[s-cars] Driving Impressions-long

[CaptMagu at aol.com]

s-heads,

I thought I'd give everybody an update on my car and see what you guys think
about a challenge that Mike Pederson and I are having. Recent modifications
have included a thorough replumbing of the intake tract from the turbo to the
throttle body hose. The big turbos that Mike and I run(plus a few other guys)
actually cause the end tanks of the 24x10x4 FMIC to flex. Mike gets all the
credit for the head engineering here. He figured we were losing quite a bit
of power from the inefficiencies of our intake tract. Dave Jones just
completed a full replumbing of my tract to a 2 1/2" piping. Dave Stone, our
machinist completely rebuilt my endtanks to incorporate fluted intake and
outflow pipes that encourages the flow to be more uniform over the entire 10"
height of the I/C. What I had before was a straight pipe end welded to a flat
surface of aluminum. The pics of Mike's new I/C give you an idea of this
fluting.

The other big mods were the elimination of the stock airbox and RS2 MAF and
the installation of the Pederhousen Big MAF and SVT Cobra airbox. We also
swapped the TurboXS H34 bypass valve for a larger Turbosmart unit. You can
see that the trend here is in the enhancement of the breathing of the engine.
This all adds up to or should I say subtracts from boost threshold
management. Prior to these mods I was getting full boost at about 3800 rpm.
Now we're down to 3100 rpm. That's about a 20% improvement. A very expensive
20% improvement. The car just feels quicker, a lot quicker.

Now on to the Hap/Mike challenge. During throttle lift from a boosted pull I
get a surge that chiffs the bypass valve. I had the same problem with the
TurboXS installed but this new valve is loud enough that I can hear it over
the engine. During a heavy loaded pull, like when I'm charging up I-70 making
the climb from Denver to Evergreen, I get this same surge and chiff with a
corresponding responce from my boost guage. I also get this same thing if I
do a pull in 6th gear from say 2000 rpm. If I downshift and still accelerate h
ard but not work the turbo quite so hard everything is just fine. Don't get
me wrong, if I get on it hard in the lower gears, the car just screams to
rdline in all 6 gears.

According to TEC the problem could be flex in the intake tract. The only long
piece of hose that's not aluminum piping is the rather long Samco throttle
body hose. I'm going to try and use a bunch of large hose clamps tomorrow to
bind that hose and see if there's any difference. Mike and I have also talked
of creating a carbon fibre overcoat for this hose to stop any flexing. Anyone
else out there have anything similar? I did notice that pics of Joern's
engine show an aluminum hose leading to the throttle body. TIA.

Hap, on the boost in Evergreen, Maguire