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toes wrote:They are brilliant bikes,honda needs floging for not producing then ,or somthing like them.
But i just missed out on the last model cr 500 for $2000.now thats a bikeOn the left is the father of the BRP on a XR600.
The guy on the right riding a CR500 was saying that
after awhile the BRP would pass him and it was load.I hope he doesn’t ban me
tramo141 wrote:
Quote:kasuyaho wrote:Quote:Cylinder head work [img]http://www.obtrailriders.com/media/kunena/attachments/legacy/images/P10003411.JPG[/img]thats rough mate check out powerflow heads web site looks like it was done with a rotary file :unsure:
It looks rough from the discoloring.
What he did was make alloy wedges that are bolted into the floor of the intake,
then it was covered with resin first then Manely resin which is fuel resistant.In drag applications they just fill the intake with resin,
but with the heat cycle of our bikes, heating and cooling the resin would fall out.Also if the port is too smooth this will reduce flow due to fiction on the walls of the port,
so good head porters will leave the port wall finish rough to produce eddies.What he has done is reduced the port volume, this is what this head needed to make more torque,
by reducing the port volume / smaller port, it increased the flow of the head.The trick what he has done here is by reducing the port runner size it makes the bowl area
under the valve larger in volume by comparison.
This might sound nothing really that big, but what it does it this.
It increases air speed in the port and,When the intake valve closes the air does not stop moving,
it keeps moving towards the valve and with a larger bowl area the pressure is inceased in this area.
Drag race guys have been doing this since the 70’s when in some classes they were not allowed to increase the valve size
as the size of the valve was a restriction.
With this head the valve size is not a restriction.
With the pressure increase in the bowl area of the port, and the air speed higher,
when the valve opens again….being a higher pressure in the bowl area the air will move quicker into the combustion chamber,
plus the air speed in the port is higher than it was at stock so there is an advantage there too.
Being fuel atomization is better, which helps to create a better burn in the combustion chamber
which creates more power.There are alot of head porters out there that just make the port larger,
flow the head and give the head back to the customer with big flow numbers.
They put it on there engine and it makes power up top but in the lower rpm range it is sluggish
and not very responsive.
Due to low air speeds in the port.With this head by putting on a smaller carby or installing larger valves
it will compound the problem with lower air speeds again.Myself i never realized all this until i went and worked a little for this guy
in the US, Dave is retired now but in his day was one of the best 10 guys in head development
and engine building in the world.How good was he,
well he had a 292ci small block chev, with steel heads, 2 valve, roller cam,
single 4 barrel carby, cast intake manifold and it made just over 600hp.
That is a touch over 2hp per cubic inch.
Our 650R makes 1.2hp per ci, the latest WR type so called high tech engine makes 1.8hp per ci.
there 4 valves engines, dave was a 2 valve engine.And dave made that power 40 years ago
Dave’s car back then. oh and he did do bike engines too, Harley’s for Probike.
