I was wondering if the hole should be located straight down parallel to the piston center line or slightly backward parallel to the venturi hole center line?
Woody
Needle Fuel Hole Location
Stuka Stunt Main Forum · 12 of 12 known posts recovered
Woody,
Past experimentation has shown a slight advantage between 5-8 degrees off straight down relative to the intake hole. That said anywhere within 20 degrees of straight down will work OK in most cases.
When I was a teenager about a million years ago some much older and wiser combat guy (Hothandle) told me to point the hole at the bottom edge of the backplate. By golly that works even if for no particular reason.
Randy C
Past experimentation has shown a slight advantage between 5-8 degrees off straight down relative to the intake hole. That said anywhere within 20 degrees of straight down will work OK in most cases.
When I was a teenager about a million years ago some much older and wiser combat guy (Hothandle) told me to point the hole at the bottom edge of the backplate. By golly that works even if for no particular reason.
Randy C
A good place to start is 45 deg towards the back. You want to keep the hole at a location where the air hasn't yet seperated from the body. This is where the static pressure in the vent is the lowest so the fuel "draw" is the best. If you get it too far down (past the seperation point) you are usually in an area where the air has stalled and so has a higher static pressure and thus lower "draw". DaveA
Hmmmmm....
Well this all sounds good but if you'll do a search on here you can turn up some actual data run by Frank Williams many years ago that doesn't exactly agree with this statement.
See my post above. Where fluid separation occurs is dependent on many factors and is likely not very predictable in the constantly changing pressure invironment inside a "venturi". However while "just out of sight" or at 45 degrees will admittedly work neither is "ideal" in typical cases.
But then, what do I know?
Randy C [photo not recovered: sipcof.gif]
Well this all sounds good but if you'll do a search on here you can turn up some actual data run by Frank Williams many years ago that doesn't exactly agree with this statement.
See my post above. Where fluid separation occurs is dependent on many factors and is likely not very predictable in the constantly changing pressure invironment inside a "venturi". However while "just out of sight" or at 45 degrees will admittedly work neither is "ideal" in typical cases.
But then, what do I know?
Randy C [photo not recovered: sipcof.gif]
>Hmmmmm....
>Well this all sounds good but if you'll do a search on here
>you can turn up some actual data run by Frank Williams many
>years ago that doesn't exactly agree with this statement.
>See my post above. Where fluid separation occurs is dependent
>on many factors and is likely not very predictable in the
>constantly changing pressure invironment inside a
>"venturi". However while "just out of
>sight" or at 45 degrees will admittedly work neither is
>"ideal" in typical cases.
>But then, what do I know?
>
>Randy C [photo not recovered: sipcof.gif]
I agree that predicting where seperation occurs is pretty hard to predict or more to the point prove. I would suspect that putting it in a position that is consistant within the scope of the individual installation would reward you with a consistant result. Starting in an area that is consistantly in a recirculation zone or consistantly in a non seperated zone would seem to produce consistant results. One thing that is consistant is that there are many opinions and more to the point many functional results. But then I would confess that 45 degrees is more ideal and typical in my experience than along the axis of the venturi. I don't doubt Frank honestly recorded his results and that you believe them. I believe the 50 years that I have been installing spray bars. DaveA
>Well this all sounds good but if you'll do a search on here
>you can turn up some actual data run by Frank Williams many
>years ago that doesn't exactly agree with this statement.
>See my post above. Where fluid separation occurs is dependent
>on many factors and is likely not very predictable in the
>constantly changing pressure invironment inside a
>"venturi". However while "just out of
>sight" or at 45 degrees will admittedly work neither is
>"ideal" in typical cases.
>But then, what do I know?
>
>Randy C [photo not recovered: sipcof.gif]
I agree that predicting where seperation occurs is pretty hard to predict or more to the point prove. I would suspect that putting it in a position that is consistant within the scope of the individual installation would reward you with a consistant result. Starting in an area that is consistantly in a recirculation zone or consistantly in a non seperated zone would seem to produce consistant results. One thing that is consistant is that there are many opinions and more to the point many functional results. But then I would confess that 45 degrees is more ideal and typical in my experience than along the axis of the venturi. I don't doubt Frank honestly recorded his results and that you believe them. I believe the 50 years that I have been installing spray bars. DaveA
phantomflier · Apr 04, 2008 05:46 PM
#8 source>Hmmmmm....
>Well this all sounds good but if you'll do a search on here
>you can turn up some actual data run by Frank Williams many
>years ago that doesn't exactly agree with this statement.
>See my post above. Where fluid separation occurs is dependent
>on many factors and is likely not very predictable in the
>constantly changing pressure invironment inside a
>"venturi". However while "just out of
>sight" or at 45 degrees will admittedly work neither is
>"ideal" in typical cases.
>But then, what do I know?
>
>Randy C [photo not recovered: sipcof.gif]
Only problem is Frank says he doesn't have a formula to calculate where the sweet spot is, but it isn't far off of the venturi axis.
>Well this all sounds good but if you'll do a search on here
>you can turn up some actual data run by Frank Williams many
>years ago that doesn't exactly agree with this statement.
>See my post above. Where fluid separation occurs is dependent
>on many factors and is likely not very predictable in the
>constantly changing pressure invironment inside a
>"venturi". However while "just out of
>sight" or at 45 degrees will admittedly work neither is
>"ideal" in typical cases.
>But then, what do I know?
>
>Randy C [photo not recovered: sipcof.gif]
Only problem is Frank says he doesn't have a formula to calculate where the sweet spot is, but it isn't far off of the venturi axis.
Put the hole straight back then rotate down untill it just goes out of sight. Any where between there and straight down will work just fine.
Giffy
Giffy
Not to say anything disparinging or however it's said, I have been setting mine at about 8 o'clock to 4 o'clock depending which side of the engine you are looking at and they have worked well for a number of years. I guess that what ever works for you is best...
Gil Causey
From all this you can deduce the "not pointing up" is the way it should be.
Randy Ryan <><
AMA 8500
SAM 36
BO all my own M's
Randy Ryan <><
AMA 8500
SAM 36
BO all my own M's
>From all this you can deduce the "not pointing up"
>is the way it should be.
>
>Randy Ryan <><
>AMA 8500
>SAM 36
>BO all my own M's
Right on Randy...
Dwayne
>is the way it should be.
>
>Randy Ryan <><
>AMA 8500
>SAM 36
>BO all my own M's
Right on Randy...
Dwayne
Keep a handle on em!
Derek Moran put up a post on this subject, or maybe he just added to an existing thread. In any case it would be worth a search.
For what it's worth I install the body as noted upstream a bit, being able to see the outlet hole and as the nut is tightened rotate the bar just enough so the hole goes out of sight while looking straight down the venturi.
Not as scientific or as trick as Derek's technique but I get satisfactory results.
Interestingly enough we get questions such as this and people follow the best advice quite nicely. Then they fail to well and truly seal up their installation with some kind of high-temp silicone between venturi and engine case, NVA and the mounting boss.
Dan
For what it's worth I install the body as noted upstream a bit, being able to see the outlet hole and as the nut is tightened rotate the bar just enough so the hole goes out of sight while looking straight down the venturi.
Not as scientific or as trick as Derek's technique but I get satisfactory results.
Interestingly enough we get questions such as this and people follow the best advice quite nicely. Then they fail to well and truly seal up their installation with some kind of high-temp silicone between venturi and engine case, NVA and the mounting boss.
Dan