Investigating Compressor Surge.. big engines, little turbos

2253 Views 52 Replies 12 Participants Last post by KBlake, Jun 18, 2006

boostd4

Discussion Starter · Jan 31, 2006

Was hoping one of the more well-read/experienced guys could help me with some forecasting.

In the next 2 months I should have my car running and tuned. I've heard from a few people that I need to beware of compressor surge because of my turbo choice.

I'm running a GT28RS with external wastegate, 3" dp/exhaust. I'll have an IC larger than a spearco sidemount (with 2 850cfm pusher/puller fans), and very short IC piping - maybe 2ft TOTAL. I'll be runnning an HKS SSQV bpv on the IC piping.

The motor (for a reminder):
2.2 3s based stroker 9:1 pistons
ChrisK mild port with 1mm OS valves and throat correction
264 cams

I'm assuming that my only risk of compressor surge would be down low, right? According to Garrett's website, compressor surge is caused by:

*A compressor bypass valve is not integrated into the intake plumbing between the compressor outlet and throttle body.
*The outlet plumbing for the bypass valve is too small or restrictive
*The turbo is too big for the application.

I don't have any of these problems. With my built head, cams and 3" exhaust with 2" EWG piping, I can't see the GT28RS outrunning my engine up top. I guess my only issue might be down low? If the RS is spooled so quickly that the RPM's are too low to process the air it's putting out, I'd have compressor surge then, right? Shouldn't I be able to tune this out by adjusting my cam gears?

Would running dual BOV's on my IC piping help combat compressor stall or damage since the RS doesn't have an anti-surge housing?

Thanks.

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JekylandHyde

· #2 · Jan 31, 2006

boostd4 said:
If the RS is spooled so quickly that the RPM's are too low to process the air it's putting out, I'd have compressor surge then, right?

Nope ... you would have a boost spike.

AFAIK, surge is only going to happen when you let off the throttle.
IF the BOV/BPV can't evacuate enough air to relieve the pressure, the pressure is going to push backward against the compressor blades.

boostd4

Discussion Starter · #3 · Jan 31, 2006

Well, hopefully, the EWG will alieve the majority of boost spiking issues (and a good tune).

As for the compressor surge.. it just might be an issue off throttle. I designed my IC setup to have the best response. There should be one 90o bend and one 45o bend, total, and definitely less than 3ft of piping. I think with such little intake tract area, my bov may have trouble releasing enough air.

I suppose I'll just run two. The HKS clone's on ebay are only $70/ea. or so

JekylandHyde

· #4 · Jan 31, 2006

... it sounds to me like you are trying hard enough to justify two valves

Quite frankly, I do not think you are going to be flowing enough air to warrant it.
I would think 2 valves would be an option if you had a monster turbo pushing out huge psi.

boostd4

Discussion Starter · #5 · Jan 31, 2006 (Edited)

I didn't think it would be a problem either, but since I got to thinking about the adverse affects of having really short IC piping, with so much less volume, it got in my head.

That, and Bryan (NoShoes) advised that my setup might have compressor surge issues.

Also, I'm shooting for at least 350whp... and closer to 400whp on race gas. When we tune, I'm all for running as much boost as it'll take within reasonable AFR's on race gas. At that point.. I might have more to worry about in terms of outflowing a single BOV on short piping.

JekylandHyde

· #6 · Jan 31, 2006

I would think with less volumn you would have less issues.
Did NoShoes say why he thought this?

Please note I am not expert on this.
I'm just sharing my 2 psi as I understand it.

I could very well be wrong. I'm great at being wrong

NoShoes

· #7 · Jan 31, 2006

boostd4 said:
That, and Bryan (NoShoes) advised that my setup might have compressor surge isssues.

I must have been up late talking on AIM then. My apologies.

You may run out of compressor though, when you attempt higher boost pulls.

boostd4

Discussion Starter · #8 · Jan 31, 2006

JekylandHyde said:
I would think with less volumn you would have less issues.

The way I understand it, the larger the volume of intake piping/IC the less air the BOV has to vent...

For instance, your setup... you have, what, 5-6ft of piping, and then the massive TMIC core itself... when you shift at redline, your BPV has to release enough air to relieve pressure in the system. However, it will take your turbo a longer period of time to fill the pipes and core up enough to cause surge after the BOV has released. By that time, the compressor should have slowed down quite a bit and it won't be compressing the air as much.

In my setup, with such a small volume of air between the turbo and TB, the BOV will vent, and the compressor wheel speed will be fast enough to fill and compress the small volume of air again, and cause surge. By running two BOV's, I could potentially release a larger volume of air, so that my compressor would have to fill more volume before the air is compressed enough to revert and cause surge.

Just my theories, too... I posted for the insight and to correct my horrible logic patterns

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JekylandHyde

· #9 · Jan 31, 2006

I think your logic on volumn is very backwards.

If you have your spare donut tire filled to 35 psi
and you have a monster truck tire filled to 35 psi
and you poke the same size hole in each one
... which one will get down to 0 PSI faster?

The smaller the volumn (intake pipes) the less you would need to vent to get back to zero pressure. You turbo will NOT be pressurizing air if you are off throttle (throttle plate closeD). When you get back on throttle, it is fine for it to start spolling up again since the throttle plate is open and the PSI is going in to the engine.

Surge only happens from the time you are OFF throttle until you get back to equalized pressure. During that time, the turbo will not be pressurizing air.

RickyB

· #10 · Jan 31, 2006

Compressor surge is caused when the engine cannot ingest enough air to keep up with the compressor's minimum flow requirements for the speed it is turning at. Aside from surge caused by having the throttle slam shut and shutting off the engine's ability to continue flowing air while the compresor is still spinning quickly which is alleviated by a blow off or bypass valve, increasing flow at lower RPMs is always going to help potential surge caused by a mismatched compressor/engine combination. Stroking and increasing cam duration will almost always help reduce the likelihood of surge.

Honestly, I don't see any way that the setup you propose is going to experience surge unless your BOV is improperly configured.

JohnSantesson

· #11 · Jan 31, 2006 (Edited)

I was getting compressor surge on Ats tdo6 and KO 46t kit. No surge on the 50 trim. Those turbo's that want to spool up very quickly have problems with surging on a high VE motors. At least thats what my experience is. You will need to run alot of boost to make 400 rwhp on that small turbo. John

boostd4

Discussion Starter · #12 · Jan 31, 2006

JekylandHyde said:
Surge only happens from the time you are OFF throttle until you get back to equalized pressure. During that time, the turbo will not be pressurizing air.

That's not true... just because you're off the throttle doesn't mean the compressor wheel still isn't spinning at high speed and pressurizing the intake tract with the TB closed. In fact, one of the BOV's jobs is to KEEP the compressor wheel spinning off throttle, but creating less resistance in front of it. The proof is the fluttering BOV sound you hear on some cars... that's the compressor wheel pressurizing the intake and popping the BOV, then restarting that cycle. Isn't this caused by a BOV that can't vent enough air that the filling cycle repeats? (either by being adjusted too tight, or being too small..)?

Your tire analogy makes sense, but I offer this one:

Take a coffee stirrer and a McDonald's straw and blow through them. Cap the end off with your finger, then release and cap again. You lose a lot more breath through the Mcdonalds straw in the time between releasing and recapping your finger at the end...

510rob

· #13 · Jan 31, 2006 (Edited)

there's no trick to make a small turbo bigger - 400HP on a GT28RS is just not possible. Even 350HP from that turbo is pushing it to it's absolute limit, and from the compressor map, I myself wouldn't plan to run it past 325HP (I like to have some durability, and 350HP would end up spinning the turbine/compressor shaft excessively fast)

boostd4

Discussion Starter · #14 · Jan 31, 2006

JohnSantesson said:
I was getting compressor surge on Ats tdo6 and KO 46t kit. No surge on the 50 trim. Those turbo's that want to spool up very quickly have problems with surging on a high VE motors. At least thats what my experience is. You will need to run alot of boost to make 400 rwhp on that small turbo. John

I'm aware of that, and that will simply be for bragging rights and the occasional shootout with the locals at the track. I'd like to make 350whp on pump gas at 19psi or so. But that's neither here nor there...

Please explain what you mean by "having problems surging on high VE motors".. I'm confused that RickyB think there's almost no way it can happen with my setup, but you, having actually had a reasonable range of turbos on your engine, do. Our setups are not that different aside from your RMR vs. my 3SGE manifold.

I like to see theory and practical application meet!

boostd4

Discussion Starter · #15 · Jan 31, 2006

510rob said:
there's no trick to make a small turbo bigger - 400HP on a GT28RS is just not possible. Even 350HP from that turbo is pushing it to it's absolute limit

That's simply not true. The Audi guys use the GT28RS to make 400whp on race gas with 1.8L on setups not much different than mine (except I have 17% more displacement). It's a ball-bearing turbo and I won't be running nearly the boost the EVO guys have been running GT series turbos to, with no problems.

At any rate, it's only a guess. If others can make ~300whp with nothing but bolt-ons, I'd like to see at least 30-50whp from stroking, built head, degreed cams, intake manifold, and 2-3psi more boost than those plots.

The 350hp "max" you see on the Garrett sites are based on a 1.8-2.0L motor running 15psi.

510rob

· #16 · Jan 31, 2006

If I told you I met a guy once who made 500HP with it on an Audi, would you believe me, or would you question it? Would you say "WOW, that's impressive... but a little too fishy to be true" or would you say "WOW" and walk away carrying that as solid credible information...

Despite the fact that you are quite certain it is true, and please don't take this as a personal attack because it is not aimed at you but is aimed at the Audi guys, I tend to think the Audi guys are lying... numbers don't lie, Garrett publishes the compressor maps, the numbers are there, I tend to believe Garrett over a bunch of Audi guys spewing off what I would call dream numbers. Even if they do make 400HP, they are way off the safe map, and that may significantly shorten the life of the bearings.

I think the difference here is that I am a HUGE skeptic of conjecture, and I don't treat "the Audi guys" as credible evidence when compared with published flow maps from Garrett, who manufacture the product in question.

Are you sure the Audi guys weren't spraying a bunch of nitrous oxide to get those numbers?!?

it's the same old problem with ego-driven "bragging rights"... who is to say a person is not lying? Magazines lie about HP all the time - it sells products by selling the fantasy/dream

I stated my opinion, of course none of it is hard fact, and there are many variables. It is quite possible you might get 400HP, but as I said, I think it is compromising long-term durability. With that said, I would like to be proven wrong, not because I am a sadist, but because it would mean you learned something new and brought that back to the community.

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boostd4

Discussion Starter · #17 · Jan 31, 2006

^^ This is the same stuff people said about the SB46. Then John made over 400whp with it on race gas. The 46 trim map and the GT28RS map aren't that much different.. the 46 trim does edge it out a bit, but not enough to say that the RS is only good for 350whp max, while the 46 trim will make 60whp more on the same setup.

I never said I was out to burn up the streets at 26psi and 400whp with race gas day in and day out. I plan on running 19-20psi on the street which should not be a problem for a ball bearing, water cooled turbo. My dinosaur-like TD05-14B ran 19psi all day long for 3 years of daily driving without ball bearings, and without failure. Ask Kris @ KO how his oil-cooled journal bearing turbo has faired after years of 19psi daily driving.

Sorry if I'm being defensive. It's just dissapointing sometimes how many people are willing to spew negatives before hand, and when it's proven, all you hear are crickets (like the SB46 issue).

And this thread was supposed to be about compresesor surge and not GT28RS max capability. That's at least 50% my fault

. Please, if you want to participate in this thread, lets stay on topic from here on out.

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JekylandHyde

· #18 · Jan 31, 2006

Thanks for the education Ricky ... as always

boostd4 said:
Take a coffee stirrer and a McDonald's straw and blow through them. Cap the end off with your finger, then release and cap again. You lose a lot more breath through the Mcdonalds straw in the time between releasing and recapping your finger at the end...

The error in that logic is you are comparing different sizes of volumn and orifices.

boostd4

Discussion Starter · #19 · Jan 31, 2006 (Edited)

Okay, take one full length drinking straw, and then cut another one to 1/3 the original length.

Blow into both straws while capping the end, then release the end for long enough to blow the existing volume of each straw out the end. When you recap the ends, the shorter straw will take significantly less time to re-pressurize.

The point I was trying to make was if the piping is short enough to repressurize before the throttle is openned again, it would surge. The compressor wheel doesn't *stop* spinning when the BOV vents. On a system with a much higher intake tract volume, wouldn't it take the compressor wheel longer to repressurize the piping? And if you're back on the throttle, the intake with higher volume may never pressurize enough to surge before the TB is open again? Just thoughts.

JohnSantesson

· #20 · Jan 31, 2006

boostd4 said:
I'm aware of that, and that will simply be for bragging rights and the occasional shootout with the locals at the track. I'd like to make 350whp on pump gas at 19psi or so. But that's neither here nor there...

Please explain what you mean by "having problems surging on high VE motors".. I'm confused that RickyB think there's almost no way it can happen with my setup, but you, having actually had a reasonable range of turbos on your engine, do. Our setups are not that different aside from your RMR vs. my 3SGE manifold.

I like to see theory and practical application meet!

I have a Chrisk intake manifold. I don't have any technical reason why my engine would surge the 46t and the td06. It seems that the stroker engine is spooling the turbo up too fast. I would have to drive through the surge. This was at low rpm's. Above 3k to redline there was no surge. With the 50t coming on 500 rpm's later there isn't any surge, ever. Maybe someone has a educated guess as to why. As far as numbers since everyone has there opinion on the gt28rs I will say 321 at 19 on pump and 375 rwhp at 25 psi on race gas. Those gt turbo's want big boost.

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