Honda Spree and Elite 50 Forums

1man8scoots wrote:Simple formula for would be engine and cylinder porters of the world....
Take your exhaust port timing, subtract your transfers, take that number and divide it by 2. There's your blow down. Simple truth.

1man8scoots wrote:I'm interested to know how it's going also. According to my test timing engine and corsas

(what crank are you using for these test)

on hand the timing you're looking for wouldn't be done with a simple 1mm base and 1mm up porting of the exhaust. The extra .8mm you added with the fiber gasket and longer stroke you would be over 190 on ex port and blow down wouldn't be near 32. Also with the numbers you're saying you have, you have 27 degrees of blow down. That's not a guess, that is simple math.

yup not sure about that but good advise.

taida ministroke is 43.4 not the 2ab 44 ministroke.

not sure if i using degree wheel wrong but i just set piston to TDC and spin crank. when the piston is just at the exhaust port opening on the down stroke i note the degrees usually between 80-85 degrees, then i keep spinning the crank until the piston completes its travel past BDC and back up to the exact same spot where i made the first not of degrees and i usually get between 70-75 degrees.

i think i ended up with
85 degrees and 272 degrees on final measurement on the exhaust port = 187 degrees if my math is correct. IF 272-85 is more than 190 then i gotta seriously think of going back to school again.

not sure about the transfer timing but i will build another corsa with taida crank again. and i will post again when that time comes around



lost all the papers that went with this build but working on another and will post soon.

this was for a customer and bike is running great.

ended up using V8 stroker exhaust to keep the noise down. great power top speed 70+.

Get your wheel on the crank, wether it be stator or cvt side, spin the crank to just above the ex port. Loosen the lock nut for the wheel. Just as the edge, or bevel, of the piston reaches the opening of the ex port you will reset your wheel to zero or tdc or bdc it does not matter. Now that it's zero, rotate it down and back up until the ex port is closed. Now you have ex port timing.
Continue to xfers, transfer 1/x1 the closest to the ex port, transfer 2/x2 closest to the rear of the cylinder but not opposite of the ex port, transfer 3/boost port/x3/b1 is the port exact opposite of the ex port.
Bring the crank around to x1 exactly how you did the ex port. Barely being able to see the edge of the port from the bevel. Then spin down and back up. There's your x1 timing. Continue to x2,x3.
Blowdown timing....
Bring the crank to ex port top, reset to zero, and rotate down until you hit the very first xfer to open barely. That number is your blowdown.
And this is how you calculate timing.

39.3,39.4,40.4,41.4,43.4,44.4,46.4,50,51,52,52.5,52.6 does not matter. The longer the stroke the faster the gradient of degrees happen per mm. May be 10 degrees per mm on stock stroke but it is 12 degrees per mm with 43.4, or 20 degrees per mm with 52.6mm.
Measure 3 times, cut once. Mantra of all machinist and carpenters. If you do not trust the numbers you see try it again, but always measure more than once.
One more tip. Do not chamfer your ports until you are done with timing. Otherwise you may not get an accurate number due to the light shining out more than just the port.

1man8scoots wrote:Get your wheel on the crank, wether it be stator or cvt side, spin the crank to just above the ex port. Loosen the lock nut for the wheel. Just as the edge, or bevel, of the piston reaches the opening of the ex port you will reset your wheel to zero or tdc or bdc it does not matter. Now that it's zero, rotate it down and back up until the ex port is closed. Now you have ex port timing.
Continue to xfers, transfer 1/x1 the closest to the ex port, transfer 2/x2 closest to the rear of the cylinder but not opposite of the ex port, transfer 3/boost port/x3/b1 is the port exact opposite of the ex port.
Bring the crank around to x1 exactly how you did the ex port. Barely being able to see the edge of the port from the bevel. Then spin down and back up. There's your x1 timing. Continue to x2,x3.
Blowdown timing....
Bring the crank to ex port top, reset to zero, and rotate down until you hit the very first xfer to open barely. That number is your blowdown.
And this is how you calculate timing.

thats how i did it.. same result different starting point.

if i start with the piston at TDC and spin down until i can see the exhaust port just open and note degrees (85) then keep spinning until the piston sees the same spot and i get exhaust duration..

exact same procedure as you only difference is you are setting zero when you hit the exhaust port opening. all i am doing is noting the degrees then subtracting to get the total degrees that the port is open. same thing.

same as blowdown.

if exhaust port opens at 85 degrees and transfer port opens at 115 degrees then blowdown is 115-85 = 30 degrees.

the reason i set 0 degrees at TDC is so that i can check TDC at 0 degrees to verify that the wheel hasn't moved while i was spinning it to get my readings.

usually check the numbers at least 4 times each spinning the degree wheel over and over again

not rocket science. piston has 1 full cycle at 360 degrees. all you doing to find duration is checking how many degrees the different ports are open of the 360 total degrees.

no s*** about the cranks! thats why i use the degree wheel to set duration when doing a build.

just thought you were thinking of a different crank and YES the duration will be different if the stroke is longer. thats simple common sense

1man8scoots wrote:I'm interested to know how it's going also. According to my test timing engine and corsas on hand the timing you're looking for wouldn't be done with a simple 1mm base and 1mm up porting of the exhaust. The extra .8mm you added with the fiber gasket and longer stroke you would be over 190 on ex port and blow down wouldn't be near 32. Also with the numbers you're saying you have, you have 27 degrees of blow down. That's not a guess, that is simple math.

how much ministroke taida cranks with corsa have you built so far? would like to know how you setup this particular combination so i can make it like your setup.

final numbers came out to be

ex- 187*
tns- 135*
bst - 128*

should be OK with 32* of blowdown should give good powerband.

any other suggestions?[/quote]

With these numbers the math is not there.

I have done over 100 stroked 2 strokes. It is not rocket science but it is a science. Math is part of science.
This is a 74cc engine, child's play. If you want 31 degrees of blow down you need 189 ex and 127 transfer.

1man8scoots wrote:I have done over 100 stroked 2 strokes. It is not rocket science but it is a science. Math is part of science.
This is a 74cc engine, child's play. If you want 31 degrees of blow down you need 189 ex and 127 transfer.

could have been a typo mistake on the transfers i'll keep looking for the paper that i wrote everything on. I was building more than 1 motor at the time with different crank/setup. I may have taken the transfer reading from the other build. now that i think about it that is quite a split in transfer and boost duration for a corsa they are usually a lot closer together.

planning to put another one together soon with same parts. how would you run a setup like that?

what duration would you have shot for?

can you recommend different durations for different pipe setups? stroker v8 vs Arrow pipe?

i would like to know what the optimum durations would be for the different RPM/pipe setups.

thanks for the suggestions

There's more to it than just numbers, and in general you can't just modify one port and not others and expect great performance. Boost port is very important. But more so is maintaining angles of the roofs when porting in relation to where the newly profiled cylinder is all going to end on what part of the stroke, wether it be down or up stroke.
So to answer your question simply is do not exceed 31 degrees of blow down on either pipe, do not exceed 130 degrees on transfer for any pipe. I don't recommend trying out radical port timing on any engine but your own I'm case it doesn't jive.

where can I buy that kind of degree wheel?