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70's stock air cleaner restriction?

Shawn

Shawn

Nuckin Futz!
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I'm curious what you guys think of these stock air cleaners back in the 70s that were put on 350ci and 400ci engines and why GM did this back then. It seems the hole for the air inlet is pretty small. Now after seeing it in person, I'm actually shocked this is getting enough air. I did happen to notice the 454 has a much larger air horn with oval opening in the 2nd picture so they did up the size on the bigger engines. Around 1979 it appears GM switched the design to the larger oval opening and cold air duct. If you wanted to keep your truck/K5 totally stock, this seems like a possible restriction to gain max power. I know Engine Masters did a dyno shootout with air cleaners but they also used powerful big block that flows tons of air. Are these stock air cleaners able to keep up with the stock engine's air requirement even on a 400ci?

1978 350ci 4bbl inlet - 1.5" diameter:
1732549056099.png

454 inlet, much larger:
1732549131676.png
 
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When those engines were stock they barely wheezed out 200 hp. As such the puny snorkel size didn’t pose any major restriction.

Would I put it on a 300hp or more small block or big block? Hell no. But if you are going for a correct type of deal with the smog era treefiddy I don’t think it’s killing a ton of power.

Totally up to you. But I’d also say 99% of the public that looks at the truck won’t know if you put the larger oval snorkel unit on that it’s not correct. Both came from the factory, they both look factory. The general public just sees a factory air cleaner.
 
If you have a vacuum gauge, you could compare high RPM WOT to flipped lid.

The flared opening and tapered snorkel may have been aimed at controlling the noise from the intake. Fast forward a few decades and you see all kinds of strange shapes and bends strictly for NVH. It's also possible the higher-velocity air aids in getting the thermal flapper back open at high throttle.
 
ZooMad75 said:
When those engines were stock they barely wheezed out 200 hp. As such the puny snorkel size didn’t pose any major restriction.

Would I put it on a 300hp or more small block or big block? Hell no. But if you are going for a correct type of deal with the smog era treefiddy I don’t think it’s killing a ton of power.

Totally up to you. But I’d also say 99% of the public that looks at the truck won’t know if you put the larger oval snorkel unit on that it’s not correct. Both came from the factory, they both look factory. The general public just sees a factory air cleaner.
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Totally agree with you and I would never run this on a higher HP engine. I just measured that inlet hole. 1.5" Diameter. Not sure how even 200hp can come through that size of hole. The K5 this came on also came with factory dual exhaust. I totally agree that most won't even notice if I put a big block or later air cleaner on. Just trying to keep it original as much as possible. I usually prefer a cold air inlet or something open. I never realized just how small these air cleaner inlets are.

I just chatted with a good friend at my local dyno shop. He owns the Carburetor Shop here in Denver and has an in-house dyno and been doing this since the 80s. He said those air cleaners will typically lose 10whp until you flip the lid.

Blue85 said:
If you have a vacuum gauge, you could compare high RPM WOT to flipped lid.

The flared opening and tapered snorkel may have been aimed at controlling the noise from the intake. Fast forward a few decades and you see all kinds of strange shapes and bends strictly for NVH. It's also possible the higher-velocity air aids in getting the thermal flapper back open at high throttle.
Click to expand...
Good idea on the vacuum gauge. I might try that when I back to my house. Right now she is in storage at my buddies house. Could have something to do with noise too.

I did find a dyno video of a guy that flipped his lid but it was a 80s K5 with the larger inlet opening on the air cleaner. There was no difference in power or torque. Keep in mind that air inlet is MUCH larger than 1.5 diameter and is more oval. See my comment above at the 10hp loss from this air cleaner.
 
I always wanted to make a duel snorkel air cleaner out of two stock ones.
Look cool, still stockiish and one wing nut to swap back.
 
max 02 said:
I always wanted to make a duel snorkel air cleaner out of two stock ones.
Look cool, still stockiish and one wing nut to swap back.
Click to expand...
I suppose the easiest way to do this would be get a 83~85/86 Z28 L-69 dual snorkel air cleaner base.
 
max 02 said:
I always wanted to make a duel snorkel air cleaner out of two stock ones.
Look cool, still stockiish and one wing nut to swap back.
Click to expand...
I would want the 454 air cleaner but two of those inlets. Looks like they had them on vettes and Camaros back in the early 70s.
1732592486088.png

Just surprised GM did something that small on the mid 70s small blocks with that small (1.5") of a single opening creating a 10hp loss on stock engines if thats really the case.

Here's the air cleaner shootout but on a powerful big block so it needs LOTS of air. Kind of interesting with all the combos they tried and a salad bowl made the most.
(sorry could not find it on you tube)
 
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max 02 said:
That’s it!
I’m just way too cheep to try to find a factory one.

View attachment 491872
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I figured the late 60’s & early 70’s dual inlet bases would be expensive so that’s why the mighty 305 H.O. was suggested.
Those should be cheap unless ya get one from a 3RD Gen F-body lover.

They also came on some L-48 Super Sports and LT1 350’s if the big block stuff is out of range.

Also the 70’s Vette L82 350’s had a dual inlet but one side was in an odd position kind of like the Olds 307 H.O. in the mid 80’s.

Of course ya could always fab one up!
 
max 02 said:
Haha! But I remember them being fairly fun to drive back then.
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I got to drive an 85 IROC ( my buddies car ) with a 5.0 H.O. fairly regularly back in 1988 and it had a 5-spd and 3.73 gear that made it pretty fun on the streets - not old school serious motor cool but it was still fun.

Maybe it was that we could go around corners at much higher speeds that made it so much fun - or it could have been the 80’s tunes coming from the ole Delco stereo that helped? Either way that car was fun to drive hard for something made in the 80’s.
 
Shawn said:
I would want the 454 air cleaner but two of those inlets. Looks like they had them on vettes and Camaros back in the early 70s.
View attachment 491869

Just surprised GM did something that small on the mid 70s small blocks with that small (1.5") of a single opening creating a 10hp loss on stock engines if thats really the case.

Here's the air cleaner shootout but on a powerful big block so it needs LOTS of air. Kind of interesting with all the combos they tried and a salad bowl made the most.
(sorry could not find it on you tube)
Click to expand...
They also used a small dual inlet on some big blocks - not 1.5” small but still fairly small.

Notice the aluminum heads - that’s a L-89 396 out of a 69 Nova. Also came on 70 Chevelle SS454’s w/o cowl induction.
IMG_1745.png
 
Shawn said:
Found a pic here of that.
View attachment 491870
Click to expand...

How much water gets in there when driving in a heavy rain? How would you combat that?

I have ideas to run intake similar to the thunderbolt, or the newer hellcats that uses a headlight opening, but concerned with water/road grime, unless it only a sunny sunday driver
 
Another way to look at this is ask "why have a snorkel at all?" It totally makes sense when there's a cold air duct connected, but without that, why is drawing air from behind the radiator and above the PS exhaust manifold any better than drawing from above the intake manifold? It isn't, but you're reducing the sound coming out.
 
Some good info on air flow measured on a flow bench. I'm not sure which style of snorkel he used for testing (BBC vs SBC) but shows you that the snorkel DOES hurt performance.

From Doug Roe's book, "Rochester Carburetors":
"Cleaner type: WOT Air Flow (CFM)
None : 713
Chevrolet 396 closed-element with single snorkel: 480
Chevrolet 396 closed-element with single snorkel cut off at housing: 515
Same as above, but with two elements: 690
Chevrolet high-performance open-element unit: 675
Same as above, but with two elements: 713
14-inch diameter open-element accessory-type air cleaner: 675
Chevrolet truck-type element (tall) used with accessory-type base & lid: 713
Foam-type cleaner (domed flat-funnel type): 675
NOTE: All data obtained with same carburetor. New, clean paper elements used in all cases except foam-type, which also was new.
Holley Tests
October 1971"

Roe also writes:
"You have noticed the long snorkel intakes on modern air cleaners. These are designed to reduce intake noise - not to improve performance. High-HP engines usually have two snorkels for more air and perhaps for 'more image,' too. For competition, the snorkel can be removed where is joins the cleaner housing. Additional holes can be cut in the cleaner housing to approximate an open-element configuration to improve breathing. Or, it is sometimes possible to expose more of the element sufface by inverting the cleaner top."

Just remember: More Air=Better Performance
 
Blue85 said:
Another way to look at this is ask "why have a snorkel at all?" It totally makes sense when there's a cold air duct connected, but without that, why is drawing air from behind the radiator and above the PS exhaust manifold any better than drawing from above the intake manifold? It isn't, but you're reducing the sound coming out.
Click to expand...


So all the talk of snorkels and intake ducting made me think about all the G-body’s we had when I was a kid. At one time we had 3 ‘78 Malibu Classic 2 door coupes, 1 ‘78 Malibu wagon and a ‘79 El Camino. Common thread between them? All four cars (3 with 305’s, 1 267) had a duct from the air cleaner to the top of the core support. The snorkel on the air cleaner had to be 2.5” at least and then necked down to more of an oval shape to go into the side of the air cleaner housing.

It’s funny to think the engineers on the truck side were still using the style of air cleaner that dated back to the late 60’s and the car engineers got wise and put what we all would call a cold air duct on the car v8’s. Which were all even weaker than the truck engines by a lot. All 4 of our cars were equipped with 2bbl carbs. The 267 using the stellar Rochester duo-jet which was a bastardized Q-jet with no secondaries. The 305’s all had Rochester 2GC units which were so much better than the duo-jet.

I think at least as far as the g-body cars with v8’s were concerned the cold air duct was standard equipment. That’s completely off of memory and not backed up by any factory specs.
 
I expect the cold air inlet was for emissions, noise, and power. By '81 I think cold air inlets were across the board. Doesn't surprise me cars were earlier, that screams emissions compliance.

Wonder what truck filters Roe tested back in 1971? The later rigs also got short or tall filters, clearly the filter element size is a significant factor in flow.
 
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