Even
with all the previous modifications, this engine still didn't have good
power at high RPMs in the 6000 and up range. No amount of tuning seemed
to make much difference up there so I decided the intake manifold
runner size was the problem. The intake ports in the head are 1.370"
and the EFI intake runners are 1.25. It was interesting to see that the
old SU carb manifold is the larger 1.370" size yet the EFI manifold was
smaller
I
ran across someone selling a custom EFI intake manifold that sunbelt
racing engines had made for them and decided to give it a try. The
difference was night and day using the exact same size throttle body as
before. I had to add 20% more fuel from 4500RPM and up to keep the same
mixture and now the car pulls like a ROCKET from 4000-7000. I just
thought it was making power at 5000+ before! Obviously after seeing
this first hand, the EFI intake is a serious problem for a performance
engine and unless you're going to be happy with the stock cam, the EFI manifold HAS to be replaced. Unfortunately there
is no good solution other than a custom fabricated unit (expensive) or
going to carburetors. That said, a set of dual SU's or triple weber
carbs will far outperform EFI
unless the
EFI intake is replaced.
Below are shots of this new intake manifold installed on my engine