Hood Questions #2

[1961BelAir427]

I had forgotten about that one while replying above. When I was using the flat hood, my car ran better with it spaced up to let out the hot air. I would just raise the hood pins to the top of their threads and put a piece of heater hose around the pin up under the hood to raise it up. Never did any back to back testing, but it certainly ran it's best times with it raised. Also not sure how that compared to the cowl induction hood because the whole combo had changed along with the hood.

 

[Ishiftem]

There is a lot of pressure at the base of the windshield. If I forget to close the cowl vent when I make a pass, there is enough pressure inside the car to bow out the top of the window frame enough to see daylight. And that's on a post sedan.

 

[1961BelAir427]

There is a lot of pressure at the base of the windshield. If I forget to close the cowl vent when I make a pass, there is enough pressure inside the car to bow out the top of the window frame enough to see daylight. And that's on a post sedan.

You wouldn't have that problem with an old (air) leaky bubble top roof or other hardtop for that matter. Those post cars just seal up TIGHT!

 

[jim_ss409]

There is a lot of pressure at the base of the windshield. If I forget to close the cowl vent when I make a pass, there is enough pressure inside the car to bow out the top of the window frame enough to see daylight. And that's on a post sedan.

I think there is a fair bit of pressure at the cowl on our cars. I've read that the pressure at the grill is even higher but they're probably talking about modern cars where the windshield tends to be more laid back.
In your case, the pressure that the cowl generates inside the car is pushing on the windows while at the same time the side windows are in a low pressure zone, similar to the low pressure zone on the roof of a car. You can really see the effect of that if you travel at high speeds in a convertible. The canvas on the roof will bulge up a few inches.

The red areas have the highest pressure.



I gather that a low profile forward facing scoop is actually in a low pressure zone. To get a good ram air effect the opening really should be raised up into the air stream.
I'm sure the Pro Stock guys have got the near ideal setup but I don't think any of us want a scoop like the one on this car...




I couldn't find the graph I was looking for but according to David Vizard's book, an ideal scoop would create 0.177 psi at 100 mph and about 0.4 psi at 150 mph.
That 0.177 psi at 100 mph should give a 1.2% increase in horsepower.
Dropping the intake air temperature 15 degrees would show a similar 1.2% increase in power.
If you can drop the intake air temp by 50 degrees, which seems like a reasonable goal, should net a 5% increase in power.
Almost any system that draws fresh air should be able to reach that 5% goal.

I'm sure a cowl setup that wasn't sealed to the carbs would help by letting some of the hot air out if the engine compartment. I think a hood scoop that wasn't sealed to the carbs might help in the same way. This guy had both a hood scoop and a raised hood.
But to really get the full effect, the carbs should be sealed to the scoop so that they can only draw outside air.

 

[Iowa 409 Guy]

Lots of good information there Jim. Thanks a lot for taking the time to find and post all the info. Also lots of good info from everyone else. I appreciate it.

 

[ROYALOAK62]

Is the ice baskets they used to use around the carb part of that theory?
Just asking as I'm not a racer and never been.

Dave

 

[BSL409]

Brian (BSL409) has or had a cowl induction hood on the '62 and a Super Duty style scoop on the '61. He could probably give some good input on the pros and cons of each. I wanted a cowl hood on my '61 way back before they became so popular just because I think they flow with the line of the hood and dash. ('61-62 dash looks like the rear of my cowl sticking up.) Now that I've found a W motor I'm leaning more towards a stock look. The cowl induction is very effective at reducing under hood temps compared to the stock style fiberglass hood I have. I've never tried sealing mine to the air cleaner to see what power advantage that might be worth.

Yes if the cowl hood is hooked up right on my 62 it is worth almost 2 tenths

 

[Iowa 409 Guy]

Is the ice baskets they used to use around the carb part of that theory?
Just asking as I'm not a racer and never been.

Dave

I remember I used to see coiled gas lines submerged in ice? Haven't noticed any lately?

A tenth here, 2 tenths there......................

Nice to meet you in Great Bend Dave.

 

[64ss409]

I remember I used to see coiled gas lines submerged in ice? Haven't noticed any lately?

A tenth here, 2 tenths there......................

Nice to meet you in Great Bend Dave.

Yep, I used to have one. Coiled steel line in a tupperware container in front of the radiator.

 

[Iowa 409 Guy]

Yep, I used to have one. Coiled steel line in a tupperware container in front of the radiator.

What happened to it Ron?

 

[64ss409]

I forgot to empty it one winter.

 

[k9hotrodder409]

Yep, I used to have one. Coiled steel line in a tupperware container in front of the radiator.

I remember having a 1 lb. "Maxwell House " Metal coffee can on the passenger fenderwell painted silver. with a copper line coiled inside from the fuel tank feed to the can , to the carb fuel pressure regulator , to the carbs. We called it the "KOOL CAN " We just filled it with ice from the Bud cooler and went racin !!
Some times it was a little tough using the cooler ice for the car instead of the Long Neck Buds. But that was racin !!My "GRUMPY " scoop seemed to work O.K. I had a 10" opening at the front and the back was fully opened at the windshield.

 

[models916]

That MOPAR is one of those "look what he did and then don't do that".