Postby Hasbeen » 24 Jan 2008 23:29
No Paul, we just copied the "good" stuff, imported mostly from the
UK. I do have an experience that shows just how critical exhaust
tuning can be.
I was racing a Brabham F2, [UK formula junior] Cosworth 1100cc Ford Anglia
105E engine, with 114 BHP at 7,600 RPM. It was an engine we had
developed ourselves, but still had a Cosworth exhaust manifold, &
their A6 cam.
Being rear engined, there was not much room to fit a long enough
tuned exhaust system. To overcome this the rear 2 feet was a
trumpet, like the old motor bikes, expanding from about 2" to 6"
over its length. It was a 4 into 2 into 1 system, & the 2 into 1
was included in the front of the trumpet.
Even this stuck out the back of the car, by over a foot, so, it was
removable for transport, held on with a small bolt, & a tension
spring.
These engines had a useful rev range from about 6,500 RPM, when the
cam came in, to 8,000, where point bounce, in the Lucas distributor
turned the sparks off. They realy had nothing below that 6,500 range.
In one race the car suddenly lost everything below 7,200 RPM. It was
as if a new cam had been fitted, with 7200 as its cut in point.
Fortunately for me, it was near the finish of the race, & I managed
to hold my place, as the loss of rev range cost me just
OVER 2 SECONDS a lap.
There did not seem to be any loss of power, once it came in, but
thats just a feeling.
It was only once I was back in the pits, after the race, that we
found the tailpipe missing, & the answer to why we lost that power,
so suddenly.
Fortunately, one of the flag marshals heard the change in engine
note, & looked quickly enough to see the pipe slide off the track.
He was also quick enough to get it off the spectator, who was going
to souvenir it, not knowing of course, just how critical it was to
me.
After this, we spent 6 months, working with Bosch, to develop a
disy that would eliminate that point bounce, & let the thing rev
to the 10,000 RPM, the bottom end was safe to. We thought we'd won
the lottery when we succeeded.
In great expectation we put the engine on the dyno.
Guess what? The cam dropped its bundle at 8,200 RPM, & the thing
still was useless over that. It just ran out of breath above that.
Cosworth had maximised the engine, with what they had, & kept out
of expensive "special" gear.
Hasbeen
