It's been a wet long weekend! i am rebuilding 2 victas; a powertorque that has been ceramic coated and a geared starter full crank. I also own a rg250 suzuki 2 stroke road bike.
Hmmm
I know the chambers on the bike allow the bike engine to make lots of power and torque as the revs rise and come 'on pipe'.
Has anyone made expansion chanbers for victas? how hard could it be? any ideas?
It would be possible to tune a Victa exhaust system but the system would be very bulky. Essentially you would probably begin by finding a motorcycle system that had the same pipe diameter as the Victa exhaust port, then tune the length of the pipe upstream of the expansion box to give boost at the chosen speed. Victa engines are limited by their mechanical strength to quite low speeds, so this section of pipe would need to be much longer than on a motorcycle. (You would want the system to operate from about 3,500 rpm). The whole system needs to be as nearly straight-line as possible: any bends must be very large-radius curves.
Ok, I think i've found a computer program that helps me do it
just 2 small (!) issues 1- I have to work out the port timings of the powertorque (or has anyone got them laying around?) 2- It looks like its gonna be around 1200mm (4 foot) long!
Hmm, more food for thought i think, any thoughts people?
to get the exhaust id try EMEX services on airds rd minto [dirt bike wrecker] maybe try a KTM 50 pipe it might fit otherwise lookup DHZ MINI MOTO on villawood rd and ask if they have any secondhand pitbike exhaust going cheap or a forum called miniriders check the for sale section people always selling them there
Keep in mind that the victa motors are solely piston port timed.
Performance is limited by that.
Engine is designed for a task and does it admirably. Victa full crank motors were all the go for carts years back. I would be looking for an old school small engine machinist, im sure there would be a few tricks that you could pick up there.
A Colt ride on would be the go. Put the Victa motor on it. Start modifying.
Pipe length depends on the exact speed you want the tuned exhaust to kick in. I think most people doing home-tuning either begin with a trombone set-up until they find the right length, or keep cutting or extending the first section of pipe until they like what they get. I can't see much point in what you are aiming to do. You could improve the power output in a specific speed band, and rotary mowers normally work in a rather narrow speed band, so that makes sense, but you could achieve more by putting a larger engine on the mower. Remember, you'll end up with the engine wrapped up in pipe like a ball of wool, with a long expansion box sticking up in your face. You can't baffle the expansion box at all, so you'll have a head-full of noise and fumes like riding an old-time speedway bike. (Add a little Castrol-R to the fuel and you'll complete the feeling.)
you could try a reverse cone it still improves the performance of your engine you said its a powertorque half crank if so its not a verry good idea to try and push excessive powere out of one better to find a full crank 125 lear how to do port work and increase the comp ratio with a reverse cone exhaust here is mine for example
made this engine for a gokart
with the right mods a victa will turn 10000+ rpms gthey were used as early kart engines for racing
