395 xp big bore porting

[farminkarman]

Ok cool. If I take the transfers up to get a 20 blowdown will the longer duration matter?

The longer duration is what you need if you want the saw to make torque at a higher rpm.

Just wondering, to save some grinding on the cylinder upper transfers, could I grind a bit off the top piston edges to make transfers open sooner?

You can do that, but you are going to make your already loose squish even worse.

 

[stuh]

Oh yes, I didn't consider that. I'll just do the cylinder.
When it comes to widening the intake and exhaust, would the best way to measure how much I can go be to put bearing blue on the piston and gently scribe a line so I know how much to take off either side?

 

[EFSM]

Just wondering, to save some grinding on the cylinder upper transfers, could I grind a bit off the top piston edges to make transfers open sooner?

You can, although it lowers compression and can deflect the air flow.

 

[stuh]

As I'm pretty green to this, if I have 28* blow down, how will the saw perform with a 36" bar vs a 20* blowdown with the same bar?

 

[MG porting]

Here's the numbers for the bb no base gasket

Intake 102* abdc open for 152*
Exhaust 118* atdc open for 140*
Transfers 129 atdc
Squish 40 thou

OEM ,no base gasket

Intake 102 abdc duration 152
Exhaust 103 atdc duration 150
Transfers. 123 atdc
Squish 30 thou

Put the OEM cylinder on without the base gasket and do a simple muffler mod and call it a day.

 

[stuh]

Is that because those Numbers are good?

 

[thompsoncustom]

As I'm pretty green to this, if I have 28* blow down, how will the saw perform with a 36" bar vs a 20* blowdown with the same bar?

I'm not a pro at porting but my understanding is that more blow down will give better torque (to a curtain point) and less is higher RPM so more speed.

 

[thompsoncustom]

In order to make room for the bigger bore, they have to infringe on the transfer tunnels. Kinda defeats the point of having more swept volume.

Anyone try welding up the outside of the transfers and then grinding the inside out so they are just slightly bigger than OEM?

 

[stuh]

I think the heat from welding could possibly distort the cylinder a bit

 

[thompsoncustom]

I think the heat from welding could possibly distort the cylinder a bit

I've been some brazing up inside the cylinder head/dome area with success and failures(warping) but I would think that controling the heat on the transfer would be easy. Is it worth doing on the other hand IDK but if you were going to increase the bore and/or stroke seems like it would be worth it.

 

[stuh]

The brazing in the cylinder head, is that to increase compression?

 

[Mastermind]

Personally, I'd throw the Chinese top end in the garbage, and invest in some proper tools if port work is something you are interested in.

 

[Ketchup]

Raising the lowers will help with the smaller transfers and also make a better line of flow through the piston windows. Raise the divider up into the tunnels and thin it. Smooth out the transition into the lowers but widening and enlarging doesn’t seem to help.

On the BB, you can raise the exhaust higher and leave the transfers a smidge lower. The tight transfers want more blowdown, kind of like a 7900.
Cut the popup off the piston and set your squish properly (0.025” is plenty tight). They don’t need much band cut. Anywhere you cut the plating diamond is best. Cut into the plating, not from behind it.

Make sure the muffler is wide open. 395 make a lot of heat when you raise the RPM.