machine-it

28cc soverign

i know theres probably loads of threads on a similar note to this but i cant find anything to answer my questions (to much contradicting info on the net)

i want to make a tuned pipe using the tuned pipe designer, so i follow instructions on working out the port timing the only thing is eveywhere tells you to work out the exhaust and intake (carb inlet )timing but the pipe designer asks for the transfer port angle ?

also the timing info i used said the transfer timing was the blow down timing but cant be right because the blow down is 28deg

one of them is wrong i think

so if some one wouldn't mind writing a small paragraph on what info i need for the pipe designer and how to get it i would be grateful.

also does anyone know of ideal port timing if i decided to modify it, what would be good figures to aim for.

thanks

av8tor1977

My Feedback: (6)

Not really sure about your first question. The blow down is the difference between the exhaust port timing and the transfer port timing. Most pipe design programs I've seen use the actual timing figures, not the blow down number.

Most non pipe engines do best with exhaust timing of 160 or less, and pipe motors 160 or more. It depends on the rpm range you want. I would probably start at 170 degrees exhaust timing. You probably already know this, but it's best to make the pipe length adjustable to fine tune it to the engine.

AV8TOR

machine-it

ok thanks
so do i just leave the transfer port as it is and am i right in thinking adjusting the intake port wont have much effect as its purpose is just to charge the crankcase with fresh fuel mixture.

chicks5

I was looking on-line for porting information, this guy was doing a testing of software on a motorcycle motor and evaluation different programs in his test. Engine optimizing software , I remember seeing he said the same thing about one of the programs.
http://macdizzy.com/2stroke.htm Read some of his explanations, might help you out.

av8tor1977

My Feedback: (6)

A hop up project needs to be a well thought out combination of modifications that compliment each other. You can't change just one thing and expect good results. You also need to have an objective. You need to plan for the rpm range you want to engine to produce it's best power in, how that will affect what it's installed in, etc.

If you modify the exhaust, yes, then you should modify the transfers and intake accordingly. You also have to plan your compression ratio, carburetion, exhaust, etc. One thing always affects another in an engine, and making single modifications rarely gives the results one is looking for from the engine. Research two stroke hop up techniques before making mods that may ruin the engine, or at the least provide poor performance.

Good luck and have fun,
AV8TOR

machine-it

chicks5
thanks for the link thats a lot of info on there, will take some time to read


av8tor1977
ok i see what your saying, i need a end target of what im looking for then need to do specific mods to achieve that, and it would probably help if i knew what the hell i was talking about

pe reivers

Look in thread http://www.rcuniverse.com/forum/m_61..._2/key_/tm.htm
You will find a link to the jenning literature, which is quite comprehensive.
When working on an engine the only thing that isreadily accessable is the exhaust port, carb duct, and the scavenge port entries. It so happens that these are of the utmost importance for tuning.
The blowdown is important for pipe adjustments, and larger blowdowns are better for all-out power, where smaller blowdowns are better for a wide power curve, but not combined with a large exhaust duration please.
like stated before, an exhaust duration of 160 or less (145) and blowdown of 20 degrees would provide a sweet running engine that will react to tuned pipes quite well. For all out power, use exhaust 185, and increased blowdown of 25. That means lifting the cylinder, modifications to the exhaust port, and adapting the cylinder head. If your engine has piston port induction, it also means modifications to the piston skirt and intake port to get the time areas aligned again to the power you want.
Lowering the cylinder and adapting the exhaust port to get increased blowdown will get a very powerful, but peaky engine. Not good for our purposes. We need a wide torque range, not all out power in a narrow rpm range.

machine-it

thanks, there is a lot more to all this than i first thought although i have thirst for technical knowlage so will still try to learn about it.

my engine has an exhaust of 150deg and blow down 28deg

if i wanted to reduce the blow down to 20deg i would need to machine the transfer ports deeper, ofcourse this is directly related to the transfer port timing and would increase the amount of deg it is open for.

or if i wanted to reduce blow down but keep the origonal transfer timing and also reduce the exhaust timing slightly. i machine the bottom of the cylinder and then deepen the transfer port back to its origonal timing, this would also reduce the exhaust timing below what was needed. which means i would then need to remove material from the top of the ehaust port to get the exhaust timing back to around 145deg. also may need to re adjust squish clearance depending how good it was before.

what is a recommended transfer port timing

i think both of those are possible depending on wether i need to adjust the transfer timing or not.

pe reivers

In our racer tuning we tended to leave the transfer timing alone, and just optimized gas transfer through the ports. Even built a vacuum cleaner driven test device to measure and watch the flow through the ports into the cylinder. Crankcase intake and carb duct were optimized. So were crankcase compression, exhaust port configuration and tuned pipe.
You WILL need several cylinders, and a handfull of pipes and carbs.

machine-it

ok thanks for going over the main points, it gives me somwhere to start, i may end up machining some new cylinders and messing with those rather than making a mistake on the one that works.