supercar cowl induction tid bit..

[black69]

I dont know how many know this, but I guess chevy really was ahead of its time compared to ford and chrysler in 69-70 in atleast one area. In an old book, I read yesterday that duntov said cowl induction basically took 7 seconds off the 0-140mph speed when comparing a 67 L88 vette to a 68. To me that is a ton of time difference on one particular supercar type! I imagine some is related to wind resistence reduction (when compared to a stinger) and the rest is mostly the pressurized air (resulting in more horsepower).

So maybe those certain 69 camaros and 70 chevelles (with cowl induction) really had an edge over the mopars and fords on the open road races (once you got over 100).

I tip my hat in the chevy direction....for today..

[black69]

for what its worth, this 7 second claim came out of a book written by Martyn Schorr (baldwin motion) on chevrolet supercars in 82.

maybe this is why some of those 68-69 L88 vettes do so well in the FAST competition (holding the top spots), etc (its in part related to cowl induction power gains).

[442w30]

I have two points to consider:

1. Chances are the A12 hoods from the Six Pack Super Bee and 440 6bbl. Road Runner are the most efficient design of all.

2. Just because cowl induction has been shown to have some value doesn't mean the 1969-72 designs (I know there are Camaros and Chevelles with the plenum before '69) were the best out there. For all I know, they they could have been less efficient than the 1970-74 Formula, 1971-72 GTO, 1966-69/70-72 Olds OAI, or any brand's Shaker.

Certainly, for all of Chevy's might, it's interesting how they took too long to jump into the ram air bandwagon.

[StealthBird]

In the F.A.S.T. Series, the 68-69 Vettes benefit more from their lightweight and aerodynamics than from their air induction. At speeds over 100 mph, wings, dams, and other aero devices start to play a significant role. A front spoiler on a 69 Camaro is good for a mph in the traps with a car hitting 100 mph.

The various cold air setups didn't provide any actual ram effect, with the exception of the car traveling in excess of 100 mph, and even then only a few setups were capable of providing a VERY minor amount of positive pressure. The factory setups were not very efficient, more for show than go. But they did draw in cold air, and they worked. Various marketing tactics made the buyers believe that ram air would make your car a street terror, and some manufacturers came up with outrageous claims. In reality, adding a cold air intake setup, and jetting accordingly, was what made the ram air setups effective.

Why didn't everyone just use a hood scoop? Well, plenum or cowl setups were preferred because many manufacturers didn't want to use a hood scoop. Hood scoops were considered boy-racer stuff, not to mention the fact that hood scoops were warranty nightmares when owners drove year round, through torrential rain, blizzards, etc.

A12 Mopars used a huge scoop, but keep in mind that they still weren't directly in the airstream. Much larger and bolder than the other manufacturers, yes, but at over 100 mph the air would be pushed up and over the scoop. It was a far more effective setup than the GTO scoops of the era, but still far from ideal. Mopar wanted the drag racer look, so they had no problem making their scoops visible. And when they weren't visible, they had a switch that raised the scoop. [img]<<GRAEMLIN_URL>>/naughty.gif[/img]

In order to create ANY positive pressure at high speeds, the scoop(s) need to be at the leading edge of the hood, and have a straight path to the carb. Lots of examples of great scoop design, which made for great marketing, but the setups had little chance of producing any ramming effect.

The 66-69 Olds OAI setup had the right idea. However, the duct work required under the hood caused a loss of ramming effect. For every turn or bump in the ducting, pressure is lost. While they did bring in cool air, they didn't provide any ramming effect. Olds switched to the 70-72 OAI setup because it was more aggressive looking, and met their marketing tactics of getting their Oldsmobiles noticed at stoplights.

The 1969 Trans Am also had the right idea, the first GM car to have functional scoops placed at the leading edge of the hood. Unfortunately, that setup was suffocated by a small air filter.

The 1970-1975 Formula hood had the scoops in an even better location than the 1969 Trans Am, but the 90 degree turns from the plenum to the air cleaner, and 90 degrees again to the carb, killed any possibility of a ramming effect.

Shaker scoops were visual and provided cool air, but no ramming effect. The design of the 1970 Trans Am shaker was flawed, with the scoop placed too far forward to get any benefit from the high pressure buildup at the base of the windshield. They wanted to extend the scoop backwards, but styling overrode engineering. The shaker was basically a door to cool air.

Cowl or plenum induction works well at getting cool air. There's isn't enough pressure buildup at the base of the windshield to provide any ram effect, but the cowl is an excellent source of cool air. No bugs, no debris, no direct inlet for rain or snow.

Overall, all these setups provide cool air, so the cowl, plenum, hood scoop, or bumper scoops are all effective. After that, it came down to marketing, visual appeal, and hype.

The most effective setups are those that have an direct path to the carb or air cleaner, with no turns, no airflow killing hoses, etc.

If the 1966-1969 Olds OAI setups could have had a more direct path to the air cleaner, they may have been the most effective of them all. The 67 setup may have been the best, but the parking light scoops had a very small cross section.

[Keith Tedford]

Since buying our 2005 Corvette, I see all the same old gimmickry all over again, headers, exhaust systems, ported this and ported that. As an example everyone is making an air intake with nice hp number gains. As far as I can see, these numbers are for the owners' egos more than reality. I think what I like most about our '05 is the lack of gimmicks. No scoops. No spoilers. No paddle shifters, just functional stuff. It has vents in the front fenders to extract engine heat, but if you look inside there is a black baffle that probably limits any decent amount of hot air from exiting. It's supposedly 16 mph quicker than the 2004 Z06 through aerodynamic inprovements.....as if I have anywhere to find out. Just bragging rights for the owners I suppose. It's all about selling cars, then and now. Still, without this stuff, the cars wouldn't have an identity like they do. Ram Air, Cowl Induction and such were all buzz words in the day. We all loved it.

[markjohnson]

I think the most important aspect of '68-'69 L-88 Corvettes being dominant in Pure Stock is the massive amount of engine setback which is a major factor in a class with such tire limitations. It's obvious that a 12.5 Compression, massive solid lifter camshaft, factory 850 double pumper on an aluminum headed 427 CID might be a small factor also! Superior exhaust manifolds also compared to Camaros, Chevelles, etc. Chevrolet started the Cowl Induction theory with the '63 Z-11 Impala and even Smokey Yunick said that during testing, a Cowl Plenum air cleaner was good for approximately 1.00 PSI at speed. When this Pure Stock way of racing took off several years ago, it was obvious that as soon as someone properly prepared an L-88 Corvette, that it would be over for everything else.

[StealthBird]

Yes, but Smokey's &quot;at speed&quot; was NASCAR speed, as in 150+ mph. On a street car, even a fast drag car, there is virtually no ram effect, and certainly not through a plenum or cowl setup.

Holding your arm out the window and cupping your hand, you feel tremendous pressure. But getting that air to the carb, through a series of hoses, elbows, or ducting, you lose a lot of pressure. When that pressurized air does get to the carb, it has to overcome a wide open throttle condition, a carb that's gulping in huge amounts of air on every stroke, to the tune of around 800 cubic feet per minute, and then you need to build up even MORE pressure to force air into the cylinders, under a wide open throttle condition, revving at maybe 6,000 rpm. Air needs to fill the cylinders and carb plenum, refreshing it constantly while the engine sucking down air. A forward traveling car does not produce this much pressure, unless it's traveling at a VERY high speed and a VERY good air intake setup. On a street car, add in the restriction of air filter, and there's no chance of getting a ram effect at all.

Pro Stock cars use a huge air scoop, taller than it is wide. They discovered the optimum scoop height and inlet opening via wind tunnel testing in the 1990's. The older scoops used in the 70's and 80's were sort of guess work, but they did know they had to get the scoop high, very high, much higher than even the A12 style scoop, to be effective.

The whole Ram Air thing was a great marketing ploy by Pontiac. It brought in cold air, but there was no ram effect. By attaching a name to the setup, and marketing it as something unique to Pontiacs, was a stroke of genius. To this day, more people use the term &quot;ram air&quot; than any other term when referring to an cold air intake setup or hood scoop.

I've built a lot of ram air setups, some using a mix of Pontiac and Chevy parts, some using the hose-fed idea (I did a lot of those), and I've tried headlight entry, parking light entry, separate bumper scoops, etc. In every case, the car runs BETTER. No doubt about that. It's also much quieter from the interior under full throttle.

But I have to chuckle when I see ads selling ram air kits claiming 20% hp improvements. That sounds great for yer ego, but lousy for your bank account. [img]<<GRAEMLIN_URL>>/wink.gif[/img]

[GreenLS6]

Being a Pure stock racer, Long time car guy . I truly believe the biggest Plus to Cowl induction- or Ram air, is the bonus of a cooler air charge entering the engine rather than a forced effect. At least in a drag racing sence 11-12 second sub 120 mph. I'm sure that would be different case in much faster drag cars.

[GreenLS6]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: markjohnson</div><div class="ubbcode-body">I think the most important aspect of '68-'69 L-88 Corvettes being dominant in Pure Stock is the massive amount of engine setback which is a major factor in a class with such tire limitations. It's obvious that a 12.5 Compression, massive solid lifter camshaft, factory 850 double pumper on an aluminum headed 427 CID might be a small factor also! Superior exhaust manifolds also compared to Camaros, Chevelles, etc. Chevrolet started the Cowl Induction theory with the '63 Z-11 Impala and even Smokey Yunick said that during testing, a Cowl Plenum air cleaner was good for approximately 1.00 PSI at speed. When this Pure Stock way of racing took off several years ago, it was obvious that as soon as someone properly prepared an L-88 Corvette, that it would be over for everything else. </div></div>

You mean the biggest carb GM ever used, highest compression ratio, Best intake, Biggest solid cam ,best GM ex. manifolds, a 50-50 weight bias, best aero package, big tires. Might be an advantage over other cars ??? [img]<<GRAEMLIN_URL>>/dunno.gif[/img] Hahaha

[StealthBird]

Yes, it's the cool air that makes ram air setups effective, not any sort of ramming effect. But marketing is a great thing, and when you see the words &quot;ram air&quot;, people assume it's ramming air, but they don't.

Sort of like when people go to cruise nights, but everyone parks. [img]<<GRAEMLIN_URL>>/hmmm.gif[/img]

For NASCAR or other forms of racing with sustained high speeds, a ram effect can actually be achieved, and additional power can be had. But not with a street car, or with any of the factory setups.