Cold air induction

azopelnut · 02-10-2005

Looking at the engine bay of any modern "rice rocket" tells you that a great deal of improvement has been made from days our Opels were made especially in the area of cold air intake.

I want to streamline my air intake on my FI 75 sportwagon and here are some thoughts:
1) Replace stock the air intake using 3" smooth tubing coming off the MAF and rerouting it back towards the firewall shelf that is underneath the plastic cowl vent that seals against the underside of the engine hood.

2) Cut a 3" hole in the underside of the vent to take advantage of the air that gets forced off the hood and windshield through the slots cut in the hood

3) Build a lightweight box that would rest on the shelf, house the air filter and permit the air to travel through the bottom of the "cut-out". into the filter without sucking in hot engine air.

QUESTIONS
If I cut this hole in the plastic vent and built a box to house the filter would I be introducing engine fumes into the cabin?

How might I be able to eliminate water from rain or car washing going into the filter area?
Your thoughts are appreciated

nobody · 02-10-2005

Cold air cowl induction is a very good idea. You need to find every air opening or outlet in the cowl to make it work. Custom filters for all openings and be absolute of your drain points. If it can be done with a GT a Manta should be easy.

RallyBob · 02-10-2005

Paul, I've had good luck pulling cold air from the stock inlet location at the grill. Except with a few mods of course. First, I cut out the actual plastic grill area blocking the air inlet. Second, I toss the stock plastic 'scoop' and make a new steel one with a 3" tube attached. Very simple, almost looks stock, and you don't need to cut the body to do it.

Bob

BQS4 · 02-10-2005

Bob;
How about that scoop as one of the items that you could "offer?" What about a box/fixture for the top of a 32/36 weber?

azopelnut · 02-11-2005

Originally Posted by RallyBob

Paul, I've had good luck pulling cold air from the stock inlet location at the grill. Except with a few mods of course. First, I cut out the actual plastic grill area blocking the air inlet. Second, I toss the stock plastic 'scoop' and make a new steel one with a 3" tube attached. Very simple, almost looks stock, and you don't need to cut the body to do it.

Bob

Do you keep the stock air filter box and the flexible rubber air tube or did you replace that with smoother plastic or metal hose.

RallyBob · 02-11-2005

Originally Posted by azopelnut

Do you keep the stock air filter box and the flexible rubber air tube or did you replace that with smoother plastic or metal hose.

You can do it either way.

azopelnut · 02-11-2005

Bob
Does the fact that the stock 1975 FI set-up basically makes two 180 degree turns adversely effect air flow to the intake?
First
Air travels away from the entry point in the grill up through the air box and back towards the front of the car through the MAF
Second
Air leaves the MAF and makes a 180 through the ribbed rubber hose into the intake

RallyBob · 02-11-2005

Originally Posted by azopelnut

Bob
Does the fact that the stock 1975 FI set-up basically makes two 180 degree turns adversely effect air flow to the intake?

Of course. Just switching to a Megasquirt (or any programable) is worth HP because the air flow meter is eliminated, along with those nasty tight bends.

heimue · 02-12-2005

As I understand the original question, you want to place the air intake in the area where the hood meets the windshield. From an aerodynamik standpoint, that's not a good place to put it. While you drive, the air "moves" over the hood, up the windshield, then back along the roof line. While the air moves faster (in the red area) the pressure sinks. This results in a low pressure area right in the area between the hood and the windshield. This is why hoods are vented on this location - to suck out hot air from the engine compartment, not to press cold air inside. The faster you go, the lower the pressure. It would be pulling against the "forces of nature" to have your air intake mounted there. Instead you better re-route it to the front of the car, where the oncoming air "presses" against the front grill. There is a lot of air turbulence, but the highest pressure of outside air on your car.

Dieter

azopelnut · 02-12-2005

I like your wheel caps with the blitz Dieter... where did you get those?

Thank you for the explanation

kwilford · 02-12-2005

Originally Posted by heimue

As I understand the original question, you want to place the air intake in the area where the hood meets the windshield. From an aerodynamik standpoint, that's not a good place to put it. While you drive, the air "moves" over the hood, up the windshield, then back along the roof line. While the air moves faster (in the red area) the pressure sinks. This results in a low pressure area right in the area between the hood and the windshield. This is why hoods are vented on this location - to suck out hot air from the engine compartment, not to press cold air inside. The faster you go, the lower the pressure. It would be pulling against the "forces of nature" to have your air intake mounted there. Instead you better re-route it to the front of the car, where the oncoming air "presses" against the front grill. There is a lot of air turbulence, but the highest pressure of outside air on your car.
Dieter

Sorry to contradict you, but the "cowl" area (the trailing edge of the hood, up to the leading edge of the windshield), is often one of the BEST places for "forced induction". The change in angle creates turbulence, which in turn creates a high pressure area. That is why most cars use this area for the inlet of the interior ventilation system. In fact, few (if any) cars use this area to ventilate the under-hood area.

Many muscle cars in the 60's and '70's that had big hood scoops facing forward on top of the hood benefited from a cooler intake air charge, but did NOT benefit from the forced induction that a cowl induction system provides. An notable exception was the early '70's Chevelle, which advertised (correctly) that its reversed cowl induction system provided a slightly forced induction of intake air. Another example was the '70's Firebird, with the rear facing "shaker" hood scoop. The same aerodynamics applied to it as the Chevelle. However, I believe that the AMOUNT of actual induction-induced performance was minimal. The main benefit was the cooler air inlet temperature.

As for taking inlet air from the grill area, this can certainly be effective from the perspective of providing a cold air intake. As for a "high pressure, forced induction" system, it depends entirely on the specific aerodynamics of the car. In most cases this area IS a higher pressure area than, say, on top of the flat portion of the hood (where the GT, for example, places hood louvres to draw out hot under-hood air, which the higher velocity air stream is "attached" to the hood and creates a low pressure area). But vehicle aerodynamics can be quite complex, so it can be presumptuous to state that the highest aero pressure is found at the grill area.

JM2CW

nobody · 02-13-2005

On a GT the cowl was designed to draw cold air to the interior. As speed is increased the given temperature decreases and pressure increases in that area. That is the reason for that upward slant at the window side of the hood. It forces air into the cowl and as it crosses the edge it disapates heat. That is why so many car designers have chosen to use it. Not that I've researched this to death or spent alot of time designing a cold air cowl induction for twins. Oh wait, maybe that was me.

ConreroGT · 02-13-2005

I'd still have to agree with Dieter on this one. I can't see how the air would be forced back towards oncoming air from inside the cowl (under the hood). Basic aerodynamics would suggest a low air pressure at the trailing edge of the hood creating a rolling turbulance right there. Air flows towards a low pressure point. The air under the hood would want to continue to flow up and out at that point. It's the same as when you open the window inside your car (hi pressure) to let the cigerette smoke outside (low pressure) because the air passing by keeps creating a void.

I guess as I re-read this the only way it would work I suppose is to have the area sealed from the edge of the hood to the intake to have continues low pressure from the carbs. But even then it would be fighting itself. It would be minimal positive induction.

I'd have an intake routed from the front of the car.

Motor Mouth · 02-13-2005

Originally Posted by ConreroGT

It's the same as when you open the window inside your car (hi pressure) to let the cigerette smoke outside (low pressure) because the air passing by keeps creating a void.

I can't beleive you smoke in your GT

RallyBob · 02-13-2005

FWIW, in Nextel Cup cars they draw in the air to the carburetor from the base of the windshield, NOT from the front of the car. Those aerodynamicists all agree this is the best place to get the air from, at least at the speeds they travel at.

Bob

nobody · 02-13-2005

On a GT with twins it works great. My 11:1 2.0 is fed this way. I don't know if anbody else has done it, but believe me it does work well.

Paul · 02-13-2005

Remember, to consider the pressure differential. To get air to flow thru the radiator, the engine compartment will be at a lower pressure than the area below front bumper. The area just below the windshield is considered to be a high pressure zone.

Visualize the air coming over the hood and piling up at the base of the windshield. Some of the air completely changes direction and bleeds off to the size of the car, around the A-pillars, mirrors and such. While the rest of the air travels over the top/roof of the car. Decreasing the angle between the hood line and the winshield serves to reduce the high pressure zone and improve aerodynamics.

Keep in mind that velocity and pressure are inversely proportional. As the velocity of the air increases, the pressure in that area decreases. And, if the velocity decreases the pressure increases. Just as when dealing with an airfoil/wing. The air traveling over the top of the wing speeds up therefore the pressure drops. The air at the base of the windshield slows down, essentially it piles up looking for someplace to go, therefore the pressure in this area increases. the more straight up the angle of the windshield, like a Manta vs a GT, the greater the pressure increase.

Relative to each other, the engine compartment is at a lower pressure that the cowl area at the base of the windshield. If given a path, the air will flow quite easily from the cowl area to the engine compartment.

HTH

namba209 · 02-13-2005

Way back when, the NASCAR folks started using aerodynamics to get the cars to go faster on the super tracks. Around the mid 60s, early 70s they found in wind tunnel tests the air pressure at the base of the windshield was significant enough and in sufficient volume that they could turn the filter box on the carbs 180 degrees and attach the air inlet to the cowl chamber and get a quasi charged intake system. This positive charging vice vacuum charging of the cylinders occurred up in the 100 MPH + range and the faster they went the more positive flow through the carbs. All this occurred with the 7 Liter engines and because of the speeds attained the restrictor plates and then smaller engines became the rule. To give you and idea of volume and pressure, last weekend, the Tide NASCAR Chevy that was campaigned last year was at the local Commissary, and the grill was totally duct taped except for an area of about 2" X 4" cut from the tape. That's all the area needed to keep the radiator cool during a race at speeds approaching and exceeding 200 MPH. A couple of notes on this after talking to the mech. By taping almost all of the grill area a smoother air flow is attained which means more speed and the high velocity air going into that small hole and dumping into a low pressure area significantly drops the air temp in front of the radiator. And the reason I got to talk to him, there was a $60K 350 under the hood, Margaret told him the same size engine I had in the monza, he didn't believe it, he said he was working Chevys for years and there was never a 350 in the monza. She called me and told me to bring it over. He's a believer now.

RacrX · 02-13-2005

Hey Bob RacrX here where can I get performance parts and a catalog of performance parts for my 74 1900 wagon. also can I go to a larger diameter rim and do you know the bolt patteren size the is standard for Opels...and are there after market rims that will fit this model?

jeff denton · 02-13-2005

Hey Ron, I see you've done some research on "cowl induction". Whether it's true or not, I heard long ago that Chevy's version as seen on '70 Chevelle, '69 Z28, etc. only worked at speeds over 80 mph.
So, what can be done, (anything?) to get some intake boost at lesser speeds, like 60 mph? Any ideas?
See what happened to Nextel Cup car #17 last night at Daytona? Too much duct tape on grille is worse than not enough! Incredible what a fine line that is...
And the Monza 350 was stock, wasn't it? I think that's the only small block they made then, other than the 400 (my favorite).

RallyBob · 02-13-2005

Originally Posted by RacrX

Hey Bob RacrX here where can I get performance parts and a catalog of performance parts for my 74 1900 wagon. also can I go to a larger diameter rim and do you know the bolt patteren size the is standard for Opels...and are there after market rims that will fit this model?

I don't know of anyone in the US with a catalog specifically tailored towards performance parts for the model 50 Opels. Opel GT Source has a lot of mechanical parts that will often interchange, and GoinManta has stock body and rubber replacement parts for the model 50 cars.

Regarding wheels, what size were you looking for? A 15x7 wheel fits with ease, but will need a 4" to 5" backspace. The bolt pattern is 4 x 100, which is quite common these days. The problem is, most aftermarket 4 x 100 wheels are designed with front-drive offsets in mind, and as a result they tend to tuck under the fenders a bit.

HTH,
Bob

02-10-2005	#1 (permalink)
azopelnut Member Join Date: Apr 2003 Location: Yuma Arizona Posts: 636 Classified Rating: 0% (0)	Cold air induction Looking at the engine bay of any modern "rice rocket" tells you that a great deal of improvement has been made from days our Opels were made especially in the area of cold air intake. I want to streamline my air intake on my FI 75 sportwagon and here are some thoughts: 1) Replace stock the air intake using 3" smooth tubing coming off the MAF and rerouting it back towards the firewall shelf that is underneath the plastic cowl vent that seals against the underside of the engine hood. 2) Cut a 3" hole in the underside of the vent to take advantage of the air that gets forced off the hood and windshield through the slots cut in the hood 3) Build a lightweight box that would rest on the shelf, house the air filter and permit the air to travel through the bottom of the "cut-out". into the filter without sucking in hot engine air. QUESTIONS If I cut this hole in the plastic vent and built a box to house the filter would I be introducing engine fumes into the cabin? How might I be able to eliminate water from rain or car washing going into the filter area? Your thoughts are appreciated

02-11-2005	#7 (permalink)
azopelnut Member Join Date: Apr 2003 Location: Yuma Arizona Posts: 636 Classified Rating: 0% (0)	Cai Bob Does the fact that the stock 1975 FI set-up basically makes two 180 degree turns adversely effect air flow to the intake? First Air travels away from the entry point in the grill up through the air box and back towards the front of the car through the MAF Second Air leaves the MAF and makes a 180 through the ribbed rubber hose into the intake

02-12-2005	#10 (permalink)
azopelnut Member Join Date: Apr 2003 Location: Yuma Arizona Posts: 636 Classified Rating: 0% (0)	Cai I like your wheel caps with the blitz Dieter... where did you get those? Thank you for the explanation

02-13-2005	#13 (permalink)
ConreroGT Senior Contributor Join Date: Mar 2003 Location: Wa Posts: 655 Classified Rating: 0% (0)	I'd still have to agree with Dieter on this one. I can't see how the air would be forced back towards oncoming air from inside the cowl (under the hood). Basic aerodynamics would suggest a low air pressure at the trailing edge of the hood creating a rolling turbulance right there. Air flows towards a low pressure point. The air under the hood would want to continue to flow up and out at that point. It's the same as when you open the window inside your car (hi pressure) to let the cigerette smoke outside (low pressure) because the air passing by keeps creating a void. I guess as I re-read this the only way it would work I suppose is to have the area sealed from the edge of the hood to the intake to have continues low pressure from the carbs. But even then it would be fighting itself. It would be minimal positive induction. I'd have an intake routed from the front of the car. Last edited by ConreroGT; 02-13-2005 at 06:42 AM..

02-13-2005	#19 (permalink)
RacrX Opeler Join Date: Feb 2005 Location: MetroAtlanta Posts: 3 Classified Rating: 0% (0)	Performance for the 1900 wagon Hey Bob RacrX here where can I get performance parts and a catalog of performance parts for my 74 1900 wagon. also can I go to a larger diameter rim and do you know the bolt patteren size the is standard for Opels...and are there after market rims that will fit this model?

02-10-2005	#2 (permalink)
nobody No Access Join Date: Nov 2003 Location: in transit Posts: 3,873 Classified Rating: 0% (0)	Cold air cowl induction is a very good idea. You need to find every air opening or outlet in the cowl to make it work. Custom filters for all openings and be absolute of your drain points. If it can be done with a GT a Manta should be easy.

02-10-2005	#3 (permalink)
RallyBob Project 1450 supporter... Join Date: Mar 2002 Location: Pleasant Valley, CT Posts: 6,552 Classified Rating: 0% (0)	Paul, I've had good luck pulling cold air from the stock inlet location at the grill. Except with a few mods of course. First, I cut out the actual plastic grill area blocking the air inlet. Second, I toss the stock plastic 'scoop' and make a new steel one with a 3" tube attached. Very simple, almost looks stock, and you don't need to cut the body to do it. Bob

02-10-2005	#4 (permalink)
BQS4 Southern Red Neck Join Date: Mar 2002 Location: Snellville, GA Posts: 4,947 Classified Rating: 0% (0)	Bob; How about that scoop as one of the items that you could "offer?" What about a box/fixture for the top of a 32/36 weber?

02-13-2005	#12 (permalink)
nobody No Access Join Date: Nov 2003 Location: in transit Posts: 3,873 Classified Rating: 0% (0)	On a GT the cowl was designed to draw cold air to the interior. As speed is increased the given temperature decreases and pressure increases in that area. That is the reason for that upward slant at the window side of the hood. It forces air into the cowl and as it crosses the edge it disapates heat. That is why so many car designers have chosen to use it. Not that I've researched this to death or spent alot of time designing a cold air cowl induction for twins. Oh wait, maybe that was me.

02-13-2005	#15 (permalink)
RallyBob Project 1450 supporter... Join Date: Mar 2002 Location: Pleasant Valley, CT Posts: 6,552 Classified Rating: 0% (0)	FWIW, in Nextel Cup cars they draw in the air to the carburetor from the base of the windshield, NOT from the front of the car. Those aerodynamicists all agree this is the best place to get the air from, at least at the speeds they travel at. Bob

02-13-2005	#16 (permalink)
nobody No Access Join Date: Nov 2003 Location: in transit Posts: 3,873 Classified Rating: 0% (0)	On a GT with twins it works great. My 11:1 2.0 is fed this way. I don't know if anbody else has done it, but believe me it does work well.

02-13-2005	#17 (permalink)
Paul Member 1000 Post Club Join Date: Mar 2002 Location: Ft Smith, Arkansas Posts: 1,364 Classified Rating: 0% (0)	Remember, to consider the pressure differential. To get air to flow thru the radiator, the engine compartment will be at a lower pressure than the area below front bumper. The area just below the windshield is considered to be a high pressure zone. Visualize the air coming over the hood and piling up at the base of the windshield. Some of the air completely changes direction and bleeds off to the size of the car, around the A-pillars, mirrors and such. While the rest of the air travels over the top/roof of the car. Decreasing the angle between the hood line and the winshield serves to reduce the high pressure zone and improve aerodynamics. Keep in mind that velocity and pressure are inversely proportional. As the velocity of the air increases, the pressure in that area decreases. And, if the velocity decreases the pressure increases. Just as when dealing with an airfoil/wing. The air traveling over the top of the wing speeds up therefore the pressure drops. The air at the base of the windshield slows down, essentially it piles up looking for someplace to go, therefore the pressure in this area increases. the more straight up the angle of the windshield, like a Manta vs a GT, the greater the pressure increase. Relative to each other, the engine compartment is at a lower pressure that the cowl area at the base of the windshield. If given a path, the air will flow quite easily from the cowl area to the engine compartment. HTH

02-13-2005	#18 (permalink)
namba209 5,000 Post Club Join Date: Aug 2002 Location: Imperial Beach, CA South of San Diego Posts: 5,974 Classified Rating: 0% (0)	Way back when, the NASCAR folks started using aerodynamics to get the cars to go faster on the super tracks. Around the mid 60s, early 70s they found in wind tunnel tests the air pressure at the base of the windshield was significant enough and in sufficient volume that they could turn the filter box on the carbs 180 degrees and attach the air inlet to the cowl chamber and get a quasi charged intake system. This positive charging vice vacuum charging of the cylinders occurred up in the 100 MPH + range and the faster they went the more positive flow through the carbs. All this occurred with the 7 Liter engines and because of the speeds attained the restrictor plates and then smaller engines became the rule. To give you and idea of volume and pressure, last weekend, the Tide NASCAR Chevy that was campaigned last year was at the local Commissary, and the grill was totally duct taped except for an area of about 2" X 4" cut from the tape. That's all the area needed to keep the radiator cool during a race at speeds approaching and exceeding 200 MPH. A couple of notes on this after talking to the mech. By taping almost all of the grill area a smoother air flow is attained which means more speed and the high velocity air going into that small hole and dumping into a low pressure area significantly drops the air temp in front of the radiator. And the reason I got to talk to him, there was a $60K 350 under the hood, Margaret told him the same size engine I had in the monza, he didn't believe it, he said he was working Chevys for years and there was never a 350 in the monza. She called me and told me to bring it over. He's a believer now.

02-13-2005	#20 (permalink)
jeff denton former opel racer Join Date: Nov 2002 Location: near some glaciers Posts: 2,747 Classified Rating: 0% (0)	Hey Ron, I see you've done some research on "cowl induction". Whether it's true or not, I heard long ago that Chevy's version as seen on '70 Chevelle, '69 Z28, etc. only worked at speeds over 80 mph. So, what can be done, (anything?) to get some intake boost at lesser speeds, like 60 mph? Any ideas? See what happened to Nextel Cup car #17 last night at Daytona? Too much duct tape on grille is worse than not enough! Incredible what a fine line that is... And the Monza 350 was stock, wasn't it? I think that's the only small block they made then, other than the 400 (my favorite). Last edited by jeff denton; 02-13-2005 at 02:55 PM..