No load - no boost - why?

Reply Subscribe

Thread Tools

Search this Thread

Aug 22, 2005 | 11:00 AM

Craze

Thread Starter

Senior User

Joined: Apr 2004

Posts: 241

Likes: 0

From: Seattle

No load - no boost - why?

Could someone explain to me how come boost pressure does not build until you have a load? It seems like to me that boost should be there whether or not you are actually moving the truck. I mean at 1500 rpms the turbo is spinning, the intake is intaking, the boost gauge is hooked up so where’s the pressure go? Just curious.

Aug 22, 2005 | 11:26 AM

Fords4Me

Elder User

Joined: Jul 2004

Posts: 756

Likes: 1

It's the exhaust flow that spins the turbo. It takes very little to keep an unloaded engine at 1500 RPMs.

With a load on it you need to increase the amount of fuel to do the same work (step on the gas). More fuel is burned, creating a larger volume exhuast flow, spinning the turbo faster, creating more boost.

Aug 22, 2005 | 11:50 AM

PowerstrokeJunkie

Post Fiend

Joined: Jul 2005

Posts: 14,582

Likes: 12

From: 21791

i agree with Fords4Me. if you ran 20psi boost constantly no matter what the load, you would be sucking a LOT more air, causing you to use alot more fuel. superchargers are like that. they arent load biased. they produce more boost by rev's.

Aug 22, 2005 | 03:05 PM

ltfox

Fleet Mechanic

Joined: Oct 2003

Posts: 1,764

Likes: 0

From: CentralEastern Utah

Its it reality heat that turns the turbo. the hotter the exhaust coming to the turbo the more boost is built. Thats why more fuel builds more boost. The hot exhaust expanding in the turbo housing spools the turbo.

Aug 22, 2005 | 08:13 PM

Kwikkordead

Fleet Owner

Joined: Jun 2004

Posts: 25,090

Likes: 1,112

From: Rio Rico, AZ.

I'm going to chime in here too and agree. No load on the engine= not much exhaust coming out=not a lot pressure to drive the turbo.

Aug 22, 2005 | 09:55 PM

johnny8

Postmaster

Joined: Nov 2004

Posts: 2,854

Likes: 0

From: New Hampshire

the answer in short is fuel... it is the expansion of the gasses as they escape the cylinder that put "compression" on the exhaust side of the turbo which spins the turbo faster and this transfers the compression to the air on the other side... this creates "boost" pressure... with no load on the engine it takes very little fuel to spin it... even 1500 rpm can be acheived with very little fuel... so... very little fuel = very little exhaust gas expansion = very little, if any, boost.... this is also the secret of how a performance chip or tuner can give you 100 more hp and 200 ft lbs more torque... they simply reprogram the injectors to dump more fuel... more fuel = more boost = more power and torque... just make sure you have gauges and improved intake and exhaust before you start dumping this extra fuel or you'll cook something..!