ATTN: Machinists - porting info

[hickskateboarder]

thinkin about doin the transfers and lifting the exhaust. my research tells me that for low-mid range porting, the exhaust should be opening 90 degrees ATDC, and transfers should open 116 degrees ATDC.

my math (hopefully correct...) tells me that the top of the exhaust port should be 32.5mm down from the deck, and the transfers should be 44.1mm down from the deck.

so what i am asking is
1) is my research correct for the port opening timing?
2) is my math correct?
3) do you have any other info/advice?

 

[quam]

pm kennedy_power. that dude's f*ckin smart w/ this sh*t, he went to school for it and has thousands of dyno pulls under his belt.
but from what i understand, you don't want to raise the exhaust port at all. raising the exhaust port increases top end and decreases low end. if you want good low and mid range, you should leave the exhaust height as is and mod the width and shape of it.
but the main parameter that will affect your exhaust flow is what your pipe is made to do. if you've got a hi revving pipe, then a low end port will be completely out of synch w/ it.
unfortunately i don't know for sure what my pipe is made to do. all i can say is that i've got kennedy's p&p for low-mid range and an F7 pipe and that biotch rips! i'd really like to see some real numbers on my pipe to see if it's the best for the trail riding that i do.

 

[FLOTEK]

thinkin about doin the transfers and lifting the exhaust. my research tells me that for low-mid range porting, the exhaust should be opening 90 degrees ATDC, and transfers should open 116 degrees ATDC.

my math (hopefully correct...) tells me that the top of the exhaust port should be 32.5mm down from the deck, and the transfers should be 44.1mm down from the deck.

so what i am asking is
1) is my research correct for the port opening timing?
2) is my math correct?
3) do you have any other info/advice?

well your transfer measurement from the deck is fairly close but the exhaust is way off basicly your blowdown will suck youll end up with poor mid-top torque ,this is why using a porting program is a huge help ..also be concerned with BDC,its not what it should be o na blaster ,on a blaster theres a slight negative deck height too! also the shape and back angles and overal larea and duration is critical to the little yfs ..my advise is to send the jug out to someone who ports them everyday for best results and widest powerband if you insist on doing it at home get graham bell's book on 2 strokes and read it till it sinks in

 

[Kennedy_Power]

Be very careful when measuring from TDC to the exhaust port opening. Remember the piston has a certain amount of dwell at TDC and BDC, the dwell depends upon the rod to stroke ratio. You must spilt the dwell before zeroing out the degree wheel. If you set your exhaust to 90 after TDC then the math is simple. 90 X2=180 360-180=180. So the total exhaust Duration= 180
Feel free to email me with questions

 

[Kennedy_Power]

If you were to run those numbers on a Blaster cylinder your exhaust would be 180, your blowdown would be 26 and your total transfer duration would be 128

 

[hickskateboarder]

hmm.. looks like i need to do more research... but info is so hard to come by. yeah it's not too hard to figure out the durations, but what about this blowdown? never heard of it before....

my deduction.... 116-90=26. so blowdown is the degrees of crank rotation that the exhaust is open but transfers are still closed.....or coming back up, the transfers have closed but the exhaust is still open. (same thing i know, but dealing w/ different gasses) ok, gotcha. so what bearing does that have on power? i guess that's the duration you want to sync with where the pipe wants to make power. and that gets complicated real quick b/c then you have to deal with speed of sound thru different viscosity fluids at different temperatures and pressures.... getting to be too much like my physics class... gosh. can someone just give me the answer? lol.

 

[FLOTEK]

theres a ratio that must be kept for best results in relation to the exhaust opening and transfers this is your blowdown its important to rememebr this and yo u can find this number by taking your exhaust timing and subtracting the transfer timing then dividing the ansewer by 2 ,example: a 192 exhaust duration and 124 transfer yeilds a 34 blowdown <not exactly what i use but this would generaly make a fun midrange play motor on gas for most off the shelf blaster pipes.this is the kind of port info most DIY people hunt the net for and usually get the runaround,a simple calculation in degrees ot linear measurement of distance is not going ot happen easily unless you can trig out every angular change the rod angle makes thorugh every degree of stroke ,say for instance a 3 degree change happens to change your exhaust port timing maybe for instance .030 to be raised ..now dow n at the bottom of your jug near BDC that same 3 degrees on your transfers might only need .015 to get the target timing ,are you more confused now lol?its not as easy as people tend to think

 

[hickskateboarder]

yeah i realize that, but it really is just trig, which is what i used to do my calculations. i actually didn't use it at first, and just thought "oh well, 1/2 the distance from tdc to bdc would be 90 degrees." then it was keepin me up at night thinking about it and i was like "no, you moron, you forgot that in moving the rod horizontally the distance of the offset of the crank it would farther lower the piston. duh" so then the next day i sat down and did it right.

really? a 192 exhaust duration for mid range? wow. i would be raising the exhaust... i forget what i figured now..... like 2mm or something i think for 180 duration. so stock its <180, thats really gotta be hurtin it. but my blaster already doesn't have a whole lot of bottom end, can't imagine whats gonna happen when i raise the exhaust..... the blaster needs a powervalve....

 

[FLOTEK]

really? a 192 exhaust duration for mid range? wow. i would be raising the exhaust... i forget what i figured now..... like 2mm or something i think for 180 duration. so stock its <180, thats really gotta be hurtin it. but my blaster already doesn't have a whole lot of bottom end, can't imagine whats gonna happen when i raise the exhaust..... the blaster needs a powervalve....

your lowend sucks mostly because your heads squish clearance is too much and your static compression (and usually igntion timing too ) is probably low
compared to optimum .as far as what port timing works for you wel lthats a tricky one and requires more than a general number theres more going on behind the ports than the opening and closing that make the power .i port different than alot of builders set them up so you should consult with several
i would say a 33.5 -34 blowdown will likely treat you good on gas for what you want to do.

 

[ridinfast03]

Just spectating

 

[hickskateboarder]

i did mill the head about 35 thou to try to get some more low end, but it didn't seem to help a whole lot. i think i need to rebuild it before i do too much more... my piston to cylinder wall clearance is over 12 thou, it's an 04 and don't think it's ever been rebuilt. i'm just really procrastinating on doin it b/c i don't want to be out of a ride for a few weeks while its away. i gotta get back to studyin for physucks, i got a test tomorow...

 

[Kennedy_Power]

Hi Zac
I will give you a call
I will help you out with your Project Fast Blaster
I can expain much faster over the phone.

 

[quam]

wow, this thread is getting pretty awesome, pretty fast!

 

[hickskateboarder]

hahaha, do u understand any of it quam? i've been doin a lot of reading, it's kinda nice to know what they are talkin about when they talk about changing the radii of the combustion chamber and changing squish clearance and angle, and port timing and whatnot.

and that's my point exactly. i was so stoked when randelator put up those pics of porting. seems like no one wants to really get into things and try and understand how and why it does what it does. i've always seemed to be that way tho. finally i found some people that know what they're talkin about lol.

i've often found that when you just start to get into something, no matter what it is, you think aw, that can't be that hard, then the more you learn, the more you realize you don't know anything, lol.

 

[FLOTEK]

it is a constant learning curve and als otheres so many ways ot skin a cat ,thats why i love doing it and it keeps things interesting
i would make a point to bore oversize and get a forged piston first ,as you probably already know no matter how good the porting combo or head work an engine will be way down on power with a loose bore

 

[Wildcard2]

Agreed, .012" is about .0085" wider than ideal.

 

[hickskateboarder]

yeah, idk how there aren't piston skirts laying in my bottom end...

 

[hickskateboarder]

hmm.. i tore it apart to port and measured bore and piston. when i measured the gap before i just used a feeler guage pushed along the top of the piston. used calipers this time. apparently the top of the piston is about 15 thou smaller than under the rings and on the skirts. don't have my measurements with me right now, but it was somewhere around 6 thou. so i guess she's still alright. i went with about 190 on the exhaust. the transfers only needed lifted like a millimeter, if that, and i tried to do it but i need to get some really long shank bits or something, i couldn't get in there to mess with them. but after re-assembly, it seems you have to rev a little higher before she snaps into the powerband, but it pulls harder way up top and seems like it will rev higher winding out the gears. which is a good thing cause i have to take 3rd way up there before it hit 4th if i want to be in the powerband.

is there a special kind of epoxy you use to change the shape of the transfers? next time i get anxious and tear it apart i'd like to smooth out a few of them. there are 2 that have like a wall that the air hits right before going into the port, i'd like to taper that out and make it smoother, and try to maybe get the ports to point a little more strait up, instead of strait into the exhaust lol.

 

[Johnny Blaze]

Great thread! I am very interested in doing this myself aswell. (myself and my atv mechanic buddy) Good show everyone for the tips! Keep up the gooder work

 

[hickskateboarder]

do your research johnny!