Shrieking/squealing in acceleration, modified intake mani

[TheGameGoat]

Heyo all!

 

A few months ago I modified my intake manifold, meaning I installed a different one, and rather than going with the TBSS manifold like many do, I decided to go with a Holley spider manifold, very similar to the Victor (I know these are best on FI setups which I am not, but they look d*** cool). It's basically a spider manifold, single plane, with a Holley 105 mm elbow, factory TB (still shopping for aftermarket) with an adapter plate cuz elbow is 4 bolt, and a CAI tube going to the typical corner. After I got everything bolted on and literal days of chasing vacuum leaks she ran/runs great, really good power, my cam has the power band starting around 2800 rpm and the intake is around the same area so you can definitely feel when things start to click. Btw, the cam is a Comp Cams XR275HR 222/224 @ 0.050, .566/.568 lift, and 112° LSA with LS6 springs. Overall it's a good setup for me, the truck is a DD so I didn't wanna get too wild.

 

Here's what the setup looks like:

 

 

So, the problem is this, when I finally got everything finished, there was this shrieking noise at around 2000 rpms and I'm about 98% sure it's the intake somewhere, I figured out eventually it was the elbow, the back side houses the vacuum ports and doesn't quite line up with the manifold flange. I bought a 1" spacer to try to fill in the gap and it worked, no more squeals, then after about a month it started coming back, and eventually it got worse so last night I started digging and put gaskets in differently and got everything back together again. I fired it up and it sounded amazing, hit the throttle a little and I could hear that baby suck the air. So, I pulled her out of the shop and started heading home, got on the road and WOW the shrieking is worse than ever, now rather than being at a specific rpm, it's across a range of rpms, roughly 1800 to 3000 yields a shriek of varying tones and decibels. I'm almost certain it's the intake, just not quite sure where. The intake tube, throttle body, elbow and spacer are all secured and sealed, I'm sure of that. I'm nearly certain all the vacuum ports are sealed, but I don't know where to look next. My dad (lifelong gearhead) took a look and gave me a different spacer, actually an isolator plate, to try so I'm gonna give that a shot tonight, and see what it yields, but I have a hard time believing it's coming from the elbow or flange area.

 

Does anyone here have any ideas? Hoping to get it sorted fairly soon, the wife is tired of me being away playing with my toys ?

[Downeast Johnny]

Sounds like a frustrating problem to figure out. Can you make it happen in park with the hood up?

 

Is there any way to pressurize the intake with compressed air to make it possible to search for leaks without running the motor?

 

Last but not least; Are you sure it's not belt squeal? (Just to mention the simplest possibility.)

 

Best luck with your search.

[TheGameGoat]

Good suggestion, I didn't think about pressurising the intake. I should be able to screw a line into one of the vacuum ports on the back of the elbow and give it a little air.

 

As far as making it happen while parked, the only way I can get it to make any noise is if I goose the throttle then I can hear what sounds more like air being sucked in through the TB, kinda like the sound you get from a factory intake manifold with CAI but more pronounced and a little squeakier.

 

But the sound is definitely not belt squeal, too bad, would be easier to diagnose.

 

Last night I removed the spacer and installed the isolator plate. This netted me the exact same results I achieved the night before. It's probably worth mentioning that I realized the sound isn't really tied to rpms but rather throttle position I think. I can hold my foot at about 35-45% throttle and hear the noise through nearly the whole rpm range while driving.

 

I'm thinking there might be a leak at my TB somewhere but the thing that's strange about this whole thing is that it doesn't exhibit a leak while idling, normally if there is an intake leak you'll lose vacuum at idle if you give it throttle, I believe. So if I were to give it some throttle while idling it would rev way too high them come down slowly as it builds the vacuum back, but I'm not getting that behavior at all. With that being said, it kinda makes me think the leak may be before the TB. Maybe I should rework my intake tube and see if that helps. Maybe that's not the way it happens, but it seems like that's what happened when I installed the intake to begin with. Looks like I have some things to try now, if nothing else I can always convert to cable driven and get a 4 barrel TB with an air cleaner. That's my plan eventually anyway ?

[Downeast Johnny]

Think about loosening and backing off all vacuum hoses and the intake tube and coating the fittings where those hoses seat up with a small amount of heavy grease. (I know; it could get messy), this would temporarily seal those spots. If that solves the squeal then think about replacing the grease with silicone.

 

Without actually working on the truck that's about all I can come up with.

 

Have you pulled your plugs, (looking for a lean running plug), to make sure it's not an intake gasket leak?

 

A potential problem with pressurizing the intake is that at least one cylinder's valves will be open and so I'm not sure how much luck you will have with that.

[TheGameGoat]

Okay, I tried a few things yesterday. Took apart the intake tube and cleaned everything up and made sure everything was making a seal, my MAF also looks like it needs to be cleaned. I also put air to the intake by way of connecting an air line through one of the vacuum ports, I couldn't hear air leaking out anywhere except through the intake tube. This morning I had a guy from work (a gearhead) listen as I goosed the throttle while parked and aside from hearing a lot of air coming in through the tube, he wasn't sure where the squeal was coming from. So I had him goose her and I listened, it sounded to me like the squeal was coming from the intake tube, so he listened again and we both agreed it is almost certainly coming from the air filter. I'm wondering if the intake is simply pulling so much air that as it's going through the TB it's making that noise because it's moving too fast for that small of a TB or my 4-3 bolt adapter is causing a problem as the air goes past it. We're gonna try a couple more things after work and see if we can pin it down. On a side note, I had a DI/DO muffler on the truck for a while, and two weeks ago we removed that and installed an X pipe and two Dynomax race bullets, I doubt the increased flow would cause this to happen, but if air is able to move through faster than it was before, maybe? I'm sure the X pipe is helping with scavenging a lot more than the DI/DO muffler was. Is it possible that with the increased scavenging that the engine is actually pulling more air on the front side as it's pushing it out faster on the back?

 

I looked into doing a DBW to DBC conversion and determined that will be a winter project haha I only started doing a bunch of wrenching in February when I installed my cam, so most of the things I've done and am doing are first times for me, but I refuse to let someone do any of it for me.

[Downeast Johnny]

My thought is that unless you have a very effective ram set up on your air intake you are not going to supply highly pressurized air to the TB. (I've never heard of a problem like this in a manufactured "ram air" set up.)

 

I think that it is far more likely that you have something loose in the system that is vibrating when the air passing over it gets to a high enough velocity, or you have a loose vacuum or pipe to fitting joint somewhere in the set up.