Aftermarket Cylinder Quality

[Ketchup]

Ok thank you. I have been searching to find examples of guys trimming a little skirt for more intake timing. I just don't want to grind the intake yet. I might try a 50mm pop up windowed piston from a 268 in the future with this cylinder, and they are shorter skirt. So if I ground on it now, it might be too much intake with the 268 piston.

The popup is underwhelming compared to good port work. That cylinder does look like a deal. If you do decide to grind, go through the plating with diamond. Especially the chamfer.

 

[isaaccarlson]

The thing with popups is the ridge can deflect the charge up and mess up the loop scavenging. A more gentle slope, rather than a ridge, can work well if done right, but can still leave a pocket of burned gasses at the rear of the cylinder. More compression isn't always a good thing. It makes more heat. You don't need loads of compression to make good power. My ported 350 makes as much power as my stock 372xp, around 5 hp with around 180 psi (no popup). I have started/run saws at gtg's that appeared to have near zero compression but made gobs of power. It's all in the porting.

 

[Ketchup]

White box 460 Big Bore:


The foredom should be able to clean up the rough edges and improve the ports where necessary. I might have to epoxy the transfers to improve the exit angles. $27

 

[isaaccarlson]

I'm not sure what's in this one, but it runs ok.

 

[isaaccarlson]

White box 460 Big Bore:


The foredom should be able to clean up the rough edges and improve the ports where necessary. I might have to epoxy the transfers to improve the exit angles. $27

Wow. Looks rough, but for $27, as long as it cleans up, I'd be happy.

 

[Ketchup]

Wow. Looks rough, but for $27, as long as it cleans up, I'd be happy.

Agreed. The port edges aren’t bad but the tunnels need serious clean-up. I’m curious if I can get a 54mm to perform. There’s no good OEM option and I hate the brittle plating in Hyway. I’m not out much if it’s a flop.

 

[Powerstroke Cowboy]

White box 460 Big Bore:
View attachment 398780View attachment 398781View attachment 398782View attachment 398783

The foredom should be able to clean up the rough edges and improve the ports where necessary. I might have to epoxy the transfers to improve the exit angles. $27

That's cheap price wise.

Is it just me, or are the threads in the spark plug whole not good? Those ports look like they will clean up good.

 

[Ketchup]

That's cheap price wise.

Is it just me, or are the threads in the spark plug whole not good? Those ports look like they will clean up good.

Good eye. That’s pretty bad.

 

[Powerstroke Cowboy]

Good eye. That’s pretty bad.
View attachment 398788

Ouch!

 

[isaaccarlson]

Oops, missed that!

 

[slackinoff]

@Ketchup - thank ya for the tips and info on the pop up! I just kinda was curious to try it using a 268 piston since they are much lighter. I have one (268 pop up) on hand and it’s gonna need about .040 taken out of the squish since the 268 piston is a lil taller….rough measurements puts me awfully close to the ring of death so….prob not the cylinder to try this on.

Trimming the piston skirt came out great. Snuck up on it and it’s opening all at once and at 77 degrees. Might effectively be more like 79 or 80 with it opening all at once?? But I’m not widening the port so it should be ok….I think.

 

[qurotro]

Ok thank you. I have been searching to find examples of guys trimming a little skirt for more intake timing. I just don't want to grind the intake yet. I might try a 50mm pop up windowed piston from a 268 in the future with this cylinder, and they are shorter skirt. So if I ground on it now, it might be too much intake with the 268 piston.

The 268 slug is higher than the 372 piston. If you get a pop up 268 I suspect you would even hit the spark plug with it when lathed?

 

[Ketchup]

@Ketchup - thank ya for the tips and info on the pop up! I just kinda was curious to try it using a 268 piston since they are much lighter. I have one (268 pop up) on hand and it’s gonna need about .040 taken out of the squish since the 268 piston is a lil taller….rough measurements puts me awfully close to the ring of death so….prob not the cylinder to try this on.

Trimming the piston skirt came out great. Snuck up on it and it’s opening all at once and at 77 degrees. Might effectively be more like 79 or 80 with it opening all at once?? But I’m not widening the port so it should be ok….I think.

View attachment 398817View attachment 398818View attachment 398819

I’ve only done the 268 piston in a 372 twice (one slab side, one windowed). Neither impressed me. They revved nicely but didn’t gain the torque I prefer in a 70cc saw. No harm pursuing your own experiments though.

How do you like the increased intake?

 

[Ketchup]

The 268 slug is higher than the 372 piston. If you get a pop up 268 I suspect you would even hit the spark plug with it when lathed?

A guy on AS cut one from a popup. It cleared but IIRC he felt the extra weight and scavenge pattern issues weren’t worth it.

 

[isaaccarlson]

I have removed the flares from the sides of pistons in husky 350's with great results. It really opens up the transfers.

I'd be willing to try it with a 372 as a way of lightening the piston. You don't have to worry about ripping the rod bosses out of the piston because the piston is always being pushed down against the rod when the engine is running. I have removed large amounts of material below the pin bosses, to the point I thought they would fail, but they revved to 15-16k no problem.
I can't say every piston will hold up or that you can't go too far, but I have removed metal that most folks would think HAS to be there, with the bottom of the pin boss even being thinned a little. So far so good.

 

[qurotro]

I’ve only done the 268 piston in a 372 twice (one slab side, one windowed). Neither impressed me. They revved nicely but didn’t gain the torque I prefer in a 70cc saw. No harm pursuing your own experiments though.

How do you like the increased intake?

I don't like the way it run with a 268 piston in 372 either.

 

[slackinoff]

@Red

The 268 slug is higher than the 372 piston. If you get a pop up 268 I suspect you would even hit the spark plug with it when lathed?

I haven’t heard of it happening….but it is something to consider.

 

[slackinoff]

A guy on AS cut one from a popup. It cleared but IIRC he felt the extra weight and scavenge pattern issues weren’t worth it.

Hey did you mean the "lighter weight" was not worth it? See scale pics above.

 

[isaaccarlson]

Here is one of the pistons I took the "wings" off of. Still running strong in a high strung ported saw after about 4 years.
I don't remember how much weight I took off, but it was a lot lighter.

 

[Ketchup]

Hey did you mean the "lighter weight" was not worth it? See scale pics above.

Yeah, it wasn’t my thread but I think he mentioned it as though a normal 268 slug cut to a popup would be lighter than the one he cut out of a Hyway 268 factory popup. Seems to me the squish and scavenging dynamics would be more of an issue than weight with a tall popup.

I’m all for lightening pistons. I agree that you can take a surprising amount off without negative consequences. It can be important how the shapes of the piston push the case charge and contribute to case volume. I’m a big fan of eliminating piston skirts that obstruct transfer lowers. In my mind the piston stroke creates a pressure wave that continues downward after the piston achieves BDC. Many people disagree.