Wastegate question

[GreaTOne65]

I have a question, about the wastegate on my Banks equiped ISB 5.9L Cummins. When it was installed it would generate 35 psi. it has steadly been going down, to where it is now at 28 psi. I have been getting it ready for our yearly trip to AZ. and decided to investigate the problem. One of the things that I would like to know, is what is the purpose for the wastegate? I have farmed all my life, and none of the tractors I have used, and even the Super Trucks never had a wastegate. I have Googled it, and know how they work, I just don't understand why they are needed? Will somebody who knows explain it for me?

[RJay]

I found this explaination on a google search.

Without a wastegate, the amount of boost that a turbocharger creates varies with the pressure of the engine's exhaust. This happens because exhaust pressure varies with relation to the engine's speed (measured in RPM's). This implies that as an engine reaches higher RPM's, increasing amounts of boost will be created by the turbocharger. The problem with this is that an engine can only accomodate a given amount of boost. Most stock engines are only meant to take about 10 PSI if not less. In order to regulate the amount of boost that comes into the engine, a wastegate acts as a door only allowing a given amount of exhaust to hit the turbocharger's exhaust turbine. Once the engine starts producing more exhaust pressure then the wastegate system will allow, a flap is opened to redirect excess exhaust away from the turbine blades. In turn, this is where a wastegate gets it's name. It's a gate to carry away waste. In order to regulate when a wastegate opens, a boost conroller can be used.

[VanDiemen23]

could be that those old tractors wouldn't flow enough air to require a wastegate to regulate the boost - or a mechanical governor takes care of it at the other end.

In some vehicles there's also a popoff valve in the plenum that controls the maximum amount of boost that the engine will see. Basically, a wastegate is a controller you can set (turbo racecars usually have a knob on the dash to dial up the boost), and a popoff valve is a resettable circuit breaker.

[GreaTOne65]

Thanks, as I said, I to googled it, and I know what it is, I know how it works, I just don't understand why the tractors and trucks, I've owned don't use one, why did they put one on these engines. The tractors run at wide-open throttle, and didn't have problems, just askin'.

[GreaTOne65]

Those old tractors, were powered by Cummins 505 cu.in. engines, the truck was a 400 Cummins. None were computer controlled, maybe that was the difference? I have just been wondering what the computer would do if the hose to the wastegate was unplugged?

[Yaj]

We have a older (1996) 5.9 mechanical (no computer) in our MH. It does have a waste gate and I have never seen it go over 28 psi boost.

[J Walker]

I don't have the answer, but I can observe that 28 psi boost is the normal maximum for an ISB. I have a 2000 ISB, 260 HP. You are no longer getting the Banks increase in boost so that is where I would start looking.

[Sundancer268]

The reason that the old tractors did not need a waste gate was because the turbo was sized large enough to pass all of the exhaust gas to create the max power that was allowed. Throttle response was not a requirement in this environment. The motor home and other over the road equipment (Gas included) need throttle response so they put in smaller turbo chargers to spool up quickly. This means the volume of gas the turbo is required to pass will drive the turbine pressure above the design thresholds of the block, pistons and combustion chamber. Some other ways they are now getting around this over pressurization and throttle response is to use a variable inlet vane system to vary the amount of air the turbo can inhale there by limiting the discharge pressure. Twin turbos with variable air vanes controlled by the computer can also make for a very responsive engine with little chance of engine damage. The Waste gate was the easiest way when the engines did not have computer control and is still used on some engines to this day. The only difference is the computer now controls the valve instead of manifold pressure directly.

[Sonnydale]

I too have a Banks on my 2001 Bounder. I installed it myself and never saw more that 30psi from the get go. It then started going down to 28psi. I took the turbo off thinking that it was damaged, but it is perfect condition. I then made some adaptors to be able to pressurize the boost pipes and intercooler, and voila, it was leaking at the hoses that connect to the intercooler. The clamps looked to be tight, but when I put the wrench on them I was able to tighten them further. You might also look at the hose that goes from the intake manifold to the air compressor as mine was torn when I bought the motorhome and did not get more the 10psi boost.
Hope this helps.

[Mr_D]

Our DSDP with ISC 350 used to show 25-25 psi when stock, now with the Banks it shows 35-36 psi consistently.

[J Walker]

Quote:

Originally Posted by Sonnydale I too have a Banks on my 2001 Bounder. I installed it myself and never saw more that 30psi from the get go. It then started going down to 28psi. I took the turbo off thinking that it was damaged, but it is perfect condition. I then made some adaptors to be able to pressurize the boost pipes and intercooler, and voila, it was leaking at the hoses that connect to the intercooler. The clamps looked to be tight, but when I put the wrench on them I was able to tighten them further. You might also look at the hose that goes from the intake manifold to the air compressor as mine was torn when I bought the motorhome and did not get more the 10psi boost. Hope this helps.

That is a great post. The simple act of closely looking at your engine can reveal an issue that a simple turn of a wrench can fix. One question about the hose form the intake manifold to the air compressor. I am not familiar with that one, although any hose connected to the intake manifold that leaks reduces turbo boost pressure.

[sjholt]

You should check the CAC(turbo aftercooler) for leaks too.
Mine leaked badly with the normal boost starting at 32psi and ending up at 24psi on a trip from east to west U.S. You can check the CAC with a soapy solution sprayed while the engine idles or build some adapters to pressurize it out of plastic plumbing.
Only pressurize it to 30psi max.
HTH

[Sundancer268]

Quote:

Originally Posted by J Walker One question about the hose form the intake manifold to the air compressor. I am not familiar with that one, although any hose connected to the intake manifold that leaks reduces turbo boost pressure.

That hose supplies clean filtered air at boost pressure to the air compressor. With out it connected your air compressor can pump oil into the air system and cause a lose of boost pressure. I was told my compressor was shot and pumping oil. When the hose was re-hooked back up the compressor oil pumping stopped.

[GreaTOne65]

Thanks for all the replies. I have checked the CAC for leaks, I also knew about the compressor hose from the intake manifold. I just finished our yearly trek to AZ, and it still never developed over 28 psi's. When the Banks was installed, it would do 35, I haven't called Banks yet, but will later. I did unhook the hose to the wastegate, and it didn't make any difference, so, before I leave AZ for home, I'll have to call Banks.
Thanks again for all your inputs.