87 Stock TBI 350 air cleaner lid flip upside down? Does it help? does it hurt? good or bad idea?

[Matt Frediani]

I have a bone stock tbi 350 in my 87 gmc 3/4 ton 4x4. It has all the california emissions equipment on it. I see lots of people flipping the top of the air cleaner upside down to allow more air to the tbi unit. Does this help? why do people do it? does it mess with the computer controlled idle or mess with the factory tune? Can someone who knows the outcome please fill me in? The truck runs fine the way it is but Im curious to know what will happen If I do this to my stock truck

 

[SquareRoot]

There's a reason GM engineers used the closed element design ducted to the core support. Flipping the lid only adds hot under hood air into the TBI.

 

[Catbox]

I ran my 1995 Suburban with the lid flipped for years.
I now have a standard open air cleaner under the hood.

I like the sound.
My fuel mileage is terrible no matter what, so I dunno on that one.

 

[fast 99]

Only thing it will do is allow heated air when warmed up and disable the hot air preheat when cold. The ECM will control the mix when within limits, heated air will lower the HP. It is hard for me to rationalize why people do things. A guess is they like the noise and don't understand TBI operation.

 

[SquareRoot]

I've had a lifetime of "It sounded good at the time" moments. With age comes common sense and wisdom.
Young=This is good idea.
Less Young=WTF was I thinking?!

 

[Craig 85]

On my '79 K15 I ran an open element air cleaner between smog tests for a while. I installed the 5" tall lid vs the standard 3' lid to the factory air cleaner base then ran a snorkel tube (photo 1). It ran way better, especially in the summer. I can't recall if the taller lid will fit under the hood on a TBI set up.

On my K30 (photo 2), it also runs the factory air cleaner set up, but I did cut the end off the deflector at the core support (photo 3). It creates a ram air set up.

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[fast 99]

On my '79 K15 I ran an open element air cleaner between smog tests for a while. I installed the 5" tall lid vs the standard 3' lid to the factory air cleaner base then ran a snorkel tube (photo 1). It ran way better, especially in the summer. I can't recall if the taller lid will fit under the hood on a TBI set up.

On my K30 (photo 2), it also runs the factory air cleaner set up, but I did cut the end off the deflector at the core support (photo 3). It creates a ram air set up.

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Respectfully, you're comparing apples and oranges. A TBI system uses various sensors to control fuel mix. If the air is hotter, it is less dense. Similar to high altitude operation. Flipping the lid will do nothing except decrease power and increasing emissions due to no hot air preheat during warm up.

GM goes to great lengths engineering these vehicles. A carbureted 1975 vehicle has no feedback controls. If it ran better with the top housing inverted [gulping hot under hood air] suspect the carburetor fuel mix was incorrect. A common Q-jet problem.

We used to do emissions testing in this area. After repairs we needed to make sure they would pass. In order to properly do that the air cleaner needed to be on, and hood shut. It would surprise most people how much difference there was. The air cleaner alone could cause a 1% change, sometimes up and sometimes down. Rarely no change on non-feedback vehicles.

 

[Craig 85]

@fast 99, I wasn't comparing TBI to carb, I should have clarified a little more. The truck ran great with both the full open element air cleaner and the factory air cleaner set up. The issue became at idle in the summer with the A/C going. It ran better with a factory air cleaner than the full open element air cleaner. Idle was a lot smoother with the OEM set up.

The '79 was a fully smogged down 350 that had to pass emissions every two years. I lived in CA at the time. One benefit to running the factory taller lid set up over the original flat one was you can run a 2" taller air filter. Most CA spec V8 trucks 81-86 had the tall lid.

@Matt Frediani I found this 89-91 Suburban for sale today. It has the taller lid with the TBI air cleaner housing. It fits under the hood with a 454. I haven't seen this snorkel set up on a TBI 454 before. It may be an auxiliary filter. I know neither my California spec 87 or 88 TBI 454's had this snorkel or tall lid.

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[85 Squarebody76]

I have a bone stock tbi 350 in my 87 gmc 3/4 ton 4x4. It has all the california emissions equipment on it. I see lots of people flipping the top of the air cleaner upside down to allow more air to the tbi unit. Does this help? why do people do it? does it mess with the computer controlled idle or mess with the factory tune? Can someone who knows the outcome please fill me in? The truck runs fine the way it is but Im curious to know what will happen If I do this to my stock truck

We did it back in the day cause it sounded great.... didn't go any faster but sounded cool !! when you hit the gas hard

 

[fast 99]

@fast 99, I wasn't comparing TBI to carb, I should have clarified a little more. The truck ran great with both the full open element air cleaner and the factory air cleaner set up. The issue became at idle in the summer with the A/C going. It ran better with a factory air cleaner than the full open element air cleaner. Idle was a lot smoother with the OEM set up.

The '79 was a fully smogged down 350 that had to pass emissions every two years. I lived in CA at the time. One benefit to running the factory taller lid set up over the original flat one was you can run a 2" taller air filter. Most CA spec V8 trucks 81-86 had the tall lid.

@Matt Frediani I found this 89-91 Suburban for sale today. It has the taller lid with the TBI air cleaner housing. It fits under the hood with a 454. I haven't seen this snorkel set up on a TBI 454 before. It may be an auxiliary filter. I know neither my California spec 87 or 88 TBI 454's had this snorkel or tall lid.

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Ok, you and I agree took it wrong. I have seen that intake arrangement before. DNK if it is for noise, water or another reason. Have seen something similar on small blocks with the cold climate option. Actually, have a complete cold climate snorkel set on the shelf.

 

[mtbadbob]

I had a '76 Monte w/sb 400. It ran better with the fuel/air screws out about 5 turns AND air cleaner lid flipped over(more air intake)-FACT! Now, with tbi, I believe the stock set up is better because of the CAI, just makes sense...

 

[Rebus]

I have a bone stock tbi 350 in my 87 gmc 3/4 ton 4x4. It has all the california emissions equipment on it. I see lots of people flipping the top of the air cleaner upside down to allow more air to the tbi unit...

Gale Banks actually dyno tested the open vs stock filter with closed hood and demonstrated the open filter had a significant HP reduction.

 

[Keith Seymore]

I designed the engine air induction system for the GMT800 program (7 different powertrains), introduced in 1999. Most of the components are still in use today.

I can say with authority that you gain more from picking up the cool air at the front of the vehicle than by drawing hot underhood air. You more than offset any increase in restriction due to the ductwork.

I ran a dual snorkel setup same as what Craig 85 is showing, with a flat hood on my Chevelle for many, many (many) years. It was easily worth .2 sec reduction in ET, from 12 flat to 11.80's.

K

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[Keith Seymore]

This is the car that Pontiac developed the "Ram Air" package on.

This setup was also worth about a .2 sec reduction in ET (from 12.40 to 12.20), back in 1965.

K

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[gsuburban]

It will lower air density due to warmer air intake in the engine compartment vs. fresh air from the air cleaner ducting to the core support. Is it a big difference? No, probably not enough to notice however, efficency will be less and why goes in that direction ! Some folks believe it helps but they are letting the sound affect their reasoning...its a dead issue there is any gain to reverse the top of the air cleaner. Go to bankspower.com and learn all about air density, cooler air intake makes HP better than some modifications do. Heard of intercoolers? Turbo and Supercharged engines usually have an intercooler to cool down the intake air because the compressers heat the air which competes with the added air/fuel mix reducing the efficency/performance etc. Flow isn’t the whole story. You’ve got to have high intake density (I.D.) because, without it, you’re leaving untold power, performance, and efficiency on the table. And that means you need cold high-flow air.