SHAKER air flow

[plumcrazzy]

My '70 Challenger is an original Six-Pack car and came with a Rallye hood. I put a SHAKER hood on it several years ago because I really like the look. The car came without the factory air cleaner lid and had a nice chrome lid installed when I got the car. After I got the car put back together and painted I ran the Rallye hood for a couple of years with the chrome air cleaner and it ran very well. When I got the SHAKER hood I used all the right parts to install the SHAKER bubble including the "Carb Air" pull cable under the dash. Everything works as it should. I have a couple of questions so here goes--  My understanding of the operation of the warm/cold air doors is that the doors should be kept closed during cold weather to help the engine warm up quickly/properly.  The doors should be opened to allow air flow into the engine but the openings for outside air are not very large and I was wondering if the engine might be starving for air because it doesn't seem to pull quite as hard as it did with the open element air cleaner. I only use the car in the summer so I think the doors should be open all the time but I have read (somewhere) that if the doors are open and you get caught in the rain you could ingest some water into the engine. 
1. Does the SHAKER set-up restrict air flow to the engine?
2. If it does restrict air flow is there a way to modify the system to allow more air flow?
Thanks in advance

[cudabob496]

The more air, and the colder, the better!

[cudabob496]

http://www.cuda-challenger.com/cc/index.php?topic=93253.msg918232#msg918232

[anlauto]

I can't answer your question with 100% certainty, but think of it as "forced air" vs non-forced air....
With the shaker sitting out of the hood, air should get forced into the engine unlike the rallye hood which just picks up air where it can..

[cudabob496]

I've read that to get any significant forcing of air into an engine, like
on my setup, you have to be going about 125 mph.  And even that is a fraction
of a supercharger or turbo.

[Topcat]

So what's a rough estimate on HP increase with Shaker Hood with cold doors open?
20-30 HP vs. no Shaker?

[cudabob496]

for every drop of 10 degrees in carb inlet temp, you get about
1.5 % power increase.  So, 50 degree drop on a 400 hp engine,
= 30hp increase

[tommyg29]

Someone who knows better correct me if Im wrong, but I understand the factory shaker setup is actually a little restrictive, and I dont think theres much danger of ingesting water if your filter is properly in place, although I guess anything is possible.
As for ram type airflow, I think that will also be minimal. The shaker intake is probably too close to the hood surface to be in the main flow going over top of the car. In fact there are definite areas of negative pressure on that surface, and wind tunnel testing would be in order to try and determine the best area on any given hood area. Not sure if that was ever done in 1969 when they designed it. Doubt it. The challenger ram air setup sticks higher up and probably allows in more clean air, but dont know if its ever been proven 
Regardless, for relatively mild tunes, the factory intake systems are probably fairly adequate. You start building a machine for 600-700 hp and up, and its gonna benefit from more air.

[tman]

From what I recall about the 69 Road Runner air grabber option, they state it improved hp by 15. 

[Racer57]

From what I recall about the 69 Road Runner air grabber option, they state it improved hp by 15.

Got to be true. The factories would never overestimate or stretch the truth when promoting something. 

[tommyg29]

From what I recall about the 69 Road Runner air grabber option, they state it improved hp by 15.

He is asking about a shaker though, which is a totally different setup.
If all the seals are properly in place, the inlet in the front of the base is supposed to be the only air coming in, and it is pretty small, oval shaped and maybe 5 inches across (picture below) but I dont think either opening, upper or lower seals off very well. With a big block in full bore sucking mode I bet it leaks all around! So I dont think its your shaker causing your problems.
But just in case you can always loosen some things up a little or do what I do, I have the upper door disconnected and just never drive it much in the rain anyway, so....

[tommyg29]

And here is an upside down picture of the upper (cool air) and lower (warm air) doors. Mine is a snobar repro but should be nearly identical to factory. The lower warm air door does seem smallish

[Chryco Psycho]

Yes the air door should be open most of the time for colder air which is a + , cold air rules !
 I can tell you with certainty that the shaker is restrictive , the # 36 square inches comes to mind to feed the engine properly but I may be low , measure the shaker openings & I think you have 24 sq " . So about 30 years ago we too an SS Hemi 70 Cuda to the dyno & tried everything to get more power , tried different spark plugs etc anything to find even 1 more pony , retuned all the carbs with the shaker off & got 15 hp gain until the shaker went back on then the tuning was adjusted for the shaker & ended up very close to where we started back down 14 hp or so .
 As far as increasing flow not much works , you can remove the grilles or take a die grinder & open up the grilles by thinning & wing shaping the vanes of the grille , also removing the lower heat door so it can pull more air from below to add to the flow .
 The 6 pack hoods are amazing , on my Duster the hood would start trying to rip over the hood pins by the time you were doing 50 MPH they grab a ton of air .
 I would guess that the ralley hood with unlimited air flow vs the shaker restricted but cold air flow , the shaker would still lose

[Racer57]

Shaker traps a lot of heat as compared to a standard style, so opening the door would help tremendously.  Whether the shaker is better than a standard style with the top flipped over, I doubt it. But who cares..... the shaker is COOL !! 

[tommyg29]

Definitely cool but also a PITA. You cant get to anything without removing it. Only takes a socket and 3 minutes, but still.
CP you sure know your stuff!
I am posting a couple pictures which give you a good idea about the relative size of the warm air opening and the carb openings, which tells you right there it looks too small. The third picture shows both openings half open, which I would think would allow the most air in. Plus, nothing seals all that well, so a little extra probably squeezes in, but overall I can certainly believe it wasnt the best design.
I would have tried to make it smaller, or at least with a much smaller base plate that doesnt cover the whole top of the engine. Then obviously the openings should have been bigger. Maybe made the bubble taller?