Cavitation/Stalling of new turbos in GTR

[haw001]

I''ve just upgraded turbos in an r33 GTR to a set of t28 cored out with roller bearing cores. Not too dramatic, still very torquy, but will do up to about 350hp each.

the intercooler is stock, but running z32 AFMs and pod filters.

The problem I am having is that under very light load when not accelerating, the turbos seem to fight each other and cause some sort of cavitation that won't stop unless you accelerate out of the rev range, or drop right off.

It's an issue when cruising, because it happens frequently when you hit a slight incline and start to give it a little gas to compensate.

The problem occurs around 2600 to 3300 rpm, and specifically, when the car is a neutral boost or very small boost (0 to .1 bar)

I have tried adjusting the actuator arms to compensate, but this only moves it up and down in the reve range, and does not completely solve the problem.

I suspect that a better BOV will fix the problem, but I don't want to vent to atmosphere.

I know this has been covered before, but I don't know what to search for. Any help would be appreciated.

Thanks,

[Ustasa]

Either your BOV is faulty and venting/closing rapidly causing a airflow fluctuation or your turbo chargers are incorrectly matched to your engine and are unstable in operation.

Don’t immediately assume the worst but if the turbo chargers are surging then they must be replaced.

[Roy]

So you have bolted on new Garret Turbos and still running same ECU maps?

What is the car doing, cavitation/stalling of turbos??? So is the engine stalling or do you think the turbine speed is stalling (ie slowing)

I dont state this with any certainty, but...

Perhaps the different flow characteristics of the new turbos is causing a fuelling (tuning) problem ????

Perhaps if you describe what the car is physically doing.

[haw001]

Running a power FC with a whole new map, slightly higher fuel pressure and bigger injectors.

I'm sure there's nothing wrong with the turbos, they are new and they are only slightly higher flowing than a standard set of T28s, slightly cored out, with a slightly higher exhaust housing. but not even as big as a set of 2530s.

The problem does not happen when on boost, but when you are sitting around 2500 to 3200 rpm cruising, not under heavy load.

My suspiscion is that the BOV is popping open then closing in rapid succession because the throttle boddies are mostly closed (no load) but the turbos are still producing a small amount of pressure.

The sound that the car makes is duh-duh-duh-duh sound about 1 every half second, and continues until you either dropt the revs, or drop a gear and up the revs. It sounds as if the turbos are stalling one another, but it's probably more likely that the BOVs are opening one at a time.

[Sydneykid]

Hi Mark, sounds like compressor surge to me. I would have a long talk with whoever did your turbo's. This is not an uncommon problem and is easily fixed with a bit of turbo tuning.

[CMS Drifter]

surge is often caused by a tight bov, but usually happens when you lift off the gas. the other problem maybe how the wastegate is plumbed up. I have a similar problem in my 33 gtst. If the wastegates are connected to the plenum, they will cause this surge problem, yet when hooked up the the i/c pipes on the turbo side of the i/c they are ok.

double check where the wastegate actuaor lines are connected.

[haw001]

Some good ideas here. The wastegates are plumbed as per normal set up, so I'm not sure if they get pressure from the plenum or just before the IC. I'll have to check.

Having had discussions with a friend, I am nearly certain that the BOVs are the problem and not the turbos. Tuning may fix the problem, but I'm not convinced. I've had similar problems before with another GTR and different turbos, just not as severe.

Another suggestion which I may also try is to put an adjustable boost controller on the BOV pressure lines and use it to tune the BOVs easily. I have a simple Turbosmart thumbscrew type which would be easy to plum in, so I might give that a quick try as well.

I'll try everything and then report back.

[raist60]

Despite the fact i have a 33 gts i had the same issue. When i first put my new turbo on i had to the std BOV blocked off. At light throttle it would start to make compressor stall noise and get worse and worse until i backed off or opened the butterfly.

I put my money on BOV not opening properly, coz when i unblocked std BOV (when i got off my arse and replumbed back to intake.) the problem was fixed.