big turbo, low boost, HELP!

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.

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 --->