I have seen a duct for sale that is smooth instead of ribbed like on our cars.I am sure that it is no mega horsepower bolt on,but it should help smooth the airflow going into the throttle body.I'm talking about where the hard plastic ends in front of the throttle body and that rubber piece is.Anyone ever seen or used one of these?

check out your local Lowes or Home Depot.head to there plumming section and look for a rubber 4" to 3" pipe connector.they'll be black and smooth.i think they run for $10.

I'm thinking of putting on some smooth tubing, just to eliminate the turbulence caused by the ribs, but I've talked to a few people about it and they generally felt that it would only help at high rpms. That's the story for many mods people make. It's still nice though to make things operate the best they can.

Yea, I never completely understood why the cars came stock with a ribbed intake duct ... either way, it gives us something to do

Here's a little more info about the ribbing. I was recently told, by someone on another forum, that ribbing like ours can cause so much turbulence that a 3" diam ribbed tube can have about the same airflow as a 2" diam smooth walled tube. That's a pretty big difference. Seems like a good reason to smooth them out.

I haven't seen anything that I could substitute easily so I was thinking I might be able to smooth the inside of the ducts by filling the ribs with a caulk or putty. I think it'll stay in place ok, and as long as I keep it in big "pieces" even if some did come loose it wouldn't be able to get into the TB, so it'll be harmless. I think that'll be my project when the weather turns cold.

Here's a bit from another post of mine...

FYI: I've heard figures like for every 10° (?) drop in incoming air temp you get a 1% increase in HP. A 10° drop in temp raises the oxygen concentration in the cooler air 3% above what's in warmer air. Under hood air is much warmer than 10° above outside air so there's a big difference in oxygen concentration. Also, according to figures and measurements found online, I calculated that without the airfoil on the TB, there is as much as 3 lbs backpressure generated by the incoming air hitting the center of the TB at high rpms. An airfoil will reduce the drag to 1/2 or 1/4 that much. That center part of the TB takes up about half the total TB area so it seems worth it to cover it with something smooth. The MAF has its screens in place. I hear it flows more than enough as is and needs the screens to even out the airflow across the duct diameter.

As popular as the airfoil is,when I saw this piece for sale I was surprised more people didnt have them(the smooth duct).It would only seem logical to want this air smoothed out just before entering the TB.I think I will try the Home Depot piece first since the one I saw was $39.95.I go to the track quite often and this would be easy enough to change at the track,so if there is any noticable improvment between the two I will let you know.

I would definitely like to hear the results!

I have done some cold-air mods. First I tried various home depot pieces duct taped together to see what the effect was. I have a '91 Formula with SD so can play it anyway I want.

I run a K&N cone filter in the right fender well having moved the canister towards the rad.
Feeding the right fender well is two ducts each running from collectors under the front nose one on the left and one on the right. I used 3 inch square gutter collectors that mate to 3 inch diameter metal flex hoses that snake from the passenger side into the right fender well (a short run and the driver side snakes behind the undercarriage air dam and ends up in the same right fenderwell). There is no shortage of cold air hitting that filter.

From the K&N in the right fender well to the TB bellows I have tried a 4 inch diameter flex hose but it would not clear the hood or A/C properly so I went with a 3 inch hose. I replaced my factory bellows with an '88 GTA bellows which has a molded 90 degree bend.

You can see from the pic that it is clean enough. Best part is it really works especially in midrange rpms once you get moving and the under the nose collectors can start working (sorry no pics of this).

IMHO the airfoil is a waste of time I have seen dynos with and without and yawned at the results. Spend your time and money on a decent cold air collection setup and you will be very pleased with the results.

Oh yeah -- my 90 degree bellows has no ribbing on the inside what is everyone talking about anyway ?

RP.

The duct on your TB looks exactly the same as mine, with the ribbing just in front of the TB. Yours is smooth on the inside, you don't see the inside of the ribbing?

I went to the track last night and tried the Home Depot piece.My first run with the stock ribbed duct was a 14.674@93.50mph, 2.049 60', 6.071 330'.Then I put the smooth piece on and ran 14.571@93.94mph, 2.028 60', 6.014 330', another run with the smooth duct-14.543@93.96mph, 2.014 60', 5.995 330'.It didnt seem to make much of a difference because my car usually runs between 14.5 and 14.6 anyway.I just figured the first run was a bad one.When I got home I compared the slips to some other ones I had,It did help on the short times.The 2.014 60' was my best ever,which are mostly 2.030 to 2.040.In fact the best my car has done is 14.427@94.67mph, 2.027 60', 5.967 330',this was with skinnies on aluminum rims on the front.If I had the skinnies on last night it could have dropped below 2.0 60'.I'm not sure on the 1/4 times,I think that is all the car has at this point.I've run it about 40 times and it stays around 14.5.I have a Crane Powermax Cam,new springs,timing chain and gears,Hedman LT headers,an AFPR and I am doing a little porting on the plenum.Once I get all this stuff installed it may make more of a difference.

Also,when I ran last night,I had a full tank of gas which was a mistake on my part.I usually have about a 1/4 of a tank but the last time I went out I had a little more than 1/2 and didnt spin as bad on the line.So that is why I put more gas in on the way out but I put in too much,I guess I didnt realize how much was already in there. Hey, It might have even ran a little faster than it did.

No ribbing until the accordion bellows near the TB. The last few inches before the TB it is heavily ribbed but I think they all are at that point ?

RP.

Pretty decent setup what altitude do you run at ?

Pretty decent launches too. Good times for an auto I think you should be running 14.2s or 14.3s with a stick (and gears). Not sure which you have ?

In any event I think you are spending too much time on this ribbing and CAI bit. Try running some collectors under the nose of your car and ram'ing air to your K&N. I found it really helps above 3000rpm. You can see from the pic where I stuffed the K&N cone. This fender well gets blasted by two three inch diameter hoses collecting air from under the nose of the car.

Oh yeah, beauty GTA man.

my .02 cents worth,
RP.

palric,I'm in Florida so I guess it's sea level It's a stock auto with 3.23 gears .As far as the ribbing thing,I was going to the track anyway and just thought I would mess around and get some real world results.After I get my cam and stuff installed I plan on getting some cold air to the filter somehow.Did you have to do any cutting on your car for your CAI ?,I dont want to cut on mine.

I got confused I didn't catch the part about the new stuff is 'waiting to be installed' in your car. In that light your times are pretty decent indeed. I have pretty much the same plans cam 210/218 .450/.460 1.6 RRs, headers, AFPR and I will be getting the heads worked over.

About the CAI, I cut the factory air can for my first go at it -- this was good for some ooooommph around 2300-4500rpm. But nothing to write home about (see pic). I replaced this setup with a K&N cone at the throttle body but it was unpredictable depending on the air flow at the time behind the rad. Not a good idea IMHO.

SLP uses the fender wells so I figured I could too hence the new location for the K&N in the passenger fender well.

The best results to-date have been from the current setup dual collectors running to the fender well with a 4 inch flex hose between the K&N and the bellows. With this setup it pulled really hard to 5800rpm and went flat at 6100. Thing is the A/C and the hood crunched it so back to a 3 inch hose. This one pulls hard to 5500rpm and goes flat. I can still get 6100rpm out of the engine but what purpose ?

There is a major diff in throttle with this setup I strongly recommend it for an SD car. Oh yeah I didn't cut anything on the car for the current CAI setup. Just a bunch of Home Depot parts and a K&N cone.

thx,
RP.

Yes, that's the part I meant. I smoothed out the accordion bellows in front of the MAF and next I'll do the part in front of the TB. I don't expect to see any changes, it's mostly a simple project to do.

Palric,

Do you have any more pics of your air duct setup? I've never seen anything like that.

1990GTA,

Have you ever tried to run your 3 or 4" duct under the overflow tank hose instead of under? I'd also like to see a better pic of your filter.

Just tryin to learn here. Thanks guys.

I haven't got pics of the underneath yet I'll try to get some it was so remarkably simple to do that it is worth sharing. Also -- it really wakes up the motor once I get rolling...

I have tried the ducting under the overflow tank hose the three inch hose will fit but the 4 inch wouldn't -- it bumped up against the A/C and that was the end of that it got shredded.

The 3 inch hose doesn't bump into anything now so I just leave it where it is. The 4 inch flex hose from the K&N to the bellows did work alot better than the 3 inch those without A/C should use 4 inch.

RP.

You could really feel the difference between the 3" and 4"? WOW

I did the test in Southern Ontario in July with mondo humidity I think the humidex was like 95 f. Good test conditions.

I find I get some surging with 3 inch tube but with the 4 inch it goes away. Hard to figure as in either case it goes into a 3.25 inch factory bellows, turns left and hits the TB ?

But yes I could tell the diff there was 'more there' between 5300 and 5900rpms and the engine came on harder from 2000 up. Not very scientific metrics eh ? All I can say is try it for yourself and use what works best.

thx,
RP.

COOL

So a guy from Pontiac Hi-Perf Mag came by yesterday and did a photo session with my car -- I volunteered to participate in a perf/bolt-on build-up article for 3rd gens so they will be keeping in touch as I go about my winter build-up. I think the car may show up late spring 2003 issue in the mag. No guarantees though and I am doing the build-up anyway.

In any event, their photographer took a pile of pics of the cold air setup and hopefully he will send a couple my way so I can post them here. Thing is I don't have a digital-camera my buddy does (I use his) and he is on holidays so I am stuck for pics of the cold-air setup from underneath.

Sorry for the delay guys.

thx,
RP.

You guys can try to cram as much air as you want into your TPI's, but just remember as long as you have the stock manifold on your car you have the biggest bottleneck TPI can offer.

It doesn't matter if you have a 3" or 4" pipe, a 3" inch will offer just as much air as a 4" because you can only shove oh so many CFM's into the TB at a time and oh so many CFM's through the base.

I read in a previouse thread that the accordian, or as you guys call it "the ribbed part," as air goes through it, when the air hits the first rib, it creates a wall of flow over the other ribs, therefore acting as if it is going through a smooth intake.


I'll search for this thread.

5SIZ -- Of course you are stating the obvious. Water hose vs. straw, decreasing radius', etc.

There are three goals with CAI:

1) provide constant engine air supply at ambient temperatures.
2) ensure there is more air available through the intake apparatus than the TPI can accomodate.
3) ready the car for 'other' upgrades than will take advantage of the increased potential of the CAI.

My CAI setup has achieved all three of the above.

I don't pay much attention to the 'ribbed' part there is such an improvement with my CAI over the stock setup that I smile everytime I accelerate...

thx,
RP.

I have also acieved those goals with my Ram Air/CAI, and those aren't bad, but i'm just point that out to the people that think maximum air flow will get them more HP, when reality there is a limit.

Uh...the ribbed smooth thing was just a simple little experiment,someone showed interest in the results so I posted them I got what I expected,little or nothing.My better 60' was probably due to the full tank of gas (no wheel spin).But,I still completly agree with palric's last post about CAI,even if youre shoving in more cold air than it can use,it is better than not enough or hot engine air.

well at least you guys proved the $$$ to HP ratio LOL.

I do also, the stock Dual snorkle intake already works as a CAI since it's in front of the radiator and out of the engine bays way, I made a ram air out of my dual snorkle for the same purposes you guys made yours, except in my case i bumped my fuel psi to 49 & got SLP Siamesed runners, If I can gett he exaust out, and get the fuel in, I need to get the air in.

The way SLP runners work is less velocity in the lower rpms due to the siameseing, but in return they give you more top end hp, so I decided to help it out and make a ram air setup.

fully ported & Siamesed plenum, SLP Siamesed runners
Best 1/4th as of 8/2/02: 14.9 @ 94mph

$$$ to HP ? lmfao

I didn't want to take it this far, and I wasn't even trying to flame, but my friend, you are a fool...


Yes that is the best 1/4th from 8/2/02 "over 2 months ago" and yes I did get a 14.9, I was practically butt bone stock when I got that time only owned the car for 3 weeks, and was still learning how to drive a manual, I now have all of the mods you see and I got the runners about 3 weeks ago.... Oh and did I mention it was a100+ degree day I got that e/t?

I am going to the track today to see how much I have improved since my last run and I will post that time in this thread, then you can see how much of a gain I really did get.

Learn whats up before you say soemthing and get burned for it.

I ran a 14.4 @ 93, feels good to go a half second faster .

Easy does it man we are all learning here.

RP.

I just had to make my point that some people rag when they have no clue about the person thier ragging on, just to look hard.

Good point, but who says our motors are maximum airflow to start with(factory)? There is a point where we can give them more air and get more power, BEFORE we max out our tpi system. Know what I mean? There's definately room for improvement over the stock air intake setup (b4 the TB). later

You are definatly right there, Whats better? a stock dual snorkle intake with a 5 inch wide and 1 inch high slit on each side for air, or a gutted air intake where the airfilter hangs freely to suck up as much friggin air as it pleases.

Same goes w/ the Firebirds, there is room for improvment, but there is also going to far.

Yeah man. Definately room for improvement on our firebirds. At least you camaro guys have a somewhat factory CAI! Well, gotta run. Later!

I'm of the opinion that the stock Y is fine... I've done dyno tests with it on and off... 3 HP diff. I ran several 12.10's with the stock Y on a 406/AFR/SR.

I've done this in my Z28.



Its just a section of 4-inch exhaust pipe.

Heres another shot of the inside, after insertion...

http://www.dzy.org/92z28/pics/intake...l-inserted.JPG

It was done out of necessity, the intake pipe was sucking shut at WOT, and I had put a coffee can in there first to keep it from crushing, and it still crushed

see:

http://www.dzy.org/92z28/pics/intake...rush-track.JPG

Later, I put in another ring, to keep the front from collapsing, I think it was still sucking shut some, my MAP was dropping to 0.97 in the high RPM's. 58mmTB, clean KnN filters, gutted airbox.

I took this to the track and gained almost a half second (down to low 12's) ... but I also did the serpentine mod I described here:

http://www.thirdgen.org/techbb2/show...54#post1503254

Not sure which is responsible for most of the gain... the air was real nice that day too, but I ran a 12.56 on almost as good a day this spring.

YMMV