Janbros' 2-stroke excel for ports, heads and pipes

see last post please

i dont suppose there is any set recommendation as to the relative percentage sizes of my main auxillary and boost ports?

Nombre de messages : 362 Localisation : Belgique Date d'inscription : 05/12/2011

aljaxon a écrit:: a quick adjustment to transfer widths and i get this. can you see any glaring errors or could i go with this?
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you better show the "new transfers" if you want to talk about them.
if you want your max torque at 8000, then your STA is ok.

i have ported the cylinder to this 189 128
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i see my effective exhaust port area is equiv 28.1sq mm.

right i tried the motor on the road and around 6000rpm it stutters and struggled to pull past. but then at 8000 it picked up and revved all the way to 11000 possibly 12 as ive disconnected the tacho.
with low gearing it pulled 50mph into a strong head wind. which is decent going past my past projects.
but temps were high. i over jetted and it was still hot. i checked compression to find i had 185 psi.
i had aimed for 135-150 with a ccr of 6.9:1. but my machinist had to stop when head was still a tad too small. but not that much surely i had thought? less than half a cc.
im getting the head machined sometime this week and am looking at the head part of the excel sheet.
any thoughts jan bros?

Nombre de messages : 362 Localisation : Belgique Date d'inscription : 05/12/2011

aljaxon a écrit:: any thoughts jan bros?

no, I'm not an expert, I'm just a guy who likes to mess up 2stroke engines and from time to time have a small succes.
it's not because I made this excel I know all the in's and out's of 2-strokes. Nothing in the excel is my knowledge, you can find it all over the internet, provided by much much wiser men than me (well, at least about 2 strokes ) . All I did was put it all together in one excel.

and because it is not my knowlegde, and the knowledge was provided for free, I put it also on the internet for free. Feel like I can't ask money for something that isn't realy mine.

JanBros a écrit:

aljaxon a écrit:: any thoughts jan bros?

no, I'm not an expert, I'm just a guy who likes to mess up 2stroke engines and from time to time have a small succes.
it's not because I made this excel I know all the in's and out's of 2-strokes. Nothing in the excel is my knowledge, you can find it all over the internet, provided by much much wiser men than me (well, at least about 2 strokes ) . All I did was put it all together in one excel.

and because it is not my knowlegde, and the knowledge was provided for free, I put it also on the internet for free. Feel like I can't ask money for something that isn't realy mine.

ok
i do the same re messing up 2 strokes.

can you guess as to why when i select a 3 stage it comes out all wrong proportions? is there anyway i can reset the sliders to default for the 3 stage? i am getting the belly as diverging or converging etc

Nombre de messages : 362 Localisation : Belgique Date d'inscription : 05/12/2011

then you do not adjust the sliders correctly. if you want to keep the FOS-length, keep the length %'s (the yellow boxes) at 100%. that means header/diffuser/baffle are exactly as long as the original FOS.
and you can also check the total lenght at the bottom of the pipe, that it remains the same as FOS.

you have a pipe and engine (the 176° exh), and you know at which rpm it makes it's top power. fill in all the data for that engine (untick the "input from data" so the FOS page becomes a stand-alone), measure the length of your pipe and than change the Speed Of Sound so that the calculated length is the same as your known pipe. use that SoS to calculate a new pipe.

JanBros a écrit:: then you do not adjust the sliders correctly. if you want to keep the FOS-length, keep the length %'s (the yellow boxes) at 100%. that means header/diffuser/baffle are exactly as long as the original FOS.
and you can also check the total lenght at the bottom of the pipe, that it remains the same as FOS.

you have a pipe and engine (the 176° exh), and you know at which rpm it makes it's top power. fill in all the data for that engine (untick the "input from data" so the FOS page becomes a stand-alone), measure the length of your pipe and than change the Speed Of Sound so that the calculated length is the same as your known pipe. use that SoS to calculate a new pipe.

but i dont know what to set the sliders for header 1 header 2 diffuser 1 2 and 3 to.
i can get 100% in the yellow boxes but i dont know how to split that up in the header 1 and 2 boxes 50/50? or the diffusers 3 boxes. 33%?? i thought they got gradually smaller. is there a forumula somewhere? i dont know what the proportions should be.

Nombre de messages : 362 Localisation : Belgique Date d'inscription : 05/12/2011

what I know about it is mentionned in the doc I made explaining the sheets. so start there.

JanBros a écrit:: what I know about it is mentionned in the doc I made explaining the sheets. so start there.

ive read that a couple of times now and sadly am none the wiser on how to get it to output a default pipe with default dimensions and angles. or why it is including two headers?
maybe if somewhere there was a reference to default angles for a 3 stage i could fit them in but is there a way to get your spreadsheet to output the default or recommended settings like the fos single stage does.

i would be happy to disable the sliders and go with what it recommends.

Nombre de messages : 362 Localisation : Belgique Date d'inscription : 05/12/2011

the only default pipe is the FOS pipe (left coloumn), with the 2 and 3 stage you can do "whatever" you want with the FOS pipe . no guidelines, no rules. only "guideline" is the grpah where you can see the difference between the FOS-pipe and what you have made of it.

JanBros a écrit:: the only default pipe is the FOS pipe (left coloumn), with the 2 and 3 stage you can do "whatever" you want with the FOS pipe . no guidelines, no rules. only "guideline" is the grpah where you can see the difference between the FOS-pipe and what you have made of it.

ahh i see. i have read there can be set angles for the 3 differing cones. but the maths involved "to the power e" which my aging brain couldnt get around.
i think i will stick with a single stage.
but thanks for the rest of the sheet it must have taken you ages with little thanks or reward.
it helped me get my porting much more balanced.

my only problem now is my exhaust exit at the cylinder flange is 26mm. my ports effective diameter is 28mm and X according to fos is 28. so how do i get from 26 to 28mm? can i step it as i read honda did once? or do i taper it sharply over a short distance? or lose it over the full length of the header which over 290mm is negligible.
what do you think janbros?

Nombre de messages : 362 Localisation : Belgique Date d'inscription : 05/12/2011

I think you have asked that 5 times, and there won't be an answer to it.
just built pipes, you might actualy learn something from them. if you have a dyno, just built straight test-pipes, they are made much faster. and than be surprised that when you make the same one with bends, the power is different.
I'd first built a pipe that starts at 26mm, but with the angles of the 28 pipe, just make the diameters of each section ever so slightly bigger so that in the end the belly has the same diameter.

thanks for that. i have so many options to get rid of the 2mm its bewildering.
as for pipes with bends here's one i made to fit in a confined space a couple of years ago.

working out the growth for each section per mm and applying it and working out the angles all with a calculator was fun.
this was before i realised i wanted power at 10000rpm instead of 7500.
btw my welding is much better nowadays. its as if the pigeons have got diarrhea. [Vous devez être inscrit et connecté pour voir cette image]

right i want to make a new pipe and alter my cylinder so the exhaust duct narrows to 90% of port area at flange and then increases back to 100% at the end of a duct. much like the wobbly duct but without the ears so lets call it a non wobbly duct..
with it being a single exhaust port do i still use the same lengths ie 1.5 x bore for cylinder duct and 2 x bore for cylinder duct plus (non) wobbly duct?
i am oversquare 47 x 43 bore stroke.
thanks for any replies

Nombre de messages : 362 Localisation : Belgique Date d'inscription : 05/12/2011

yes, single port 90%, double or triple port 75% . everything else the same.

even better would be to use the effective blowdown port area instead of the %'s.

thanks. just to confirm the blowdown area is the area of the exhaust port above transfer opening?.
and that is the area of my duct at the distance 1.5 x bore. ?

just did a port map and using your spreadsheet filled in all the values and i get effective flow area of EX port 448. (soon to be new = 495). but the blowdown will be only 255 which is only 50% of the (new) ex port area/
so if i use that for the narrowist bit on the non wobbly duct i go from port windows effective diameter 25mm to 18mm then back to 25mm. that 18mm seems too small.
using the recommended 90% of window area i get 23.8mm diameter
so 25mm to 23.8mm then back to 25

do you think i should stick with the 90%?

Nombre de messages : 362 Localisation : Belgique Date d'inscription : 05/12/2011

I think yes you should, but that's only me. Wobbly's percentages areestablished through lot's and lot's of tests, while Frit's effective blowdown area is more theoretical for high performance engines (almost every thing he says is). But I may be wrong about that, and I'm sure he'll state so if he read's this.

wobbly says 90% so ill go with that. just means i have to weld up my cylinder duct for the first 20mm of the 70mm long "duct" and the rest of it will be part of the header.
cheers!!

JanBros a écrit:: ... Wobbly's percentages are established through lo's and lots of tests, while Frits' effective blowdown area is more theoretical for high performance engines (almost every thing he says is). But I may be wrong about that, and I'm sure he'll state so if he read's this.

I will take that as a compliment Jan. But my intention was to provide a theory that is valid for all two-strokes, even a Solex
(with decent results, I might add Wink

)

i made the first 2 sections of my header follow the duct dimensions and only noticed a slight improvement but my cylinder duct needs some more welding.
i am going to make another FOS pipe. if i wanted a slightly wider powerband due to my gearings not very close ratios would i reduce the belly from 3.5 x to 3 or maybe even 2.75?

also i have a discrepancy. using the fos recomendations on this new project bike X = 26.4mm which is ar3ea of 547mmsq
but the ex port area effective diameter using janbros spreadsheet is 25mm and at the end of the duct it will return to 25mm (after the 90% reduction at 3/4 bore length) . i am at the limit 66% of opening my exhaust port up anymore. is it due to my single port? the fact i dont have the area a triple ex port would have? so X is 25 or 26.4. i could taper out the last section of my imitation duct to meet this bigger diameter.

i made the first 2 sections of my header follow the duct dimensions and only noticed a slight improvement but my cylinder duct needs some more welding.
i am going to make another FOS pipe. if i wanted a slightly wider powerband due to my gearings not very close ratios would i reduce the belly from 3.5 x to 3 or maybe even 2.75?

also i have a discrepancy. using the fos recomendations on this new project bike X = 26.4mm which is ar3ea of 547mmsq
but the ex port area effective diameter using janbros spreadsheet is 25mm and at the end of the duct it will return to 25mm (after the 90% reduction at 3/4 bore length) . i am at the limit 66% of opening my exhaust port up anymore. is it due to my single port? the fact i dont have the area a triple ex port would have? so X is 25 or 26.4. i could taper out the last section of my imitation duct to meet this bigger diameter.

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