Cold air induction

[ConreroGT]

Ok, after reading thru the logic, you've convinced me. Thanks Nobody for the specific comment. I did think of that possibility of induction (the access hole above the heater box) but conventional aero logic made me think otherwise. I'm familiar with aircraft aerodynamics but havn't proven anything with the forces the shape of a car can produce. Learn something new everyday. :o

...and no, I don't smoke in my GT!

[nobody]

I haven't done any air temperature readings on it. However I could tell the difference even at a standing idle. It seems to draw air better from about 40 mph and better. I did it this way becouse the twins are a hard fit for cold air intake on a GT.

[namba209]

Jeff, Actually I haven't done any research on cowl induction at all. I just happend to be around during the time of the 7 L engines and read most of the stuff in the car mags. Having a fair good memory helps sometimes too.

As for the monza, in 75 they offered an in-line 4 and the 4.3 L V-8, but the V-8 couldn't pass the smog restrictions here in CA, so they put in the 350, 2bbl carb, and a single exhaust that would pass smog here. But it was only available here in CA and only for 75. All the other 5.7 L engines in the monza were after market installations and were suspect depending on whether the additional approximately 600 lbs of body beef-up were added along with the engine.

[GTJIM]

Originally Posted by RallyBob Grey area, I understand.... How 'bout this then? (I'm doing something similar for the LSR GT and my Dad's turbo GT). The stock twin nostrils on the GT....make a duct (attached to the underside of the sheetmetal in the nose of the car) that collects the air from there, and feeds it to the carburetor....except in your case don't connect it. Leave a 1" gap or so. The tech guys would have to admit there is no actual ductwork attached to the carb inlet, but you and me both know that once the car is under way it will get a steady stream of clean, cold air from outside the car. But you didn't add any 'scoops' or 'spoilers' or make any holes in the bodywork to do it, and there is nothing attached to the carburetor. You know the tech guys better than me, so you can think about whether or not it would fly. Bob

Bob,

Looking at the Stuttgart University "Windkanal" picture in Das Grosse Opel-GT-Busch and from my boat hull flow experience (most of which just proved assumptions and "commonsense" wrong!) it looks to me like the air flow over the "nostrils" is speeding up and is thus a low pressure area and air will be coming OUT of them. Unlike the area at the base of the GT screen where air is "piling up" and slowing down to create a higher pressure area, before speeding up again to spill around the sides of the screen and flowing up over the roof.
Generally, forward facing air "inlets" do not work as common sense would think as there is a standing (pressure) wave that builds up in front of them that effectively diverts the air from flowing into them. That is why the area in front of the GT screen is so good - it has the edge of the hood projecting back over the heater air inlet grille and a nice rear facing inlet is made there.
A bit of work with a differential manometer hooked up in these areas and tested at speed would show if any of these hypotheses have any validity ......

[RallyBob]

It definitely warrants testing. I won't head out to Bonneville without a LOT of pre-event evaluation. I was making the assumption the scoops were functional, and that the air passing beneath the vents (after the grill opening)
would draw air thru the vents themselves. I forsee some highway runs with tufts of string attached to the car and video cameras everywhere...

Bob

[GTJIM]

A lot depends upon whether those "nostrils" were placed there by the stylists or designed by the airflow people! As you say, Bob: "It definately warrants testing" !

[jeff denton]

This is neat. A great example of what wisdom abounds at gt.com.
Wasn't it proven decades ago that the only real effective forward facing air scoop was the "NASA duct"? I recall reading that as a kid when a funny looking new hood appeared on the new Boss Mustang, was it 1971 or so?
I've never worked with the "strings" method of watching airflow, but a competitor in my class runs "another damn Pinto" with as much Lexan windows (right side and rear) as allowed, says he did string testing before and after and proved to himself that the car is slipperier with the cab closed in. At only 60 mph, mind you. Who knows, but every little bit helps if it works...
Bob's LSR GT would be where such attention will be absolutely critical, not only for improved top speed but even for safety.
Remember when a new Monte Carlo body came out in the eighties, NASCAR boys naturally used it but found out instantly that because of the shape of the rear window the rear of the car shot skyward at about 200 mph! Bad, bad, bad situations developed. That's why in the middle of that production year you could buy a limited edition Monte Carlo with a very different rear glass shape. Problem solved.
Jim, do you think the grille of the GT, under the bumper, would be the best place to find high pressure cool air at 60 mph?
Bob, I hadn't heard much mention of the LSR GT lately. When does this fun begin, and do you have any help? Bonneville is just overnight drive from here, we have lots of people from Montana competing there, I even know one of them.

[RallyBob]

Originally Posted by jeff denton I've never worked with the "strings" method of watching airflow, but a competitor in my class runs "another damn Pinto" with as much Lexan windows (right side and rear) as allowed, says he did string testing before and after and proved to himself that the car is slipperier with the cab closed in. At only 60 mph, mind you. Who knows, but every little bit helps if it works...

It's a pretty cool way to figure airflow out. Back when my buddy Dave was running his Ascona in circle track I asked if I could borrow it for a road race lapping session. He had lexan for a windshield, so there were no wipers, and no side windows either. Just in case it rained, I used Rain-X on the windshield, and with a little 'string testing' on my street car, I came up with some little 1.5" wide lexan 'wings' that attached to the A-pillars to deflect airflow (hopefully) around the side windows to deflect the rain.

Well, it worked wonders. It ended up pouring that day at the road race course, and even at 120+ mph I could stick my hand out the side window 2" and not get wet...everything was deflected by the little wings I had made, and I never felt a drop of water on me.

[GTJIM]

Originally Posted by jeff denton This is neat. A great example of what wisdom abounds at gt.com. Wasn't it proven decades ago that the only real effective forward facing air scoop was the "NASA duct"? I recall reading that as a kid when a funny looking new hood appeared on the new Boss Mustang, was it 1971 or so? Jim, do you think the grille of the GT, under the bumper, would be the best place to find high pressure cool air at 60 mph?

Yep, the NASA Duct is about the best there is for collecting high pressure air - lets the air drop into it at the narrow front then build up pressure as it slows down and spreads out.

I fear that both under and over the front of the GT the air flow speeds up and the pressures are lower than in front of the radiator ( the air comes in through the small grille area and the spreads out and slows down against the radiator - some "leakage" through the radiator though! - and a the base of the wind screen. However a couple of NASA ducts "hidden" in the belly pan may work wonders - and not be seen.

[nobody]

intresting idea, run a tube to one nostril, center of the cowl, before the radiator and under the car. I have the manometer and probably enough tubing to test it in one shot.

As far as Bonneville goes, it's close to Salt Lake, I'll be there this weekend and will look at the requirements to set down some hard numbers maybe this summer. Sooner or later I'm bound to take Thumper to Utah. April is looking good for that trip.

[Travis]

I had the opportunity to sit down with a friend of mine this morning and discuss the various type of air intakes that have been discussed. While not an aerodynamicist he does have wind tunnel experience mostly with aircraft wings.

To sum up the conversation:

NACA ducts do a good, but not great job of ingesting air. Their primary advantage is that they allow air to be ingested without disturbing the flow of air behind it. This allows the aerodynamics of the rest of the car to function properly. This is why you see them on real racecars.

In general, concave surfaces cause an area of high pressure and convex surfaces cause an area of low pressure. The back of the hood/bottom of windshield area forms a concave shape resulting an a high pressure area and a great place to ingest air. Also note that this comes largely for free as this concave shape is just a natural shape on the car. You're not adding any drag by using this method where as you would be by adding a ram air system or to some extent a NACA duct. He also commented that he'd expect newer, more streamlined cars to be less effective at creating this high pressure area.

Bob, I should get the two of you together to discuss your plans for the LSR car. He may have some insight that could help you out. When you get back to working on that car again, let me know...

-Travis

[hrcollinsjr]

All of this discussion about cowl induction? Where does the car interior air come from? <BG>

And I believe I read somewhere that the extra hood vents, not sure if they were just talking about the louvers, were added because the original design didn't have enough cooling capacity.

Harold

[nobody]

The interior air comes in through two ducts from the cowl area at the outer edges. It's also ducted into the heater area from the cowl. I don't know if anybody else has taken this route but it does work well.

[baz]

Originally Posted by hrcollinsjr All of this discussion about cowl induction? Where does the car interior air come from? <BG> And I believe I read somewhere that the extra hood vents, not sure if they were just talking about the louvers, were added because the original design didn't have enough cooling capacity. Harold

hi harold the air for inside comes from the front of the windshield where the grill is
and on a gt there are 2 plastic flip vents in the footwells to get cold air from the wheel wells

the louvers are to aid getting air out at the back of the engine bay as all cars have a problem there this was opels fix

some newer cars have a seal that isolates the air inlet for the heater to help stop engine fumes get in to the cabin but they stop short at the ends to get the hot air out of the engine bay
this is some thing to watch for when looking for a ram air pick up as you want the cold air not the hot

if this is done for a road car with a carb then you must make allowances for 1 thing when setting up the carb
a carb is made to have air pulled through by the engine
when you feed ram air you are forcing air in which spoils the jetting at higher speeds (i think from memory that you only get a ram air effect over 60mph)
the 2 eyes in the front are good for cold air pickup at normal road speeds as you don't get over 60 all that often but as said they are on a convex curve so drop pressure at high speed
there is 1 place that no one ever thinks about for high pressure air thats i said earlier
if you fit some mesh wheel arch covers to fill the rear of the front wheel arches (a good air filter in the orig can filter and a custom pipe fed to it from inside the car ) you have a high air pressure (open the side vent and see how cold it is with your hand at 60 ) this air is trapped by the fender lip and is drag most of the time
I THINK I MAKE NO LEGAL CLAIMS TO THIS JUST A BIG THOUGHT
must go have a lie down too much typing and no jokes must be the chemo

[Scott McDonald]

Baz-I wish you the best. Hopefully the chemo won't be for long. Another thing...your avatar is a bit unnerving.

[hrcollinsjr]

Actually my question was either meant to be sarcastic or rhetorical, I haven't decided which?

Did learn a few things from the earlier posts and some from responses to my "DumB Question", there is such wealth of info in this group. I actually try to avoid this group because long periods of time can pass without my realizing it (compliment). Wish I could just download all of the info and read it at my leisure.

BAZ, I read the chemo part. I had hoped that was a joke, a bad one.

Anyway best of luck.

Harold

[namba209]

Baz, et. al., "nobody" and I went through the flow of air through the cowl into the interior of the GT. Because I had only a shell at the time it was easy to trace the air flow. And I found out all the flow into the inside of the car comes through the cowl at the base of the windshield and because of the structure design, from the headlight buckets. Consider the cowl area as a reservoir, air flows into it through the screened area and it is an open area clear across to the fenders just in front of the doors. There is an inner structure that makes up the wheel well, and the void between the wheel well and the fender also opens up behind and outside the headlight buckets. So basically, the area inside the fenders and the cowl itself is where all the air comes in to the interior of the GT. Even the air for the heater enters that way by a hole in the floor of the cowl, As "nobody" indicated there are two hoses that feed air from the cowl to the air vents in the dash and that same air feeds the foot vents in the kick panels. I found all this out while trying to find a more favorable routing of the main wire harness from the fuse panel to the front of the car. HTH.

[nobody]

I did the cold air intake based on information from Rallybob and Otto. Bob informed me that on a dyno a performance motor can gain 8 to 10 HP by utilizing cold air. GTJim helped me with flow rates and tubing sizes. Namba helped with the "where are the holes?" issue.

At low or high speed it works the same. Carbs will only take so much, and the jetting wide open in 5th still doesn't change things. I also put in new locks and new hood gasket to keep out any heated air from the motor.

I do have an air harmonics issue at high RPM. It could be from the very short exhaust or maybe the lack of air horns being installed yet.

For those that don't know, this is an 11:1 2.0L, twins, 2.0 sprint exhaust, roller rocker with huge cam motor....cold air cowl inducted GT.

[baz]

hi hr sorry but its no joke and
scott it will be about 6 months
as to the avitar look at
http://www.badgerbadgerbadger.com/

and im sorry if you are stuck with it for the rest of the day /week / your life

[greensmurf20]

i gotta buncha little animated badgers as my walpaper here at school now, you come up wiht the funniest things baz.

[Scott McDonald]

Originally Posted by baz and im sorry if you are stuck with it for the rest of the day /week / your life

heh...heh..I'm sure you are.

Did I forget to mention, I quite like unnerving.

That really is a shame about the chemo. If you ever need someone to yell-at, feel free to PM me and vent.