From exhaust porting to your wife's snowmobile... Here at the Rubber Side Down Showdown, we have it all!!

BTW, some of the new 2-stroke outboards claim to be just as clean and efficient as the 4 strokes & still making more power.

I've got a 4-stroke weedeater now and IT SUCKS! It's heavy, less power even with a bigger engine & it doesn't have that 2-stroke smell that gets me fired up on a Saturday morning. Maybe I'll port the head on that sucker... What do u think Bill??

'scuse me, I confess I am "snow ignorant" pretty much.  

To me that's the dingus that gets you to the top of the bunny slope so you can fall down a lot on the way to the bottom.

          

And yes we do enjoy our windy meandering little discussions around here quite a bit.

Johnson/Evenrude/Mecury/Mariner ARE trying to come up with a decent fuel economy and pollution control out of a two stroke engine.   They have made improvements but are not EPA compliant but for another few more years.  They are frantically buying time while they work on their new stuff.

They certainly can see the handwriting on the wall though --  and guess who is busy developing a full line of four stroke line of outboards to try to compete with Honda and Suzuki outboards .....

http://www.outboardrepairs.com/4_stroke_outboards/#johnson_4_stroke_outboards

http://www.marineroutboards.co.uk/products.php?range_id=1&section_id=NULL

Ditto for all the rest of the "same name" American outboard companies,  they will have different cowlings but very similar 4 stroke engines living underneath it.

Can't speak to weedeaters and chain saws -- I think your package size dictates a very light two stroke single cylinder engine pretty much.  

Research shows that Honda, Ryobi, Stehl and others all have commercial 4 stroke weed eaters out there that folks don't like because of the extra weight -- chainsaws and weedeaters really have packaging/size limitations that may keep them 2 stroke even if EPA doesn't care for it.

Now, ask yourself this -- if chainsaws and weedeaters get an exemption from EPA to stay two stroke why can't the Chinese make a cheap 50 hp RD400 rip-off copy and bring 'er on into the USA ????

Like I said, some things simply have package/size limitations and the RD 400 was as big as it could possibly be and still be a neat/nifty pocket rocket like it was !!!!

Finally, somebody said it.

only if you're running an open pipe...

Porting will just allow a less restrictive pipe to flow at  it's full potential...  
Probably won't do anything with a stock muffler...

That pipe is perfect...
You may run a little leaner after the porting, it's hard to say until you do it. Be prepared to check it but If I had to take a guess I'd say you will be fine, especially at your elevation. We're not talking about major surgery here, just letting your lung exhale a little easier. Your engine will rev up a little faster & it will be a little more efficient. There's potential for more power, because your getting more bang out of the work the engine is already doing.

What pipe is that?

Quote:


most automotive companies don't port thier heads.. the odd shapes inside and around cast cylinder heads are mostly due to the casting process and how they have to make the molds.  Also some of those odd shapes are there for extra structural support to prevent cracking.  

In order to get smooth intake and exhaust ports it would need machining which is an extra expencive step in production.. so cost is the main reason why ports are not polished and smooth..

You do lose a little low end power when you increase exhaust flow.. if you equally increase intake flow you should keep your low end power though.. the reason is compression.. at low RPMs there isn't enough momentum in the air charge to pull it in especially with a longer intake duration(as seen in performance cams)..  when you have a restricted exhaust some of the gas is not eliminated on the exhaust stroke and stays in the cylinder.. but that's ok because you can't get the air into the cylinder fast enough anyways.. but the extra gas contributes to higher compression which gives you more low end power.

at higher RPMs the air actually forces itself in by momentum even after the piston is done sucking it in.. This allows you to get more air/fuel and more power.  

the power you get in your engine is a direct result of the pressure caused by fuel combustion.  In a case where the air/fuel is less than optimal as in low rpms having extra gas in there increases the pressure also increasing power..

Porting and polishing are usually just to get that last bit of power you can't get any other way.. It's also free if you do it yourself, but very labor intensive(expensive if you have someone else do it).. a new exhaust or a free flowing air filter will give more power, but if you've already done all of the above you might get a few extra pony's from it..

almost everything to improve performance is done to increase air(oxygen) in the combustion chamber.. then as a secondary thought of course you can easily increase fuel to match the air..