Welcome to the Corvette Forums at the Corvette Action Center!

I Installed Ram Air In My '71 Big Block

Joined
Mar 9, 2009
Messages
1,026
Location
Yemen
This last summer I decided to convert my L-88 style hood to ram air; mostly for the cool air because ram air doesn't do much good until 100+ mph. I started by installing a 24" X 32" piece of 24 gauge galvanized steel on the underside of my hood then fabricated a shelf with a lip sticking up that extended out from my air cleaner base. It took me a whole month of tinkering to get everything to match up but in the end it came out great. The 2" X 14" air inlet is just ahead of the top of the radiator and with it's frontal location I'm getting a lot of bugs and sand and such in my air filter.

I was hoping the cold air would give me a little fuel mileage increase but to my astonishment it gave me a 33% 3-1/2 mpg increase; going from 10-1/2 to 14 mph. I wondered if I had somehow miscalculated but after running about 10 tanks of gasoline thru it and always getting the same 14 mph I knew it wasn't a mistake. When winter set in I began having choke/fast idle problems as my engine was fast idling at every stop. It appear the in-rushing air was buffeting the choke butterfly and causing it to lift the fast idle cam to it's first step. I solved that problem by modifying my choke housing to use engine vacuum to force the choke butterfly open.

I have a feeling the 1" Wc worth of pressure I am getting at 60 mph is the cause of the huge mileage increase. Maybe the in-rushing air is foaming the gasoline more and making it more combustible. So now on a 100 degree day my engine is sucking in 100 degree air instead of 200+ degree under hood air. And under a full throttle I no longer hear the "ROAR" of the 14" open air filter.
 

Attachments

  • 1971 Corvette Ram Air Hood 035.jpg
    1971 Corvette Ram Air Hood 035.jpg
    246 KB · Views: 62
  • 1971 Corvette Ram Air Hood 030.jpg
    1971 Corvette Ram Air Hood 030.jpg
    245.1 KB · Views: 66
  • 1971 Corvette Ram Air Hood 001 (2).jpg
    1971 Corvette Ram Air Hood 001 (2).jpg
    247.7 KB · Views: 59
  • 1971 Corvette Ram Air Air Cleaner 007.jpg
    1971 Corvette Ram Air Air Cleaner 007.jpg
    252.7 KB · Views: 65
Joined
Mar 9, 2009
Messages
1,026
Location
Yemen
I just finished reworking my air cleaner base to get a better base-to-hood seal. I'll post some pictures of what I did tomorrow because I'm too damned tired right now. Been a long hot day (in the 90's now).
 
Joined
Mar 9, 2009
Messages
1,026
Location
Yemen
Here's a picture of my newly modified air cleaner base that uses a flat weatherstripping seal to mate with the hood's flat weatherstripping seal. Looks and works much better.
 

Attachments

  • 1971 Corvette Ram Air 005.jpg
    1971 Corvette Ram Air 005.jpg
    256.9 KB · Views: 47

Vettehead Mikey

Well-known member
Joined
Aug 26, 2003
Messages
3,486
Location
Not that far from Ottawa
Corvette
1973 Coupe
So now on a 100 degree day my engine is sucking in 100 degree air instead of 200+ degree under hood air.

I think if you measure that actual underhood temps withe car in motion, you'll find it's nowhere near 200 degrees. Probably pretty close to ambient actually.

In an effort to evaluate the effectiveness of the '73-'75 Corvette factory cold air intake and calibrate it against the seemingly optimistic claims of the GM marketeers, I instrumented my own car. While the air temp near the filter did rise dramatically with the car sitting idling, it dropped to a reading of only 2 degrees F warmer with the car in motion.
 
Joined
Mar 9, 2009
Messages
1,026
Location
Yemen
Out of curiosity I put a new oven thermometer next to my HEI one 100 degree day then took it for a 30 mile trip. When I got home I popped the hood and found it was reading 200 degrees which I thought was pretty low considering I have a big block. Now that I have the ram air hood with it's 2" X 20" vent the temperature would probably be a bit lower.
 

Vettehead Mikey

Well-known member
Joined
Aug 26, 2003
Messages
3,486
Location
Not that far from Ottawa
Corvette
1973 Coupe
Out of curiosity I put a new oven thermometer next to my HEI one 100 degree day then took it for a 30 mile trip. When I got home I popped the hood and found it was reading 200 degrees which I thought was pretty low considering I have a big block. Now that I have the ram air hood with it's 2" X 20" vent the temperature would probably be a bit lower.

Given the time it takes to get up a driveway, stop the engine, open the hood and look at a thermometer, I'm not surprised it read 200.

Try taking live real-time data while on the move as I did.
 
Joined
Mar 9, 2009
Messages
1,026
Location
Yemen
Given the time it takes to get up a driveway, stop the engine, open the hood and look at a thermometer, I'm not surprised it read 200.

Try taking live real-time data while on the move as I did.


I don't have any way to measure the temperature when it's in motion so it'll remain an unknown. What did you use?
 

Vettehead Mikey

Well-known member
Joined
Aug 26, 2003
Messages
3,486
Location
Not that far from Ottawa
Corvette
1973 Coupe
I had access to laboratory grade equipment from work and ran wires from under the hood to a recorder sitting on the passenger seat. Today I'd use a home weather station or cooking thermometer with a wireless or bluetooth transmitter.
 
Joined
Mar 9, 2009
Messages
1,026
Location
Yemen
I had access to laboratory grade equipment from work and ran wires from under the hood to a recorder sitting on the passenger seat. Today I'd use a home weather station or cooking thermometer with a wireless or bluetooth transmitter.


As it's not an issue I'll likely never find out. My severe duty fan clutch and 7-blade fan moves a LOT of air so I would imagine it wouldn't get very hot.
 
Joined
Mar 9, 2009
Messages
1,026
Location
Yemen
I think if you measure that actual underhood temps withe car in motion, you'll find it's nowhere near 200 degrees. Probably pretty close to ambient actually.

In an effort to evaluate the effectiveness of the '73-'75 Corvette factory cold air intake and calibrate it against the seemingly optimistic claims of the GM marketeers, I instrumented my own car. While the air temp near the filter did rise dramatically with the car sitting idling, it dropped to a reading of only 2 degrees F warmer with the car in motion.


I suggest you borrow that test equipment again and run the test over again after you calibrate that equipment. When an engine is idling in NEUTRAL it's only producing the power needed to spin it at 750 rpm but when propelling a 3500 pound C3 down the road at 60 mph it's producing around 20-22 horsepower. That creates a lot of heat and 1/3 of that heat is being shed from the radiator core; heating the engine compartment WAY above ambient temperature. Its common to see underhood temperatures at cruising speeds that exceed 350 degrees; enough to cook a roast if you have a place to put it. I used to have a "Intake Manifold Cook Book" that gave the mileage needed to cook roasts, bake cookies, cook casseroles, puddings, and you name it. No different than cooking something in your oven.
 
Last edited:

Vettehead Mikey

Well-known member
Joined
Aug 26, 2003
Messages
3,486
Location
Not that far from Ottawa
Corvette
1973 Coupe
I suggest you borrow that test equipment again and run the test over again after you calibrate that equipment. .

Coming from a person that's not done any testing himself and on top of all the other bad advice and fractured fairy tales I don't think you're in a position to dismiss any data out of hand and so obviously because it blows a giant hole in your theory.

It is true that some surfaces do reach relatively high temperatures in the area of 350 degree (exhaust manifolds) but the majority of the engine externals are at or below that of the coolant itself. A journeyman mechanic or high school physics student would realize this. If the engine externals are at 350, how do you explain the coolant and oil being at temperatures far below that?

There again, if you rely on a cookbook as an engineering reference manual to guide engine or vehicle design, I think you're already beyond reasoning with. But-I have seen the cookbook you mention, and a cursory analysis of any of the recipes shows that the times they mention for cooking lumps of meat do not match using an oven at 350*, or anywhere close. In fact, they are similar to the use of a low and slow BBQ or smoker style of cooking which is done at 175 or 200 degrees. This now makes sense as that's close to what the engine's surfaces run at.

Since you're interested in learning, please brush up on the differences between conduction, convention and radiation as applies to heat transfer. The food is being cooked by conduction as it's sitting directly on a hot engine component. You seem to have concluded that the entire volume of air in the engine compartment is somehow heated via convection or radiation, not just to the engine surface temps of 175-200, but to temperatures at least 150 degrees hotter than the engine itself.

This in itself defies all laws of physics, but with the knowledge that the body of air is constantly being diluted with fresh cold air (ambient temp) once the car is in motion then it's not difficult to understand why carb inlets temps have nothing to do with exhaust manifold surfaces temps. There again, I give credit for having at least minimal common sense.
 

Antz81

Well-known member
Joined
Dec 21, 2013
Messages
936
Location
Auckland, New Zealand
Corvette
1981 4 speed
Its common to see underhood temperatures at cruising speeds that exceed 350 degrees;

The exhaust manifolds yes, but nothing else. If the temps really did get to that level then the wiring in the engine would have no insulation left and we'd all be sitting on the side of the road.
 

Antz81

Well-known member
Joined
Dec 21, 2013
Messages
936
Location
Auckland, New Zealand
Corvette
1981 4 speed
I'm curious you told mike he needs to redo his test after calibrating the equipment. How did you calibrate your ovem thermometer?
 
Joined
Mar 9, 2009
Messages
1,026
Location
Yemen
Another Ram Air Air Cleaner Base Modification

Although I had modified my Ram Air air cleaner base a few days ago to give about 1-1/4" of clearance to my HEI I just modified it again to add another 3/16" of clearance. Now I have close to 1-7/16" clearance and THAT should be plenty. I just washed it off with soap and hot water and after the water dries I'll paint it. I'll take a close-up picture of it installed after I get it painted and the paint is dry. I feel pretty embarrassed over having my spliced #2 wire way too close to the base but life IS a learning experience and even the best of us make mistakes; me being one of them.
 

Attachments

  • 1971 Corvette Ram Air 002 (3).jpg
    1971 Corvette Ram Air 002 (3).jpg
    245.6 KB · Views: 58
  • 1971 Corvette Ram Air 001 (2).jpg
    1971 Corvette Ram Air 001 (2).jpg
    247.7 KB · Views: 51
Joined
Mar 9, 2009
Messages
1,026
Location
Yemen
My Ram Air Was A LOT Of Work

After I fabricated the first Ram Air hood plate I immediately ran into problems because the plate hit the top of the fan shroud and the top radiator hose REAL hard. I dimpled the plate to allow clearance but the dimpling was so deep the plate got real distorted. I finally resorted to making a new plate but with fiberglass dimples that ended up being about 3/4" deep. It ended up being an awfully big job requiring at least 100 hours of labor and recently another problem revealed itself when my #2 spark plug wire began flashing to the rear of the air cleaner base. I believe it will be trouble free now.
 

Attachments

  • 1971 Corvette Ram Air Hood 035.jpg
    1971 Corvette Ram Air Hood 035.jpg
    246 KB · Views: 50
  • 1971 Corvette Ram Air Hood 030.jpg
    1971 Corvette Ram Air Hood 030.jpg
    245.1 KB · Views: 48
  • 1971 Corvette Ram Air Hood 001 (2).jpg
    1971 Corvette Ram Air Hood 001 (2).jpg
    247.7 KB · Views: 52

kpic

Well-known member
Joined
Mar 29, 2014
Messages
2,292
Location
Columbus, NC/NE Georgia
Corvette
1997 boosted silver coupe
Just a shame the lesson you should be learning is not to splice spark plug wires.

A simple piece of common sense advice which was ignored as usual.


It ended up being an awfully big job requiring at least 100 hours of labor and recently another problem revealed itself when my #2 spark plug wire began flashing to the rear of the air cleaner base. I believe it will be trouble free now.

100 hours is 12.5 days. Are you serious??

It would have been a lot easier and simpler to purchase a longer spark plug cable.

As Mikey said a band-aid.
 
Joined
Mar 9, 2009
Messages
1,026
Location
Yemen
The Benefit Of Ram Air

I just did some calculations to see how much heat an average C3 radiator core sheds at 60 mph when consuming 15 mpg. It'll shed 150,000 BTU's per hour which is about twice as much as your home furnace cranks out. That heat goes right into the engine compartment and that is what is going thru your carburetor. But when using Ram Air the carburetor is only swallowing outside ambient air at a fraction of the under hood temperature.
 

Vettehead Mikey

Well-known member
Joined
Aug 26, 2003
Messages
3,486
Location
Not that far from Ottawa
Corvette
1973 Coupe
I just did some calculations to see how much heat an average C3 radiator core sheds at 60 mph when consuming 15 mpg. It'll shed 150,000 BTU's per hour

Again I'll ask which box of Cracker Jack your "Engineering Degree' came in. If scoring an 8th grade physics class, I'd give your answer a D-, not just because the answer is so incredibly wrong but because of the way in which it was calculated. Using the volume of fuel consumed per distance to calculate heat produced was a fatal error, as was using total heat energy produced over a given period of time (BTU/HR) to calculate heat rise under the hood.

An engine in a car cruising at 60 mph is producing (being generous) about 30 HP. One horsepower is equal to just under 43 BTU,
Cooling System Basics - Keep It Cool - Super Chevy Magazine

so 30 HP is equal to 1260 BTU. Only about one third of that heat energy, or 430 BTUs, ends up in the coolant or being shed form the external surfaces of the engine.

This real number is quite fortunate as the capacity of the best-of-the best Corvette radiators on the market today is only 4600 BTU. The stock GM radiator is about 3290.
1963-1972 Restoration Radiator No Detailing – DeWitts Direct Fit™ Aluminum Radiators

Back to reality, a measly 430 BTU (slightly more than that wasted by two 60 watt light bulbs) being tossed into the turbulent airflow under the hood of a car moving at 60 mph helps greatly in explaining why carb air intake temps are only slightly above ambient temps. Thanks for helping my case.:chuckle
 
Last edited:

Corvette Forums

Not a member of the Corvette Action Center?  Join now!  It's free!

Help support the Corvette Action Center!

Supporting Vendors

Dealers:

MacMulkin Chevrolet - The Second Largest Corvette Dealer in the Country!

Parts/Accessories:

Vetteskins

Advertise with the Corvette Action Center!

Double Your Chances!

Partners

Top Bottom