registered user Posted June 25, 2015 Report Share Posted June 25, 2015 if everybody is just copying the next guys port job and using the same domes then there must be alot of cloned engines out there that would indeed have a common comp ratio and static cylinder pressure and thus all needing the same fuel. surely there must be some diversity or no ? Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted June 25, 2015 Report Share Posted June 25, 2015 if everybody is just copying the next guys port job and using the same domes then there must be alot of cloned engines out there that would indeed have a common comp ratio and static cylinder pressure and thus all needing the same fuel. surely there must be some diversity or no ? There is for sure. The point I was making though, is that with as many of these things I've put together I know when someone tells me what a particular combo is cranking at, with a little past education it's pretty easy to know what fuel something may need, and I would assume there are several other folks qualified to do the same. You're pretty fluent in the Honda based 250 motors right? So if some guy says "My 01 CR has FMF pipe, V force reed, 18CC head with .052 squish, and Eric Gorr MX port, and it cranks X psi on the compression gauge", wouldn't you be able to just know if it needed race, blend or pump fuel based soley on your experience? (Not trying to be shitty) I'm all for being precise and really figuring stuff out, but sometimes it seems that things around here are far more over complicated then necassary. Yes there is a proper way to figure out compression ratio, and that alone isn't always enough to determine fuel type. You can have a heavily ported motor making a calculated compression of 16.5 to 1, but then cranks at 140. So most guys just belch out 140psi is fine for pump, when in fact it could just be a drag motor with heavy exhaust work and a conservative squish. Of course I could name different variables off all day. But the point I'm trying to make is that I agree it's best to calculate, but with a little knowledge on a combo you can totally use cranking compression to tell you what a motor might need. Is that for anybody to determine? Probably not, it's obviously better for someone with a bit of experience to make that determination. I don't think you'll agree with all that, and I see why. I just think it's a little far fetched that people don't think you can use cranking compression as a sort of baseline to see what a motor needs. However I say that only if someone knows what is inside a given motor. I will agree it is just a useless number if you don't have an engines specs though, and just blindly kicking a gauge and dumping fuel based on the gauge could be asking for trouble. 2 Quote Link to comment Share on other sites More sharing options...
sheerider1026 Posted June 25, 2015 Report Share Posted June 25, 2015 ^^x2. I'm with tricked on this Quote Link to comment Share on other sites More sharing options...
registered user Posted June 25, 2015 Report Share Posted June 25, 2015 if you see similar stuff day in and day out, 12ish:1, 150 typically. its the same ol fuel. ya i get all that. but uncle larry wants you to look at his triple port stocker with mikes pipes and franks head. static pressure isnt what you would think. now what ? ive always figured even a pipe change would alter kicking comp but never cared enough to do the test. anybody got a spare set of pipes and a half hour ? check pressure then swap a pipe and check again. just for the hell of it i wouldnt mind knowing Quote Link to comment Share on other sites More sharing options...
n2otoofast4u Posted June 25, 2015 Report Share Posted June 25, 2015 FFS 1 Quote Link to comment Share on other sites More sharing options...
registered user Posted June 25, 2015 Report Share Posted June 25, 2015 for a minute there i thought you might be contributing somehow. just a big let down again Quote Link to comment Share on other sites More sharing options...
registered user Posted June 25, 2015 Report Share Posted June 25, 2015 i think whats happeneing here is somethings getting lost in translation along the way. were trying to figure out what static pressure has to do with fuel. tricked has seen a pile of similar engines with similar cylinder pressures, need similar fuels. ok but that doesnt answer the question of what non-running cylinder pressure has to do with a fuel. for a while ive tried and been unsucessful to determine any correlation between this pressure and such and such fuel. Quote Link to comment Share on other sites More sharing options...
sheerider1026 Posted June 25, 2015 Report Share Posted June 25, 2015 I think we need to call a scientist on this topic Quote Link to comment Share on other sites More sharing options...
Larry's Shee Posted June 25, 2015 Report Share Posted June 25, 2015 ive always figured even a pipe change would alter kicking comp but never cared enough to do the test. anybody got a spare set of pipes and a half hour ? check pressure then swap a pipe and check again. just for the hell of it i wouldnt mind knowing With the way an expansion chamber works I doubt you could. Hell, even if you spun the engine at the projected power peak you might not see anything. Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted June 25, 2015 Report Share Posted June 25, 2015 if you see similar stuff day in and day out, 12ish:1, 150 typically. its the same ol fuel. ya i get all that. but uncle larry wants you to look at his triple port stocker with mikes pipes and franks head. static pressure isnt what you would think. now what ? If I have something completely unknown in front of me, well then it's obviously time for math. But if Joe Schmoe can't tell you what's inside, you would definitely have to pull the head and acquire a few measurements to calculate the compression. At a minimum, bore,stroke, and CC the head. If it looks worked over, take porting in to consideration when doing said math. Question RU. I was re reading a previous post and you touch on a two strokes ability to dump volume before it's compressed, but then the supercharging effect kinda comes in to play and stuffs it back in. This definitely never shows on a gauge but when the motor is running it is happening. Any way to really calculate that additional volume? Quote Link to comment Share on other sites More sharing options...
registered user Posted June 25, 2015 Report Share Posted June 25, 2015 So you want to know the cylinder pressure of a running engine at a given engine speed then figure out the required fuelair mixture to achieve said pressure. Probly need a scientist like larry said haha. Check blairs book. Might be something in there Quote Link to comment Share on other sites More sharing options...
J-Madd Posted June 25, 2015 Report Share Posted June 25, 2015 if you see similar stuff day in and day out, 12ish:1, 150 typically. its the same ol fuel. ya i get all that. but uncle larry wants you to look at his triple port stocker with mikes pipes and franks head. static pressure isnt what you would think. now what ? ive always figured even a pipe change would alter kicking comp but never cared enough to do the test. anybody got a spare set of pipes and a half hour ? check pressure then swap a pipe and check again. just for the hell of it i wouldnt mind knowing Calvin always said this ^^^^^ Menz tested with and without pipes on his motor and made zero difference he said. Quote Link to comment Share on other sites More sharing options...
registered user Posted June 25, 2015 Report Share Posted June 25, 2015 Good to know. That seems to suggest the pipe does very little until it has hot gas in it . ie engine running Quote Link to comment Share on other sites More sharing options...
wv redneck banshee Posted June 26, 2015 Report Share Posted June 26, 2015 I did a search on here about Ken oconnor no luck.... I bought a bike beginning of this summer, the porting was done by him,it hasn't been ran, is this guy worthy of such a task??? Quote Link to comment Share on other sites More sharing options...
Nightmare Posted June 26, 2015 Report Share Posted June 26, 2015 I did a search on here about Ken oconnor no luck.... I bought a bike beginning of this summer, the porting was done by him,it hasn't been ran, is this guy worthy of such a task???WUT! Quote Link to comment Share on other sites More sharing options...
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