Sep '18 Hyway Big Bore 346xp (45mm) vs OEM NE Mahle

[Spring1898]

Greetings all, just picked these two up to do an informal comparison.
Cost of the Hyway $79
OEM = $110

Overall I am intrigued by the Hyway Big Bore version. We already know from testing by a certain Dentist that the aftermarket Big Bore 346xp cylinders can make good power compared to OEM with minimal to no work.

Here is a close up as to why that might be.

Description:



Cosmetically, the OEM cylinder has nicer finish. No surprise.
The Hyway fins are also thicker, leading to a 2.4oz increase in weight.

The coating inside the Hyway is smooth in both. Hyway has a coated chamber. Both chambers appear to be the same size.

Note the OEM decomp port is more off center than the Hyway



Intake and Exhaust:



The Hyway exterior exhaust and intake ports are notably larger, averaging larger 1/16" in each dimension.

The interior sides are also larger and wider by a lesser degree probably between 1/16" - 1/32"

Ridges on the inside of the ports of both cylinders are present but minimal.

Smoothness and uniformity of the channels goes to OEM. A few minutes with a dremel would equalize/improve the Hyway. The intake port on the Hyway is slightly off center (or rather the enlargment is off center).

Bevelling around the intake and exhaust is less uniform on the Hyway but adequate. There is sufficient doming that I would not be concerned for caught rings.



The transfers: Things are a little more interesting here as the Hyway transfers are basically factory ported.



Interior openings on the uppers seem very slightly larger on the Hyway. Pictures don't demonstrate this well due to the uneven bevelling. There is minor slag present inside the transfer ports. It is smooth, but still larger than what is left in OEM. Interestingly there are large portions of the transfer that are smoother than OEM.
The lip that hangs down from the cylinder in front of the lower transfer has been milled back slightly on the Hyway cylinder and is now 0.05" above the base.

Now here is the most interesting/different part.
The OEM transfers follow the elliptical path from lower to upper with uniform dimension.
The Hyway has a narrower divider between the two lower ports which increases the size of the opening. While it maintains the curvature toward the outside, the inner portion is cut straight up the side. The ports are effectively the shape of a woodruff key rather than the 'C' of the OEM cylinder. The "porting" on the Hyway appears in excess of what the extra displacement should need. Not a bad thing.

Another benefit I see is that if you had a long enough head you could effective clean up almost the entire transfer without a right angle tool.


Observation:
The "Big Bore" aspect isn't much, it is a nominal increase of 0.7mm.
Unlike other "Big Bore" applications, the 346xp has more than adequate material/space in the sides for larger transfers.

 

[Spring1898]

Pistons:
Nothing too interesting here. Skirt thickness is the same, casting is slightly different. Ring groove on the highway is uniform
Slightly different casting underneath, OEM a bit more beefy

 

[Deleted member 150358]

Seems like they are working to actually innovate instead of just knockoff OEM stuff. The h272 popup kit looks like fun.

 

[jltrent]

For $30 bucks more I would get the Mahle. From my experience the liner is not as thick in the AM cylinders and want make as good compression.

 

[cuinrearview]

I'm new at porting theory, but wouldn't larger uppers hurt transfer velocity? @drf255

 

[drf255]

I'm new at porting theory, but wouldn't larger uppers hurt transfer velocity? @drf255

The answer is “maybe” unfortunately.

If one is increasing the bore size, bigger lowers will add needed case volume to the saw. Maybe Hyway knew that, maybe they didn’t.

You’re right about the velocity issue. Case in point, Dolmar 7900. Smallish tiny ports with huge Blowdown. Hog them out or raise them up, you kill the saw.

The plated chamber bothers me. Heat transfer is affected. The hotter a chamber gets, the lower rpm it will run safely at. It will simply 4 stroke at a lower rpm. Unless they lowered the static compression to compensate. Again, not sure how much is accidental vs purposeful. One needs to think about why the oem went through the added expense and trouble of leaving their chamber unplated. It wasn’t an accident.

For $30, I’d get the Mahle as well. Plus, should one ever decide to part with the saw, which one do u think would sell easier?

 

[cuinrearview]

For $30, I’d get the Mahle as well. Plus, should one ever decide to part with the saw, which one do u think would sell easier?

It seems perfectly logical to me, but logic seems to go out the window around this place.

Thanks for the answer on the ports Al, clear as mud. I think aftermarket parts remain serviceable at best, destructive at worst. Having the ability and desire to finish what those on the other side of the ocean started certainly appears to help.

 

[drf255]

Oops, you said larger uppers, not lowers.

In general, you are correct. Factory sized tight uppers tend to make better torque than giant hogged out and extended ones.

But that all depends on the saws purpose. A cant cutter/limbing saw will be different than a saw one would mill with.

I built an 026 with huge ports when I started out. 4 stroked to 16500 and fell on its face in the cut. The ones I generally do now 4 stroke to 14k but can pull a 20” 3/8 bar with ease.

 

[drf255]

Here’s an 024 Super I just built running a 24” 3/8 chain, standard 3/8, in hardwood.

It’s not the correct size bar for this saw, by any means, but you can get the point.

Factory width uppers.

 

[wcorey]

To me the big performance downfall with this cylinder is what the op describes as the transfer profile being "the shape of a woodruff key".
That straight up inner wall means the tunnel bulges larger in the middle with smaller entry and exit,
generally not good for maintaining velocity and direction when pushing air through a plenum.

They just don't seem to get the whole direction and flow thing...

 

[Spring1898]

I thought of that too, but then most porting jobs do the same thing, so I assume the net increase in size overcomes the decrease in flow efficiency

The question isn't really 'will it work' because they do work well and seem to perform on par or above a stock OEM cylinder if they are allowed to breath, at least according to the few tests I have seen.

If you were doing all the porting on OEM yourself, it could turn out better. This does most of the work for you and just needs minor clean up you don't need special right angle tools for.
But a guy who machines all his own stuff and has enough money to play with would have no reason to mess with these.

Hyway has pop-up pistons available for these (and others). That would be a fun back to back comparison.
That kit is only $87 direct from overseas. (whole kit not just the piston)
May have to bug @Mattyo to test one of those in his 350 builds.

 

[cuinrearview]

Is the $23 difference worth it? Are you changing the ring to a caber? Is the labor the same porting both? Are the materials comparable? I know that one member loves to flame me for this, but it just doesn't seem worth it to me given the questions.

 

[sunfish]

OEM is by far the best option!

 

[Mattyo]

yeah, i dunno if the difference in money justifies not getting oem.

for me, i just don't like grinding on pristine oem cylinders. i do it, have done it, but don't like it. the am cylinders, hyway or otherwise i grind on without 2nd thought.

which is better is really tough to say. if you just want to slap on best quality, get the oem, obviously. if you want to fiddle, then fiddle with whatever you want.

so far, i like fiddling and getting these am heads to run with the big dogs. but maybe thats just me.

 

[Spring1898]

I don't think it does for a lot of people, especially when you can find OEM (husky) even cheaper if you hunt around.

But I as well don't like messing with brand new OEM on principle.

I am looking forward to playing with these though

 

[smokey7]

Personally feel that the plating is just as hard and strong as oem on the hyway kits ive seen. I got a kafar kit o bought for 40 bucks from my buddy missing the piston. That 346 setup lightly ported runs way way better tgen my stock 350 set ran. I have a hyway 346 kit here now that has copied oem to the t. Will do the same porting i did to kafar kit and see how it does. I would run bout 95% of hyway kits out of the box without reservation. The last 5% only "might" have actually needed bevels touched up. Interested to see how they run and last for you. My kafar kit has atleast 50-60 cords under its belt. I have gotten my money out of it for sure.