Super Jet 5mm Stroker cylinders - port timings??

Knoxie

Knoxie

www.kp-parts.com
Location
New Zealand
I got hold of a 5mm stroker engine in pieces (minus head).....looking at the port timing of the ported 61x cylinder that came with, it seems pretty aggressive....(measured with stock base gasket, so piston comes ~2mm out of cylinder)

82° Exhaust Port Opens (+/-1)
114.5° Transfer Port Opens (+/-1)
So....
196° Exhaust Duration
131° Transfer Duration
32.5° Blowdown Time

Not too sure how well this would go?? seems like it would have screaming top end...?

What im thinking of doing is using a stock 760 cylinder that i have ...i calculated should give the follow port timing with the 5mm crank:

86.5° Exhaust Port Opens
117° Transfer Port Opens
So......
187° Exhaust Duration
126° Transfer Duration
30.5° Blowdown Time

Anyone got an idea if these numbers stack up ok for a good freeride engine???
 
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Knoxie

Knoxie

www.kp-parts.com
Location
New Zealand
CARBONX2 said:
The 760 will work much better
Click to expand...

another option, I could get another 61x cylinder and use that.....calculated I should get something like:
89.5° Exhaust Port Opens
117° Transfer Port Opens
181° Exhaust Duration
126° Transfer Duration
27.5° Blowdown Time

Im guessin most strokers use re-sleeved cylinders or billet so you can set-up how you like......but these timings for 61x & 64x cylinders seem ok?? (i think??, havent really played around with this stuff before)
 
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S

Schmidty721

someone turf my rails
Location
WI
I picked up the same style 5mm last summer. Has a 61x cylinder without a spacer. It's been re-sleeved i think and ported. I have no clue who built the engine or what it was built for. I ran it last summer with a set of OEM 44's and a 650 coffman pipe with MSD enhancer. It made nice smooth power everywhere. I had Art at Jetworks bore it this winter for my new topend. He didn't feel any additional port work was necessary. I'll be running Mod B-pipe, 44 blackjacks and EPIC this year in my BOB.

Here are the timing specs I measured last summer when I first got the engine.

Exhaust open: 89
Transfer open: 122
Exhaust duration: 182
Transfer duration: 116
Blow down: 33
 
Knoxie

Knoxie

www.kp-parts.com
Location
New Zealand
tofa said:
Whats up Knoxie?...Are you looking for more power cause Kim smoked you in the racing last weekend lol...
Click to expand...

Ha ha ! yeah need to make up for skill with horsepower =)

munki63 said:
There are some specs on a 5 mil in this thread http://www.x-h2o.com/threads/21863-...Specifications&highlight=port+timing+duration
Click to expand...

Yeah have checked out that post a fair bit.....took this comment from it:

"I was told about the same thing from some other well known engine builders.
They like to run their freestyle engines around 123° ~ 124° with a maximum being 127° on the transfer port duration and 184° ~ 193° with a maximum being 195° on the exhaust duration."

So it looks like the 760 cylinder & 5mm should give port timings within these ranges.....
 
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#ZERO

#ZERO

Beach Bum
Location
Florida - U.S.A.
For freestyle use I'd recommend using a 61X cylinder with the standard NW big bore sleeves because the transfers roofs are 2mm lower than stock and the transfer floor is extended further down which makes them perfect for the 73mm cranks with the stock length rods.
 
Knoxie

Knoxie

www.kp-parts.com
Location
New Zealand
#ZERO said:
For freestyle use I'd recommend using a 61X cylinder with the standard NW big bore sleeves because the transfers roofs are 2mm lower than stock and the transfer floor is extended further down which makes them perfect for the 73mm cranks with the stock length rods.
Click to expand...

yeah I noticed some of those aftermarket sleeves seem to have ports more suitable for stroked cranks......do you know much about these: http://www.blowsion.com/products/839-yamaha-850-big-bore-sleeves-blowsion.aspx , mentions they can be used with stock to 6mm stroker.

At this stage I dont really have the $$ to spend on new sleeves etc, was hoping to just put something together out of the parts I have (760 cylinder)
 
jetski9010

jetski9010

Team RTYD
Location
Lancaster PA
Knoxie said:
yeah I noticed some of those aftermarket sleeves seem to have ports more suitable for stroked cranks......do you know much about these: http://www.blowsion.com/products/839-yamaha-850-big-bore-sleeves-blowsion.aspx , mentions they can be used with stock to 6mm stroker.

At this stage I dont really have the $$ to spend on new sleeves etc, was hoping to just put something together out of the parts I have (760 cylinder)
Click to expand...
The sleeves can be setup at different heights in the cylinders so you can get the port timing you want with different motor setups. If you looking for the cheapest way to get your motor together you can take your 760 cylinders you have and get some cut off the bottom of the cylinders to help lower the port timing some. I am guessing the pistons already poke out the top some as it is so you will not be able to cut much off. You will then just have to get your domes cut back more to accept the pistons. If you can port the cylinders some yourself so get the timing you want after chopping the cylinders that would be your cheapest way. Again this is not the right way to do it just trying to give you an way to get it together and ride.
 
davidescu_radu

davidescu_radu

sea riders
Location
Constanta,Romania
still interested in this thread - have same parts here: plus 5mm crank stock rods and 62t cylinders 84.75 bore - have cut the bottom of castings 2 mm - what should i do next? Cut the domes on ada head - ok - but then the dome size become too small - get very high compression
 
Nuklear6

Nuklear6

I Dream 10' Surf!
Location
Bordentown, NJ by week / Brigantine, NJ by weekend
davidescu_radu said:
still interested in this thread - have same parts here: plus 5mm crank stock rods and 62t cylinders 84.75 bore - have cut the bottom of castings 2 mm - what should i do next? Cut the domes on ada head - ok - but then the dome size become too small - get very high compression
Click to expand...

I'm going to talk inches...

If you cut 2mm or .078" of the bottom of cylinder and are using a +5mm crank with stock thickness base gasket the piston pop up will be too high. You'll have the top ring coming too close to the deck surface and risk catching the ring. I'd have to measure for exact but I believe most Yamaha style pistons have the top ring glad about .150" down from top of piston. You can safely only run the top of the piston at or little over .120" above the deck at tdc. Your math is
Stock deck height is -.030"
You 'll add for the crank +.098"
Then you'll add +.078" for the machining you did
Giving you a deck height of +.146"
Which is way too high for Yamaha style pistons.
If your going to use kawi small pin flat tops this math is completely out the window but then so is your port timing. Kawi small pin flat tops have a lower top of wrist pin to top of the piston measurement.

Chuck Palmucci
CPT Enterprise LLC
609 510 3062
 
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