Considering a +3 stroker crank now and just wondering what sort of modifying to the port i will have to do with this to get the most gain with the stroker
Karterphil, here is the secret to making power... PLAN
Pressure, average pressure in the cylinder
Length of stroke, part of displacement
Area of the piston, other component of displacement
Number of power strokes per minute, takes into account rpm and cylinders
These factors are multiplied together and then divided by a constant to get gross hp developed. This comes from back before even gas (petrol!) engines. We don't need to get into complicated math to see that the percentage that we increase pressure (which comes indirectly from compression and flow), displacement, and rpm has a direct relationship with power.
Your 3mm stroker will raise your displacement from 195cc to 205cc, a 5% increase. Expect this same increase of power if nothing else is changed.
So if you made 17hp, expect it to jump to 17.8hp. Sad isn't it?
Well, Luckily there are other factors at work too. By increasing the displacement you are potentially increasing the compression (head volume stayed the same) and a stroker can potentially change the port timing which can affect the rpm range. So if you increased displacement by 5%, compression (and potentially pressure) by 5%, and raised the rpm of the powerband by 5%, this could be a 15% power increase.
So your stock 17hp now becomes 19.5hp. Better, but you were looking for more, right?
There is more. Here is the good news:
A Blaster motor is heavily detuned, so unlike most motors, you can expect to increase the average pressure about 50%.
That is a lot. Most motocross engines and 4 strokes are lucky if you can raise average cylinder pressure by 10%.
Displacement can be raised 5% by stroke, 6% by boring, 19% with a Big Bore Kit, or about 25% maximum.
And rpm, this comes from port tuning. This engine has a fair amount of rpm potential (trading reliability). To raise it 20% is totally possible.
Add these all together comes out to about 100% potential power increase with your 3mm stroker, or about 34hp.
About 40-45hp would be near maximum for an all-out narrow powerband, high rpm drag engine.
So, now that you know how it works, getting back to you original question:
"what sort of modifying to the port i will have to do with this to get the most gain with the stroker"?
You can see the stroker truthfully represents only a 10% increase of power (compression and displacement).
It is the port timing affecting the rpm range that can give you the real (20%) power boost. This you can do without the stroker.
To prove it to yourself, raise the cylinder by adding an extra basegasket and get the head back in place by leaving out the headgasket and just using Yamabond or Hylomar sealer. Yes it will work for a test. I have not done it with a Blaster but have done it with Rotex engines. You can file or sand (sandpaper on glass) the head and cylinder flat if you want to run it longer like this. This effects raising the ports without actually grinding the cylinder out. It allows you to test and feel the effect of increasing port timing without ruining a cylinder. It will raise your rpm range and hp, but kill some low rpm power, which a quad could really use.
So, to answer your question, displacement and port timing are two different power effects. With the extra displacement, you can shove the powerband higher because you have the extra bit of displacement induced low end torque. You can also tweek the compression while at it. Vitos has thought it all out with their 1mm spacer under the cylinder with their 3mm stroker kit. Displacement, port timing and compression all boosted.
But then, you really don't need a stroker crank to get the rpm and compression gains...
