supercar cowl induction tid bit..
 

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..

Re: supercar cowl induction tid bit..
 

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).

Re: supercar cowl induction tid bit..
 

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.

Re: supercar cowl induction tid bit..
 

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.

Re: supercar cowl induction tid bit..
 

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.

Re: supercar cowl induction tid bit..
 

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.

Re: supercar cowl induction tid bit..
 

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]

Re: supercar cowl induction tid bit..
 

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.

Re: supercar cowl induction tid bit..
 

<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

Re: supercar cowl induction tid bit..
 

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.

Re: supercar cowl induction tid bit..
 

My personal favorite ram air setup of all time has to be the Ford Thunderbolt.

Re: supercar cowl induction tid bit..
 

Maybe ram air rules the day for drag racing up to 100-110, but go faster than that, and drag takes over. I still dont get how the 68 L88 beats the 67 by 7 seconds. same engine. 68 is heavier (I think). that leaves aerodynamics (drag) and the differences in the scoops. Did the stinger on the 67 vette add too much drag? 7 seconds is a HUGE difference in times. btw, I dont buy the tire difference between a 67 vette and a 68 being significant part of the potential time difference, for example a 67 hemi gtx took the best FAST times on skinny 14inch redlines. I would concede maybe a second or 2 at best in the time to get to 140 on the tire difference front. Engine setback differences are lost once the car is launched, and that would only buy tenths of seconds in a difference in 0 to 140 times.

One very interesting thing, I noticed in the baldwin motion pictures, the 69 camaro stinger scoop was opened up on the BACK to take air maybe from front and back of the scoop. rosen was playing both sides of the fence with his scoop. To me he was not betting on ram air, but more on taking air from the windshield area.

Re: supercar cowl induction tid bit..
 

wouldn't it be cool if they could mimic in FAST drags where they could get supercars up to 140mph? then you could see which factory car reigns supreme...a corvette 68-69 L88 or a superbird/daytona hemi [img]<<GRAEMLIN_URL>>/smile.gif[/img]

lets go to an airport and find a vacant landing strip....

Re: supercar cowl induction tid bit..
 

When comparing the 67 vs 68 Corvette L-88, I can actually see how the 68 was 7 seconds faster to 140 mph. I'd bet up to 110 mph, the cars were nearly identical. Then beyond that, the better aerodynamics of the 68 begin to show. I'd bet from 130 to 140, the 67 was hitting an aerodynamic brick wall, and the 68 cruised to 140 mph much easier.

Aerodynamics play a huge part over 100 mph. Under 100, aerodynamics are more important for fuel mileage, but over 100 mph, the horsepower required to overcome aerodynamics goes up exponentially.

[img]<<GRAEMLIN_URL>>/beers.gif[/img]

Re: supercar cowl induction tid bit..
 

I have to agree about 1963-67 mid-year Corvettes being terribly un-aerodynamic regardless of how &quot;swoopy&quot; they look. As much as I think that they are the most beautiful car the General ever released, stand to the side of one someday and check out the side profile of that near-vertical windshield and a front nose that pushes as much air under the car as over it. I've seen reference to that 7-second reduction time before and it makes me wonder if some automotive writer mis-quoted Zora and meant to say 7 tenths, because that would actually be believable especially if you go by that basic rule of thumb that says a tenth is a car length at the top end. It's not to hard to imagine a 7 car length/7 tenths difference between two cars but think about how big the gap is between two roundy-round cars that finish 7 seconds apart! That's a big gap!

Re: supercar cowl induction tid bit..
 

Well, what I was trying to say in the earlier post (not sure if I conveyed this properly) is that the 67 and 68 may have been within a car length of each other up to around 125-130 mph. At that point, the 67 may have taken another 20 seconds to get from 130 to 140 mph, while the 68 may have taken 13 seconds, thanks to the better aerodynamics.

The speeds quoted would have been at the limit of these cars top speeds back then, so I would imagine that the 7 extra seconds for the 67 model was all from 130 to 140 mph.

Re: supercar cowl induction tid bit..
 

Lets put this to rest. Who owns a whole bunch of L88 Corvettes that will let me personally take them all up to 140 mph to settle this dispute. [img]<<GRAEMLIN_URL>>/headbang.gif[/img]

Re: supercar cowl induction tid bit..
 

Aerodynamically the 68 is the obvious front runner. I don't know about 7 seconds but I'm sure there was definitively a difference. It would be more noticeable on a lower HP car. Take my old Mini for instance. When I lived in Italy I drove a 1991 Mini 1000. It had, you guessed it, a 1000cc engine and about 35hp. Shaped like a brick it would max out at 135kph and it took a while getting there. That was as fast as it would go, but the engine was not even close to red line. If I remember red line was at 5000 and at 135 it was running at about 3200. The same motor in a more aerodynamically conducive car, even with a little more weight would go faster. (After driving it for a couple of years and tuning on it and some custom paint I did get the max up to about 142kph)
The Mini http://jirehcustoms.net/?p=113

Re: supercar cowl induction tid bit..
 

Custom paint will do that for you. http://www.moppo.net/links/195384001265684433-final.gif

Re: supercar cowl induction tid bit..
 

Knowing that every company, on occasion, &quot;accidentally&quot; sent out a special car for some of these test, I would think what could have been going on under the hood would be the real debate. Comparing a 55 Chevy to a 67 or 68 Vette with the same drive train....7 seconds maybe from 120 to 140. 67 and 68 Vette and the drive trains being equal, I would have to see it.