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too much freakin' boost 

 

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 Post subject: too much freakin' boost
Posted: Tue Jun 13, 2006 8:31 pm 
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i am happy to finally get my car goin, but have been pullinh my hair out for the last week, with a problem of it making too much boost...

i can imagine most people thinking so what, more bost the better...

but i want to run 7-8psi for low boost, and 15psi for high boost. problem is, everything in my setup likes to flow REALLY well, too well infact, especially the cam, thats one of the biggest problems i think, its designed to create heaps of exhaust gas to give max spoolup, and therefore, i have a major excess of exhaust gas to get rid off, to allow me to run 8lb

i started with a single 1.25in wastegate outlet off the inside of the collector, that really did nothing for being able to lower my boost, i was making 12lb at 2200rpm, with a 7psi wastegate spring. so i thought, maybe i need two outlets, to help the gas escape the collector, so i removed the manifold, welded in a second outlet, still didnt put a dent in my boost problem, so we thought, perhaps the wastegate is too small (48mm turbosmart) so we removed the wastegate completely and took it for a thrash, still made 14lb at 4500rpm with no gate attached!!!!

so then i was thinking, F**k, how bout we go all-out, and fit two 1.5in outlets on the collector... so we did, tonight i drove it again, still made 13psi at 4600rpm with wastegate completely open....

F**k me, how much gas do i need to vent to get my boost down??? im going to have to remove the gate and drive it with it blowing out the outlet pictured, that will tell me if i need to upgrade to the 50mm wastegate, or whether i still need to have more out the collector.... maybe i need two gates, with their own outlet.

oh well, if i cant get it any lower, ill just have to have a 15lb low boost.... OR upgrade to a gt42r turbo, cos atm i have the 1.06ex housing on a gt35r


so much for my nice pretty, ceramic coated manifold, its become a big r&d item

cheers, brad

this is the latest version
Image
Image
Image

 

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Posted: Tue Jun 13, 2006 10:00 pm 
Getting Side Ways
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ha looks like we have similer proble,, did u get it on the dyno anyway???

 

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Posted: Tue Jun 13, 2006 10:29 pm 
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umm blow off valve???


would that help?

 

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Posted: Tue Jun 13, 2006 10:48 pm 
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yes u can use a blow of valve to regulate boost but the wastegate is a far better option

 

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Posted: Tue Jun 13, 2006 11:19 pm 
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twas my understandint that for best boost control you would use both.....

 

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Posted: Tue Jun 13, 2006 11:22 pm 
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fritzz wrote:
yes u can use a blow of valve to regulate boost but the wastegate is a far better option


soz was thinking both options...

ie wastegate and blow off valve or twin blow off valves

 

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Posted: Tue Jun 13, 2006 11:32 pm 
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a blow off valve isnt made to control boost, its made decress pressure spike when the throttle is closed by realising a pressure diffrence on ether side of the trottle blade, stops the comp wheel stalling.

the wast gate by passes the exhaust gasses to regulate boost.

some off the big guy in the states use a wastgate in the inlet piping to regulate boost.

 

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Posted: Tue Jun 13, 2006 11:42 pm 
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Just trowing some ideas around but would the position of the wastegate feeds be effecting your abillity to control your boost.
I cant really tell from the pics but could it be that the exhaust gases are flowing strait past your wastegate feed?.

I gather that you have one pipe to feed each back of 3 cylinders?. Or have you feed them both into the colleters of the manifold?.

I dont know what turbo you are running but could it also be that the turbine housing on the turbo is becoming a restriction?.

Anyway just thinking about your problem and different reasons that it may be happening. Not having a go at your workmanship or anything like that.

Cheers
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Posted: Wed Jun 14, 2006 12:29 am 
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yes, outlet angle has a fair affect on the ability for the gasses to escape the collector, especially if you have a high enough gas velocity...

so originally, the outltes came out horizontally from the collector, but as you see now, we have angled them up slightly...

matty, in the first post it says i have a gt35r, 1.06 ex housing, considered a reasonably large turbo, maybe not big enough for a free flowing 4l that is only wanting to run 7psi... fine for 15psi> or a std engine, with std cam.

im thinking bout the w/gate in the cooler piping....

what turbo is yours fritzz???? btw, didnt get on dyno, cancelled it when i couldnt fix my overboosting, it would have been a waste of time

 

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Posted: Wed Jun 14, 2006 12:33 am 
Getting Side Ways
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lol my turbo is a cheapy of ebay, t70. .84a/r rear

 

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Posted: Wed Jun 14, 2006 5:28 pm 
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Welcome to my nightmare, I have a single 48mm progate and a 35/40R also, and have seen 20psi with a 3psi spring. I have a free flowing system both in terms of intercooler piping/size and exhaust, so I'de say its just that we all bought a turbo thats too damn small (even though everyone keeps saying their perfect size). My car is currently having the gearbox rebuilt, however after that its going in to have the wastegate put on the turbine housing which should fix the problem - mosty. I'm hoping for 8-9psi with the 3psi spring. Just goes to show how incredibly restrictive and inefficient all the pipework and manfolding must be on BA's.

I hope you can fix your problem, and welcome to the boost club :)
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Posted: Wed Jun 14, 2006 9:08 pm 
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Be very careful with the blow off valve idea in the intake. Venting excess boost this way is a great way to over speed your turbo. Wastegates keep compressor wheel RPM within correct ranges. Venting off the boost removes back pressure which limits compressor wheel speed, and will allow it to continue to increase in speed uncontrollably. A spinoff from this is a decrease in adiabatic efficiency and dramatically increased compressor outlet temperatures.

If you have the facility to monitor the rotating assembly's RPM and the outlet temps you may be able to determine whether or not you will be in for trouble.

Food for thought.

Chris.
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Posted: Thu Jun 15, 2006 8:45 pm 
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it could be that you just have too much of an effient system to allow it to run low boost. I would try a 10psi spring and have 10psi as your minimum level.
My ED has a similar sized T4 with a smaller 38mm tial gate and 10psi spring and Ive never had creep issues ( but, I dont have the same kind of manifold ) so I too am scratching my head on this one...

As an example of flow vs restriction...on my BA XR6T, the stock dump pipe looks to be 2.5in with a very small internal wastegate and a ordinary looking cast manifold, not exactly flow city there, but I know guys that have put larger dump pipe and exhaust on only to end up with boost creep ( and thats with standard edit )... same deal as what your getting

MAybe your only easiest solution is a decent EBC to hold boost down
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Posted: Thu Jun 15, 2006 8:54 pm 
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would an EBC solve the problem though? If the wastegate still doesnt flow enough when it has been totally removed then an EBC wont do anything exept have the possibility of increasing boost or getting the turbo to spool faster

I have been wrong though so feel free to correct me
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Posted: Thu Jun 15, 2006 9:08 pm 
Getting Side Ways
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CHEF wrote:
it could be that you just have too much of an effient system to allow it to run low boost. I would try a 10psi spring and have 10psi as your minimum level.
My ED has a similar sized T4 with a smaller 38mm tial gate and 10psi spring and Ive never had creep issues ( but, I dont have the same kind of manifold ) so I too am scratching my head on this one...

As an example of flow vs restriction...on my BA XR6T, the stock dump pipe looks to be 2.5in with a very small internal wastegate and a ordinary looking cast manifold, not exactly flow city there, but I know guys that have put larger dump pipe and exhaust on only to end up with boost creep ( and thats with standard edit )... same deal as what your getting

MAybe your only easiest solution is a decent EBC to hold boost down


he isnt getting boost creep, he is having trouble with getting to much boost. creep and over boost are the opisit

 

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