Air pressure @ 100 mph?

[Rick!]

Real data from a MAP sensor inside the tunnel ram which is downstream of the scoop on my brothers SPro dragster:
+.25-.29psi @ 140mph
+.50-.59psi @ 171mph

your pressure may vary

[MadBill]

Real data from a MAP sensor inside the tunnel ram which is downstream of the scoop on my brothers SPro dragster:
+.25-.29psi @ 140mph
+.50-.59psi @ 171mph

your pressure may vary

So, downstream of the butterflies? (i.e. pressure at carb inlets would be more?)

[swampbuggy]

Bill , the sensor would have to be below the b-flies if it was / is ( inside the manifold ) as stated, correct ? This is for the fellow who made the comment as well, Mark H.

[MadBill]

Yes, just emphasizing that the positive pressures recorded were despite the pressure drop across the carbs, so actual ram pressure might be plus say another 0.8 to 1.? "Hg.

[Stan Weiss]

Remember that air density has an effect on the psi you will see at a give MPH

My program calculates @ 29.9213 BP @ 170.01 MPH - .5132 PSI

Stan

[swampbuggy]

So Stan..if i am reading your numbers correctly it would be an added pressure of just a tick over 1/2 of 1 pound per square inch at the top side of the Carb / carb's / throttle body or where ever the reading was taken ?? . Mark H.

[F-BIRD'88]

If when comparing underhood air pressure VS A effective RAM AIR scoop's in carb box air pressure the realized difference can be even higher.
Why? Because underhood air pressure is always a bit LOWER than ambient AND spot air pressure at the bumper and at the windshield cowl area on typical full body vehicles..
The underhood air pressure has to be a bit lower relative or air would NOT FLOW thru the cars radiator at speed to cool the engine..

[JC565Ford]

This is an old thread, but there are a few circle track boat racers who just run a standard scoop backwards and it acts as a cowl induction. With a tunnel ram the front carb gets good airflow to it.

[Stan Weiss]

So Stan..if i am reading your numbers correctly it would be an added pressure of just a tick over 1/2 of 1 pound per square inch at the top side of the Carb / carb's / throttle body or where ever the reading was taken ?? . Mark H.

Mark,
Yes above the carb.

Stan

HS_PSI_Graph.gif

[Stan Weiss]

If when comparing underhood air pressure VS A effective RAM AIR scoop's in carb box air pressure the realized difference can be even higher.
Why? Because underhood air pressure is always a bit LOWER than ambient AND spot air pressure at the bumper and at the windshield cowl area on typical full body vehicles..
The underhood air pressure has to be a bit lower relative or air would NOT FLOW thru the cars radiator at speed to cool the engine..

Even before the scoop generates any pressure you should see a difference because of the air temperature difference.

Stan

[F-BIRD'88]

If when comparing underhood air pressure VS A effective RAM AIR scoop's in carb box air pressure the realized difference can be even higher.
Why? Because underhood air pressure is always a bit LOWER than ambient AND spot air pressure at the bumper and at the windshield cowl area on typical full body vehicles..
The underhood air pressure has to be a bit lower relative or air would NOT FLOW thru the cars radiator at speed to cool the engine..

Even before the scoop generates any pressure you should see a difference because of the air temperature difference.

Stan

Yes air temp is an imporant factor. Even when considering where on the vehicle is the best spot to pick up the air for the ram box. Cooler, denser, high pressure, cleaner air is better.

[MadBill]

Short of Dry Lakes, the effect of cold air way outweighs ram air, but yes, why not get both if you can?

[Rick!]

This is an old thread, but there are a few circle track boat racers who just run a standard scoop backwards and it acts as a cowl induction. With a tunnel ram the front carb gets good airflow to it.

Cowl induction works because of the slight "high pressure" at the intersection of the hood and windshield. No hood or windshield, no free positive pressure.

For the above questions, the MAP sees pressure below the throttle blades. There are 8 throttle blades of 2" in diameter which make for minimal pressure drop due to the venturi effect. The 8 holes added together are larger in area than the scoop entrance by a few square inches.
The dark green line is the MAP sensor in the graph below.

[Kevin Johnson]

Rick! 's picture:

Induction Pressure.png