Sport moped exhaust on 66cc (Build thread)

[Frogslayer]

Polished intake for?

 

[FurryOnTheInside]

I got my engine from ebay. It's the most basic crappy type that probably isn't even sold at all in North America anymore. I used a £20 cordless drill to rebalance the crank and did my own ports with a £20 rotary tool on my coffee table lol. It is really smooth up to 7000, and 8000 feels fine for short periods.
Solid mounting into the frame is important. No rubber!

 

[Frogslayer]

How did it feel before the port and balance?

 

[Vikingimike01]

I got the cheapest one as well from china... But even then, it was better! It came with stainless steel hardware, allen hex screws, and upgraded gaskets too (That match the ports, for example the intake is like a grey colored, O shaped one. Mine is widened, matched (Both intake manifold and intake ports are matched too) and is brown. Same for the exhaust gasket!

 

[Frogslayer]

Definitely no stainless hardware or matched gaskets with mine. Easily 1/4"of gasket overhang on the exhaust and probably half that on the intake side. I twisted off a stud in the front mount as well.

 

[Vikingimike01]

Holy. I've had that on my 49cc. It broke in two months.

Anyways. What would happen, if I got that scooter exhaust, and took off the muffler part, the cylinder at the end? As in power/rpm, I know it will be louder.

 

[Street Ryderz]

I don't know where you guys buy your engines at but I've only held the throttle open for a few seconds on mine but there is no way i would turn this thing 7k with stock ports and stock balancing. I'd probably vibrate right off the seat lol. It will take off from a stop without pedaling and cruise nicely down the street though.

Tune it to go over the 7k and it will smooth out,stock timmings will suport 10k+ if you want it too!

 

[FurryOnTheInside]

How did it feel before the port and balance?

I didn't feel that I would get anything useful out of installing and running a terrible unfinished unbalanced engine that I would have to uninstall and fix sooner than later, so I just didn't!

I had read enough posts here to know that a few things need doing no matter what the end goal. Hardware replacement, some change to the crank balance, and cleaning up the ports, gaskets and intake tube were the very least I could do.

I still have a few improvements to make beyond what is needed just to make it roadworthy. A reed conversion will suit the engine characteristics that I want.

I don't know if my engine could be made to turn 10k, but I built it with reliability, torque, and stealth as the priorities, and I would not want to run the stock bearings at 10k when I use this bike to go on long trips carrying too much cargo.
Getting power from limited rpm by maximising torque is part of the stealth as well as the reliability, of course.

EDIT: forgot to mention that on this old style engine that is still common in Europe, I also retarded the base timing of the ignition by offsetting the magnet key 5.4°, which gives better ignition timing at the top of the RPM range with the stock CDI. That and the change to the crank balance and good mounting into the frame is probably all contributing to smoother running at the top end.

Holy. I've had that on my 49cc. It broke in two months.

Anyways. What would happen, if I got that scooter exhaust, and took off the muffler part, the cylinder at the end? As in power/rpm, I know it will be louder.

I only learned about engines from reading and studying this forum (and a few select pages from Jennings). I mostly learned about tuned pipes from Street Ryderz' posts so I can only agree with him that the scooter pipe pictured above looks great for a single speed. It has a long baffle cone to spread the effect over a greater range. You'll have to try it out and see if you get the effect you want.
Try changing the header length a little bit and see what effect that has. That will be really easy if you have to have it in separate pieces clamped with hose anyway.

I have a nice Italian made Aprilia RS50 pipe that I'm saving for a geared (Shift Kit) build because from what I've learned the steeper (shorter) baffle cone will have a greater effect but at a narrower range of rpm.

Loud unmuffled exhausts and high rpm on the street are a magnet for predatory police, and the absorption type mufflers are made to not restrict flow much anyway. Imo there's no good reason to delete it.

 

[Vikingimike01]

Nice. I'm not going to remove it then. I was reading Gordon Jenning's 2 stroke tuning handbook. I learned a lot. I'm alredy over the expansion chamber part. I've read, that some pipe manufacturers include the muffler part with the whole thing, and it may even reduce performance if I remove it.

The model is a "Gianelli Next 31623X"
It says it's a sport exhaust for Benelli 49X and Keeway X Blade

I didn't try fitting it yet, but it looks like I will be able to do it. It's still winter here, lots of snow, very cold.

As I can't weld yet, and don't want to ruin the pipe trying, a relative will do it for me, or our car mechanic neighbour.

I'll either update this thread, or create a new one to keep you guys updated on how it goes.


This is the pipe:

 

[JerboaJohn]

there is the thing that the 48cc is near a good balance as is. the 66cc + notorious for vibration and many need attention