[johnbran]

Well, I need to pick the brains of the Opel Masters again. This may be way off base, but bear with me. I am hoping to use some of the performance advice I've gotten off here and design some sort of cold air induction on my '70 GT, but I've run into a few hangups. I managed to get my hands on a factory (non-functional) cowl induction hood scoop from a chevy citation a few years back and, much to my surprise, it is almost a perfect fit for the GT hood. So, it is now trimmed and awaiting permanent attachment, but I had some questions regarding making this a functional cowl induction. Has anyone out there done such a mod? My biggest problem is getting the air from the rear scoop opening at the winshield area down into the carb while still using some type of air filter and without risking getting water into the filter/carb should I get caught in a sudden downpour. The scoop is just barely taller than the origional hood bulge, so there is little to no extra room between the carb (Solex, of course) and scoop to put in much of an air cleaner/air box. Also, the origional GT air cleaner is mounted so far forward that it would take quite a maze of hose to clear everything and route the air intake to pick the air up at the back of the scoop. I have removed most of the hood bulge, mainly to clear the installing of the scoop, but I have not made any other cuts to the remaining hood beneath the scoop. So, I thought of just filling in the opening where the origional hood bulge was and then routing the air intake of the origional air cleaner straight up into the opening between the hood and scoop through a fabricated connection plate. This would have to be able to seal when the hood is closed but still be able to come apart when the hood is opened. This would allow the air to pass into the scoop at the rear, using the hood and scoop as the air box, and then be drawn into the origional air intake to the filter/carb. The question is, do any of you think this would work? One of the potential problems I see is the fact that if the hood heated up due to engine temp, then it wouldn't really be much of a "cold" air induction. Granted, the hood could be coated with an insulating material to reduce the heat transfer, but this may not be enough. I guess the biggest question is, would this be worth attempting in the first place? Would the gain really be worth the extra work and trouble? Or could this just be another one of my crazy ideas? The scoop is going on regardless, even if it's just for looks, but I thought it might be worthwhile to take advantage of it and make it functional. What do you all think? Any ideas or suggestions?

Thanks as always,
John

 

[RallyBob]

Changing to a Weber will gain you more power than having cold air induction on a Solex. Seems like a lot of work. I spent 8 hours fabricating a NACA duct for a racecar and also fabricated a sealed, insulated cold air box. It lowered the air temp by over 40 degrees. It was worth 6 hp on a 185+ hp engine. So on a stock engine, I'd guess it was worth maybe 2-3 hp. That's assuming you're going fast enough to take advantage of the airflow, since sitting at a stoplight will heat-soak the intake and carburetor and negate the effects of the incoming air somewhat. But hey, it'll probably look cool. My friend Al used to have a 1984 Citation X-11, it went pretty damn good, had the factory fiberglass hood with all the cowl-induction stuff installed, but inoperative. Always wondered why they went to all that trouble....

Bob

 

[johnbran]

So much for that idea.......

Yeah, that's kinda what I figured, but it sounded cool at the time. Actually, the Citation X-11 is exactly what this scoop came off of. I believe it was even an '84. Like I said, it fit like a glove to the stock GT hood once I removed the top of the hood bulge. It really makes the 'ole GT look more aggressive, too. Maybe they went to all that trouble because they knew someday us GT owners would be scouring the junkyards for cheap and different body upgrades. Hmmmm.......now if I could just find a cheap rear spoiler out there that would fit the GT......
If anyone is interested in what the citation scoop looks like on a GT, I'm hoping to take some "in progress" pics of it this weekend, so maybe I can get them and the "before" pics posted when the upload page gets working again.
Thanks,
John

 

[chuckspeed]

On a Cavalier Z-24, the scoop is functional, and draws from the leading edge (front) of the scoop. I'd set it up the same way on a GT - see if you ant get your hands on a Z-24 airbox to get the rigght aircleaner and such.

While I agree with Rally Bob's assessment of HP, it always seemed to me that a cold air induction motor had a fatter torque curve. Initial tip-in throttle response was crisp - overall driveability improved as a result of getting cool air to the carbie.

I had one buddy who re-directed the intake of his GT to pick up air from the passenger side snout scoop. Didn't seem to make his car any faster, tho. The area of the snout slots is a high velocity area - not a good place to pick up air.

 

[RallyBob]

While I agree with Rally Bob's assessment of HP, it always seemed to me that a cold air induction motor had a fatter torque curve. Initial tip-in throttle response was crisp - overall driveability improved as a result of getting cool air to the carbie.

You know Chuck, after thinking about it a bit, it makes perfect sense what you said. I'd probably guess and say the cooler air to the carb improved driveability and crispness mostly because it cooled the fuel....you know how Opel carbs can get VERY hot and even boil the fuel (vaporlock). Keep the carburetor body cooler and it will keep the fuel cooler. It would be an interesting test to attach a temperature probe to the fuel bowl area and drive around both with and without the CAI installed just to see.

Bob

 

[chuckspeed]

Thanks.

The other bennie of cold ram air has to do with the inertia of the air mass - with positive pressure 'filling' the air box, the air mass can accelerate a tad quicker to aid low RPM volumetric efficiency (assuming the car is in motion) thus providing a boost in low-speed torque. At higher speeds, the benefit of ram-air airbox filling is negated by the design pressure drop of the intake tract - which is why ram-air engines don't show big HP gains at the top end.

It would be possible to check temps using a Minitemp (handheld infrared pyrometer) by using a hot-shutown loop. Minitemps are really cool for all sorts of diagnostic work - once you know what you're looking for - and you do!

Yah - the Solexes are vulnerable to heat soak. It's amazing how much better they run simply by cleaning the heat shield and the exterior of the carb.

 

[johnbran]

Ok.....so then do you guys think this WOULD be worth pursuing? As I said the Citation scoop is ready to go on and be molded in as soon as I make up my mind on whether or not to make it functional. What about my idea of using the space between the hood and scoop as an air box and run the air cleaner intake straight up into it for picking up the air. The scoop would draw the cooler air from the natural low pressure area in front of the windshield and the hood could be insulated underneath to prevent heat soaking from the engine heat. While I agree that the Z24 scoop might be a better idea, I've already got the Citation scoop and it's ready to mount, so how about it guys? Would this work or not? One other question I had is concerning the heat shield you guys keep talking about. Either I'm misunderstanding this, or is there supposed to be some sort of shield between the intake and exhaust? If so, mine doesn't have it. In fact, mine doesn't seem to have anything between the two. If there is something missing that goes between the two manifolds, where could I find one or at least a pic of one so I could fabricate one up?
I really appreciate all the help you guys provide. I'd be lost without it.
Thanks again,
John

 

[chuckspeed]

John-

the heat shield is a piece of formed metal sandwiched between the carb and intake manifold. There is no shield between the intake/exhaust manifold, as the two are close-coupled on every 1.9 save the 1975 FI variant. This was done to improve cold-weather driveability.

I can't seem to visualize how you're going to get air into the Solex AND get a reasonable air cleaner in place, too. There isn't much room between the top of the airhorn and the top of the scoop you propose to use...

One solution may be to adapt a Manta/Ascona air cleaner to fit up in the space of the hood scoop - just expect to do a lOT of cutting!

 

[johnbran]

I don't recall having anything between the carb and intake except for the gasket when I switched carbs, but I may be missing something. I'll check it again. After all, the carb was not on my GT when I got it, so if the piece comes off, it might have been lost before I got it.

As for the carb/filter/scoop clearance problem, what do you think of my idea of using the stock GT air filter and just run the air intake straight up into the scoop instead of it just poking through the radiator panel? The scoop would still take in air at the rear, but the air intake for the air filter would be drawing its air from the space between the hood and scoop. Maybe I'm wrong, but it seems like the hood and scoop would serve as sort of an air box and I would still be drawing in the cooler air from the natural low pressure area in front of the windshield. Do you think this would be a possible solution, or would it just simply not work? As you said, there's not too many options with the limited clearance between the carb and scoop, so this is what I came up with. Any advice or tips would be appreciated. Still looks like it might just be a better idea to forget the whole functional scoop and just stick it on there for looks.

Thanks as always,
John

 

[chuckspeed]

sounds like I misunderstood what you intended to do in the first place...

The reroute will work. The only flaw may be the pressure drop of the attenuator - yo may have to do some cutting and fabbing of the stock aircleaner to get it to work. Work diligently to keep the pressure drop of the intake tract as low as possible - it makes a difference in HP.

Work on a heat shield, too. It's darned important.

Cold air induction will imrove your throttle response - it's like advancing your timing - without the loss of power at the top end.

 

[johnbran]

Ok.....so here's another question on rerouting the air intake to the scoop. I was thinking about it some more and there's really two different ways that I could re-route the air intake. I could either just fab up a 90 degree bend in the origional "snorkel" before the air filter which would probably work, but it's still going to only be about a 2" inlet due to the size of the origional air intake. On the other hand, I could re-design an entirely new top plate for the origional air filter housing itself and run this up to an opening in the hood, which would give it a much larger opening to draw air from. Would completely doing away with the origional "snorkel" air intake and going directly from the air filter housing up work better in regards to preventing a pressure drop as you mentioned? Which part of this change would you see as the biggest threat for causing a pressure drop in the intake tract? It may not make much, if any, difference in HP, but I definitely do not want to lower the HP just because this isn't designed correctly. Also, another factor that I am concerned about is the fact that the scoop does not overhang the rear of the hood any (actually it ends right in line with the windshield washer nozzles), and this may not be far enough back to tap into that low pressure area at all. Do you think that this will affect the air flow into the scoop? Any further suggestions would help greatly as I am getting close to a point where I need to start working on getting the hood finished, mods or not.

As for the heat shield, I am planning to check that out tomorrow (hopefully), and if it doesn't have one, I'll be getting one made up.

Thanks again,
John

 

[chuckspeed]

John-

The snorkel is a sound attenuator which does indeed add some pressure drop - your second suggestion is identical to how ram air is set up in the old Z24's, and should work fine.

As for location - while further back is better, it will work okay where it's currently at. When testing was done on Shelby's 350 GT's, it was discovered the hood scoop was MUCH more effective when rotated to face the windshield. Pontiac learned from this - hence all shaker T/A's had their scoops facing rearward.

 

[johnbran]

Thanks for all the useful info Chuck. Sounds like I'll probably go ahead and try to modify or fab up a new lid for the air filter and open it up to the scoop before I permanently mount the scoop down to the hood. I've got a couple extra top covers, so if something goes terribly wrong or things don't work out, I've got a spare to put it back to origional. As I said, it may not make much difference, but at least I'll be able to honestly say that my GT has cowl induction!!

Thanks again for the help and advice,
John

 

[bear]

Cool air induction is already present in a stock GT air filter system. The inlet to the snorkel is in front of the radiator and gets cooler air from the grill opening than being behind the radiator, like most Weber carb mods with no snorkel. Ram induction was found to be most effective in the 70s on NASCAR racers. What was done, was to build a duct from the heater air inlet at the base of the windshield and route the air into the air filter housing on the carb. This produced a mild ram air induction, pressurizing the intake manifold for better (more) air going into the cylinders. The only drawback was you had to be going above 150 MPH to realize the benefits of cylinder charging.

Ron

 

[ConreroGT]

GT Induction for side drafts

Here's my attempt at a cold air induction for side draft carbs. It's basically a walled off section that allows the velocity stacks to poke in and grab cool air. I added a rubber "boot" to block the rest of the hole. This allows the carbs to vibrate around and not disturb the walled section. The hood acts as the top when closed helping "seal" the box close.

 

[GTJIM (R.I.P.)]

Cowl Induction

Nobody's "Thumper" has cold air cowl induction with the mesh vent to the winscreen wiper motor being doubled up with some air cleaner foam in between. Ducting the air to the twin SD Webers was a real challenge but he achieved it with a couple of cake tins and some plastic plumbing ducting.
There was quite a bit of long distance discussion involved before it all came together - but the thread ended up deleted a couple of years ago when people could edit their threads at any time (That is what brought about the 24 hour limit on editing -- but that is another story best told over numerous beers!). I am sure that I saved some pictures - somewhere ........

 

[nobody]

Speaking from experience on this I'd be concerned with engine movement. I have been known to get on it a bit and it moves more than you would suspect.

 

[spamseptictank]

Consider the Gen2 Trans Ams

John,
You may want to look at the design of the cowl induction used on the second generation Trans Ams. The cowl was connected to the air cleaner and completely separated the air coming in from the air in the engine compartment. The cowl came up through a hole in the hood. If you decide to look at this design, make sure you look at the early Gen2 T/As. The noise laws changed somewhere in the mid/late 70s that required Pontiac to close off the cowl to reduce noise. Hope this helps.
Grace and Peace,
Dave