[Supras] performance loss with hardpipes and larger IC?

[berniek at technicaldevelop.com]

Over Christmas week I installed a Treadstone IC, a spitting image of the 
Spearco.  Using the stock IC outlet pipe as a template, I made up 
hardpipes from 2-1/4" exhaust tubing, with one section, where it comes 
through the passenger's side fender coupled with about 4" of stretched 
stock hose.  Outlet of the turbo is still the stock hose into a2-1/4" 
tubing mandrel bend replacing the stock cast elbow, feeding a 2-1/2" 
silicone elbow into the IC.  The 3000 pipe inlet hose is now fed with 
2-1/4" tubing, "fishmouth" cut and welded to clear the strut tower.  The 
black rigid plastic piece is gone. 


Now as before, I take the signal for the boost controller from a tapping 
in the 3000 pipe.  After reading postings from Jeff Mohler and others 
about restriction in the stock cooler and piping, it was clear that a 
modified CT26 (57 trim in my case) could use all the outlet pressure 
reduction possible to avoid bearing wear. 


Now, as before, I have not yet installed the under-engine cover, as I 
still need to change the A/C suction hose (and filter dryer, and 
recharge the system, probably in the spring).  In an event, since I take 
boost control from the 3000 pipe, I expected the performance to remain 
essentially unchanged, but with less stress on the turbo.  I took the 
car out for the first time tonight since cleanup work and other 
commitments got in the way.  In 40F weather, I would expect the same 
push in the back as before.  But now it does not break traction in 
second gear as it was on the verge of before with the stock IC and piping. 


It seems to have lost something in performance.  The problem could be 
me, or the weather or something else.  Clearly there is far less 
restriction than was formerly the case in the IC and piping.  But it 
seems to build boost a bit more slowly, and it feels as if I need to 
push it to 6000 RPM.  Before, the boost would come on at 3000 and the 
car would rush right up to 6000 RPM or beyond.  The gas in the tank is 
unchanged (good quality Amoco) as is the fuel mixture, in the range of 
9.5 to 11.0:1, sometimes rich but again unchanged from before.  Under 
normal conditions the engine runs fine, evenly and smoothly.  I'm 
certain there are no piping leaks.  I know there are some who claim that 
increased volume of a better IC and bigger piping cause lag, but at 
most, less than half a liter was added to the air path volume, an 
insignificant consideration. 


Boost is presently measured using the stock sensor, with a resistive 
divider to make the dash gauge read 14.5 to 15 PSI full scale.  I'll 
take a reading with a real gauge to confirm the boost, but taken from 
the 3000 pipe, it should not have changed.


Any ideas about performance reduction would be appreciated.  Thanks and 
happy new year.


BernieK