modifing husqvarne 372xp wondering iff anyone would have sugestions

[mathieu larocque]

I want to port my cylinder and I am looking for tips

 

[mathieu larocque]

I made the head, what do you think?

 

[CR888]

I think it looks fantastic and done well! l hope other can advise you on a good porting recipe but my you have alresdy demonstated some true talent making a two piece head. I don't think this looks like a 'practice' cylinder so maybe a second cylinder may be a good idea to test various porting ideas so you get a top result on the two piece. Very inspiring!!

 

[mathieu larocque]

I think it looks fantastic and done well! l hope other can advise you on a good porting recipe but my you have alresdy demonstated some true talent making a two piece head. I don't think this looks like a 'practice' cylinder so maybe a second cylinder may be a good idea to test various porting ideas so you get a top result on the two piece. Very inspiring!!

Thanks! spent lots of time on the head, hope I can do as good on the cylinder and find a good porting idea for my very hi compression ratio

 

[weimedog]

very nice! better upgrade those bearings in the bottom end! Good NSF or Nachi's at a minimum. Are you going to start with a little higher exhaust port? In the mid to upper 90 degree after tdc range?

 

[mathieu larocque]

I'm not quite shore, i've ported a few cylinders before, but never changed the port timing. If I understand, I bolt the timing wheel on the crank, mark top ded center and turn 90 deg. the top of the piston will give me the maximum height for the port

 

[mathieu larocque]

If I port my cylinder, install a tune pipe and the high compression head, should I put a bigger carb and if yes to what extent

 

[weimedog]

All this is a blend of concepts. Answer is it depends but probably yes to a larger carb. Have to roll back to the beginning and decide what the goal is then build a blend to have the best chance of achieving those goals. Usually if you are going to the trouble of building a pipe... "more" of everything is the goal! But if the goal is more torque and power at lower than typical stock saw RPM's it's possible the stock carb size will help do that in conjunction with port timing and the pipe to enhance power at those RPM's. If your goal is to make more power period, packing more charge into the top end, burning that charge more efficiently, along with burning those "charge's" at higher frequency, you will need the ability to get more fuel/air mixture into that saw. Also this obviously will equal more heat and power! Simple as that. If that saw runs for a few seconds... the additional heat won't be as much of an issue as it would should that saw run hours on end in southern climates! The compression changes relative to the charge mass can be optimized to make a more efficient burn therefore more "power" out of each "pop" of a given charge amount/mass. The use of a pipe is about packing more charge into the combustion chamber so there is more mass of fuel/air in that combustion chamber when the spark plug lights is off. Altering port timing helps define the RPM the 2 stroke "pump" & use of primary compression most efficiently moves charge from the intake through to exhaust and effects everything. SO assuming you optimize all these things at the MAX RPM's that set of cases can handle before the bearings fry, then a stock diameter carburetor will be inadequate to feed the monster you have created. And like everything, there is a point of diminishing returns. THAT is the simple explanation.

All of this is a blend and this is why those who have spent the time working with combinations tested in the racing world and even in the work world are worth spending money with to help. Guys like "tree monkey" and "spencer paving" have spent time there and really should be the ones you hunt down for advice relative to piped saws...

 

[mathieu larocque]

All that sounds great, but unfortunately cant afford to pay anyone. Fortunately have access to cnc technologies, materials to perfect my parts and lots of patience. I want to get as much power as I can get out of this saw and wont be running it for hours. I have a good knowledge on two stroke motors but am looking for little tips from people that have modified saws before. My knowledge is more from two stroke motocross bikes, they can take lots of air and gas... just how much air and gas can the 372 take. Obviously going whit a bigger carb, but don't want to over do it and choke the motor. I was looking at the stihl 090 carb, would that be good or to big

 

[mathieu larocque]

working progress

 

[mathieu larocque]

Does anyone know if changing the timing buy slotting the coil to give the fire some advance could help at high rpm?

 

[fordf150]

Does anyone know if changing the timing buy slotting the coil to give the fire some advance could help at high rpm?

normally you file the keyway on the flywheel to advance the timing and leave the coil stationary. only takes .020 or so off the keyway to give as much advance as you'll need but advancing/retarding timing is a very big trial and error mod. some engines like more timing and some like less. that changes with the specific saw your dealing with as well as the mods you have done.

 

[mathieu larocque]

normally you file the keyway on the flywheel to advance the timing and leave the coil stationary. only takes .020 or so off the keyway to give as much advance as you'll need but advancing/retarding timing is a very big trial and error mod. some engines like more timing and some like less. that changes with the specific saw your dealing with as well as the mods you have done.

Thanks, I'll try filing the keyway, sounds better than filling the coil

 

[mathieu larocque]

A couple pictures, working progress, the pipe is almost done

 

[axlr8]

How did you do the calculations for the pipe?

 

[blsnelling]

You can play with it, but the 372 is one saw that I do not advance the ignition on.

Port timing is going to be quite different if this is to be a dedicated pipe saw. You need a higher exhaust port with a lot more blow down. My piped 390XP is all the way up at 83° on the exhaust, 115° on the transfers, and 85° on the intake. That gives you 32° of blowdown. These numbers are WAY different than I would run for a muffler saw.

 

[blsnelling]

That's a tiny combustion chamber! What do you expect compression to be?

 

[mathieu larocque]

How did you do the calculations for the pipe?

For the pipe calculations we looked around and its going to be trial and error we found a couple tricks to make the pipe ajustable

 

[mathieu larocque]

You can play with it, but the 372 is one saw that I do not advance the ignition on.

Port timing is going to be quite different if this is to be a dedicated pipe saw. You need a higher exhaust port with a lot more blow down. My piped 390XP is all the way up at 83° on the exhaust, 115° on the transfers, and 85° on the intake. That gives you 32° of blowdown. These numbers are WAY different than I would run for a muffler saw.

You can play with it, but the 372 is one saw that I do not advance the ignition on.

Port timing is going to be quite different if this is to be a dedicated pipe saw. You need a higher exhaust port with a lot more blow down. My piped 390XP is all the way up at 83° on the exhaust, 115° on the transfers, and 85° on the intake. That gives you 32° of blowdown. These numbers are WAY different than I would run for a muffler saw.

I did'nt want to go to far on the port timing, i'm still going to take some off but i want to go gradually, i don't want to go to far, but thanks for the tips, i could try that setup on my other cylinder

 

[Marshy]

This looks like a perfect project for a set of those hybrid ceramic bearings and a Dominant piston. That piston in conjunction your head might push the compression way to high and the only fuel it would tolerate might be alcohol.