Cold air intake plumbing/routing: Fit a BB?

69427

The Artist formerly known as Turbo84
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Clinging to my guns and religion in KCMO.
I currently have a homemade air box that seals up to the L88 hood rear opening. The concept works (efficiency = ?), and with some string lengths hanging down over the hood rear opening I can see the strings being pushed inward at speeds above about 15 mph. I'd sure like to do some efficiency comparisons of that versus getting the air from in front/above the radiator, but damn, with the shape of the hood (particularly the dip/valley in the front portion of the scoop), and what looks like the fan being positioned higher in the car versus a small block position, I'm striking out trying to route a clean looking (and decent size) hose/tube to the carb airbox. Anybody ever run a CAI hose in a BB? I'd like to do some box interior pressure measurements, with just the present box, and then with the extra hose inlet (with perhaps a reed valve setup in the box rear to seal off the windshield area source in the event that the front hose setup supplies more air than the rear.

Longer story than I planned. Anybody have any thoughts on running a front air source in a big block?

Thanks,
Mike
 
I currently have a homemade air box that seals up to the L88 hood rear opening. The concept works (efficiency = ?), and with some string lengths hanging down over the hood rear opening I can see the strings being pushed inward at speeds above about 15 mph. I'd sure like to do some efficiency comparisons of that versus getting the air from in front/above the radiator, but damn, with the shape of the hood (particularly the dip/valley in the front portion of the scoop), and what looks like the fan being positioned higher in the car versus a small block position, I'm striking out trying to route a clean looking (and decent size) hose/tube to the carb airbox. Anybody ever run a CAI hose in a BB? I'd like to do some box interior pressure measurements, with just the present box, and then with the extra hose inlet (with perhaps a reed valve setup in the box rear to seal off the windshield area source in the event that the front hose setup supplies more air than the rear.

Longer story than I planned. Anybody have any thoughts on running a front air source in a big block?

Thanks,
Mike

You must be reading my mind. I am almost finished moving the motor back some more until it put the throttle body (Wilson- like a big 4-barrel) just in front of the cowling lip. I will have to run a small cowl hood scoop with a rear facing opening, which I plan on having open in the rear and mated to an air box. However, I also have an opening above the radiator that is ducted to the front of the grill. Half of the air goes to duct work for the oil cooler, but the other side could be ducted around the radiator "chimney" (air from the radiator ducted vertically out the hood) and into the intake air box. I really like your idea of a reed valve set up that would let the highest air pressure source feed the engine. In the photo below you can see the opening (duct) above the radiator. The drivers side (half) is ducted through a scoop on the bottom of the hood to the opening on the driver's side that feeds air to the oil cooler. the passenger side half could be ducted into a 4 inch hose (or fabricated duct) to go down the passenger side of the engine compartment to the air box.

56 photo 2 (3).jpg
 
Are cool air boxes for injected motors?
I don't think they work well with carbs
 
Find a swap meet hood and graft on a 67 stinger hood scoop. Some guys were putting them on top of l88 hoods, but a careful graft might be better. Front facing should be higher pressure.
 
Constructive criticism... :censored:

I dont foresee a way to get clean airflow (for ram air effect better than the cowl) over the radiator and to the carb... Also, how much is that gonna weigh?? :p
 
I was looking at this a while back. The immediate problem is the area between the top of the radiator and the underside of a big block hood. The other difficulty is when the hood is raised the underside is very close to the radiator so that doesn't give much room for a filter.

The first thing I found is that there probably is enough room above the radiator to run a duct. Can;t remember but I think it's about 20 square inches. The hood opening problem could be helped by restricting the opening of the hood but that makes it's own problems. Instead, you could move the pivot point of the hinges forward about 2 inches. That's what I did in the photo below. I tried this on my car and found it worked. Gives you a little more space for a duct.


45d8e3623ec01b.jpg
 
I was looking at this a while back. The immediate problem is the area between the top of the radiator and the underside of a big block hood. The other difficulty is when the hood is raised the underside is very close to the radiator so that doesn't give much room for a filter.

The first thing I found is that there probably is enough room above the radiator to run a duct. Can;t remember but I think it's about 20 square inches. The hood opening problem could be helped by restricting the opening of the hood but that makes it's own problems. Instead, you could move the pivot point of the hinges forward about 2 inches. That's what I did in the photo below. I tried this on my car and found it worked. Gives you a little more space for a duct.


45d8e3623ec01b.jpg

That's a novel option/solution. :idea: I'll keep that in mind. I've already made a couple iterations of hinges in aluminum to cut weight and adjust the hood height, so I'm not too shy about fabricating one more iteration.
 
What if, similar to the L88 box, the duct was part of the hood? That way it wouldn't have to clear the hood when opening because it's already part of the hood. Then mate up to a stationary piece in front of the rad when in the closed position.
I'm curious what you feel are the downsides of the cowl induction?
 
What if, similar to the L88 box, the duct was part of the hood? That way it wouldn't have to clear the hood when opening because it's already part of the hood. Then mate up to a stationary piece in front of the rad when in the closed position.
I'm curious what you feel are the downsides of the cowl induction?

Didn't the early Crossfire C4's have ducts built into the underside of the hood that sealed on the air cleaner box on the engine?
 
What if, similar to the L88 box, the duct was part of the hood? That way it wouldn't have to clear the hood when opening because it's already part of the hood. Then mate up to a stationary piece in front of the rad when in the closed position. With that unproductive dip in the L88 hood scoop, I think the main flow bottleneck is still there (the height between the radiator support upper surface and the bottom of the scoop dip.
I'm curious what you feel are the downsides of the cowl induction?

I don't presently have any hard data to support any of my current ideas/concerns. Given how much life-sapping distraction from extended family I've had to deal with this year, I suspect the only real progress I'll probably make on this item in the near future is to plumb up my Magnehelic differential pressure gauge, and compare the WOT/hi-speed pressures in the hood/carb airbox and the pre-radiator plenum volume. Given that most new cars take their intake air from the front of the car instead of at the cowl area, I just want to see if I'm leaving any performance (ie: intake pressure) on the table.
 
What if, similar to the L88 box, the duct was part of the hood? That way it wouldn't have to clear the hood when opening because it's already part of the hood. Then mate up to a stationary piece in front of the rad when in the closed position.
I'm curious what you feel are the downsides of the cowl induction?

The first post in this thread has a photo of a hood scoop mated to a stationary piece over the radiator:
http://www.vettemod.com/forum/showthread.php?t=6797

Edit: As I moved the motor further back I had to do away with the scoop on the bottom of the hood. I added a "chimney" duct from the radiator up and out through the hood - this blocked the air path of the original scoop. I still use the fixed duct above the radiator to move air to the oil cooler that is behind the left front wheel well. I went with a cowl hood, more out of necessity than anything else. The intake on the new motor is taller, and even with the engine moved way down, the top of the throttle body is just below the stock hood height (way back against the cowl). Adding a 3 inch cowl hood gives me plenty of clearance for good air flow - hope the air pressure at the bottom of the windshield is adequate.
 
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What if, similar to the L88 box, the duct was part of the hood? That way it wouldn't have to clear the hood when opening because it's already part of the hood. Then mate up to a stationary piece in front of the rad when in the closed position.
I'm curious what you feel are the downsides of the cowl induction?

The first post in this thread has a photo of a hood scoop mated to a stationary piece over the radiator:
http://www.vettemod.com/forum/showthread.php?t=6797

Edit: As I moved the motor further back I had to do away with the scoop on the bottom of the hood. I added a "chimney" duct from the radiator up and out through the hood - this blocked the air path of the original scoop. I still use the fixed duct above the radiator to move air to the oil cooler that is behind the left front wheel well. I went with a cowl hood, more out of necessity than anything else. The intake on the new motor is taller, and even with the engine moved way down, the top of the throttle body is just below the stock hood height (way back against the cowl). Adding a 3 inch cowl hood gives me plenty of clearance for good air flow - hope the air pressure at the bottom of the windshield is adequate.

I'm assuming the windshield angle (from horizontal) is greater on the earlier body styles, which should help that pressure.
 
[/QUOTE]
I'm assuming the windshield angle (from horizontal) is greater on the earlier body styles, which should help that pressure.[/QUOTE]

Correct. I'm not sure how much the cowl hood changes things, or how much the air from the "chimney" being directed slightly towards the outboard ends of the windshield will effect the pressure at the cowl opening. the other issue is whether hot air from the radiator vented out of the hood opening will enter the cowl - hot air is obviously not desirable.
 
I'm assuming the windshield angle (from horizontal) is greater on the earlier body styles, which should help that pressure.[/QUOTE]

Correct. I'm not sure how much the cowl hood changes things, or how much the air from the "chimney" being directed slightly towards the outboard ends of the windshield will effect the pressure at the cowl opening. the other issue is whether hot air from the radiator vented out of the hood opening will enter the cowl - hot air is obviously not desirable.[/QUOTE]

That's been the reason (for years) I've been holding off opening up the vertical area in the dip portion of my L88 hood. I didn't want the radiator exhaust warm air to dilute the cold air intake at the cowl.

But, I now find myself entertaining that option. With the weight reduction I've achieved on the car, I have a respectable power to weight ratio, enough to where I'm rarely outpulled by other Corvettes on the straights, and perhaps it might be a productive exchange to give up a touch of horsepower (due to slightly increased intake air temperature) to get a bit better/reduced aero drag down the straights, and reduced lift through the corners.

But, if I could package a CAI from in front of the radiator, I could open up the hood vents and get both cold air for the engine and reduced aero lift at speed.
 
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