WOT boost surge. WTF?

[trbo355]

Why does my twin turbo firebird start surging out of the turbo's above 8 psi which also happens to be the cracking point of my gates? I took it to 15 psi and the fluctuation gets worse as i add boost.
The boost needle will vibrate 3 psi as i hear the pitch of the turbo's oscillate. I just put on some much bigger TE-44's with big .72 exh. housings that really dont spool all that well. Im going to switch back to .63 housings soon but i wondered what causes this phenomenon? The wastegates are perfectly in sync and it is all in perfect working order otherwise. Thanks in advance!

[talntid]

What kind of wastegates? Have you checked the car for boost leaks? Is it blowing black smoke when this happens?

[trbo355]

What kind of wastegates? Have you checked the car for boost leaks? Is it blowing black smoke when this happens?
They are turbonetics EVO's and have always worked perfect. It is the same basic tune as before with the old turbo's but i did richen it slightly in the higher boost areas since the turbos should have gained a ton of efficiency compared to before. It pulls really strong with no black smoke. Whats weird is it worked perfect the first time i drove this new combo but then i blew the hell out of the transmission. Once i fixed the trans, it started doing this. All the hose connections check out since i thought maybe i yanked something loose during the tranny removal. It all looks good. I had to modify my layout with the new turbos to get the air cleaners to fit back on and since i reinstalled them, the problem has disappeared for now. It did work though with no air cleaners so i dont have a lot of faith in the system yet. Im just bugging cuz for once i dont have an answer to a problem!!! What do you think???

[96gsx]

Weird.. I've never heard of that..**Does it start at boost threshold, then continue to get worse as you flow more air?**What does the math say when you caculate airflow/pressure and compare it aginst the compressor map?**You have done a boost leak test, yes?

What year is your firebird?

[rrussell]

I can't find a compressor map for these turbos.:(

TE44 are they normally used on the 4.3L V6 Buicks?

[trbo355]

Weird.. I've never heard of that..**Does it start at boost threshold, then continue to get worse as you flow more air?**What does the math say when you caculate airflow/pressure and compare it aginst the compressor map?**You have done a boost leak test, yes?

What year is your firebird?
Thats exactly what it does.My car is the black 88 firebird that was out at the track last summer. If i look at the map, it isnt anywhere near the surge line. In reality, each turbo is only fed by 175 cu. inches and they are designed for a 231 ci. buick Grand National to be used as a single setup.

rrussel, they are supposed to support around 550 HP apiece on a Buick GN and all the GN guys bitch about the .72 housings. With only 175 cubes feeding it, they are definitely right about LAAAAAZY spool. But holy shit when they are on, they run hard! LOL It still doesnt explain why they act so weird though. The wastegates must not be doing very much bypassing though since my boost controller is EXTREMELY sensitive now.Im using a POS regulator as a bleed valve since my $200 EBC never has worked right. Instead of blowing it up trying to fix it, i just went back to the old setup for now. I have some .63's in the works to put the combo back in line and the problem may just go away but damn i want to know whats going on for the next time it happens i might have a clue! It bugs me to get kicked in the balls and walk away not knowing.

[Kolat]

port the wastegate if your using internal gates :-)

T

[talntid]

i, too, blame the wastegates

[rrussell]

Due you have any pics of the compressor map?

A couple things to consider.

231CI
500HP
5000rpm
IAT125
mass air flow 55lbs/min
pressure ratio 2.74
gauge pressure 22psi

175CI
300HP
5000rpm
IAT125
mass air flow 33lbs/min
pressure ratio 2.20
gauge pressure 15psi

You can see that the smaller CI 175 is now closer to the surge line

Now look at the 231 CI making 300hp

231CI
300HP
5000rpm
IAT125
mass air flow 33lbs
pressure ratio 1.70

The same air flow but with a lower pressure ratio.

The second major factor running twins.

The turbos compressor feels the pressure from the other turbo. This creates a high pressure ratio with a low air flow from each turbo.**Making the air want to reverse flow or cause compressor stall.

[trbo355]

Due you have any pics of the compressor map?

A couple things to consider.

231CI
500HP
5000rpm
IAT125
mass air flow 55lbs/min
pressure ratio 2.74
gauge pressure 22psi

175CI
300HP
5000rpm
IAT125
mass air flow 33lbs/min
pressure ratio 2.20
gauge pressure 15psi

You can see that the smaller CI 175 is now closer to the surge line

Now look at the 231 CI making 300hp

231CI
300HP
5000rpm
IAT125
mass air flow 33lbs
pressure ratio 1.70

The same air flow but with a lower pressure ratio.

The second major factor running twins.

The turbos compressor feels the pressure from the other turbo. This creates a high pressure ratio with a low air flow from each turbo.**Making the air want to reverse flow or cause compressor stall.

Ya know, i do believe you might be on to something there. Excellent math there too BTW! I will find a comp map for ya and post it.

[trbo355]

Took me a minute to remember what comp. it has! It is a TO4E-60.
Here ya go.

[rrussell]

175CI
300HP
5000rpm
IAT125
mass air flow 33lbs/min
pressure ratio 2.20
gauge pressure 15psi


Also these numbers were based on 100% VE.

If you keep the values the same and change the VE to 85% you then get a pressure ratio of 2.72 @ 33lbs/min mass air flow.

[trbo355]

175CI
300HP
5000rpm
IAT125
mass air flow 33lbs/min
pressure ratio 2.20
gauge pressure 15psi


Also these numbers were based on 100% VE.

If you keep the values the same and change the VE to 85% you then get a pressure ratio of 2.72 @ 33lbs/min mass air flow.
Ok so in laymans terms, how do my new hairdryers stack up now that you have had a looksee at the comp. map? Here is the map of the old stock Buick GN turbos to see where iv'e been.

[rrussell]

Heres your new turbo plot
http://www.hostdub.com/albums/rbr20/Marty_new_turbo1.jpg

Heres the GN tubo plot
http://www.hostdub.com/albums/rbr20/GN_Turbo1.jpg

Both plots are at the same values
175CI
300HP
5000rpm
125*F
VE 90%

= 33 mass air flow lbs/min and a pressure ratio of 2.43

The new turbos are right at the surge line. Where the old GN 's are more to the right side.
This also doesn't take into affect the twin turbo pressure variable. This will cause it to move way closer to the surge line.

One other thing you could try is to build some anti surge rings. They use these a lot on the new Monster size turbos when used on a small displacement engine.

[trbo355]

Thanks for the info man! So do you think by creating a slight restriction by installing the air cleaners it somehow helped it by running in a different pressure ratio? What is the story with anti surge rings and how do they work? Thanks in advance!

[rrussell]

So do you think by creating a slight restriction by installing the air cleaners it somehow helped it by running in a different pressure ratio?

I'm thinking it is acting like a anti-surge housing. How and why. You got me;) That would be aerospace stuff.:cool:

I'l try to find the anti-surge ring info.

[96gsx]

What are the specs of your engine? Bore, stroke? Are you running an intercooler?

[trbo355]

What are the specs of your engine? Bore, stroke? Are you running an intercooler?

4.040 bore, 3.48 stroke. It runs a big intercooler from a freightliner with the navistar engine. It's as big as my radiator! The motor is honestly the biggest joke and actually has 150k miles with stock everything but a cammotion cam and ported stock heads now. With commercial truck small valve heads it had, it took 22 lbs. boost and a 100 HP NOS shot and went 9.75. Yes im crazy but it started out as a joke to put it in when the good motor puked and now it wont die!

[KryptoSol]

i don't know if this was already asked, but are you running internal or external waste gate? and how many psi??

My car currently does something similar to what you are discribing, but i'm running a 6psi spring in the Tial waste gate, and at about 20psi its starts to bounce really fast +/- 3-4psi, and then steadies out at 24psi and upper RPMS. I can hear my wastegate opening and closing really fast which could be mistaken for surge? its a med-high pitch tsk tsk tsk tsk....

I think i just need to replace the waste gate spring to something stiffer.

I don't know if that helps you any but it dons't hurt to check it.

good luck

[trbo355]

i don't know if this was already asked, but are you running internal or external waste gate? and how many psi??

My car currently does something similar to what you are discribing, but i'm running a 6psi spring in the Tial waste gate, and at about 20psi its starts to bounce really fast +/- 3-4psi, and then steadies out at 24psi and upper RPMS. I can hear my wastegate opening and closing really fast which could be mistaken for surge? its a med-high pitch tsk tsk tsk tsk....

I think i just need to replace the waste gate spring to something stiffer.

I don't know if that helps you any but it dons't hurt to check it.

good luck

They are external turbonetics evolution gates. That is just about the exact same thing my car does. All i hear is the compressor RPM varying along with the boost gauge fluctuating rapidly with the change in turbo pitch. Funny thing is, sometimes it works, sometimes the phase of the moon changes and it doesnt! I havent gone above 15 psi yet cuz she is burning pump gas right now. I wonder if it would quit?

[KryptoSol]

i don't know if this was already asked, but are you running internal or external waste gate? and how many psi??

My car currently does something similar to what you are discribing, but i'm running a 6psi spring in the Tial waste gate, and at about 20psi its starts to bounce really fast +/- 3-4psi, and then steadies out at 24psi and upper RPMS. I can hear my wastegate opening and closing really fast which could be mistaken for surge? its a med-high pitch tsk tsk tsk tsk....

I think i just need to replace the waste gate spring to something stiffer.

I don't know if that helps you any but it dons't hurt to check it.

good luck

They are external turbonetics evolution gates. That is just about the exact same thing my car does. All i hear is the compressor RPM varying along with the boost gauge fluctuating rapidly with the change in turbo pitch. Funny thing is, sometimes it works, sometimes the phase of the moon changes and it doesnt! I havent gone above 15 psi yet cuz she is burning pump gas right now. I wonder if it would quit?


yeah, that sounds exaclty like my car does, about 8 out of 10 times i get the flutter. I'm pretty sure my situation is wastegate spring related because i can distincly hear the wastegate-dump open and close rapidly. I hear that you are only supposed to run no more than double the spring PSI. What are you using for boost control?

According to the compressor maps, i don't think you are surging. You arn't that far off... considering ive seen a lot worst on Honda applications with little or no surging.

Is there any way you can monitor the waste gate dump while driving if you can't hear it?

Maybe you could clamp a high temp hose on one of the dumps and route it into the cabin?


J/K... don't try that. :P

[trbo355]

i don't know if this was already asked, but are you running internal or external waste gate? and how many psi??

My car currently does something similar to what you are discribing, but i'm running a 6psi spring in the Tial waste gate, and at about 20psi its starts to bounce really fast +/- 3-4psi, and then steadies out at 24psi and upper RPMS. I can hear my wastegate opening and closing really fast which could be mistaken for surge? its a med-high pitch tsk tsk tsk tsk....

I think i just need to replace the waste gate spring to something stiffer.

I don't know if that helps you any but it dons't hurt to check it.

good luck

They are external turbonetics evolution gates. That is just about the exact same thing my car does. All i hear is the compressor RPM varying along with the boost gauge fluctuating rapidly with the change in turbo pitch. Funny thing is, sometimes it works, sometimes the phase of the moon changes and it doesnt! I havent gone above 15 psi yet cuz she is burning pump gas right now. I wonder if it would quit?


yeah, that sounds exaclty like my car does, about 8 out of 10 times i get the flutter. I'm pretty sure my situation is wastegate spring related because i can distincly hear the wastegate-dump open and close rapidly. I hear that you are only supposed to run no more than double the spring PSI. What are you using for boost control?

According to the compressor maps, i don't think you are surging. You arn't that far off... considering ive seen a lot worst on Honda applications with little or no surging.

anyway you can monitor the waste gate dump while driving if you can't hear it?

Maybe you could clamp a high temp hose on one of the dumps and route it into the cabin?


J/K... don't try that. :P
Ha ha, i wont! I do believe its true about doubling the wastegate spring pressure. I used to run my gates with metered boost feeding the atmo. side of the diaphragm and with a 9 lb. spring, i couldnt get over 17 lbs so i went to a bleed valve in the main signal line to get it to go higher.
I cant hear my gates cuz they are tied into the rest of the exhaust.

[rrussell]

I would first try to figure out if its compressor surge or waste gate dump noise.

I use a mechanics stethoscope with a 3/8 fuel line and run it to the air cleaner. You will instantly know if its surging its loud as hell.

[rrussell]

According to the compressor maps, i don't think you are surging. You arn't that far off... considering ive seen a lot worst on Honda applications with little or no surging.

On the maps I plotted keep in mind that these plots are based on one turbo not two. That's why I wrote with two turbos the plot will move over to the surge line. Another words if it was a 175CI engine with one turbo it would be good enough to run without a worry of surging and the plots show this.

But in the case of a twin setup like Marty's each turbo compressor is working against a high pressure that each turbo only produce half of.
The turbos have a lower shaft speed with a much greater pressure ratio then they were designed for.

I hope this makes sense. The Garrett rep at SEMA was much better then me at explaining it.

Also on a side note the Garrett rep at SEMA said a large percent of the Honda customers are killing their turbos do to compressor surge. He said they just don't hear it. So that's why all the large frame
GT 42R etc. type turbos come standard with anti-surge housing.

[KryptoSol]

Hmmm... makes sense. I guess i should actually read the post instead of just looking at pictures huh? :?

"But in the case of a twin setup like Marty's each turbo compressor is working against a high pressure that each turbo only produce half of.
The turbos have a lower shaft speed with a much greater pressure ratio then they were designed for."

Thats interesting, i never thought about that.

[trbo355]

Well i think i solved the mystery. Everyone that said to check the wastegate sync was basically right but with a twist! The GN based turbo's have a wastegate hole in the exh. housing that is no longer used on my setup with external gates. The downpipe flange simply blocks the hole. Well i never noticed it at first but the flange didnt seal right to the turbo and it has been blowing exhaust soot out one corner of the flange all over the fenderwell. At first this seemed like no big deal as it should just be exhaust exiting the turbo and have no effect. Well it aint sealing the bypass hole and has been totally unbalancing the exh. flow and barfing the WASTEGATE sync! Jeez, maybe i shouldnt have painted the fenderwells cheap ass Krylon semi flat that is the same color as exhaust soot. Hopefully next week i will dyno it and turn up the boost as high as a giraffe pussy and see what it puts out! LOL

[talntid]

lol :)

Ok Dr. Horsepower, ler 'er drip!... err.. rip!

[KryptoSol]

glad you got it figured out!