So are Surge ports just for looks or what?

Once I turned up the boost on my GT3561 past 21psi it starts surging, now this with with the Surge Ported T04S Cover.

Anyone care to explain?

even with that cover the map wasn't widen'd enough for you to be moving enough air to be past the surge line at that psi. Increase the engine's VE or run a bigger hotside to make it spool later where your moving more lbs/min to be past the surge line and a biggerhot side will increase ve as well. What hotside are you running?

Its the bolt-on .63

I know slowing spool will fix it as I can turn the gain way down on my EBC and slow the spool and it won't surge as bad, but I don't want to make it really sluggish...no fun for my DD.

I just figured it wouldn't Surge with the SP cover, I guess I'll have to live with it.

what rpm are you getting full boost/surge? I'd say without changing the turbine the only way to stop it would be to up your engine's ve but you've already got cams and smim not alot of easy places to go from there.

Looking at the compressor map and my logs it looks like I'm just on the other side of the surge line (roughly in the circled area)

Are you on a 2.0? At what RPM is it reaching full boost?

Stock 7bolt, full boost is right at 4400 in 3rd.

I ran it over 21 psi when I had it and it didn't surge. I was getting full boost by 4200 in 3rd. I really don't think the problem is related to the turbo. Do you have a map sensor you can datalog with Dsmlink?

Yep sure do.

I graphed out where I actually am on the compressor map using my DSMlink logs.

Can you post a datalog of the surge occurring ?

I have since played with the gain on my EBC to slow the spool so the surge isn't as bad.

I've only seen one other datalog with compressor surge and it didn't look anything like that. Are you sure your bov isn't cracking open at the higher pressure? What does your boost gauge do when the surge occurs?

The compressor map you posted is for the regular S cover, not the surge ported cover. The surge ports should move the surge line to the left by a few lbs/min.

GVR4592 said:

I've only seen one other datalog with compressor surge and it didn't look anything like that. Are you sure your bov isn't cracking open at the higher pressure? What does your boost gauge do when the surge occurs?

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BOV never did this with more boost from my 50 trim last year, also the spring in it is so strong it barely opens unless you blow off with 15+psi. The boost gauge bounces back and forth.

Theoretically if the BOV was cracking open under the pressure, that would make the turbo more likely to hit choke, rather than surge, wouldn't it? The extra airflow would move him further to the right of the surge line, and closer to the choke limit, although from his datalog and compressor map plots it doesn't look like he's anywhere near that.

In fact, adding an artificial boost leak would probably fix his surge in this case by moving the operating point further to the right.

CanadianTSI - if you're using a MAF-T, speed density conversion, AEM EMS, or some other airflow measuring method that doesn't mind venting a little boost, you might want to consider doing exactly that (adding a controlled boost leak) if you're having surge issues.

You could buy a cheap eBay MBC and set it to a few PSI below where you're having your surge issues, and just have it vent to atmosphere at that boost level to get you out of the surge region. It looks like you're not exactly starved for compressor flow anyway.

ThingyNess said:

Theoretically if the BOV was cracking open under the pressure, that would make the turbo more likely to hit choke, rather than surge, wouldn't it? The extra airflow would move him further to the right of the surge line, and closer to the choke limit, although from his datalog and compressor map plots it doesn't look like he's anywhere near that.

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Absolutely. . . What he's saying is that perhaps it's not surge but just BOV flutter.

However. I think surge is more likely considering his plots as well. . .

A controlled leak. . . man what a way to make up for a poor turbo choice for the mods. . . I'm definately not flaming YOU. . . I definately is a way to stop a surge problem . . . But I think other more profitable tools acan be employed.

CanadianTSi said:

I have since played with the gain on my EBC to slow the spool so the surge isn't as bad.

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CanadianTSi, you have an intake manifold that doesn't flow as well as a stocker at 5000 rpms but will help increase spool rate. You have cams that sacrifice low range torque (low range VE) for high torque an high horsepower at over 5000 rpms. You have a higher flowing exhaust manifold that SHOULD increase spool. Where are you surging? what is your rev limit?

You need more VE at the alleged surging event. Where is that? It looks like you are trying to avoid surging at peak hp but destroying flow at a point where the turbo starts to push hard (4500 rpms?).

My suggestion . . . FP2Xs are fp3s w/ more distant centerlines and higher lift. Adjusting for more overlap on the fp2Xs (by retarding the exhuast cam by around 3 crank degrees) will yield the same lift, ramp rate, duration, and power band as fp3s. BUT! w/ more peak lift! This would cause your VE to soar at around 6000 rpms. Also, the duration still "comes into play", so the peak hp should still be at a decent rpm level to get the neccesary flow from a 2.0L block. Also the ramp rate at the "down turn" of the lobe will lend to the valve being open long enough to fill the cylinder well at higher revs. So increasing the overlap SHOULDN'T bottle neck the SMIM exhaust mani and turbo as much as could be expected. . . Fp3s are great for mid range torque as they're designed for strokers that can't successfully rev over 7500 rpms for long periods of time w/out special care and attention to the bottem end fasteners.

I would try that but I don't have adjustable Cam Gears.

Well I don't have any to lend you