Modern Buddy

Looky what popped up on the Scooterworks website:

"Sito Plus Exhaust; Stella 4T
This high quality Sito plus performance exhaust won't break the bank, only hearts.
For Genuine Stella four stroke."

http://www.scooterworks.com/sito-plus-e ... -12475.php

My Stella is brand spankin' new, so I will have to wait a bit, but I sure do wonder what the real world benefit will be.

but I sure do wonder what the real world benefit will be.

I doubt they will crack and require welding like the stock ones I read about do. But being that it's for a 4 stroke, they probably will not provide the same level of performance boost that a tuned 2 stroke exhaust can over the stock one.

What other work will need to be performed to install this? I've heard that you might have to rejet when you put these on?

Probably will need a rejet, as it's less restrictive without the catalytic converter in the downpipe. I suspect that the 4T Sito pipe costs the rider a little torque but allows the motor to rev a little higher.

Looks a lot like a Sito (non plus) replacement for a stock 2T muffler, except for the downpipe. They didn't bust the bank on R&D, but it's good news for folks when they're out of warranty and the stock pipe breaks (again).

SWEET! Well, sweet price at least.

Not sure how much performance gain anyone gets solely out of adding a pipe. It might do well in conjunction with the bigger carb, though.

I'm on the "to mod/not to mod" fence with my Stella 4T right now, but having a much cheaper pipe available adds a little more weight to the "to mod" side.

Eric,

I've been investigating the carb thing. Bought jimmbomb's old Pinasco setup and figured out a few things. Primarily, it's a fair bit overpriced. It can be replicated for about $135 plus shipping with real Dell'Orto bits ("special" manifold adapter included). I built a second one from Treats moped store to confirm that (and be ready when I get my own 4T ).

I'm hoping to install it on my buddy's 4T soon and get it tuned, then I'll document the how to make it work. Out of the box, it came with the wrong throttle slide for a 4T. The slide would be appropriate for a smaller engine and generates too much vacuum at idle to half-throttle for the fuel needle and jetting installed. I bought a range of jets, a few different slides and fuel needles in order to figure out the right configuration for a four-stroke 150cc.

I have been doing some research trying to wrap my head around what this pipe will really do. I know that a pipe added to 2 Stroke motor has a much different affect than one added to a 4 stroke. The 4 stroke will breathe better, but I cannot see getting the scavenging affect that a 2 stroke pipe would. I guess someone will need to be a guinea pig and buy one... My Stella has only 11 miles on it so far, so I have a ways to go...

In a four-stroke, the exhaust scavenging depends on valve timing and duration. The camshaft dictates how far and how long the intake and exhaust valves are open. There is a point at which both valves are open, which is referred to as overlap. As the combusted gasses are pushed out of the exhaust valve, the intake valve is opened. The vacuum created by the expelled exhaust aids the atmospheric pressure which is driving the fresh charge into the cylinder, resulting in increased volumetric efficiency. An added benefit is that some of the fresh charge helps cool the exhaust valve.

The upshot of this is that the four-stroke exhaust is not required to provide backpressure in order to complete a scavenging cycle. The less restrictive a four-stroke exhaust is, the more effectively the exhaust gasses can be expelled from the cylinder. I suspect that there are elements of the design which can optimize the amount of vacuum generated by an exiting exhaust pulse in order to increase the scavenging (eg. pipe diameter, length and taper), but the result would be less dramatic than a carefully constructed expansion chamber would have on a two-stroke engine.

Those who mention having to wait, why? To complete break in first or some other reason?

My Stella is brand new, and I 1) want to break it in properly, and 2) want to wait until the warranty is past.

Break in makes sense but you do know it has no effect on your overall warranty right? Under Magnusson-Moss a warranty can't be voided due to upgrades/changes etc. unless it is proven that was the direct cause of a warrantable failure and even then only to parts and systems directly related. That of course presumes U.S.A. ownership and residence.

I thought if you upgraded the exhaust you would need to make other modifications in order to realize the potential of changing the exhaust. And it's those addl changes that could have an impact to your warranty coverage. I'm 9 months into ownership of my 4T and its that concern that has prevented me to doing any performance mods. Strictly cosmetic thus far.

...but what does it sound like?

We just got these in at Motoretta in Toronto, I'd offer free labour to anyone wanting to try one out and be a guinnea pig for us. Just not today, Saturdays are bonkers for us.

So what would give me the most performance gain, or bang for my buck if you will.

Doing an exhaust upgrade, or something else?