I was busy doing some R&D late last night and stumbled onto a phenomena that might have an answer for the guys that are having on-boost compressor surge, or what is known as bouncing off the surge line. BTW, this thread has nothing to do with a BOV/DV so don't ask.

From what I read on here, most of you with the problem elect to go with anti-surge compressor housing covers or ported shrouds, etc. Even though this is at the expense of some points of efficiency it is an aid to the problem. To simplify, on-boost surge is too much boost too early. However, this doesn't really define it properly. Surge is due to high exit mach numbers at the impeller so that for that given compressor wheel profile, the slip losses at the boundary layer lead to flow reversion that cascades in a resonant frequency, eg cha cha cha (Covered well in Watson & Janota ~1982). Without digging too deep, there may actually be a very easy solution that doesn't impact horsepower one bit.

Here's my question to you guys: If you are getting on-boost surge, are you running a stock frame turbo, and what is the diameter of your intake pipe? If it is bigger than the compressor inlet flange diameter, where is the reducer located, right at the compressor, or by the MAF?

If you aren't getting this surge, what is your intake like in terms of the question above.

 

I have this problem, 4th-5th gear, 3000-4500rpm anything from 1/3rd to wide open throttle.. FP Black turbo with a custom intake pipe and reducer, the rubber/silicone reducer is right on the turbo inlet.. if I recall it's about a 3" pipe and 3.5" compressor (or whatever the standard FP antisurge cover is....

Do you have any recommendations for me to try out?

 

I either get surge or there is some sort of tuning issue with my second pump kicking in, but anything 3rd gear and up seems to cause sputtering if I lay into it below 4500k rpm or so. I have a .63 a/r hotside standard gt35r. This only happens when running higher boost (above 25psi). I have a 4inch intake.

I think with a .82 hotside, some of the issue would clear up, but that would require me to buy a new o2 housing and downpipe or modify them.

I don't think the issue is necessarily ignition related because at long as I am above 5500rpm or so I almost never have issues.

 

Sounds tune related

 

Yeah, compressor surge is when the compressor wheel is trying to push too much boost/pressure ratio at too low of a mass flow rate. Now the pressure ratio is the difference between the absolute pressure at the compressor inlet and absolute pressure at the compressor outlet.

If you have a dirty air filter and small intake piping, it reduces the absolute pressure at the compressor inlet effectively increasing the pressure ratio. So having the most free flowing intake can reduce the occurance of compressor surge.

FYI, going up to altitude can cause a turbo to go into surge too because the absolute pressure is lower.

 

Interesting, I think a test is in order

 

This is a SD setup(no MAF sensor), right? Can you post any pics featuring your intake system?

 

 

Yes speed density, I took some pics it's a pretty basic setup and needs a bath! I drive it in the winter though...









As you can see it necks down immediately at the turbo

 

What size hotside do you have? Probably bigger than .63. Then of course there are other factors like cams, intake manifold, displacement, etc.

 

So your intake actually goes from large inlet to smaller intake pipe. This is kind of counter to what I've seen. I'll have to look at the data again.

I could possibly replicate this too on the dyno in a couple of weeks and see if I can make it go away

Edited: You're right, what you're describing sounds more like inducer stall.

 

Excellent! So did you find a piping size and layout that did NOT exhibit the problem there and a different one that did? I'd be interested to know!

 

I have the same setup 35r/.63 with the same issues ur describing. I spoke to Tial about it, and from what they have seen is the smaller hotside is one of the factors played into surge.
It kinda makes sense since it doesnt seem right for the comperssor to push more air than what ur engine can process thru the smaller hotside. I will be swapping mine soon, so I will report back my findings.

 

Yea, I suspected that as being part of the issue. The only reason I don't think I had issues earlier on was a boost leak I never knew about keeping it under check (EGR valve). Now that all my boost leaks are fixed, surge and spiking are my new friends. I know the spikes can be controlled by using electronic boost control, which I might do via a GM solenoid and the AEM, but the surge is in large a result of the tiny hotside.

Will be interested to see your results.

 

To add to the data, here is my 3.5" custom aluminum intake. Silicon adapter is 3.25" - 3.5". Zero turbo surge.

The FP Black is 3.25" so theres no reason to go to a larger than 3.5" except to say you have a 4". If you have a 3" one then your probably having problems.