Pontiac Ram Air II, Oldsmobile Force-Air Induction, Chevrolet Cowl Induction – Did These Ram Induction Systems Actually Increase Power?

 

In the December 1968 issue of Hi-Performance Cars (aka CARS) magazine, automotive writer Roger Huntington examined four GM cars with ram induction systems — a Camaro Z/28 with the new ZL2 cowl induction hood, an Oldsmobile 4-4-2 W-30 and an Olds Cutlass Ram Rod 350 W-31 with Force-Air Induction, and a Ram Air II Pontiac GTO — to see if these systems really improved power at higher speeds. Here’s what he found.

Cold Air and Ram Air

Hood scoops have been a popular form of automotive costume jewelry for decades. In many cases, they’ve been strictly decorative — at most, they might provide a bit of extra clearance for some under-hood component. However, in the late 1960s and early 1970s, there was a brief vogue for functional scoops, designed to admit outside air to the engine.

Huntington began by recapped why one might want functional hood scoops, which fell into two categories: cold air and ram air. He explained:

You all understand the effect of cool intake air on engine horsepower and torque. The simple fact is that cool air is just heavier or denser than hot air. Since an engine cylinder can suck in only so many cubic inches of air/fuel mixture on the intake stroke, you will get more power and torque if the air is cooler—because you will be sucking in more weight of air/fuel mixture. The difference between drawing in cool outside air at maybe 80 degrees F. temperature and pulling hot underhood air at 130 or 140 degrees can add 3 to 5 percent to your horsepower. That would be 10 to 15 extra hp on the average Detroit engine. And it doesn’t cost you a thing.

The photos on the above page are of an aftermarket ram induction system offered by Joel Rosen’s Motion Performance on Long Island, New York, although that system wasn’t tested in this article.

Ram induction systems also claimed an additional benefit beyond cooler intake air:

There’s another vital factor in this air scoop picture and that is ram effect from the car’s forward speed. In other words as the car goes faster the air is literally forced or rammed into the carburetor through the air scoop, under a slight pressure. The faster the speed the higher this “ram pressure.” And of course the engine hp at a given rpm should theoretically go up and up as this ram pressure goes up. That is, you should get more hp (at a given rpm) in high gear than you get in the next lower gear at the same rpm, because the car speed is higher. Furthermore this hp increase due to ram pressure will be added to the hp increase due to the cool air—so you could end up with as much as 30 or 40 hp more at the car’s top speed than you would get at peak rpm in low or Second gear, where car speed is only 50 or 60 mph.

Of course, simply having an open section doesn’t make a scoop functional. There has to be a sealed channel to the air cleaner inlet so that the engine will draw air through the scoop rather than from under the hood, and the shape and placement of the scoop have be designed to actually admit air when the car is in motion, rather than just collecting rainwater and dead bugs.

 

The photos on the top of the page above are of a Motion Performance Camaro with a highly modified 466 cubic inch Chevrolet big block and a functional hood scoop. (CARS editor Marty Schorr was a good friend of Motion founder Joel Rosen, and the magazine use Motion’s shop and dynometer, so Motion Performance/Baldwin-Motion cars and products got a lot of ink in the magazine.)

Huntington continued:

All this is theory. But it got me kind of interested. Especially as the different companies have such widely different air scoop layouts. Some are on the hood, some have high hood openings, others low and streamline. Chevrolet’s inlet is under the cowl vents, where the heater air comes in. Olds puts their scoops ’way down below the front bumper, piping the air to the carb through long flexible tubes.

It occurred to me that some of these air scoop systems must be more efficient than others. They’re all so different in design that they couldn’t all work with the same effect. For instance it is known that there is a “boundary layer” in the air flow along the hood that causes the air to slow down close to the hood surface. Wouldn’t this hurt the efficiency of the GTO air scoops, which arc very low on the hood? By the same token, Olds puts their scoops down below the front bumper in an area of high ram pressure. Wouldn’t this setup be more efficient than hood scoops? Or would air flow friction losses through the long tube ducts cancel this improvement? Chevrolet’s system that uses the cowl vents is in a region of “over-pressure” at high car speeds. But the air has to make a complete turn to get back to the carburetor. Would this kill the efficiency of the cowl vents?

I decided to do a little testing and find out for sure.

In this era, you would ordinarily expect the testing strategy to focus on standing-start quarter-mile ETs and trap speeds, which were still the principal performance focus of American supercars. However, while trap speed is a strong indicator of an engine’s developed horsepower, an increase in trap speed or a decrease in elapsed time with functional hood scoops might be due to a cooler intake charge, a ram air effect at higher speeds, or both.

 

However, Huntington had already developed a methodology for calculating a car’s actual engine power at the flywheel based on speed and accelerometer readings. (These estimates pop up from time to time in the various road tests he wrote for auto magazines, and he compiled many of them in his 1983 book American Supercar.) Using this methodology, he decided to measure the test cars’ power at the same engine speed at increasing road speeds, “to show the effect of increasing ram pressure.”

 

He obtained four test cars for this purpose: a 1968 Camaro Z/28 with the newly optional ZL2 “Cowl Induction” ducted hood; a 1968 Pontiac GTO with the Ram Air II engine package; and two 1969 A-body Oldsmobiles with Force-Air Induction: a Cutlass S with the W-31 350 and a 4-4-2 with the W-30 engine.

 

The text doesn’t explain why Huntington limited this exercise to GM cars. It sounds like the new Chrysler system wasn’t yet available when his tests were performed, but it’s not clear why he didn’t include the system offered on the Ford 428 Cobra Jet engine.

 

Since this test required holding specific engine speeds at different road speeds, the test cars all had four-speed manual transmissions. Ideally, they would have also had the same axle ratios, giving the same speeds in gears, but all of these cars were rare, and Huntington presumably had to settle for what was available. The GTO and 4-4-2 had 4.33 axles, the Z/28 the standard 4.10, and the Cutlass a 3.42 axle with a wide-ratio rather than close-ratio gearset.

 

He ultimately decided to measure the horsepower of the GTO and 4-4-2 at 5,000 rpm in second, third, and fourth gears, and to measure the output of the Olds W-31 at 5,000 rpm in first, second, and third. For the high-strung Z/28, power was measured at 6,000 rpm in first, second, and third.

While he was at it, Huntington also used accelerometer readings to calculate “the actual peak hp put out by these various engines in the bread-and-butter highway speed range around 60 to 80 mph.” These figures are loosely comparable to modern net output ratings, although I don’t know if Huntington’s calculations included correction for air temperature and atmospheric pressure as a DIN or SAE net rating would.

Ram Air Test Results

Here are the results Huntington calculated for each car:

Chevrolet Camaro Z/28 with ZL2 Ducted Hood

• 276 hp @ 6,000 rpm @ 51 mph (first gear)
• 273 hp @ 6,000 rpm @ 69 mph (second gear)
• 274 hp @ 6,000 rpm @ 88 mph (third gear)

Huntington observed:

Note that the cowl intake on the Z-28 gives no ram effect at all. In other words there was no increase in HP with increasing car speed. However, on a separate test we did determine that this sytem [sic] was effective in getting cool air to the carb. We checked hp with the plenum duct disconnected, so the engine was getting hot underhood air. The difference was anywhere from 8 to 12 hp at different rpm’s between the hot air and cool air. So the Z-28 cowl system is effective in getting cool air—but gives no appreciable ram effect at increasing car speeds. (At least not up to 90 mph.)

 

 

He calculated that the 302 cu. in. (4,942 cc) Z/28 engine had a peak output of 290 hp at 6,500 rpm. Chevrolet rated this engine at 290 hp at 5,800 rpm, although it would certainly have justified a considerably higher gross rating.

Pontiac GTO Ram Air II

• 301 hp @ 5,000 rpm @ 55 mph (second gear)
• 300 hp* @ 5,000 rpm @ 71 mph (third gear)
• 322 hp @ 5,000 rpm @ @ 91 mph (fourth gear)

* The summary on p. 25 actually said “200 hp @ 71 mph,” but this was clearly a typographical error inconsistent with the main text.

Huntington said:

The GTO hood scoops did better than I expected. There was no ram increase between 55 and 71 mph; but we got an extra 23 hp between 71 and 91 mph. Apparently the air flow over the hood is not too good at medium car speeds, so the system is effective only in pulling cool air. But above 75 mph or so the air flow apparently smooths out and hugs down tighter against the hood, so the low scoops get a solid bite of ram air.

 

 

He calculated the peak power of the 400 cu. in. (6,554 cc) Ram Air II engine as 315 hp at 5,500 rpm, and called the Ram Air GTO “a strong, solid car” that “pulled strong in every rpm range.”

Oldsmobile 4-4-2 W-30

• 286 hp @ 5,000 rpm @ 54 mph (second gear)
• 292 hp @ 5,000 rpm @ 70 mph (third gear)
• 316 hp @ 5,000 rpm @ 89 mph (fourth gear)

Huntington found that the Oldsmobile Force-Air Induction system was very effective, remarking:

Obviously the Olds system, with the low bumper scoops and ram ducts to the carb, is the most efficient of all. Don’t judge the system on the basis of absolute hp increase—but on a percentage increase basis. That is, between about 70 and 90 mph the 4-4-2 system gave about one full percentage point greater hp increase than the GTO hood scoop system. … The increase given by the Ramrod 350 is even more remarkable.

 

 

However, he still found the W-30 engine’s output disappointing, calculating that its peak power was only 295 hp at 5,200 rpm. He felt that the 400 cu. in. (6,554 cc) Oldsmobile engine was hampered by its longish 4.25-inch stroke, which meant “more friction inside the engine—plus higher inertia forces and bearing loads.” He wished for the return of the 1966–1967 E-code Rocket 400, which was very slightly smaller in displacement (6,548 cc), but had a wider bore and shorter stroke.

Oldsmobile Ram Rod 350 W-31

• 252 hp @ 5,000 rpm @ 45 mph (first gear)
• 258 hp @ 5,000 rpm @ 60 mph (second gear)
• 290 hp @ 5,000 rpm @ 76 mph (third gear)

Oldsmobile’s smaller W-31 engine benefited even more than the W-30 from the cold air system. Huntington said:

The [power] increase between 60 and 76 mph was over 30 hp—or some 12 percent. This is really more than it should be, by theory; but it’s possible there was some air flow blockage condition at the lower speeds that choked off the engine. I know the car felt tremendously strong in Third gear around 70 and 80 mph. And then when you shifted to high the acceleration felt almost as strong at 90 and 100 mph as at the lower speeds. … It was obvious that the ram pressure from the car’s forward speed was really getting to the engine above 70 mph.

The readings Huntington calculated were particularly impressive if you consider that the road speeds in each gear were significantly lower than for the other cars, which didn’t demonstrate much ram effect below about 70 mph.

Huntington calculated that the peak power of the 350 cu. in. (5,737 cc) W-31 engine in the 60 to 80 mph range was 310 hp at 6,000 rpm, 15 hp more than the bigger W-30 engine.

 

He observed:

The [Ram Rod 350] engine would wind to 6200 rpm without a whimper, and the pull between 4500 and 6000 was wild. It’s obvious that the 308-degree cam is a lot more effective in this small-inch engine than in the bigger 4-4-2 engine. And I think the relationship between valve size, port size, port contour and cylinder size is just about right. This looks like one of those “natural” engines for performance like the small-block Chev. We pulled a solid 310 horses at 6000 rpm—and that might even go up another 10 or 20 horses at car speeds above 100 mph, due to more ram pressure. This is a fantastic combination.

Given the power he measured at the clutch, he felt the W-31 engine’s 325 hp gross rating was highly conservative — a big advantage in the NHRA stock stock classes, which generally classified cars based on their ratio of shipping weight to advertised horsepower. “Ramrod 350’s have been winning more than their share, and now I can see why,” he said.

 

He concluded, “I think you’ll have to agree that Detroit has really given us some effective ‘free horsepower’ in these new cool-ram air systems.”

I must admit I’m somewhat dubious about the methodology of this exercise, although I imagine that a more elaborative procedure, such as setting up a chassis dynamometer in a wind tunnel, would have been prohibitive for cost and logistical reasons. Also, while Huntington found that these systems did produce more horsepower, this article didn’t attempt to quantify what that was worth in actual performance. (He had previously evaluated a 1968 W-31 Cutlass set up for the strip, but hadn’t made any attempt to evaluate how much the Force-Air system contributed to its performance.) Judging by other contemporary tests, the answer was “a little bit”: a few tenths of a second through the standing quarter mile, with the benefits not really felt until speeds that were illegal on most public roads in the U.S.

 

For hardcore drag racers — the kind who would consider ordering a GTO or 4-4-2 with a 4.33 axle ratio a reasonable choice — that was probably worthwhile, but they were the minority even among contemporary muscle car buyers. For most people, ram air systems were expensive relative to their benefits (the W-30 package listed for $263.30, the W-31 for $310.69), and often involved obnoxious practical limitations (for example, the W-31 package wasn’t available with power brakes and couldn’t be ordered with front discs).

 

The most common of these three systems at the time was probably the Camaro RPO ZL2 ducted hood, which was the least effective of the bunch, but also the cheapest, listing for only $79 when new. According to the Camaro Research Group, it was ordered on 10,026 1969 Camaros, since modern reproductions are available, it seems to be a popular collector add-on. The Pontiac and Olds Ram Air and Force-Air Induction systems were much rarer.

Today, they’re now far more common in clones and “tributes” than original survivors, inevitably accompanied by vehement arguments about authenticity and performance bragging rights — ironically generating far more hot air than cool.

Related Reading

Curbside Classic: 1968 Pontiac GTO – Redpop! (by Joseph Dennis)
Curbside Classic: 1969 Pontiac GTO Convertible – Hi-ho Silver! (by J P Cavanaugh)
Curbside Classic: 1969 Pontiac GTO The Judge: Here Come Da Judge! (by J P Cavanaugh)
Vintage R&T Road Test: 1968 Chevrolet Camaro Z-28 – “7500 RPM Is A Good Shift Point” (by Paul N)
Curbside Classic: 1968 Oldsmobile 442 – It’s All In The Numbers (by Paul N)