Air flow
 

Some may find this useful:

Playing around at the track recently, I’ve discovered a HUGE difference in Performance using different air cleaner bases.

Using the same 3” air filter, I have found my engine will ONLY perform adequately with the stock base dual snorkel and a filter top that just covers the filter, NOT the entire base like a stock lid.

Tried a whole pile of combos and nothing bested this combo.

The worst base( Alluminum with a sharper roll into the carb) reduced et by .3 and 4mph!!

Drop bases produced the same poor results.

Seems my qjet is VERY Sensitive to the base and will not tolerate anything but a stock shape??

Question:
Have any of you found a base and lid that will work better than stock ?

...wondering what I’m leaving on the table by not being able to use a 4” filter with a stock base?

This is all based on a qjet carbed engine.

On a good note I was able to get my first 6.981 1/8 mile et and a best 60’ of 1.52 on a different pass...not terrible for this old pig

Thanks for any insight

This chart may help explain your experience in picture form, and also folks should make note that once a given mass of air reaches a certain velocity it will not follow along anything greater then a 15 degree radius without sheering away from where you want it to go!

Just like water air wants to take the path of least resistance.

Also not that with Q-jets that the speed of the air entering the primary's is far faster then those big secondary's, so a air cleaner base with a bigger gentler radius around those small primary's helps a bunch!!

Don't hesitate to aid that radius shape with some epoxy.

Weather more air cleaner area will help you out all depends on how much HP the motor is making and how much air that perticular brand filter your running flows

Exactly what I like playing with at the track and enjoy reading posts like this.
I did this years ago with a couple different cars. I'm surprised you found gains with that filter top lid. I never could get those to work good for me.

Makes me wonder what kind of clearance you have from the top of the carb to the bottom of the lid when you're running stock lids? I've found that to affect performance just as much as the base used. With some cars it's impossible to get the lid far enough away from the carb to make any difference. So dropping the base for more filter is the only solution, but as you found, that has mixed results, sometimes not so good. I think the proximity of the lid to the carb is a big player. In fact tests have shown that a flat base works best with a 3 or 4 inch filter, which gives copious amounts of room above the carb, and lack of drop base gives a straighter shot of air to the carb, but that setup never fits under a stock hood.

Which dual snorkel are you using? I may experiment with the filter lid again next time at the track now that I have changed the setup around a bit. Basically most every car here is now using a stock air cleaner base setup with taller filters, stock lids. Mainly for fitment and functionality more than anything else. Waiting for the track to open again for more testing.

When I pulled off the L-88 base and the 4" filter ion the 500" IA Camaro I picked up 0.3 seconds!

You were using the L88 base with a full diameter filter and lid?

Those things were originally designed for a small screen and lid the diameter of the throat of the carb, with a filter in the hood. Just like in the picture of the one I built for dad's GTO.

Used this way they are very effective as the outside air coming in has a straight shot to the throat of the carb when the hood is closed. I think what helps this design is what I eluded to in my first post. The small lid holding the base to the carb is about 2 or 3" above the carb itself. Plenty of room. I forget how far that drop base is now, but it's alot. I would have to check but seems even a 4 inch filter wouldn't put the lid very far above the carb??

Another thing to add...

I did try NO filter and I also tried a stock base and lid with NO filter.

Both of these resulted in very poor et and loss of MPH

LOL yep!!

I tried no filter in the stock base with the stock lid. It absolutely KILLED ET and MPH. When I tried that scenario, mine was in a ram air situation (70 RA Formula) with fresh air pushed in. Led me to believe the filter does act in slowing down the air flow and possibly straightening it to some degree to be more beneficial.

Action shot ....trying to unload..........getting closer............bwaaaaaaaaaaaaaa

Two of the base variants that produced very poor results....had to beat one into submission to clear the qjet linkage

This is the variant that provided the best performance....

Unfortunately, with a RPM intake it is the only setup I’m able to run without modding the hood.

Okay, so a stock style Pontiac dual snorkel base and a standard 14" diameter lid (not a filter lid)

:thumbup:

I've seen setups similar to this at the track that worked well. I had a theory that keeping the stock base like you have sort of insulates the carb from ingesting a ton of heat, especially any heat soak coming up from the bottom.

Rather than a simple open element that isn't shielded.

Yep.....works best on my rig with a qjet

Nice testing..fun part of the hobby! With that 1/8th mile time that is a sub 11.0 time

What base is this off of? My dual snorkel looks longer in the snorkel? Did you cut it back some?

Yes, the dual snorkel I’m running had been cut down in the late 70’s by the original owner of the car.

Although I have an original one that’s uncut, I’ve grown fond of this one and have been running it for 20 years or so..... I’m no purist by any stretch

Great thread, loving seeing threads like this, real world testing!

Based on my testing years ago q-jets seem to be pretty sensitive to how the air enters. We made a top that was very nice, by cutting the choke tower off and really smoothing out the entry (like a holley) and it hated it.

Makes me want to find that old pic of Jim hands carb and air cleaner base. He made some forms that fit to the carb and blended it to the base. I’ve seen it and thought “how much difference could that make”

Now I want to duplicate it....it could make much more of a difference than first thought....

Are they here ?

https://pontiacstreetperformance.com...455jh2006.html

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Thanks !

Looks more complex than I thought.....give me something to play with

The base he’s using looks exactly like mine.

Holy cow 3/10s and almost a full tenth on your 60' is huge! That air cleaner setup looks great and I wonder how it would perform on a Holley. Great pics and I'm jealous of you guys down south that can still go to the track now.

Just to clarify:

The .3 and 4mph difference was from changing my “normal” base/lid combination to other combinations mentioned above.

The worst of these “other” combinations resulted in a .3 et gain and a 4mph loss....other combinations were slightly better than the worse but still waaaaaay slower than the “normal”.

The 1.52 60’ and 6.891 1/8 mile were recorded the same day using my “normal” base/lid combination.

Hope this helps

Yep.....might’ve cracked it but I screwed up my 2-3 shift and ran an 11.04....still a best but disappointing

Could always try a blow thru hat with a tube and cone filter.


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that base & lid looks nice. very similar to what i run on a 72 firebird with a formula hood that has terrible clearance & doesnt allow for an RPM or other taller intake, i run a SD ported HO intake & Q-jet.

the base & lid i use is a W72 T/A style with the wide oval snorkel, it has the smaller lid like yours from the factory that leaves about 1-2" of the air filter exposed around the perimeter & has a tall dome for clearance to the top of the carb. after reading your results i will just keep this set up & not mess with aftermarket drop bases.

i did try a k&n filter lid the first time at the track with no hood on the car, ran 12.2... with no other changes besides the W72 air cleaner & installing a hood i was in to the mid to upper 11's the next time out. changing to M/T drag radials from worn out BFG drag radials i was doing low 11's. these were all different days so the improvements are hard to say what changes did what, but they were almost a half second each change.

good to know the factory drop base are close to the best set up for a q-jet. i like the epoxy mods jim hand did, kind of like a "stub stack" for the q-jet.

I was looking at possibly using the cowl area, build dividers to block off one of the square openings, and use a flat filter.

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Regarding the Holley carburetors and a similar situation Jim Hand did for the Q-Jet carb and the mention of the Stubstack. Testing has shown that the contoured venturi inlet on the Holley 'HP' series carburetors offers balanced airflow for increased horsepower over a carburetor design with a choke tower. The Stubstack with its smooth contour cleans up the flow and the engine responds to that.

https://www.knfilters.com/racing/stubstacks.htm


A fwiw, it's nothing new. One of the all time best custom carburetor builders Brad Urban did a similar thing many years ago. On his high performance Holley carburetors for maximum airflow the choke tower was machined off and he did a CNC radiused air entry.


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wish they made a stub stack for the q-jets. i still have a stub stack from back in the 90's when i ran a holley carb.

Yep I did that back in the 80's to a 3310, milled the choke horn and spent a ton of time with a flapper wheel smoothing the contours of the bore entry, and even used a little epoxy in small areas.

That was a whole bunch of work for not much gain at all, lol. I still have that main body. It went on the shelf when affordable main bodies that looked much prettier started hitting the market.

I never could find any gains with a stub stack. Not sure why, but after all that work modifying that 3310 with little benefit I wasn't the least bit interested in making a stub stack look-a-like for a Q-jet or even modifying a Q-jet air horn for that matter.

What is interesting though is that home made funnel Jim used on the bottom of the lid. Some of the OEM lids found on Chevrolets that have a much deeper recess for the wing nut kind of mimic this and I can see how that may be beneficial.
Some of the aftermarket aluminum dome lids you see used a lot on sprint modifieds also have this feature.

I however have no room for that mod on my Formula. With it's factory ram air setup, the bottom of the lid at the wing nut is only 1/4" from the choke horn, and I have no room at all to move the lid higher.

The biggest gain I've found with air cleaners at the track is finding a way to ingest outside air.

All the air cleaner setups I've tried never worked as well as the factory cold air setup on my ram air Formula.

I'm surprised Mchell that with your 71-72 GTO hood you haven't tried the same air cleaner my Formula has. They are reproduced and aren't overly expensive.

I found similar differences with my Chevelle and it's cowl induction setup. The difference in IAT temps is night and day.

It's very effective. Chevrolet did the cowl plenum in 67-68 on the Z before eventually moving it to the rear of the hood in 69.

There are ram air boxes made of fiberglass now, I believe the company is "ram air boxes" and they do have a cowl plenum setup that accepts a 14" filter element, bolts on like a factory air cleaner. Just have to make the hole in the firewall and fasten with the rubber sleeve and you're there.

I'm still looking FJ, but am not finding it. I know on 2nd gens there's a shaker kit that uses a flat filter, but forget which one was the better one. Blocker maybe?

I can't do the cowl setup on my 'bird, I welded a brace along the cowl lip and not going to remove it. I used a piece of angle iron and ran it pretty much from hinge to hinge. I was getting movement when using the structural braces so beefed it up.


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I haven't seen the flat filter. Blocker does sound familiar. From the sound of it, you are sticking with the shaker setup? Sorry I thought you were looking for the cowl plenum setup.

My body is using the short bushings, so it's tight. I fixed the shaker to the hood, lack of options at the time it was done.

Yeah, just checked, it's the Blocker Performance one that uses the flat filter:

http://www.blockersperformance.com/products.html

I may be limited to that type of setup with the intake I'm running. I think there was another one that also uses a flat filter, but would have to search it.

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That's slick, and fits with a Victor intake even!!

The other one is WFO Performance one that Butler carries:

https://butlerperformance.com/i-2445...tegory:1234772

I can't find the original WFO website, interesting...

Yeah, some work with the RPM, and some can accept the victor. One I recall specifically requires the shaker to be mounted to the hood, forget which one.

PTFB makes one too, but uses a round type filter.

http://www.pro-touringf-body.com/engine.html

All offerings on the Butler site:

https://butlerperformance.com/c-1234...a-shakers.html

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My 71 hood is capable of using the same ram air setup that was used on 71 gto’s and the formulas.

However there are trade offs and complications associated:

- the rpm intake sits A LOT higher, throwing the sealing geometry off and likely not allowing hood clearance for the air cleaner at all
- the pan and air cleaner assembly is weighty, possibly negating any benefits

You did give me an idea tho. Might try sealing the forward edge or back edge of the air cleaner base to the hood with foam to figure out if it likes air from the front of the engine or the back. Might reduce turbulence as well.

Can only try.

I am going to try a mock up of the the Jim hand carb mod to improve air flow into it.

FWIW, many years ago on my 67 GTO dirt car, I tried the cowl source of air with a 73 style air cleaner with the fuzzy hose connecting the air cleaner to the cowl area. It was the same idea that Jim Hand used on his wagon. It worked well enough that the buttmeter could discern a difference over just under hood warm air.

The problem was that not only did it pull in higher pressure air, it also pulled in a ton of debris such as dirt and small stones that ended up in the air cleaner housing. Looking back, I should have done some further investigation into this modification and solved the problem with a screen, or a layer of cloth to keep the larger stuff out.

Whatever the reason, I never tried it again, but probably should have as the cooler air, with some positive pressure, definitely made the engine run better.

Ah, I didn't realize you had a taller intake manifold. Yeah this setup doesn't give much wiggle room for clearance.

I've never been able to make the car run better with any form of an open element air cleaner in there though, so they are worth the investment if you had the room.

What you are thinking about now (sealing the front edge of the air cleaner) Is one reason why I believe your setup you have now works the best out of things you have tried so far. I've seen people do that before, and I think it's the factory base that somewhat shields the hot air that radiates off the engine and is somewhat of a shield for the hot air the fan blow back off the radiator. Where as an open element does none of that.

Now that I'm monitoring IAT's with a Sniper Stealth unit on one of the cars it's amazing how changes like this affect the temp of the incoming air. What is even more interesting is watching the computer change the fuel demand when you change the IAT's. So far with fresh outside air coming into the EFI, and early morning ambient temps in the 20's, my IAT's are 30 degrees when moving and I can watch the EFI add as much as 12% fuel. So it's easy to see why a cold air package is beneficial at the track and why my Formula slows down without it.

For inspiration check out some Nascar cowl setups and also the "Jim Hand" style of tubing off the cowl.

Exactly, where I got the idea for doing the cowl setup on my dirt car. The pressure is high at the base of the windshield because at 50 MPH there is quite a bit of airflow into the interior of a non A/C car..:2cents:

Yes, thank you have looked at the NASCAR setups. I had gone as far as researched particular duct fittings etc. Some IMSA type brake ducts would work well, and there is a wide variety. Some have small openings, but there are some that are used for directing radiator and cooler air flow, those would work great.

EDIT: I was going to use a carb hat, and a cooler duct on the cowl, with a hose between. Carb hats provide a lot of flexibility as to where you mount the filter. Once you remove the limitation of size/space from the top of the carb, the sky's the limit.

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I know from track testing on cool nights my cowl air cleaner takes full advantage of the cooler air.

The one cringe-factor is though, cutting into the cowl/firewall.

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I tested different bases (also some elements) on a chassis dyno, about 10 years ago. I've posted results before.

The biggest drop base (the rounded one, in your photo) was down 10+ rwhp across the entire test I performed, compared to other bases.

I've seen losses over 30rwhp with certain filter/bases combinations, on the dyno.

Using a higher rise intake may give someobdy a few HP, but they can lose all of that and more with a restrictive filter/housing.

On the Year One Bandit Trans Am project with a 535 combo Jim Butler used a Victor intake with the carb flange milled down 0.650" to help it fit under the hood. With the cut down intake he used a WFO drop base unit for the TA Shaker scoop. Tested on the engine dyno at peak power rpm it gave up about 15 hp by milling the intake.

On my current 505 street engine prior to the fuel injection I did the same thing with a Victor intake & HP950 carb. On the dyno I lost about 8-10 hp at peak power rpm after milling the intake flange 0.650". Not a race deal so for me I did not miss the 8-10 hp on the street.

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No comments on the air cleaners/filters, but on the same topic:

In a different lifetime, when I still had time to build carbs; built several for the circle track racers that, by rule, had to run a single Rochester 2 barrel. Found by actual racing that leaving the choke butterfly in place made the cars faster than removing it! Used to remove the choke shafts and mill them almost paper-thin, then reinstall and pop-rivet the choke butterfly in place, and zip-tied the arm to always be in the fully open position. The butterfly acted as a straightening vane to help the air coming into the carburetor.

Be interested see dyno results, but the track time proved the modification.

Jon.

If you use the factory stuff, the cool factor of a real cowl plenum will quickly diminish any cutting concerns ;)

In the car crowd I'm around, anything with a factory appearing cowl plenum setup is Ooo Aaaa at any local car event, if people actually know what they are looking at. Especially if it's a car that fits the era that these things were used.

All that stuff is reproduced now, or like I mentioned earlier, RamAirBoxes sells a fiberglass aftermarket version that doesn't technically look like an original setup but it uses the same idea. I've had in the back of my mind to run one on the nomad if I ever get that thing on the streets.

If you go the carb hat idea, I did that in the past on my little H-bodies, but I didn't tap into the cowl, I went to the front grill area. That's the nice thing about the carb hats, you can point them anywhere and run a 4" hose anywhere you want. I even went as far as to rob all the turbo inlet stuff to the carb from a 79 turbo regal eons ago for a factory appearing setup.

I will say the cowl plenum stuff works extremely well though if you're looking for a clean way to do it. My chevelle I mentioned earlier is the same idea, grabbing air from the high pressure area at the base of the windshield, and the IAT temps I've monitored are always nearly spot on what the outside ambient temps are, as long as I'm moving.

In fact our 69 Z has the same setup. I have the door removed from the hood so it's functional all the time. I don't have a way to monitor the IAT's on this one but I can say after driving it in the early morning when it's 20-30 degrees outside, I can pop the hood and put my hand on the top air cleaner lid and it's ice cold, in fact everything inside the hood seal is ice cold, but the base of the air cleaner outside the hood seal that is subject to engine heat is very warm to the touch.

That's nice info. Years ago I added the factory divider piece to a quadrajet and it was good for almost .5 mph...The car I had at the time was consistent but not super fast..it would run 99mph without it and 100 mph with it...dis 6 passes one night back to back to test..I think I'm going to try a funnel type divider next year to see if it does anything.

Lord .... you guys are going to make me put my choke butterfly back in and try it...who knows?

Being in South Florida I’ve had no use of a choke of any sort. Like most, I thought less junk in the way must be better, so out it came.

Keeping that choke flap in place works out for the better on Q-jets and 2bbl Carbs due to as Carb king posted which ties directly into the greater air speed of small Carb bores like they have.