big turbo, low boost, HELP!

Rob1 · 02-15-2011, 07:39 AM

So on my 89 supra turbo, previous owner upraded to a T61 turbo, not sure what brand, and the car is( well was before i disconected ecu lol) pretty fast.

so i hooked up a temporary boost gauge and ran it through the passengerside window to see what i am pushing.

If im not mistaken, disconecting the waste gate line from the charge pipe will alow for maximum boost because the waste gate stays closed under a boost right?

So with waste gate hooked up i was getting around 7 psi and unhooked i was getting about 7.5 maybe 8 pounds of boost. correct me if m wrong but stock they run 8 right? so why the low boost?

I checked the turbine shaft and there was very very little if any play in it so i think the turbo is fine but why such low psi? any advice appreciated.

Supra Saiyan · 02-15-2011, 07:41 AM

Quote:

Originally Posted by Rob1

So on my 89 supra turbo, previous owner upraded to a T61 turbo, not sure what brand, and the car is( well was before i disconected ecu lol) pretty fast.

so i hooked up a temporary boost gauge and ran it through the passengerside window to see what i am pushing.

If im not mistaken, disconecting the waste gate line from the charge pipe will alow for maximum boost because the waste gate stays closed under a boost right?

So with waste gate hooked up i was getting around 7 psi and unhooked i was getting about 7.5 maybe 8 pounds of boost. correct me if m wrong but stock they run 8 right? so why the low boost?

I checked the turbine shaft and there was very very little if any play in it so i think the turbo is fine but why such low psi? any advice appreciated.

Pretty sure stock is like 6.5....

Rob1 · 02-15-2011, 07:48 AM

well even if that is right, i know i have seen the stock turbos push at least 10psi with a boost controler so with my waste gate disconected i should run at minimum as much as a stock turbo is capable of right? since mine is bigger than stock?

cre · 02-15-2011, 10:56 AM

You need to get your head out from under your hood... NOW.

You can destroy your engine in one hard pull that way.

Big turbos may have the capacity of moving more air but the potential is defined on the exhaust side. The size of all of the wheels, the aperture size, the volume and velocity of exhaust gas all define when a given boost level will be reached. You could run a turbo off of a MAC truck but your little engine will barely have it spinning just before you reach redline.

Most turbo's sold for passenger vehicles include wastegate actuators made to open between 6 and 9 psi. You can't really say they open at a given pressure.. they start opening, slowly, pulling the compressor's speed down.

Running a turbo without a wastegate is a recipe for a new engine. There's nothing in place to keep your boost to a respectable level. You go to get on the highway, love the insane pull so you decide to stay on it close to redline... 22psi, a HG, 2 pistons and a rod through the block later you remember you were going to take it easy. :P

The other factor is practical limit. This is where the turbo is compressing so much air that all the combined stresses and all the heat from the compression actually start to cost you power. With the CT-26 this is between 13psi and 14si.

Rob, I mean thins nicely.... go buy and read a good book. My suggestion would be something by Corky Bell. As for why you weren't seeing more boost.... any number of reasons... the turbo is too big, you're hitting fuel cut, the wastegate is stuck open, you pulled and capped the wrong line.

Rob1 · 02-15-2011, 04:27 PM

ok thanks
----------------

Rob1 · 02-15-2011, 05:17 PM

With all that other stuff aside, could i have a boost leak? when i tied in the boost gauge i tied into the nipple on the turbo just before it met the charge pipe, if i have a boost leak somewhere that would cause the gauge to read low cuz regardles how much air is being pushed by the turbo, if its leaking out then it cant build in the system meaning the gauge will only read how much boost im actualy able to build with the leak right?

can a vacumm leak cause a boost leak since all vacumm becomes positive during boost? and i have heard of something called a smoke test to test for leaks, how does that work?

And what about the factory recirculation valve, if its bad then that could also cause low boost pressure right? im expirienced with the 7mge but turbo is a new world to me i just want to learn all i can about it to get the most out of it. thats why i like asking specific questions here so you guys who know what your doing can help walk me through things as opposed to reading a book

02-15-2011, 07:39 AM	#1
Rob1 3" Exhaust Join Date: Aug 2009 Location: tennessee Posts: 137	big turbo, low boost, HELP! So on my 89 supra turbo, previous owner upraded to a T61 turbo, not sure what brand, and the car is( well was before i disconected ecu lol) pretty fast. so i hooked up a temporary boost gauge and ran it through the passengerside window to see what i am pushing. If im not mistaken, disconecting the waste gate line from the charge pipe will alow for maximum boost because the waste gate stays closed under a boost right? So with waste gate hooked up i was getting around 7 psi and unhooked i was getting about 7.5 maybe 8 pounds of boost. correct me if m wrong but stock they run 8 right? so why the low boost? I checked the turbine shaft and there was very very little if any play in it so i think the turbo is fine but why such low psi? any advice appreciated. __________________ My work in progress!!! 1989 toyota supra turbo targa top 7mgte, Five speed left hand drive.

02-15-2011, 07:48 AM	#3
Rob1 3" Exhaust Join Date: Aug 2009 Location: tennessee Posts: 137	well even if that is right, i know i have seen the stock turbos push at least 10psi with a boost controler so with my waste gate disconected i should run at minimum as much as a stock turbo is capable of right? since mine is bigger than stock? __________________ My work in progress!!! 1989 toyota supra turbo targa top 7mgte, Five speed left hand drive.

02-15-2011, 10:56 AM	#4
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	You need to get your head out from under your hood... NOW. You can destroy your engine in one hard pull that way. Big turbos may have the capacity of moving more air but the potential is defined on the exhaust side. The size of all of the wheels, the aperture size, the volume and velocity of exhaust gas all define when a given boost level will be reached. You could run a turbo off of a MAC truck but your little engine will barely have it spinning just before you reach redline. Most turbo's sold for passenger vehicles include wastegate actuators made to open between 6 and 9 psi. You can't really say they open at a given pressure.. they start opening, slowly, pulling the compressor's speed down. Running a turbo without a wastegate is a recipe for a new engine. There's nothing in place to keep your boost to a respectable level. You go to get on the highway, love the insane pull so you decide to stay on it close to redline... 22psi, a HG, 2 pistons and a rod through the block later you remember you were going to take it easy. :P The other factor is practical limit. This is where the turbo is compressing so much air that all the combined stresses and all the heat from the compression actually start to cost you power. With the CT-26 this is between 13psi and 14si. Rob, I mean thins nicely.... go buy and read a good book. My suggestion would be something by Corky Bell. As for why you weren't seeing more boost.... any number of reasons... the turbo is too big, you're hitting fuel cut, the wastegate is stuck open, you pulled and capped the wrong line. __________________ If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum. If you're so inclined I'm always more than happy to accept tips via PayPal. Tip Jar --->

02-15-2011, 04:27 PM	#5
Rob1 3" Exhaust Join Date: Aug 2009 Location: tennessee Posts: 137	ok thanks ---------------- __________________ My work in progress!!! 1989 toyota supra turbo targa top 7mgte, Five speed left hand drive.

02-15-2011, 05:17 PM	#6
Rob1 3" Exhaust Join Date: Aug 2009 Location: tennessee Posts: 137	With all that other stuff aside, could i have a boost leak? when i tied in the boost gauge i tied into the nipple on the turbo just before it met the charge pipe, if i have a boost leak somewhere that would cause the gauge to read low cuz regardles how much air is being pushed by the turbo, if its leaking out then it cant build in the system meaning the gauge will only read how much boost im actualy able to build with the leak right? can a vacumm leak cause a boost leak since all vacumm becomes positive during boost? and i have heard of something called a smoke test to test for leaks, how does that work? And what about the factory recirculation valve, if its bad then that could also cause low boost pressure right? im expirienced with the 7mge but turbo is a new world to me i just want to learn all i can about it to get the most out of it. thats why i like asking specific questions here so you guys who know what your doing can help walk me through things as opposed to reading a book __________________ My work in progress!!! 1989 toyota supra turbo targa top 7mgte, Five speed left hand drive.

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