I have a friend with a 93 truck with a 16cm housing on the stock turbo and a very tweeked pump. He has a complete 4 inch exhaust all the way back. He also swapped an NV4500 in place of his old auto.

He has a really loud turbo bark but ONLY when he tows. It will bark quickly when you get on the throttle at low RPMs and slow down as the RPMs rise. If you keep your foot in the throttle it will get really loud but the barks get REALLY far appart. He can eliminat the bark once up to speed by backing out of the throttle but it comes back if you give it a little to go up an incline. Of course he also has the bark when he lets off the throttle quickly. Same sound but at a different time. Same noise in both cases.

If I understand correctly from reading a number of threads today the bark is simply air pressure pushing backwards through the compressor when it has no where else to go. Thats why bark typically happens when you let off the throttle quickly. The part I don't understand is why he has such bad bark when accelerating and any time he's under heavy load.

His setup is really common. What would cause him to have such bad bark?

What are common solutions to turbo bark?

I've read about changing turbos and such as well as something about grooving the intake for a better map . . .Not sure what that means exactly. It doesn't seem like he should be having this trouble with a 16cm housing to me.

Thanks,
Chass
ct

 

The only thing that I can think of, and it's a stretch, is to check all of the (4) hump hoses. The factory ones are thin and can split or slip from under their clamps. Just a guess...

 

It shouln't bark under acceleration. I second goodtyms, check all connections for hose leaks etc... I had a boost leak one time due to a broken clamp and whenever my boost came up, it would make a loud squealing noise.

 

We have planned on doing a complete check . . . BUT, I don't see how a leak would cause bark? It seems like a leak would decrease boost pressure and subsequently reduce barking.

We will check them though!

I didn't think it should bark under acceleration either but its the same noise that I heard in gas turbos before when you let off the throttle fast. Its also the same noise that I heard in a couple videos about turbo bark. I'm pretty darned sure thats what it is.

Chass
ct

 

It's compressor surging, not barking. 5 speed trucks with a good amount of fuel at low RPM will do it when running a smaller turbine housing. 12 cm housings are notorious for doing this, but 14 and 16 cm housings are not immune. Automatics with a stock TC won't do it because the engine never gets loaded at low RPM.

Your buddy needs a compressor with a MWE slot to allow the turbo to recirculate the excess boost. If you can get a WH1C or HX-35 cheap, those will cure it. All the HTT upgrades have an MWE slot, too.

 

It's caused by going to the left side of the straight line at the beginning of the compressor map In other words, trying to create too much boost with too little airflow (low RPM). An HTT Stage IV is an excellent cure

 

I gotcha! So the cure is a later model turbo with the slot.

So the surging is effectively the same thing as the "bark" though correct? Its the same noise just under slightly different circumstances.

Last question, are there any negative effects of turbo surge? What are they?

Thanks!
Chass
ct

 

Under extreme cases its possible to break the turbo shaft, your turbine wheel will come out your exhaust. lol Less extreme would just shorten the life of the turbo shaft bearings.

 

This "compressor surge"...what does it sound like? I believe I may have the same symptom.
Does it sound almost like an automatic cooling fan kicking on, gaining RPMs, then slowly cutting out maybe 20 seconds later?

(BTW: Do cooling fans in all first gens run constantly?)

Thanks

 

No, thay turn on and draw air and make noise when there is enuff heat going thru the radiator to lock up the fan clutch so it starts to roar and then when the air gets cooler it will shot off or slow down.

that could be what your noise is!

 

I think SWANK cut his own MWE slot back when he had a single charger, might want to go take a look in his gallery. (or i could be wrong and having another pre-senoir moment ).

 

I remember seeing that too. That would work if you have the tools, but it's still going to be the little 54mm wheel. It's fun being able to claim you have a bigger compressor inducer than any of your tractors, combine, or grain truck do.

 

Ok, another question about this,

Could the 60mm wheel from HTT help this problem?

Or would the potentially higher boost make for even more surging?

Chass
ct

 

I'm assuming the 60mm upgrade would come with an MWE housing, so it shouldn't surge

 

60mm HTT compressor= More efficient air, and MWE slots to cure the low RPM surge!