When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
The 1970-72 Olds with the W-25 Ram Air Hood. Were these hoods actually functional in bringing cold air into the engine intake or were they mainly for show/looks?
I read and heard from others that the ram air setup was not that great. Air wouldn't be "rammed" or forced in as the front end of these cars was not aerodynamic and air actually jumped over the hood scoops onto the windshield. Has any tunnel testing been done since to test this theory?
The attached photo shows a modified setup. A wider and enlarged area for the air to come in, a better compressible foam surround which seals better, and a K&N top and side filter for more cfm of air.
The W-25 may not have been an efficient "ram air" setup, but it seems it worked very well at drawing cooler, outside air into the intake as opposed to the hot underhood air of a regular breather with snorkels in the engine bay.
Olds had one of the better designs with the scoops far forward. They talk about air close to the hood surface or boundary layer moving slower than air 1"-2" above the surface. The area near the headlights is high pressure and the lower windshield cowl area (which nascar uses). Getting an actual ram effect may take some effort. Colder outside air is definitely helpful but 5-10 horsepower may be hard to feel in the seat. Chevy's cowl induction and Dodge's T/A hood were good attempts.
Years ago, I have read Olds actually did wind tunnel testing on this hood during development. And testing showed it generates positive pressure (2 to 3 psi) at highway speed. Maybe one of our experts can point out that publication. It may have been a marketing press release? Tom
PS I put a small foam football in my aircleaner snorkel to seal the system and prevent pressure loss there.
Headlight & cowl (thinking early Z28 optional style (like nascar)) seem to be the best. 70-72 style said to be not as good as 68-69 under bumper style. My son swears by his 68 OAI on his 70 Cutlass, says he can feel the difference when it is closed off for winter. I have seen it posted that people ran a .1 faster drag pass with OAI. I also remember someone saying engine ran hot if the foam seal/top adapter wasn’t in place. All anecdotal I know. Some racers went to the available “tall scoop” aftermarket hood & I have no doubt that works.
As for air riding over the scoops - I have never had a car that collects the volume of bugs & other flying garbage on windshield in such a short time as my 70 OAI so I think there is some proof there as well.
Despite the marketing BS, NO musclecar "ram air" system actually rammed much air. What they DID do is allow cooler air to be ingested by the engine. Tests have shown that there is about a 1 HP increase for every 7-10 degree Fahrenheit drop in inlet air temp. Sucking 70 degree outside air instead of 180 deg underhood air could be worth more than 10 HP. Wind tunnel tests of musclecar scoops show that most were less than worthless as far as placement. Shaker scoops and those in the center of the hood are actually in a LOW pressure area and result in less air being ingested. The front of the car and base of the windshield are the two high pressure areas, so a cowl induction scoop, the 1966-1969 Olds under bumper scoops, Ford Thunderbolts, and scoops at the leading edge of the hood (1966 Mercury Cyclone and 1970-72 W25) are among the best designs. The fact remains that turbulent flow through those ducts pretty much negates any "ram" effect, however.
On 70-72, any "ram affect" is zeroed out by the fact that any extra pressure is blowing out the open snorkel in the air cleaner base. I am not aware of Oldsmobile ever making the claim that it increased pressure, just cooler air. I always laughed at people that would cut out the top of the OAI air cleaner top and then not close off the snorkel. Not that I think either helped but if you think it is helping to cut the top why would they not close off the snorkel.
I just added OAI to my 71.
I have no idea if it helped add any HP because 5 or 10 HP would be very difficult to notice with the seat of your pants dyno. I do believe it does help because of the cooler air. But with the added weight of the hood does it really help?
I can say adding OAI did change the sound of the car during wide open throttle,it is sucking much more air now then with the regular air cleaner.
On 70-72, any "ram affect" is zeroed out by the fact that any extra pressure is blowing out the open snorkel in the air cleaner base. I am not aware of Oldsmobile ever making the claim that it increased pressure, just cooler air. I always laughed at people that would cut out the top of the OAI air cleaner top and then not close off the snorkel. Not that I think either helped but if you think it is helping to cut the top why would they not close off the snorkel.
What about this setup? The base is completely sealed and the compressible foam seals to the air inlets.
What about this setup? The base is completely sealed and the compressible foam seals to the air inlets.
As said, there's no "ram" benefit. It's not like a turbocharger/supercharger. There's just not enough pressure. Pulling cold air - whether from the hood or from a correctly connected snorkel - is the important part.
Originally Posted by My442
Back in the spring of 1970, my best friend Rick had a brand new 1969 Plymouth RoadRunner with a 383/4 speed/3.91 drivetrain.
It had the Coyote Duster cold air hood, with a red pull **** under the dash that read "Carb Air".
If you pulled the Carb Air ****, the tone of the engine changed noticeably, to a louder, throatier sound.
The hood did not have scoops, just two raised areas with screens.
It felt and sounded like it made a small difference to the power output.
Yeah, the butt dyno strikes again. We would always flip the air cleaner lid upside down. Made the '79 88 into a speed demon.
The snorkel on the stock cleaner is there specifically to muffle noise, just like all the little voids and blobs hanging off the intake tracks on new cards. Cracking it open (or replacing a new car's intake run with a smooth pipe) just changes the noise.
This is correct, it is simply outside air, which does help. And they look cool. That's all that's needed.
Superchargers, turbo or conventional, work not because they ram more air in, but they compress that air mechanically. Consider a coffee can, facing forward, going down the road. You will not have any more air in the can facing forward, or backward, or even sideways. Now, if you have a device on the front of the can, mechanically cramming more air in, then pressure would go up.
True. The colder the intake air, the more HP and better atomization and ignition. Hot air is less HP and can lead to pre-ignition on some engines.
My car ran 12.10 with the ram air setup I showed. The air intake is completely sealed from engine bay air. It's wider intake area and the K&N top and side filter helps with more cfm. It seals tightly to the hood area.
Maybe next time I will remove the setup and go back to stock and see if the car slows down in the 1/4 mile.
True. The colder the intake air, the more HP and better atomization and ignition. Hot air is less HP and can lead to pre-ignition on some engines.
It has nothing to do with atomization or ignition. The benefit of colder intake air is that it is more dense. Higher density means more oxygen per cubic foot. Horsepower is a direct function of how much mass flow of oxygen you can get into and out of the engine, period. Higher RPMs mean more mass air flow, thus more HP. Forced induction means more mass air flow. Cold air is exactly the same, just on a smaller scale. ASSUMING the carb is jetted to take advantage of that, it means more HP. Actually, if you don't rejet the carb to account for the added mass air flow, the mixture will be lean, which DOES lead to preignition.
FYI, here's another case where the Qjet has an advantage. Contrary to popular belief, the secondary air valves on a Qjet are not vacuum operated. They are opened by mass air flow - essentially, they are a mechanical MAF that controls fuel by changing the position of the secondary metering rods. This allows the Qjet to take advantage of that increased mass air flow without necessarily requiring rejetting.
About 10 years ago I was at the Lansing Homecoming event, I met one of the engineers who designed the hood. He said they actually did a lot of testing and it theoretically would make a difference at enough speed. But from what I remember he said even then, not much. He also said that his original design was one wide scoop not the two that ended up being produced. He also mentioned that GM was so departmentalized that once his group provided the prototypes and the research results they were never involved again. He was just as surprised to see the final product as anyone else. I thought this last part was the most interesting but form what I hear lots of organizations had their employees work in vacuums.
He also said that his original design was one wide scoop not the two that ended up being produced. He also mentioned that GM was so departmentalized that once his group provided the prototypes and the research results they were never involved again. He was just as surprised to see the final product as anyone else. I thought this last part was the most interesting but form what I hear lots of organizations had their employees work in vacuums.
While I can understand that, the reality is that the dual scoops line up with the grills and really look a lot better. In fact, this is my fundamental complaint when people put W-25 style hoods on other years (like the 73-77 cars). The scoops no longer line up with the grills and look like an esthetic hodge-podge.
[QUOTE=oddball;1129519]...It's not like a turbocharger/supercharger. There's just not enough pressure.../QUOTE]
Exactly
Assuming a perfect ram air collector with no pressure loss, car going 100 mph, the ram air effect would produce five inches of water column pressure, and this would theoretically produce 1.3% more horsepower. At 60 mph the ram air effect would give a theoretical 1/2 of 1 percent power increase.
Accounting for imperfect sealing, imperfect scoop placement, limited car speeds, air friction through the long duct, there is zilch divided by 2 horsepower increase due to ram air effect.
True. The colder the intake air, the more HP and better atomization and ignition. Hot air is less HP and can lead to pre-ignition on some engines..
Originally Posted by joe_padavano
It has nothing to do with atomization or ignition. The benefit of colder intake air is that it is more dense. Higher density means more oxygen per cubic foot. Horsepower is a direct function of how much mass flow of oxygen you can get into and out of the engine, period. Higher RPMs mean more mass air flow, thus more HP. Forced induction means more mass air flow. Cold air is exactly the same, just on a smaller scale. ASSUMING the carb is jetted to take advantage of that, it means more HP. Actually, if you don't rejet the carb to account for the added mass air flow, the mixture will be lean, which DOES lead to preignition..
If the air is cold enough it might lead to worse atomisation, this is bit theoretical on a warmed up engine, but street driven cars back in the days of carburetors usuallt had some means to warm up the manifold quickly to enable the choke to be dispensed with as early as possible. Carburetor icing was a problem for side draft carbs on inline engines without a means of warming the inflowing air to the air filter. This was particularly a problem in damp weather with temperature a few degrees above freezing. Like for example a typical British winter.
Roger.
Last edited by rustyroger; Oct 9, 2018 at 02:14 PM.
Either I misread the advertisement from back then, but did not one of the Oldsmobile advertisements or brochures show a carburetor next to the OAI hood and state a specially calibrated carburetor was part of the W-25 package?
Carburetor icing was a problem for side draft carbs on inline engines without a means of warming the inflowing air to the air filter. This was particularly a problem in damp weather with temperature a few degrees above freezing. Like for example a typical British winter.
Roger.
This is why they had to add a coolant jacket to the turbocharger and throttle body on the 62-63 Jetfire. Had to warm them up to prevent icing.
You guys are nuts, I'm telling you for a fact on both my W30's I'm getting at least an extra 75+ HP by the time i'm hitting 20 mph with the OAI hood. By the time I hit 60 mph I swear its 150 hp - to the wheels!, I can just feel it!
Carburetor icing was a problem for side draft carbs on inline engines without a means of warming the inflowing air to the air filter. This was particularly a problem in damp weather with temperature a few degrees above freezing. Like for example a typical British winter.
Roger.
Originally Posted by jensenracing77
This is why they had to add a coolant jacket to the turbocharger and throttle body on the 62-63 Jetfire. Had to warm them up to prevent icing.
I would have thought by the time intake air had been compressed by a turbo, which normally run pretty hot, and forced under pressure into the manifold it would be pretty warm. Many turbo engined vehicles, from 1.6 liter Peugeot cars to locomotive engines run intercoolers to bring the intake air temperature back down.
However I know very little about the Jetfire turbo layout, can you give me a link to a diagram?.
Either I misread the advertisement from back then, but did not one of the Oldsmobile advertisements or brochures show a carburetor next to the OAI hood and state a specially calibrated carburetor was part of the W-25 package?
It wasn't. W-25 cars got the same carb as non-W-25 cars. You may be thinking of W-30 ads, which DID get a "specially calibrated" carb - primarily due to the lack of manifold vacuum with the 328/328 cam on MT cars.
Read for yourself what it said in the W-machine brochure about RPO W25.
Also specifically note that the brochure refers to the benefits of Cold Air Induction, not "ram air" (which is a Pontiac thing, anyway... )
I would have thought by the time intake air had been compressed by a turbo, which normally run pretty hot, and forced under pressure into the manifold it would be pretty warm. Many turbo engined vehicles, from 1.6 liter Peugeot cars to locomotive engines run intercoolers to bring the intake air temperature back down.
However I know very little about the Jetfire turbo layout, can you give me a link to a diagram?.
Roger.
The carburetor was a draw through and the icing was in the throttle body and around the turbo intake. It was a single bbl side draft and I would suspect the velocity is pretty high at times. After the turbo is where the temps go up from boosting and an intercooler would be used.
Ah, a draw through system and a sidedraft carb, it all makes sense. I only ever dealt with a turbo system with a pressurised carb and that was a custom fabrication. All other gasoline powered turbo cars I had anything to do with had fuel injection, Turbo diesel passenger cars are ubiquitous in most of Europe, although after the scandals with VW and others sales have taken a significant dip lately.
I am aware the intercooler goes after the turbo btw.
You guys are nuts, I'm telling you for a fact on both my W30's I'm getting at least an extra 75+ HP by the time i'm hitting 20 mph with the OAI hood. By the time I hit 60 mph I swear its 150 hp - to the wheels!, I can just feel it!
Um, thats broken seat springs jabbin' you in the cheeks 😊
