Loud air sucking noise on acceleration

[Asshat]

When I accelerate the noise is really loud. I have the stock air cleaner, so that’s probably not it. I know my exhaust leaks here and there, but it doesn’t sound like exhaust. It idles fine too, so I don’t think it’s a vacuum leak.
Any idea what it could be?

[Steeveedee]

Can you get an audio/video of it?

[Asshat]

Originally Posted by Steeveedee

Can you get an audio/video of it?

No, didn’t get a video.

[bsarts]

I wanna say check timing.

[Asshat]

Originally Posted by bsarts

I wanna say check timing.

Timing seems ok, right about 4 degrees BTDC.

[doobiebro]

What engine are you running? Last time I heard something similar to your explanation it was leaking intake gaskets on my V-8

[Asshat]

Originally Posted by doobiebro

What engine are you running? Last time I heard something similar to your explanation it was leaking intake gaskets on my V-8

Inline 6, 292. One bbl carb, new from Rock Auto.

[doobiebro]

Originally Posted by Asshat

Inline 6, 292. One bbl carb, new from Rock Auto.

pour a little water around intake gaskets while running and see if engine misses.

[AcampoDave]

If you have power brakes it could maybe be the check valve gizmo where the hose connects to the booster but then again, that might be more of a "throttle closed" type leak

[caseyjones]

I have the same engine and carb. I have an open element filter and the intake noise is very noticeable. I suspect you are hearing what engineers have spent years designing out of our newer cars with big plastic air boxes and convoluted intake snorkels.

[Asshat]

Originally Posted by caseyjones

I have the same engine and carb. I have an open element filter and the intake noise is very noticeable. I suspect you are hearing what engineers have spent years designing out of our newer cars with big plastic air boxes and convoluted intake snorkels.

I have had older vehicles and never experienced this loud of air suck.

[Short 3/4]

Originally Posted by caseyjones

I have the same engine and carb. I have an open element filter and the intake noise is very noticeable. I suspect you are hearing what engineers have spent years designing out of our newer cars with big plastic air boxes and convoluted intake snorkels.

Same here, even with the stock air cleaner, I have to agree with CaseyJ

[Steeveedee]

Has it always done it, or is it a new symptom?

[Asshat]

Originally Posted by Steeveedee

Has it always done it, or is it a new symptom?

I have only had this truck since April 2019, and I just got it on the road this past week. Most of the time it was up on jackstands in the garage.

I am thinking it could be an exhaust leak; I assembled the entire exhaust from pieces I had in the garage, and a few new ones. I may just take it to an exhaust shop this Saturday and see what they will charge me.

I could pull the air cleaner off and drive it, see is that makes any difference. It sounds good at idle, and once it warms up it accelerates ok.

I have the 4-speed, stock transmission, it shifts fine. The rear end is a 14-bolt GM, 4:10 or 4:11 gears, from my calculations. The truck seems to top-out at about 55mph, primarily cuz it sounds like I am really pushing it, at about 2k rpm (if my tach is correct). It just seems so loud going down the road, but not like exhaust noise. As it is, the muffler I have installed is one of those quiet mufflers.

Brings me to another question... if its worth putting 3:42 gears in it vs a 5-speed OD trans. A ring and pinion will cost about $300, and a 5-speed is probably north of $800.

I think the 3:42 will only drop my rpm by about 500rpm, if I'm not mistaken. I'll have to check some gear tables.

[Riverstory]

fan would be my guess

[Asshat]

Originally Posted by AcampoDave

If you have power brakes it could maybe be the check valve gizmo where the hose connects to the booster but then again, that might be more of a "throttle closed" type leak

No power brakes.

[Wrenchbender Ret]

I'm thinking you have too much back pressure in the exhaust system. 292 engines have a very restrictive exhaust system. That "quiet" muffler is causing a lot of back pressure. Have them build a system with 2 1/4 or 2 1/2 pipes & a free flow muffler.
4:11 gears are as high as thy come for that rear end. A 5 speed with o-drive would be the way to go.
George

[Asshat]

Originally Posted by Wrenchbender Ret

I'm thinking you have too much back pressure in the exhaust system. 292 engines have a very restrictive exhaust system. That "quiet" muffler is causing a lot of back pressure. Have them build a system with 2 1/4 or 2 1/2 pipes & a free flow muffler.
4:11 gears are as high as thy come for that rear end. A 5 speed with o-drive would be the way to go.
George

I spoke with a gear outfit, they told me the 14-bolt GM can go as high as 3:42.

I’ll check with the muffler shop, see how much they’ll charge.
Not even sure what it should cost.

[Wrenchbender Ret]

The original rear end in the 3/4-1ton trucks 72 on back had 4:11 gears as the highest ratio available. The 73 up had 3:42 ratio.
George

[Asshat]

Originally Posted by Wrenchbender Ret

The original rear end in the 3/4-1ton trucks 72 on back had 4:11 gears as the highest ratio available. The 73 up had 3:42 ratio.
George

That was for the original HO52/72 rear end; I swapped mine with a later ‘73-up rear end.

[Steeveedee]

I don't remember if you have an oil bath air cleaner. If so, make certain that the oil level is where it should be.

[Asshat]

Originally Posted by Steeveedee

I don't remember if you have an oil bath air cleaner. If so, make certain that the oil level is where it should be.

No, regular dry air filter.

[Steeveedee]

Originally Posted by Asshat

No, regular dry air filter.

OK, just checking off another box.

[88Stanger]

So I have a 1966 C10, took rearend out, had complete new carrier and gears installed. with the carrier i have you can only go to 3:42 which i did, the other carrier allows for much taller gears, above 4:11. cost was not cheap, but with stock carrier i had, only could go to 3:42. you mentioned 14 bolt GM rear, did you mean 12 Bolt? i have GM 12 Bolt Truck rearend.

as for the exhaust leak.... i would no rule out vacuum leak. i had a 1966 Chevelle that had a 327ci that made a wierd sucking like sound that ended up being a damn vacuum leak, BUT it ran ok because we had timing and carb adjusted enough to cover the vacuum leak, or so we thought. fixed it and damn, what a difference.

fix? carb base plate was leaking along with the damn main rod that holds the butterflys in the carb. so crazy.... so, if after exhaust, start with basics, vacuum: air cleaner, intake, vacuum advance on dist., other potential vacuum lines that could be split, carb base plate or rods. I understand that the carb may be new, but you never know, also gaskets could be messed up. not sure what you hooked up, but check the PVC too maybe??
Good luck on this quest.

[Asshat]

Originally Posted by 88Stanger

So I have a 1966 C10, took rearend out, had complete new carrier and gears installed. with the carrier i have you can only go to 3:42 which i did, the other carrier allows for much taller gears, above 4:11. cost was not cheap, but with stock carrier i had, only could go to 3:42. you mentioned 14 bolt GM rear, did you mean 12 Bolt? i have GM 12 Bolt Truck rearend.

as for the exhaust leak.... i would no rule out vacuum leak. i had a 1966 Chevelle that had a 327ci that made a wierd sucking like sound that ended up being a damn vacuum leak, BUT it ran ok because we had timing and carb adjusted enough to cover the vacuum leak, or so we thought. fixed it and damn, what a difference.

fix? carb base plate was leaking along with the damn main rod that holds the butterflys in the carb. so crazy.... so, if after exhaust, start with basics, vacuum: air cleaner, intake, vacuum advance on dist., other potential vacuum lines that could be split, carb base plate or rods. I understand that the carb may be new, but you never know, also gaskets could be messed up. not sure what you hooked up, but check the PVC too maybe??
Good luck on this quest.

It’s definitely 14 bolt, yours is 12 bolt because it’s 1/2 ton; mine is 3/4 ton, 8 lugs.