We don't have cents here, so here's my 2 pence worth (3.2 cents, approx.):
Modifying versus leaving well alone: You will never get back the money and
time you put into modifying a bike. With engine mods especially you'll
lose out big time. But every one has slightly different ideas of the
"perfect bike", and some people just can't resist fiddling about. The
people who say it's best to leave the bike standard (stock) are absolutely
right, and so are the people who want to strip everything out and change it
all. They're just having different types of fun.
Catalysts: On a *typical* 2-litre modern car, ditching the cat and
replacing it with a straight tube will get you between 5 and 12 bhp. All
production cars are fitted with cats that restrict exhaust flow - a cat big
enough to not be restrictive would be HUGE (do you want a big lump in the
floor?) and HUGELY expensive. BTW the cat is also most likely too small to
take out all the impurities much above a fast idle speed so riding a GTS
probably doesn't qualify you as an eco-warrior. At a guess ditching the
cat on the GTS might be worth 4bhp.
Where is the GTS engine choked? The header pipes on my GTS 1000 are 28mm
outside dia. The header pipes (Hindle) on my Kawa GPz750 are 38mm outside
dia and are thinner-wall tubing - this engine is under 90bhp. For the GTS,
the FZR engine is detuned to 100bhp from 125bhp; I reckon the teeny header
pipes would do all of that detuning on their own. But it may also be
choked in terms of the size of the injector throttle bodies, I haven't
looked yet. Choked in the cylinder head itself? Possible but not likely,
my guess is that Yamaha would use the same casting as the FZR.
What will I do? My thoughts at the moment tend in the direction of
acquiring a mild steel Hindle exhaust system for the FZR and bashing it to
fit. I'd have to weld on a threaded boss for the lambda-sensor of course,
it's a closed-loop system.
Will it work? Maybe. See comment about throttle bodies above. Also, if
the exhaust was much freer-flowing, I'd have to check that fuel delivery
was still adequate at the top end, fuel pressure might have to be tweaked
to suit. I think it's pretty unlikely that midrange power would suffer,
the exhaust tuning length is not going to be a lot different. What is most
likely is that the top-end power would go up significantly (10 - 25%) but
the midrange power would increase somewhat less or stay the same, therefore
the "character" of the motor will have changed quite a lot - whether that's
good or bad is up to the individual (see first para.), the stock motor
actually has as much power as
Will I ever get round to doing it? Depends on availability of Hindle pipe,
availability of money to pay for it, work, girlfriends, British weather . .
. setting up the suspension properly would be a lot more sensible way to
spend my time.
David Thurgate http://www.uranus.co.uk/M_cycles.htm
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Kawasaki ZX750-A1 in Tony Foale HCS frame
Current status: Dismantled!
Yamaha GTS1000a in Yamaha HCS frame
Current status: Taxed and tested!
