay air will make a difference in performance.
You might want to try blocking the scoops and just running the air cleaner without the foam. At high speeds it may be hard to evacuate all the air coming through the radiator. This may actually create a high pressure area under the hood, or vice versa block the grill and use the hood scoops.You may go the same time or quicker. It's all theory but worth a try. The W-25 hood looks cool though. Vortex generators may pull above boundary layer air into the scoops if set correctly. Lots of theory. Yarn, tape and somebody video taping near the finish or driving along side your car may provide some ideas what the air is doing near the scoop.
Location: Colorado Springs Colorado/Thousand Oaks Ca
Posts: 1,719
Originally Posted by pettrix
The top plate allows more airflow. No doubt smaller air cleaner surface areas for a 468 cubic inch engine will hurt performance.
I agree on the RAM AIR not really doing anything but the COLD AIR will make a difference. Bringing in outside (let's say 75F) air versus 200F+ engine bay air will make a difference in performance.
It ran a 12.10 at 110mph
11.5 has been the cut off for years, 120 mph @ 12.00 is insane. I like your setup can you post more pictures of the car?
The top plate allows more airflow. No doubt smaller air cleaner surface areas for a 468 cubic inch engine will hurt performance.
I agree on the RAM AIR not really doing anything but the COLD AIR will make a difference. Bringing in outside (let's say 75F) air versus 200F+ engine bay air will make a difference in performance.
It ran a 12.10 at 110mph
Larger than necessary air cleaner surface area will do nothing at all if the filter is clean. It will only help to increase surface area IF your current setup does not have enough surface area. In other words, if your current setup is too small, it’ll make a difference. If it is properly sized, it will not make a difference.
The outside air temperature improvement will show up on a chassis dyno. It’s the only place it can pull air from if you’ve properly sealed it off.
Last edited by Bubba68CS; March 10th, 2020 at 08:12 AM.
1) the scoops aren't in a position to receive that level of stagnation pressure. They're back away from the leading edge of the hood, and down low on it. So they're dealing with the boundary layer from air impacting the front of the car and making the turn to go over the hood. As Joe said in your other thread, you've got so much turbulent flow going through those scoops that there basically is no ram effect.
2) A low 12 second car like yours should be going through the traps at about 120 mph. So you wouldn't see any real benefit until the absolute end of your run.
The benefit to the scoops is pulling in cold air - not ram air.
I'm not in total agreement with this part. Olds was one of the first manufacturers to exploit the cool outside air to increase HP. When the OAI moved from under the bumpers in '69 to the hood in '70, the placement towards the front of the hood was intended to place the air entrance where the boundary layer is thinner than it is further back where other divisions were putting their "Ram Air" scoops (Pontiac, Buick, I'm looking at you). Pontiac got with the game in '71 w/ the new GTO hood that had openings in nearly the same place as the W25 hood (not to mention the scoops on the early Formula Firebird hoods). So, while not perfect, the W25 hood scoops were more effective in snatching cool outside air and routing it to the carb than most other manufacturers.
While not directly comparable to the W25 hood, there's been alot of debate on the effectiveness of Pontiac's "Ram Air" hood on the 4th gen WS6 Firebirds. Case in point: In the Aug '98 issue of C&D, they tested 3 convertible pony cars for the '99 MY: 30th Anniversary WS6 T/A, Camaro SS, and Mustang Cobra. All featured OAI, all had MTs and all engines were rated at 320 HP. (making the SS and WS6 identical except for weight and aero). While the Cobra was smoked by the F-body twins in about every test of performance (this was the test that revealed Ford's intake casting flaws), what was revealing about the 2 different approaches to OAI used by the GM twins is the top speed achieved during testing. In case you don't know, the WS6 openings are at the nose of the hood with a short, direct path to the engine air intake, while the SS opening is in the middle of the hood with ducts that route the air back to the front of the engine to the air intake. The SS maxed out at 158 MPH (drag limited) while the WS6 hit its speed limiter at 162 MPH (and the WS6 was not only heavier, but some have argued that it has a nose that is more "blunt" than the SS). Seems Pontiac's more effective "Ram Air" setup does help performance (at least above 100 MPH it does).
So while no "Ram" effect would be expected below 100 MPH on any OAI setup, I believe Olds, and later Pontiac, had some of the more effective OEM systems.
Last edited by JohnnyBs68S; March 10th, 2020 at 01:37 PM.
I'm not in total agreement with this part. Olds was one of the first manufacturers to exploit the cool outside air to increase HP. When the OAI moved from under the bumpers in '69 to the hood in '70, the placement towards the front of the hood was intended to place the air entrance where the boundary layer is thinner than it is further back where other divisions were putting their "Ram Air" scoops (Pontiac, Buick, I'm looking at you). Pontiac got with the game in '71 w/ the new GTO hood that had openings in nearly the same place as the W25 hood (not to mention the scoops on the early Formula Firebird hoods). So, while not perfect, the W25 hood scoops were more effective in snatching cool outside air and routing it to the carb than most other manufacturers.
While not directly comparable to the W25 hood, there's been alot of debate on the effectiveness of Pontiac's "Ram Air" hood on the 4th gen WS6 Firebirds. Case in point: In the Aug '98 issue of C&D, they tested 3 convertible pony cars for the '99 MY: 30th Anniversary WS6 T/A, Camaro SS, and Mustang Cobra. All featured OAI, all had MTs and all engines were rated at 320 HP. (making the SS and WS6 identical except for weight and aero). While the Cobra was smoked by the F-body twins in about every test of performance (this was the test that revealed Ford's intake casting flaws), what was revealing about the 2 different approaches to OAI used by the GM twins is the top speed achieved during testing. In case you don't know, the WS6 openings are at the nose of the hood with a short, direct path to the engine air intake, while the SS opening is in the middle of the hood with ducts that route the air back to the front of the engine to the air intake. The SS maxed out at 158 MPH (drag limited) while the WS6 hit its speed limiter at 162 MPH (and the WS6 was not only heavier, but some have argued that it has a nose that is more "blunt" than the SS). Seems Pontiac's more effective "Ram Air" setup does help performance (at least above 100 MPH it does).
So while no "Ram" effect would be expected below 100 MPH on any OAI setup, I believe Olds, and later Pontiac, had some of the more effective OEM systems.
Your points aren’t really disagreeing with me - they’re just a bit off from what I was saying, which is that they won’t receive maximum stagnation pressure because of location. I did not say they’ll see no pressure rise at higher speeds. It will simply be reduced from what the tip of the nose sees.
The WS6 inlets have the benefit of being farther forward on a streamlined nose. I have no doubt those are effective at higher speeds. A Kawasaki ZX14 motorcycle is rated for an additional 5% power at 120 mph from its ram air, though again, it is farther forward on a streamlined nose. Those are apples and oranges to the W25 scoops being farther back with a blunt nose.
I'm sure this one works better (65 Cyclone), but not nearly as good looking as the W25:
Anything you can do to reduce restrictions and heating of the air by the time it reaches the carb helps. I added a shaker CAI to my '99 Dakota R/T CC, dropped 0.27 sec in the 1/4, and picked up 2.6 MPH without doing anything else.
Sorry for threadjacking.
Last edited by JohnnyBs68S; March 10th, 2020 at 05:52 PM.
Sealing the hood to the carb was worth 2 mph on the big end of the 1/4 mile for me. Simple as that. I usually remove the air cleaner which is just for the street and use a mesh screen. Open carb vs tray with screeb was worth 2 mph. The air filter chokes the engine so bad on the street it holds it back above 6k RPM. But that's because it's very low and restricts air flow. Engine masters did a test. A 5 inch tall solid flat lid made the same HP as a 3 inch tall flow through lid. You guys are talking about Hp losses you will never feel in the street lmfao.
I'm not in total agreement with this part. Olds was one of the first manufacturers to exploit the cool outside air to increase HP. When the OAI moved from under the bumpers in '69 to the hood in '70, the placement towards the front of the hood was intended to place the air entrance where the boundary layer is thinner than it is further back where other divisions were putting their "Ram Air" scoops (Pontiac, Buick, I'm looking at you). Pontiac got with the game in '71 w/ the new GTO hood that had openings in nearly the same place as the W25 hood (not to mention the scoops on the early Formula Firebird hoods). So, while not perfect, the W25 hood scoops were more effective in snatching cool outside air and routing it to the carb than most other manufacturers.
While not directly comparable to the W25 hood, there's been alot of debate on the effectiveness of Pontiac's "Ram Air" hood on the 4th gen WS6 Firebirds. Case in point: In the Aug '98 issue of C&D, they tested 3 convertible pony cars for the '99 MY: 30th Anniversary WS6 T/A, Camaro SS, and Mustang Cobra. All featured OAI, all had MTs and all engines were rated at 320 HP. (making the SS and WS6 identical except for weight and aero). While the Cobra was smoked by the F-body twins in about every test of performance (this was the test that revealed Ford's intake casting flaws), what was revealing about the 2 different approaches to OAI used by the GM twins is the top speed achieved during testing. In case you don't know, the WS6 openings are at the nose of the hood with a short, direct path to the engine air intake, while the SS opening is in the middle of the hood with ducts that route the air back to the front of the engine to the air intake. The SS maxed out at 158 MPH (drag limited) while the WS6 hit its speed limiter at 162 MPH (and the WS6 was not only heavier, but some have argued that it has a nose that is more "blunt" than the SS). Seems Pontiac's more effective "Ram Air" setup does help performance (at least above 100 MPH it does).
So while no "Ram" effect would be expected below 100 MPH on any OAI setup, I believe Olds, and later Pontiac, had some of the more effective OEM systems.
Noticed I had one in my calendar(1965) to look at. Is that the long hole in the front bumper? Or was 1969 the first year?
Last edited by Letsrunum; March 12th, 2020 at 08:20 AM.
What intake manifold model is that and how thick is that filter to get that beast to fit under that hood?
I was told I could gain 1" of clearance to change my hood for sizing different on high rise intake manifolds. How big can go under both hoods?
Can your drop bases cause restrictions? Mine is 3" drop base and 3" thick.
Found yours copper(beast)
My 350 with a holley street dominator intake with a welded on spacer milled to turn it from spreadbore to square bore then a super sucker spacer I have 2.5 inches of space. I have the regular ram air hood from glasstek. that's a pizza pan, HVAC foam and a cooking strainer for my ram air set up. It works lol.
I seen that 2" air-inforced hood shown by someone else as well.
Last edited by Letsrunum; March 12th, 2020 at 09:13 AM.
I could run a 3 inch tall filter if I used a drop base. But common air flow theory shows air does not like to turn so I like to use flat based air cleaners but technically with the flow through lids it's null and void but I still think straightening the air flow into the carb is important.
I could run a 3 inch tall filter if I used a drop base. But common air flow theory shows air does not like to turn so I like to use flat based air cleaners but technically with the flow through lids it's null and void but I still think straightening the air flow into the carb is important.
That is called friction loss(psi) on flow charts(gpm) in my world(submersible pumps).
I would like see those specs on your intake manifold compared to performer rpm intake manifold(yours looks bigger in the pictures to me). Sounds like room to go bigger!
I would like see those specs on your intake manifold compared to performer rpm intake manifold(yours looks bigger in the pictures to me). Sounds like room to go bigger!
Thinking matching the opening for a throttle body to work properly on throttle response(this sound right for sizing?).
Well. There is no real scientific data on my intake. We / my Porter and machinist and I decided the best way to turn the spread bore to square bore was to weld a spacer fill and blend it in. Then I decided to run a super sucker. This was done as a compromise between an RPM and a Victor intake. Best E/T to date 11.85 @ 110 on pump gas with a 3500 stall and 3.90 gears. We got room to drop the e/t. But I keep it street friendly. This engine easily spins to 7k. and is still pulling.
Last edited by coppercutlass; March 12th, 2020 at 09:15 PM.
Well. There is no real scientific data on my intake. We / my Porter and machinist and I decided the best way to turn the spread bore to square bore was to weld a spacer fill and blend it in. Then I decided to run a super sucker. This was done as a compromise between an RPM and a Victor intake. Best E/T to date 11.85 @ 110 on pump gas with a 3500 stall and 3.90 gears. We got room to drop the e/t. But I keep it street friendly. This engine easily spins to 7k. and is still pulling.
Very nice! What size cam was used? Answering some of my other questions on sizing the stall and gears for street friendly and I was wanting highway driving at a reasonable speed(maybe, what transmission you got?).
You might want to try blocking the scoops and just running the air cleaner without the foam. At high speeds it may be hard to evacuate all the air coming through the radiator. This may actually create a high pressure area under the hood, or vice versa block the grill and use the hood scoops.You may go the same time or quicker. It's all theory but worth a try. The W-25 hood looks cool though. Vortex generators may pull above boundary layer air into the scoops if set correctly. Lots of theory. Yarn, tape and somebody video taping near the finish or driving along side your car may provide some ideas what the air is doing near the scoop.
Very interesting dragline. I read the Daytonas and Superbirds had vent scoops on top of the front fenders to let air pressure escape but that's at 200mph. I saw the movie Ford vs Ferrari and they used the yarn and tape. Nascar seems to prefer cowl induction.
March 6th, 2020, 08:01 AM
