Subaru Turbo Boost

[Odyknuck]

Over last winter I replaced the 2332 VW Turbo motor with a 2.5 Subaru Turbo motor. It does not spool up until 4000 or so RPM in 2nd gear and does not build Boost much above 2 to 3#.  On the VW motor this same Turbo T-3 60 Trim would Spool up at 2500 and go to 8# (wastegate setting) quickly. The waste gate is working etc.   The differences between the VW setup and the Subaru setup is longer exhaust pipes (same diameter) up to the Turbo. The rear cylinder pipes are aprox. 3.5' long and the front cylinders are Aprox. 2' long. The VW pipes are probably a foot shorter on the rear cylinders. Also  larger diameter intake track tubing (From 2" ID to 2.75"ID). My theory is the longer Exhaust is loosing way too much heat and velocity pressure to spin the Turbine. Also the 2.75" Intake track tubing has a lot more volume than the 2" to build pressure quickly.  How much difference would heat tape make on the exhaust side? Any thoughts

[fastcorvairs]

Over last winter I replaced the 2332 VW Turbo motor with a 2.5 Subaru Turbo motor. It does not spool up until 4000 or so RPM in 2nd gear and does not build Boost much above 2 to 3#.  On the VW motor this same Turbo T-3 60 Trim would Spool up at 2500 and go to 8# (wastegate setting) quickly. The waste gate is working etc.   The differences between the VW setup and the Subaru setup is longer exhaust pipes (same diameter) up to the Turbo. The rear cylinder pipes are aprox. 3.5' long and the front cylinders are Aprox. 2' long. The VW pipes are probably a foot shorter on the rear cylinders. Also  larger diameter intake track tubing (From 2" ID to 2.75"ID). My theory is the longer Exhaust is loosing way too much heat and velocity pressure to spin the Turbine. Also the 2.75" Intake track tubing has a lot more volume than the 2" to build pressure quickly.  How much difference would heat tape make on the exhaust side? Any thoughts

Odyknuck

      Hard to believe that the longer exhaust pipes would make that much difference in the spool up time.  The subi is making much more heat then the VW.  The large intake track could but not that much.  Have you checked for leaks in the exhaust? Any leaking in the exhaust is cause for concern. The t3 should be making much more boost quicker with the subi then the VW.  I would be checking for eqhaust leaks. Just my .02cents.

[Yummi]

Where is that engineer fella? 

The 2.75" is the culprit - you have lowered the pressure by increasing the volume.  Well, just my guess and I dont have a second cup of coffee yet.

[fastcorvairs]

Where is that engineer fella? 

The 2.75" is the culprit - you have lowered the pressure by increasing the volume.  Well, just my guess and I dont have a second cup of coffee yet.

      Yes he has increased the volume but that should only slow down the time it takes to spool up to pressure.  Liken to filling two air bottles to say ten PSI.  One five gallon and one two gallon. The two gallon would fill up first but both would get there eventually.

[Yummi]

It does not spool up until 4000 or so RPM in 2nd gear and does not build Boost much above 2 to 3#. 

      Yes he has increased the volume but that should only slow down the time it takes to spool up to pressure. 

Exactly. 


Another way to reduce lag is to change the aspect ratio of the turbine by reducing the diameter and increasing the gas-flow path-length. *  A veturi (Reducer) on the 2.75" pipe will resolve this problem as it will increase the velocity of the exhaust gas.   I think - still working on the 2nd cup......


* http://en.wikipedia.org/wiki/Turbocharger

[fabr]

I'm looking at a leak for the reason for only 2-3#'s boost. I could be very wrong tho.

[Odyknuck]

I do not see any Indications of Exhaust leaks, ie; no carbon streaks  at flanges etc.  I used all Copper gaskets. The Blast gate appears to be tight. I would think I would hear it if it was leaking enough to not build Boost.  It also worked fine on the VW motor.   The Intake tract is made up of aluminum tubing with silicone fittings and "T" band clamps. The BOV only releases when I get out of the throttle and you definatly hear it when it does.   Here is a link to the motor swap to get a better Ideal on what I have done.  I will have to take a closer look at the Intake tract.
http://www.woodsbuggy.com/index.php?option=com_jfusion&Itemid=10&jfile=viewtopic.php&f=33&t=6013

[Boostinjdm]

are you sure your BOV is plumbed and tuned correctly?  Vacuum line has to come from intake manifold after the throttle plate and be as short as possible.  Spring tension also has to be right.

[Odyknuck]

The BOV line is connected to to the Intake manifold between the engine and Throttle plate.  The BOV did not come with any directions to adjust it. I tryed it the way it came and it appeared to work correctly. It is not sucking air during normal Vacumme operation. Only releases when there is a sudden closure of the the throttle plate.  What is the proper way to tune it? 

[Odyknuck]

Well I found the problem over the week endDUH! I assummed the BOV was working because it released when I quickly let of the throttle. As it turns out at around 3000 RPM and up while stilll in Vaccumme it was also releasing. So I readjusted it so it would only release when the throttle plate closes. On a flat road it now Builds Boost at 3000 RPM and is a 10 PSI by 3800 RPM and the Buggys going sideways. :shock: With the offroad gearing there really is not much load on the motor at lower RPM. I suspect that on the trails and climbing hills it will Boost earlyer in the RPM Range. Thanks for all the help.

[fabr]

That'd be a vacumn leak alrighty! LOL! Glad you found the prob. Should be FUN now.