Odd noise....SBC after hard accel.

Hey there, as some may know the S10 has a 305 swapped in and it runs great. I cant be sure when this developed but it did develop a noise.  Here is the setup.  

1. Warm or cold engine

2. On a hard accel the engine picks up and at some point seems to lose ass until you let off a little bit

3. If you power through it and go back into it, once you let off you hear a noise from the passenger side near the firewall

4. The noise sounds like this. Say you have a container thats under vacuum, and you go prying on it. Say you crack the corner a little bit and it makes that squeaking/wooshing noise.  Thats the best way I can describe it.  

Truck runs fine. I feel the bogging is a spring issue (too weak) for the secondaries, I also want to up the pressure to around 7 psi from the current 6.5. I also want to tweak the timing and give it a once over.  

The noise makes me feel like its a fuel issue, and I am hearing the bowls running dry? Which I cant see happening as it continues to drive fine after. Leading me to a intake manifold leak? Thoughts?

Thanks!

I think that if it sounds like a vacuum leak, start there. 

Vacuum canister failure? Vacuum solenoid in the AC system failing? 

Sometimes at WOT, the HVAC solenoids will relax against the spring due to a lack of vacuum. As soon as the throttle closes they pull back. You may be hearing them move. 

Sounds like it's leaning out as well.

The truck has no vac cannister, no HVAC at all. System was gutted from the front to the back - nothing at all in the dash not even the ducting.

Im leaning (see what I did there) towards the intake manifold leaking. I will go back and make sure all bolts are tight and regroup.  

Will update!

Vac modulator on trans?

Video would be helpful

In reply to AngryCorvair (Forum Supporter) :

It doesnt have one AFAIK

In reply to AngryCorvair (Forum Supporter) :

I will try to make that happen!

Quick video uploaded as requested.  
 

That sounds like a vacuum leak to me. 

Maybe brake booster ? 

It's a rare condition....

Wait for it...

Throttle blades closing.

Seriously.  That's what the air sounds like as the velocity increases while you cut off the air.  I think you just may have a vacuum hose under there left over from something.

Curtis73 (Forum Supporter) said:

It's a rare condition....

Wait for it...

Throttle blades closing.

Seriously.  That's what the air sounds like as the velocity increases while you cut off the air.  I think you just may have a vacuum hose under there left over from something.

I chuckled. That was perfect! Will look and see. I didn't see anything earlier nor did it act up when running and I sprayed carb cleaner. It did burst into flames though. That was fun. Apparently some wire I no longer use wasn't terminated right and with the fumes and me spraying. Whoosh!