Project Big-Bang pt4

don’t
Firing it up
Project Big-Bang pt4
y it
u
b
What are we doing?
it
s. The ignition
The BB2 engine is in the chassi tered, but the
al
bu i ld
and injector wiring have been
it run? And
ill
w
…
is
on
ti
es
qu
e
Th
k.
oc
st
ECU is
wiring and ECU?
e
th
t
ou
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bu
ut
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n
will it ru
Game
Words Olly Crick Photography Rory
T
Yoshimura collector
installation at 180
and 360 degrees
> Power & torque
175
150
BB180
short
stacks
125
148.13bhp,
62.67lb-ft
BB180
long
stacks
156.35bhp,
65.50lb-ft
BB360
short
stacks
> power/torque
75
50
131.34bhp,
61.96lb-ft
750cc long
stackspre-BB
140.37bhp,
62.27lb-ft
25
> rpm x 1000
0
3
4
5
6
7
8
9
10
11
12
13
14
BB makes more power and torque low down on short stacks, as you might expect. But on long
stacks the party really gets going when the revs rise above 9750rpm. So long stacks it is
[102]
BANG
!
Who’s doing it?
Tim Radley, proprietor of
Gloucester-based Race
Developments, a Dynojetapproved tuning centre.
Tim has been building and
tuning engines for race
bikes for 20 years.
Targets
his is the moment we’ve been waiting for. It’s tense
and nervous in Tim’s freezing-cold dyno room. I can
see my breath and he hasn’t even switched on the
cooling fan yet. With two cylinders firing at once plus
the extra compression designed in by Tim squishing
the engine (see PB last month) to around 14:1, there’s no chance of
starting it off the battery. Tim demonstrates... click, engine limps
once over TDC. ‘See,’ he says, ‘we need an SP2 battery.’
He’s going to try a bumpstart on the dyno, but such is the
compression force Tim needs his apprentice Rob to push the rear
tyre down on the roller. He drops the clutch, the bike jolts,
kangaroos, jolts again and fires. It’s running and we can’t believe it.
Well, I can’t. I suspect Tim has more faith in his abilities than he
shows. What a feeling. Along with Tim’s expertise, all it has taken
to make our BB2 engine is a set of special Piper BB2 camshafts.
‘It doesn’t start too easily,’ says Tim when he eventually turns the
bike off and manages to stop smiling, ‘but I’ve taken out the
100
In essence, chasing traction. We’re
BB2 big-banging (see PB, Jan 07)
a GSX-R750 K3 that’s bored out to
800cc. Then we’ll re-strip it and turn
it into a BB3. Kawasaki used these
configurations (plus others) during their
2006 MotoGP campaign.
secondary throttle valves (butterflies) to get more peak power and
welded the pivot holes to stop air leaking in. That could be why’.
He starts it again. Already warm, the engine fires up with much
less fuss this time. Tim’s going to do some proper dyno runs. He
points out two fault codes flashing alternately on the GSX-R’s
clocks – C24 and C25. But he’s doing the dyno test anyway. When
he stops he says the fault codes are ignition coil-stick failure
warnings. ‘It’s because of the way I’ve wired it,’ he says.
Cylinders three and four are the lead cylinders because of the way
the cams have been made. Tim has simply spliced into the feed
wires for cylinders three and four (for both coil sticks and
injectors), and connected the feeds to the coil sticks and injectors
for cylinders two and one respectively. The original feeds for
cylinders one and two are cut and blanked off. By doing this Tim
has risked blowing the ECU and melting the wiring, ‘If it was
going to happen, it would have by now,’ he grins. ‘It’s only revving
to 13,300rpm instead of 13,600rpm,’ he says. ‘That will be its safe
mode because of the fault codes. And it’s drinking petrol. That
could be because it’s big-bored to 800cc and the ECU’s confused.’
There are some big troughs in the power curve (green graph
trace lines). Tim says it could be the exhaust and in no time
swivels the Yoshi collector box (see left). ‘It could be that we’ve
paired up the wrong cylinders with the collector, or it could
possibly do with two silencers,’ he says. With this Yoshi collector
box and the BB2 configuration, what you could have is two slugs of
exhaust gasses meeting at exactly the same time, depending which
cylinders it has paired up. By swivelling it, we now have cylinders
one and four and two and three paired. On the next run that
causes it to lose lots of top-end power (black graph trace).
Tim comes clean and admits he’s fitted short inlet stacks inside
the airbox to chase peak power. He puts the original longer ones
back in (the same items with which we dyno tested the engine in
its 750cc configuration), swivels the collector box back again
(pairing up cylinders one and two, and three and four – meaning
the exhaust gas slugs exit one behind the other to start with, still
coming together but just a little further down the collector) and
does another run. The power curve comes out really well (red
trace), the troughs have all but gone and power is right up. ‘BB2ing
the engine has made it much more sensitive to inlet and exhaust
tuning,’ says Tim.
He’s already considering adding a partition in the airbox between
the trumpets of cylinders two and three as they’re close together
and both gulp air at the same time. ‘Trumpets one and four are at
opposite sides of the airbox and should be okay,’ he says.
Next month will see the comparison between 800cc BB2 and the
(already datalogged) stock GSX-R750 K3 at Mallory Park. We can’t
wait. Meanwhile, log on to www.performancebikes.co.uk to hear
our BB2 engine running. OC
We datalogged the K3 around Mallory
Park before working on it, taking
acceleration figures out of three corners
– Gerrards, Edwina’s and exiting the
Bus Stop into Devil’s Elbow. The figures
were published in PB January 2007
and they are our baseline numbers to
measure our new engine configurations
against. In addition to that the K3
had a peak torque figure of 59lb-ft @
10,200rpm and a peak power figure of
133bhp @ 12,500rpm.
1
2
3
Close up with BB
1 Welded-up secondary throttle valve pivots
show where the butterflies used to be. They
have been sacrificed in pursuit of more
peak power. 2 Long and short inlet trumpets
(stacks) make a big difference with a BB2
engine as our dyno runs revealed. 3 It might
look like a bodge, but our wiring mods worked
without the need to buy an aftermarket ECU.
Next month: Stock bike comparo
>>>
[103]