Mike Ward

Well, that is a good question and I'm willing to give it a try. Opportunities to do this right now are getting rare- we normally have a good amount of snow on the ground by now, so testing might have to wait till spring.

Three other things-

1) I had all the Astro Ventilations ducts in the 'closed' position during the test in an attempt to maximize pressure in the windshield plenum. That, and it was just cold too open them.

2) With the system functioning as designed, the duct, the adjoining hood surface, the air filter, the filter element and even the air sitting stagnant in the duct itself are at underhood temperatures when the flapper is closed. The flapper only opens when the throttle is on the floor. While running up though the gears, this means the flapper is only open for a few short seconds between shifts and then held open for a few additional seconds until max. desired vehicle velocity is reached and the test aborted. This means that the air entering the engine is not a true ambient temperature as it is absorbing heat from the surrounding hardware. This means that a car sitting idling waiting it's turn to do a 1/4 mile test would spend more energy trying to cool the duct work than a car that had no cowl induction.

3) I got a PM from a fellow member regarding my test results. He pointed out that it's probable that non-cowl induction Corvettes would also benefit from the 1 degree prevailing wind effect, which is 66% as good as us cowl induction guys get. He's right. On the other hand, pushing a car into a 20 mph headwind more than offsets the piddly amount of HP gained. Funny, I didn't think of this person as being 'contrary', but as an intelligent, thinking person who has contributed valuable info to this exercise.

Eddie & the Cruisers

I think the snorkels not being plugged or blocked off would dilute the cooler cowl air when it reached the area of the filter housing whether front, back, or side locations measured in your tests. Perhaps the air would have been 11* or more than 2* cooler.
Ya up for making a few more 100 mph runs?

GM should have included snorkel valves to close when the cowl induction was in effect. Have you ever heard of a snorkel not having valves? Well, its an idea!

74 LS4-454

Although I don't know Mike, I totally agree with him, it has been known from years gone by, that this system was more of a marketing tool than a performance enhancement. In fact all of the car manufactures from the early days used these said systems in their HP vehicles. I get Hemmings Muscle Car Mag, (which is a great pub) and it has been pointed out in various articles about the "cowl induction" offerings and how they were more of a marketing tool than anything else....
Not saying that you won't feel a slight SOP feeling or that incresed induction noise....
Not trying to start a flame here, but it seems that Mike knows what he is talking about, and he backs up what he is saying.

To the other posters who mentioned about putting important people on special assignments and why would they do such a thing if there was no benefit to it???? Well there was a benefit to it and that was to sell cars, whether the benefit was for marketing or performance purposes, the ultimate goal was to sell more cars than the competition....

Mike, I enjoy reading any of your threads, to those who oppose, it is always good to have a debate, but leave the flaming out.....
........................................ .....................Tom

moonsteel

Some other thoughts

Is it possible that at WOT the engine needs more air than the front snorkels can provide?

Perhaps we can improve on the system GM provided us with.

a) plumb the front snorkels to the front so they don't pick up hot air from the rad/engine bay
b) remove the flapper and have the cowl open all the time
c) add something like K&N x-stream to the top of the air filter to allow it to access that air easier.

Thoughts?

7T1vette

There is higher pressure at the base of a vehicle's windshield, IF that area is not vented. That pressure can be used to some [small] advantage by the induction system IF it is channeled directly to the intake and without other possible areas of 'leakage' (such as open air cleaner intakes, etc.).

The cowl induction mechanism is meant to: #1) convince Corvette buyers that their low-compression, low power, mid-70's, high-priced sports car is still, well, a sports car; 2) add some miniscule amount of power to the engine at WOT and at high speeds (if there's enough HP to get it to high speeds); 3) close off the excess/colder air flow from the intake when the engine is first started so that the choke system can do its job properly [warmer air to the carb during start-up is a 'good' thing].

I'm sure the cowl induction system is NOT exactly what the performance engineers envisioned [before marketing got hold of the idea], but the EPA's requirements and GM's dislike of performance cars (at that time) put the 'damper' {pun intended} on that system. If that system (as it was produced) was all that beneficial, it would have stayed a part of the car longer than it did.

Mike Ward

Thanks for your insight Tom.

I have acquired some additional info that backs up the 'marketing cr*p' assertion. The referenced magazine article above spoke about the ZL2 option as installed on Camaros. I made contact with someone who drag raced a Z28 back in the day and used the ZL2 set up. This person is considered to be one of the most technically astute Camaro/Corvette people around and has probably forgotten more about the 60s-70s cars than all of us put together actually know. He is to this day very active in the hobby. If anyone will be at the Kissimmee NCRS show in Jan, I'll be glad to make the introductions.

Let me quote his responses:

"In 1970, I switched to drag racing with my 68 Z28. It still had the GM 2x4 crossram and early cowl air setup off the firewall. Mid season 1970, I build and installed a steel hood very similar to the GM fiberglass hood with cowl air intake. The car was immediately almost a 10th slower than with the old system. Rejetting eventually brought the times back but it was a lot of work for no gain......."

I responded: "So, if I understand correctly, the car was slower with the ZL2 option."

To which the following was offered:

"Yup, slower than it was with the early firewall mounted cold air system. Slower top end MPH too and that's the end that would show a drop in HP.

All else was the same on the car. Only the hood was added, along with the proper 2X4 air cleaner base that sealed to the hood. I used the GM screens and covers that XXXX (another contributor) mentioned.
If I remember correctly, the jetting had to be leaned off one or two numbers with the new hood. I don't remember if the top end MPH was ever the exact same though. I seem to vaguely remember it dropping a bit.

I should have experimented more but I moved on to other items and never really sorted out the new hood.

In the end, I feel that the 67-68 firewall air system was at least just as efficient as the new hood system, and possibly more so. Lotta air went into those cowl vents at high speed.

We worked pretty close with the boys in the back room at GM on this car and none were surprised at the results of the hood change. They imediately suggested a jet change, which we had already done."


I purposely did not reveal the reason I asked to avoid possibly skewing the responses. Well boys and girls, I think I'm quite sure that my original statement of 'all show and no go' was not far off the mark.

The OP brings up the topic of experimenting through modification of the stock system. I have no reason to believe that the stock air filter or snorkels are insufficient in flow capability and certainly the K&N filter gizmo has been thrashed to death far too many times, so I'm not interested in going there again.

With respect to re-doing the ductwork, I'm sure that the air inlet temp can be reduced by replicating the later Corvette set up. A point to consider is that duct work = friction (flow restriction). Whatever is gained in temperature reduction might be offset by reduced flow.

I'll let somebody else play scientist on that one.

gr8t73

All I know is it looks and sounds cool so I will keep it.

GREGG-73

I think Mike has proved his point, beyond reproach. As to the naysayer’s here…..in regard, as to if it was a GM marketing ploy…well, it look’s good, sound’s good…and Hey, we can charge extra for it. The induction system had been around for many year’s prior to being a add on in 73. So, if you think you are getting anything (other than smoke & mirrors) out of capping off the snorkels and other…get a life…its nominal at best and that is not saying it makes any difference at all. For all those whom still want to pursue this issue further…I ask that you answer this question first and foremost….

Is it really true, and in fact, that the color of the twisty-tie on a loaf of supermarket store bought bread, actually determines its freshness????????????? Hey, I just have to know!

73, Dark Blue 454

To those who don't believe rain and snow were two of the reasons for the flapper,..from here:

http://www.camaro-untoldsecrets.com/...es/rpo_zl2.htm

...is this:

"Engineers used and air-valve to control when fresh air was allowed into the air-cleaner assembly. This was done to improve driveability in extreme weather conditions."

...and this:

"WHY AN AIR VALVE?

The air valve was specified for use on the production RPO ZL2 option for the sake of better overall drivability. Taking into account the diversity of climatic conditions and their effects on the system, it was determined that the system should function only when called on. If the system remains open in extreme cold weather, icing of the carburetor could occur."

Also, if one test is worth more than a 1000 opinions, then this "yarn test" (five 6" strings of yellow yarn) clearly demonstrates cool fresh dense air is being pushed to the air cleaner when the Vette is at speed:

http://s421.photobucket.com/albums/p...=YarnTest2.jpg

And, somebody above compares the early Z-28 (67-68) plenum fresh air system with the (ZL-2) cowl hood set-up of 1969. The finding was that there was no gain. Fine, but, the arguement is fresh air vs. snorkle air; not fresh air from plenum induction vs. fresh air from cowl hood induction. Obviously, the 'tester' whoever it is, believes in a fresh air system. I completely agree with him.

TW, from your post, I've no idea what testing results and testing methodology were used that show the minimal reduction of induction air temps. So I can't agree or disagree. So, I'll side with the GM engineers on this one.

Also, TW,..you say the 69 Camaro cowl hood system is different from the 73-75 Vette. I'll point you to page 74, second paragraph of this:

http://books.google.com/books?id=KIb...iggins&f=false

(Again, seems I'm the only one citing published works and real photographs to support my position).

noonie

I have yet to see any real documentation supporting the marketing or the performance aspect. Just because opposing opinions have been recirculated for years in magazine articles and the internet doesn't give either view any more credability.
Perhaps someone who actually worked and had hands on experience at GM in cold air development or was a marketing exec paticipating in that area could chime in.......

Other than that the concept is pretty basic.
The OP asked about cold air and yes it is obviously beneficial.
All you experts just need to look around.
On vettes in 76 and almost all other GM's even full size, of that era, cold air intakes via the snorkels and bellows were being incorporated.
The later C3 L82 used the 2 snorkels instead of 1, but both were cold air. A lot of expense added to all cars and certainly not for marketing.

Today, every vehicle made has cold air induction of some sort, whether it be a Hyundi or a Vette or a Mercedes, even forklifts and other industrial equipment, even if the filter box is still inside the engine compartment.

I would guess it has a lot to do with efficiency and mileage and due to the cost of some of these intricate systems, it would also have to have a measureable effect.

BTW, I had a 72 T/A HO that had the operating flapper on the shaker, but also had the snorkels that were ducted way down by the bottom of the inner aprons. That system was much, much louder than the vette system. I made it full time too and gained a small increase in highway mileage. They discontinued it in 73, supposedly because of driveby noise, but the flapper could just be unbolted.

Mike Ward

To summarize:

-We all agree that there proof that cowl induction works in NASCAR

-We all agree that cold air is better than hot air.

-The item still being debated here is whether the '73-'74 Corvette cowl induction system as installed by GM actually works.

-I can find no proof that it works.

-No one else has come forward with proof.

I'm done on that side of the issue. Repeatedly posting the same Camaro advertising stuff or pictures of an aftermarket hood on an earlier car is at a minimum annoying, proves nothing and is starting to be borderline troll.

On the other hand, there is a mention of why the flapper exists at all. In the above post, there is the mention of 'carb icing'. AH HA! That is a valid concern.

Carb icing is a serious concern on light aircraft, or any piston powered aircraft for that matter. This condition occurs when the temperature of the air drops below the dew point inside a carb causing suspended moisture to drop out of suspension causing condensation. If the carb surface itself is below the freezing point, the suspended moisture can turn into ice.

I had a car in the 70's that suffered from carb icing when not fully warmed up. In my brilliance, I had removed all the thermostatic devices built into the engine to preheat the air which would have prevented this.

On the other hand, carb icing occurs in clear air just as much as any other weather condition. It's a function of humidity and temperature, nothing much to do with rain or snow.

Aircraft do have means to deal with rain and snow entering the intake- they're called inertial separators. Since water has considerable mass, it tends to go in a straight line once moving. Air on the other hand air has very little mass by comparison so can be convinced to turn sharp corners with little effort or energy loss. The company I worked with for 31 years holds the patents on multiple example of inertial separators. One of my former neighbours was the principle inventor of once such device put into production in the late 50s. He always admitted that his inspiration was the grill installed in his office door to deflect the air conditioning.

It might be true that there is a danger of carb icing on a '73-74 Corvette since it has only passive means of heating the carb, unlike later versions. My tests show that underhood heat increased inlet temps by approx 50*. I suppose that if that heat were not present, carb icing might occur. There's two ways of inducing this- test the car again with colder ambient conditions or test it with a cold underhood environment.

The coldest inlet air I could induce was 86*. I'm not likely to drive my Corvette when it's 55 degrees colder outside to see if it works, nor am I ever going to induce the flapper to open until the engine, carb and everything else is good and warm.

Somebody else can take over at this point. This is not fun anymore.

Ganey

It should be obvious to test it, it would need to be tested disabled & operational. For ex, disable on a warm day, do accel. runs from 0 to at least 100, then enable system & do runs.

moonsteel

and more importantly, can we improve on it 35 years later, armed with what we know...

LS4 PILOT

Zora Duntov seemed to think it the 73-74 air induction worked. His word is GOOD ENOUGHT for me. He described its function and performance advantage in at least one national magazine test I have around here somewhere. He seemed to be very results oriented person that didn't waste time or money for no result.

I have owned four of these cars. I don't think at low speeds it notoceable power increase. But Zora drove wide open , and he was always looking for more power at top end., high speed road racing or making fast lap at Milford proving grounds.

I believe there is a Hp gain , but mostly at speeds we can't maintain on public roads. Most drivers will never approach the speeds required to see the claimed results in average driving. I don't think short drag racing bursts will reveal much gain. But a few 125mph laps around Daytona might. Be that extra few mph gain he was looking for ie. faster lap times. , or bragging rights for his product. and were intented were for the people who really liked to drive VERY fast ALOT. This was mssing the mark by 75 So this system disappeared not long after he retired.

I would like to test all this at Michigan Speedway with my old girl .......LoL

Solid LT1

I would agree with your assesment but, hey your not as smart as Mike! (a legend in his own mind!) so, your opinion dosen't count! I guess we will have to wait until the spring thaw so Mike can do some more studies (I just shipped my 74 Vette off to Australia so I have no data base.) Mike have you got any snow tires for your Vette? maybe you can do it by March if you do

I wonder based on his testing methods if he isn't one of the Climatologists working for Al Gore's "Tax and Trade" plan with his flawed reasoning.

Dropping intake temprature WILL increase HP and closing off the A/C snorkles WILL drop intake temprature. Duntov was QUOTED as saying in the December 1972 issue of Car&Driver magazine: "compared to a non-ducted hood Corvette, the 73 Vette cold air system was responsible for a 1 second decrease on 0-60 times in a standard engine Corvette." Not my words, just the words of some guy who had a little better engineering background than our "Expert" from the "Great White North" EH?

Solid LT1

What I would do if I wanted maximum performance from a 73 and later cowl induction system: Remove the flap in the hood, block the underhood snorkles, insulate the metal lower air cleaner housing and install a K&N filter.

Try that and then tell me you don't see a significant drop in intake tempratures EH?

Mike Ward

And as Paul74 likes to say, 'now we know why Lars left'

You may disagree with my opinions and I may disagree with yours- but I don't resort to personal insults, nor do I go after the worn out stereotype cheap shots. Pretty sad, but not unexpected given the track record.

As for Duntov's quote, think about it for a minute- 'improves 0-60 times by 1 second' Somebody please calculate how much HP it takes to get a car weighing as much as a '73 to drop 0-60 times by that much. Second point- the cowl induction system relies on the supposed body of high pressure air at the base of the windshield. Well, there is none if the car is starting from 0 mph. If you want to believe that there's a huge amount by 60mph, go right ahead.

BTW- Mr Duntov had another favourite quote. The reason that Corvette got a big block engine was for weight savings. The holes in the cylinder block for the pistons are bigger in a BB than an SB so it weighs less.

Finally, I've communicated with the OP on the original question and a possible strategy for further testing. If anybody has any hard proof of effectiveness (other than the boy racer stuff that's formed 90% of this thread), please send me a PM. I've recieved great photos of both the ZL2 and plenum induction systems which demonstrates why one works and the other doesn't. The Camaro guys are having a good laugh at you guys going over ground that they beat to death almost 40 years ago.

Thanks and good luck.

7t5

Don't leave. Sometimes you just give answers we don't like to hear, but we need to hear them anyway.

LS4 PILOT

Why in the world would we believe dumb old Zora , Vince , or unqualified engrs from GM , we have our own "KNOW" IT ALL" right here to teach us everything .
Thanks for providing the exact info from CAR & DRIVER . Seems ol Mikey has frozen his brain up there in CA

Ganey

Not at all. Duntov did not want to put the BB in the Corvette. The smaller cars were limited to 400 c.i. by GM policy. John Z. DeLoren, Pontiac put the 389 in the mid size Tempest to create the GTO in 64 model year.
Duntov, Chevrolet gave the 427 a smaller bore to create the 396 & was in the Corvette in 65 model year.
The following year model 66, full 427 displacement was used.
Duntov cleverly said "This was done primarily to save weight. You must remember that cast iron is very heavy & by removing 30 c.i. of it we have made a significant reduction in weight."