quote:Originally posted by Daniel_Jones:
That's not why I'm going with IR EFI. I'm doing it to tame a big cam in
a 90 degree V8. Since the runners are isolated from each other, reversion
from adjacent cylinders does not foul the intake stroke, allowing a longer
cam duration with a streetable idle and better low-to-mid range performance.
Kirby Schraeder runs a PPC-sourced IR EFI system on his 377 cubic inch
Cleveland stroker (iron 4V heads with Weber lower and 48mm TWM throttle
bodies). He runs a fairly large overlap 288FDP Crower solid flat tappet oval
track cam on the street. Specs on his cam are 254/258 degrees at 0.050"
(288/294 degrees advertised), 0.569"/0.580" lift (0.022"/0.024" clearance hot)
with 105 lobe centers. That's a lot of overlap for a street car. According
to Kirby, with a 700DP Holley on a Ford aluminum dual plane intake manifold,
it had a wild idle and wouldn't start pulling well until 3000 RPM (Crower
rates the cam range as 3500 to 7000 RPM). When he installed the independent
runner EFI, the first thing he said was "Where'd my idle go?". He noted it
now pulls 5th gear from 1500 RPM. Kirby also noted it's tough staying off
the 7200 RPM rev-limiter in lower gears.
Dan Jones
Dan, Here I have to disagree with you. In the case of Weber 48 IDA's on an IR manifold, camshaft overlap needs to be limited as much as possible.
The reversion from the valve overlap pushes the raw fuel back out of the stack.
In the INDY cars in '63 and '64 you could clearly see a fuel plum (cloud) starting at the velocity stacks and be drawn behind the car by the aerodynamics.
I have run a cam with as little as 28 degrees of overlap to reduce the reverb.
I now think that as much as 40 degrees is probably ok.
You can make argument with me that because the fuel injector is timing the fuel shot that the reversion is reduced, but it certainly isn't eliminated, not at high rpm.
If one runs a high overlap with an IR manifold at speed for any kind of distance and sooner or later it's gonna be a kaboom baby.
IR manifolds do not fix the reverberation issue. They accentuate it.