Ram Air Carb Tuning

[AL427SBF]

The condition: Let's say you have a 750-800 cfm carb housed in a well sealed turkey pan with a hi-flow air element. You've also measured positive pressure in the pan @ 4 psi going 60 mph @ 2100 rpm.

The question: How do you jet (or otherwise tune) your carb so that you are not running too rich in the lower gears or too lean in 5th going 80 mph @ 2800 rpm?

[Gaz64]

I don't think it really matters whether you get a pressurised condition while you have manifold vacuum at part throttle.

Does your measured pressure vary according to throttle opening and road speed?

In other words, is the pressure only there and diminishes to zero as you open the throttle towards wide open regardless of road speed?

Are you using a wideband O2 Air/fuel ratio gauge for tuning?

[AL427SBF]

Gary, those questions cut right to the heart of the bigger question for me - does a turkey pan actually do anything for you even if installed properly (meaning truly sealed). The conditions I listed above are what I could do if I got one, I used the carb and gearing my car will have. Here is what a turkey pan manufacturer says -

Turkey pans are one of the most misunderstood engine accessories. Today with all the high tech stuff we undertake, we as a group don't often give credit to the racing people of the 60's. They did something quite unique in getting a sports car with the aerodynamics of a barn door to go 160+ mph.


Doing the Turkey Pan Mathematics
The "Turkey Pan" (cold air box) was one of the reasons that the 427 performed like it did. Doing the math helps us understand why. A hood scoop opening of 2"x10" or 20 sq. in. moving through the air for one mile at 60 miles an hour takes in nearly 8,000 cubic feet of air. Your 427 cu. in. engine, traveling the same speed, turning 2500 rpms is only using 350 cubic feet or so of air. When sealed against the hood with a rubber gasket (which most folks don't like doing because the gasket chafes the paint) forms a high pressure area between 2-5 psi of cold air pressure, depending on how fast you are moving. The excess cold air spills out through the bottom opening, thus cooling the intake manifold and the air charge running through it. It creates "free horsepower" and the only drawback to this is that you must be moving!!

I read a forum post one time where two cobra guys where talking about turkey pans and got a little chuckle when one said "I don't think the turkey pan helps at all." To make such a statement is idiotic at best. "Every" high performance intake system uses cold air under pressure to gain a horsepower and fuel mileage increase!!!

I've also read on forums that a turkey pan doesn't buy you much. I think I see the "cooler air" argument, but that's about it. My assumption on the positive pressure is that the faster you go the higher that positive pressure at the air cleaner filter gets (ram air is speed dependent).

[Gaz64]

God knows where they got 8000 cfm from.

60 miles/hr = 1 mile/minute

2" = .166666 foot
10" = .833333 foot
1 mile = 5280 foot

volume of air through inlet opening = .166666 * .833333 * 5280

= 733.3 cubic feet/minute at 60 miles per hour.

Personally I can't see any benefit from pressure, it's the cold outside air that gives more horsepower. Plus any cold airflow over the manifold may help.

[deckofficer]

I always thought it was for cooler, denser air. My underhood temps are high in the summer and a denser air charge can combine with more fuel for more power. Air that has been compressed via a supercharger is heated, so an intercooler is employed.

[AL427SBF]

Gaz, I agree on the math, should be 733.3 cubic feet/minute, not 8K.
deck, I think you nailed it, that's got to be the reason why.

[deckofficer]

Originally Posted by AL427SBF

Gaz, I agree on the math, should be 733.3 cubic feet/minute, not 8K.
deck, I think you nailed it, that's got to be the reason why.

I know I stated the obvious and everyone knows that, but for awhile the conversation turned to "4 psi of static pressure" while another member correctly stated that 4 psi would disappear faster than Trump's hair on a windy day as soon as the throttle plates were cracked.