hi guys

after years of regret after selling my 21, i got a 28sp for the road

when i had the 21 (std motor, jha pipes) i used to race it on pump gas (96 here in nz)

Ive now got another 21 on its way for the track, the previous owner was running a 50/50 98 + avgas mix (av is 105 here in nz)

any advantages? I plan to pullk the motor down and check her over but expect from what ive been told that squish is std

if so, any reason to change from pump gas?

cheers

paul

A fuel's octane rating is the measure of it's resistance to detonation, that's all.

So a fuel with a higher octane enables you to tune the engine to a higher state, more compression or increased ignition advance (this may or may not make more power).
Or it gives you more leeway to be less than spot on with the jetting.

Avgas (well, the Avgas we get here) is very high octane (around 112) and has around 5 times the lead of old leaded 4* fuel and is here illegal to use on the road.
So it is very resistant to detonation, you can be numerous sizes too lean and it just loses power. The lead content is also a good thing for engine life.
However Avgas does burn quite slowly so although you end up running a lot more advance (we found we needed around 3° running 50/50 Avgas/97 RON UL) a lot of that advance is required as the burn is slower so the advance is not helping power, in fact the slow burn is making the situation worse as more of the compression cycle is being completed after ignition. This "negative work" is a bad thing.

Ultimately Avgas (or 50/50) has the potential to produce more power than normal pump UL however if you're running normal road bike head volumes (std NSR squish is a fairly slack 1.2mm) and stock ignition timing you will make more power on normal pump UL.
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Hi Paul ,

if your nsr is even slightly tuned it will be safe on pump fuel . You can mix 10- 20 % avgas for eg to add some safety on your jetting as unleaded pump fuel is very unforgiving as you tune the motor up ,
the higher spec you tune your bike the greater the need to jet it correctly .

Hey mate, you've got Glenn Mason's old bike (black MC21 with a white stripe across it) which went to Jason Dawes last i heard before you bought it. Its a reliable bike with good, sensible mods and a proven good performer in its current setup so if you run it as it is, on the 50/50 fuel mix that Glenn used then you'll know for sure you're well in the green. If you go to just plain 98 Ultimate unleaded (premixed of course) then you'll want to look at messing with the jetting. As far as i remember its got an NSR world carbon carb shroud, foam filters and Kerry Dukie did some work on the suspension.

There's tv footage of it in its old colour scheme at Pukekohe: http://www.youtube.com/watch?v=5zijfYb3Yk0

Go to 5:00 minutes in and look for bike 555. You see it again at 8:00 minutes - avoiding a load of carnage - its a good race!
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After years of moaning about immigrants now i am one...

thats the bike

sounds like its got fairly big mains in it now, but what ever the go a few plug chops will be the order of the day

That looks like a good race ! Pity about the guy who fell off , looks like he got a fright when he was lapped .
Do those 450'S still race ?

Yeah they're quite popular now - you get the very best chassis and braking packages but with a castrated engine so you can race with the 650cc twins and (up to) 350cc two strokes in F3. The guy on the silver SV won the F3 title again this year - on the same bike - its got a bespoke frame and carbon wheels among other (unfair and expensive) advantages. Skachill on the 450 GSXR only won in this old video because he's one of the country's outstanding young talents and is nowadays a title contender in NZ supersport (F2). Its interesting to note that Skachill also won a club level 600 supersport race on an NX5 RS250 earlier that year.
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After years of moaning about immigrants now i am one...

That is serious competion , i think you need to develope a 350 nsr !