With the commentary on the 400 vs 350 TPI, I edited some info that was
published on the SCCA Solo2 (autocross) BSP (class B, street/prepared) list.
The car that this engine was in ran at the Dogwood Grand Prix this year
(fastest Solo2 event in the country and only one on city streets I know of).
It took second out of 100 cars entered; first was also a Corvette with a
later engine. . .didn't beat him by much though.
The SCCA SP class doesn't permit nonstock head/cam swaps. . .mostly just
tuning, balancing, etc. He put alot of time into the car but not parts
dollars so this could be considered an alternate approach to building a 350
TPI motor. This car as modified below was very fast but of course I don't
have hp numbers. I hope to follow this guy's example with many of his mods
this year.
And even with the mods listed, it also passes emissions tests. . .interesting.
I cut out all of the suspension mod stuff as irrelevant for the old trucks
but it was just as interesting to me!!!. . . .
Mark Noakes
58/56 Suburban
66 Corvair Monza turbo
86 Silverado short bed
86 Corvette Indy convertible, SCCA BSP #32
Knoxville, TN
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Engine-
I decided to take a conservative approach. I know the L98 has killer low
& midrange torque in stock form. So, I just balanced the 90 engine when I
built it. Then I did a bunch of die grinding on the intake and exhaust
manifolds just to clean it up so it would flow a little better.
Specifically, I rounded out any corners and rough areas and totally
ground down the "dams" behind the throttle body since I disabled the EGR
system. I also matched the upper plenum openings to the runners that go
down to the lower manifold. On the lower manifold, I just made sure the
air would make a smooth turn from the runners to the heads.
The exhaust manifolds had some really gross AIR tubes protruding into
them. So, I ground them down and smoothed up the welds in the collector
area. I also "knife edged" the collector cross piece and rounded the edge
of the cone shaped collector transition. I capped the AIR tube on the
upper end. I had the EGR tube welded up on the passenger side manifold.
I got an 84 front Y pipe and gutted catalytic converter (plugged the AIR
tube). Then bought a new 85 rear Y pipe and connected up my Borla
mufflers.
Transmission -
Stock 700R4 as per Solo II rules (rebuilt last year). However, they allow
any torque converter, so I bought an Art Carr 2400 stall lock-up
converter (thanks for the tip Ken Mitchell!). I have the 3.07 rear gears
so my theory is that with the stock intake and stock free-flowing exhaust
that the converter would put the motor right in it's sweet spot.
Performance -
With only 650 miles on the motor the acceleration was VERY strong. It
corners very flat and is dead neutral handling. I can use the throttle to
set the car where-ever I want on the course.
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