Ironworker
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What's a good recipe for porting a 390
102 122 78
I have found that the 390 really wakes up with more intake. Matter of fact, I find it key to stand out performance.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...
Width or durationI have found that the 390 really wakes up with more intake. Matter of fact, I find it key to stand out performance.
What's a good recipe for porting a 390
Have you tried windowing instead of trimming the skirt to maintain piston stability?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.
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.
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.Windows in the skirt? I would think they would be too close to the edge and liable to crack.
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