How to create a fire breathing GN250

**ready4whatever** · 23rd July 2009, 14:35

put a massive spoiler on the back it'll go hard

**vifferman** · 23rd July 2009, 14:39

Originally Posted by ready4whatever

another dredged thread

What is it with you?
Do you have shares in a trawler or summat?

**The Pastor** · 23rd July 2009, 14:45

i think a cam regrind would and a big bore kit would work wonders on a gn250

**Brian d marge** · 23rd July 2009, 16:53

Power =( nf Nv N Vd Qhv p ( F/a ) ) / 2

Nf = fuel conversion efficiency ( V good is 30% my enfield is 18% )
nv =Volumetric eff
N = Rps

Vd = volume displacement

p = density inlet

f/a = fuel air ratio

there are different versions of this , but basically the answers are there

becareful with cams, they aint the panacia of engines

Stephen

also if for some reason u get huge power from the engine , are the othe parts rated for the increase in power

got some money?

**The Pastor** · 23rd July 2009, 17:23

Originally Posted by brian d'marge

power =( nf nv n vd qhv p ( f/a ) ) / 2

nf = fuel conversion efficiency ( v good is 30% my enfield is 18% )
nv =volumetric eff
n = rps

vd = volume displacement

p = density inlet

f/a = fuel air ratio

there are different versions of this , but basically the answers are there

becareful with cams, they aint the panacia of engines

stephen

also if for some reason u get huge power from the engine , are the othe parts rated for the increase in power

got some money?

so what would you suggest for gn250 power mods?

Is ur engfield modified?

**Rodney007** · 23rd July 2009, 17:41

Originally Posted by FzerozeroT

Hollowmen asked so lets figure this one out:

INCREASING COMPRESSION
borexstroke = 72x62.1
so displacement = 252.8cc
divide by 8.9 = combustion chamber volume = 2.8cc
we want 10:1 so ideal combustion chamber volume = 2.5cc
difference of 0.3cc is taken out of barrel so as to not change combution chamber shape.
So i ended up with 0.767mm shave to achieve 10:1, because of increased compression 96 would be used, flame propagation would be faster so therefore more controlled
Because of the head being lower the slack would have to be taken out of the cam chain as well.

ADVANCE IGNITION
simple as making the woodruff key thinner and rotate the flywheel, would need to be done on dyno.

EXHAUST
Ditch it from the footpegs back for some straight pipes. Probably lose power but the diapproving looks from old ladies makes it worth it.

CAMS
throw a few $$ at a cam grinder and see what he comes up with, I'm thinking you want stage3+ and you'll need to replace the valve springs at the same time with something a bit more heavy duty.

CARBS
Will need some serious work with these mods, specialist work with that high tech system.

TURBO/NOS?
You know you want it.

sounds like a whole bunch of bs to me, ...

any pics yet?

**Pedrostt500** · 23rd July 2009, 18:03

I think just junk the GN motor and slot in a SV 1000 donkey.

**SARGE** · 23rd July 2009, 18:07

cheaper, more effective and heaps more fun....

**Brian d marge** · 23rd July 2009, 18:11

Originally Posted by renegade master

so what would you suggest for gn250 power mods?

Is ur engfield modified?

very modified I race it ........ try increasing the fuel conversion efficiency after all that's where the process starts, ( but if you release heat ,,,you must control it !)

if you have 1 gram of fuel...............

Stephen

**FzerozeroT** · 23rd July 2009, 21:54

Well, this thread just came back from the dead, good thing Jackos casket is sealed with concrete.

I don't think that anyone around KB now has appreciation for these quality threads, they were from a time when KB posts were free from trolling, input was constructive, and those who posted actually rode bikes.

**gwigs** · 24th July 2009, 10:43

Just smoke a shit load of weed before you ride it ...wont be any quicker but it will certainly feel like it

**The Pastor** · 24th July 2009, 10:56

Originally Posted by gwigs

just smoke a shit load of weed before you ride it ...wont be any quicker but it will certainly feel like it

typicall comment from someone who lives in the haven

**The Pastor** · 24th July 2009, 10:57

Originally Posted by brian d'marge

very modified i race it ........ Try increasing the fuel conversion efficiency after all that's where the process starts, ( but if you release heat ,,,you must control it !)

if you have 1 gram of fuel...............

Stephen

do you have a thread or blog or something about ur mods? You sound like you have a bit of knowledege in making things go faster

**tychver** · 24th July 2009, 11:19

A properly jetted modern motorcross carb in the 35mm range and a decently flowing exhaust would make a fair bit of difference. Whether it's worth the $1200 dollars is a different matter!