Jvette73

So the years 73-75 came factory with functional cowl induction. Its known to be an advantage in the power department. Anyone got a clue as to why they quit with it?

TedH

My guess: Weight savings and complexity/number of components to implement.

There are power gains using the ram air setup introduced with 1976. By 1980, the L48 was standard with the L82 'dual snorkel' setup which obtained air from forward of the a/c condenser/radiator.


[Modified by TedH, 10:48 PM 7/16/2003]

45ACP

Noise. The intake howl was unacceptable.

Tom73

:iagree:
That is my understanding, it was just too loud. The Vette was in the process of changing from a performance car to a boulevard cruiser and excess noise was a no-no.

tom...

BSeery

My 1980 has a very nice cold air induction setup from the factory. It has a dual snorkle air cleaner that picks up cold air from between the hood and the top of the radiator. It also serves as the ducting to seal the radiator as well.

Very nice piece of work and I will keep it on there just for the perfomance.

Fevre

Those sissies! Mine is not fully hooked (yet!) but I love the sound of the air being sucked in when you drop the :smash:.

Ken74Conv

The intake howl and the rumble of the exhaust are what makes up a
performance sports car.
I love it!!
:cool:

lars

The guys are correct in that it was a noise issue. However, it was not eliminated because GM didn't like the noise: It was an EPA-mandated noise reduction. The same thing happened with the blocked hood scoop openings on the Trans Am (but Pontiac made the block-off plate removable - bless their hot-rod hearts). The GM guys actually like producing performance car sounds, but our Government watchdogs don't care much for it...

flynhi

I've read about the evidence of high air pressure at the base of the windshield and that this pressure is positive for air intake.
However - a year or so ago, I did a "tuft test" with yarn strips taped all over my 71 vert. A friend took pics alongside at various speeds up to 90.
I observed laminar flow across the hood and no turbulence (indicating some pressure) up to about 75.
This tells me that cowl induction is ineffective for ram air at most driving speeds.
Shortly after that I built a forward facing cold air set up similar to later C3s. I measured intake air temps with a digital thermometer in on top of the hood (unaffected by engine temp) and in the duct feeding the enclosed air cleaner.
I showed a diff of only a degree or so. I didn't have instruments to measure ram air effect but clearly there is some at speed.

I don't disagree with the other comments about noise, but I have to believe that GM engineers came to the same conclusion that I did.

Glutamine83

i've kept my air cleaner assembly intake for that very reason

lars

flyn -
There is no question that the factory "ram air" systems (not only on Vettes, but on cars such as the GTO, Firebird, Camaro, etc) have very little, if any, effect on performance: I've measured and documented similar results showing little, if any effect from the systems, and I've seen similar documented results during my research at GM Engineering. Rather, the systems were marketing tools, and the marketing department knew that the cool sound and "ram air" words sold cars.

The current version of completely ineffective "performance" items that are sold by most manufacturers are rear spoilers: Few, if any, production rear spoilers are actually tall enough to get out of the turbulent boundary layer air to be effective. Even the large GTO spoilers used in 1970-1971 actually produced LIFT instead of downforce (documented by Pontiac Engineering as completely ineffective, but used in production anyway).... So just because a "performance" item doesn't work doesn't mean it won't be used in production if it helps to sell cars.

(...and on that subject, one of my favorite "hot" topics is that dual overhead cams is just a marketing gimmick and serves no performance purpose that can't be achieved by 2 valves per cylinder... try that one with the Ricer crowd..)

Matt Gruber

:iagree:
i've always suspected the cowl induction hood was a fire hazard(hood open)
a carb without an enclosed air cleaner can burn easily with a backfire.
i built my own enclosed filter that works thru the cowl opening.

theoUK

Lars, Thats an interesting idea, about the gimmick value of DOHC. I can see you point about the "ricer" value (we just call em boy racers in the UK, don't give them the satisfaction of making up a whole new name for them :lol: ) since these guys just want some cool sounding names to bounce around, regardless of whether they know what they mean or not.
But surely having four valves in the head is a more effective use of space, and hence a better way to admit the charge? I think another one of the main benefits is reduction of the reciprocating mass - four small valves move up and down a bit more happily than two big ones. Thats a help in the FMEP department. What do you think? I'm sure the engine design ethos is a different in the UK to how it is in the states, so please don't get the impression I'm disagreeing with you :lol:
This is an interesting question - tell me what you know!

Neo Fender

That began with the 1979 models.

gdh

first few times I drove with the L-88 hood on I thought there was something wrong, now I luv the sound as fevre said. :thumbs:

Jvette73

Well I can see there is some mixed opinions on the effectiveness of cowl induction. I wonder though, doesnt NASCAR have thier breathers connected to the firewall which draws air from the cowl? I wonder why they would choose that location? Maybe cause its best for performance?

Fevre

John

But remember they are travelling at speeds that are 100 mph faster than most of us travel. The pressure that is built up in front of the windsheild at 180 mph is much greater than at 80 mph. Would be interesting to see what the pressure is at diff mph.

Matt Gruber

i read they use the cowl for cool, smooth air, not for any ram effect.

Wrencher

As for actual gains, we're all saying about the same thing. DOHC and true ram induction only have value very high performance applications.

However, "slight improvements" when grouped together can add up to a noticeable difference. Take the '78 Trans Am. Came with a 403 Olds engine in CA, with single exhaust and full (manifold) vacuum to the distributor at idle and a small air inlet on one side of the air cleaner assembly.

I would open the shaker, go up one size on the jets and needles, re-curve the distributor, hook it up ported vacuum, install a set of Hookers, and run duals out the back. Those changes turned that engine into an animal. Granted, stuff like the exhaust mods made a huge diffence, but all together it was a great package. By the way, I also love that sound...

Hans


[Modified by Wrencher, 2:49 PM 7/17/2003]

Wrencher

True in race applications, but put a restrictive filter and a heat riser on the package and it kinda' defeats the purpose...