Numbers on a ported 390

[Ironworker]

What's a good recipe for porting a 390

 

[David Young]

102 122 78

 

[Chainsaw Jim]

I'd say a good recipe would be to leave the port timing alone and give it some good breathing treatment with transfer to case matching and opening things up a tad bit.
A muffler mod alone really wakes these things up, so it won't take much to make this thing noticeably stronger.

 

[fearofpavement]

Husky 390? Or Stihl 390?

 

[Ironworker]

Husqvarna.

 

[wcorey]

102 122 78

390xp?
How do you get the exhaust to 102? Didn't think that was achievable on this saw by any normal porting technique.
And then you would definitely be epoxying the intake to get back up to 78...

 

[blsnelling]

390xp?
How do you get the exhaust to 102? Didn't think that was achievable on this saw by any normal porting technique.
And then you would definitely be epoxying the intake to get back up to 78...

I have found that the 390 really wakes up with more intake. Matter of fact, I find it key to stand out performance.

 

[Ironworker]

I have found that the 390 really wakes up with more intake. Matter of fact, I find it key to stand out performance.

Width or duration

 

[blsnelling]

I go with 18-20* blowdown and put the intake at 85*. At one time I preferred the 385 to the 390 because they just didn't respond as well. Giving the 390 more intake made a big change in my results. Trim the intake piston skirt to get your duration. If you don't like it, you can easily throw a new piston in it and be back where you started. Additionally, I fully case match the cylinder base to the crankcase using the gasket as a template. I also widen the intake and exhaust ports to 65% of the width of the bore. I also widen the transfer ports towards the intake. BTW, do not try this recipe on a 372 or 346, you'll kill them.

 

[Four Paws]

What's a good recipe for porting a 390

Weren't you trying to sell a ported 2188? Whether you like it or not, having the numbers out of that saw will give you an idea of what to do, or not do.

I think it's more about the shape and less about the numbers.

 

[Chainsaw Jim]

I go with 18-20* blowdown and put the intake at 85*. At one time I preferred the 385 to the 390 because they just didn't respond as well. Giving the 390 more intake made a big change in my results. Trim the intake piston skirt to get your duration. If you don't like it, you can easily throw a new piston in it and be back where you started. Additionally, I fully case match the cylinder base to the crankcase using the gasket as a template. I also widen the intake and exhaust ports to 65% of the width of the bore. I also widen the transfer ports towards the intake. BTW, do not try this recipe on a 372 or 346, you'll kill them.

Have you tried windowing instead of trimming the skirt to maintain piston stability?

 

[blsnelling]

Windows in the skirt? I would think they would be too close to the edge and liable to crack.

 

[wcorey]

I go with 18-20* blowdown and put the intake at 85*. At one time I preferred the 385 to the 390 because they just didn't respond as well. Giving the 390 more intake made a big change in my results. Trim the intake piston skirt to get your duration. If you don't like it, you can easily throw a new piston in it and be back where you started. Additionally, I fully case match the cylinder base to the crankcase using the gasket as a template. I also widen the intake and exhaust ports to 65% of the width of the bore. I also widen the transfer ports towards the intake. BTW, do not try this recipe on a 372 or 346, you'll kill them.

What * number do you use on the exhaust?

 

[Chainsaw Jim]

Windows in the skirt? I would think they would be too close to the edge and liable to crack.

I guess...If you were to put the window that close to the bottom edge, but you don't need to make it that close. I've heard old school builders talk about doing it with incredible gains. And like you said...you're not messing your cylinder up to try it out.

 

[tree monkey]

with a reed block