Something For You To Ponder

[toobroketoretire]

This last summer I converted my L-88 style hood to ram air and I immediately got a 33% fuel mileage increase (from 10-1/2 mpg to 14 mpg). Using a simple water manometer it is showing 1" Wc of inlet pressure at 60 mph and 1-1/2" Wc at 80 mph. What is puzzling to me is why did it gain 33% from such a simple modification? The 1" Wc is not only pressurizing the #3310 Holley's inlet but it's also pressurizing the fuel in the fuel bowl which would make the fuel mixture richer IF the pressure in the venturi remained the same (which it didn't) and the air bleeds are also getting pressurized. So with the venturi, the fuel bowl, and the air bleeds receiving the same 1" Wc of pressure why did my fuel mileage increase so much? The only thing I can think of is the normally liquid fuel is getting foamed as it is forced thru the butterflies so it's more combustible.

And then as winter set in I immediately began having fast idle problems as the incoming pressurized air was apparently buffeting the choke butterfly and lifting the fast idle cam to it's first notch. My choke would come completely off in my garage after a few minutes of running but after traveling 30 miles and pulling up to a stop sign it would be fast idling again. So the pressurized air is causing some weird things to happen (although the 33% gain is certainly welcome).

Do any of you have any idea why my fuel mileage increased so much? This one has me puzzled.......................

 

[Mac]

Best guess is the conversion to RAM removed a restriction on the intake side which was preventing effective airflow.

Mac

 

[Antz81]

The RAM air would also have a lower temperature; giving more oxygen for the same volume of air.

 

[toobroketoretire]

The RAM air would also have a lower temperature; giving more oxygen for the same volume of air.

Looking back at my quest for additional fuel mileage and performance here's the progression from where I started:

1. 454" engine with 220/220 .500" lift marine cam, TH400, and 3.08's.................7.5 mpg

2. Installed a TH700R4, Air Gap, and #3310 Holley..........................................8.5 mpg

3. Installed 3.70 gears...............................................................................9.5 mpg

4. Installed a 236/236 .556" lift Magnum cam and 10 to 1 pistons......................10.5 mpg

5. Converted L-88 style hood to ram air........................................................14 mpg

So over the last 5 years I have achieved an 86% fuel mileage increase by matching the parts and got a terrific performance gain along the way. After I installed the TH700R4 and hardly got any mileage increase I realized the engine was spinning way too slow for the Air Gap manifold to be effective as the runner velocity was too slow. By installing the 3.70's the runner velocity increased and fuel mileage went up 1 mpg and I got a terrific boost in performance. But oddly the biggest gain came from the ram air.

Right after I bought it in September 2009 it went 80 to 85 miles from FULL to EMPTY whereas now it'll go around 150 miles using the same amount of fuel. It illustrates what can be achieved by matching the parts to the rpm the engine is spinning at cruising speeds; in my case around 2050 rpm @ 60 mph. With my 3.70's and TH700R4 my final drive ratio in 4th gear is 2.62 which is fairly high. The Air Gap is a great intake IF the rpm is fast enough to allow a high enough runner velocity. My mileage figures are based on a 45-55 mph cruising speed and I expect it'll be a lot higher at freeway/turnpike speeds when the engine is able to spin faster.