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Engine basics => Engine set up tips => Topic started by: Terry Bentley on April 06, 2018, 05:28:08 AM
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when you have spray bar with one hole how should it be set.
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Single hole: Those I setup to spray in the same direction as the air going through to the crankshaft.
Double hole: i setup perpendicular to the air flow.
Al T.
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Most spray bars have one hole in them. Point the hole straight down the center line of the venturi, or down and slightly towards the cyliner, but not so far as you can see it. This is the point of highest vacuum. It helps to have two socket type tools , onwe to hold the position adn one to tighten the nut. Tighten fifrmly but gently. Tons has been written in the engine section on the subject.
Type at you later,
Dan McEntee
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Not to contradict anyone, but years ago I was told that setting the one hole spray bar works good with the hole set at about seven (7) o'clock, from the intake side, and at five (5) from the exhaust side, and I have found this to work well for me..
The modeler that suggested this was Marvin Denny...
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Thanks guys for your help. this has been a great help.
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http://www.nclra.org/TechTopics/NeedleValvePlacement/NeedleValveAlignment.pdf
Bottom line: If you can't get it RIGHT, anywhere downstream where you can't see it is just fine.
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One of those very nice "Stunt" Gentlemen from Texas did some fairly sophisticated vacuum testing about 25 or more years ago on what was the "Sweet Spot" for fuel suction from a single hole needle valve. Memory says it was 5 to 7 degrees off the centerline of the hole in the venturi in either direction. I also remember that it didn' seem to make a lot of difference as long as it was somewhere in the down direction. Just a little better in that particular area!
I think it was Frank Williams but that could be wrong!
Randy Cuberly
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One of those very nice "Stunt" Gentlemen from Texas did some fairly sophisticated vacuum testing about 25 or more years ago on what was the "Sweet Spot" for fuel suction from a single hole needle valve. Memory says it was 5 to 7 degrees off the centerline of the hole in the venturi in either direction. I also remember that it didn' seem to make a lot of difference as long as it was somewhere in the down direction. Just a little better in that particular area!
I think it was Frank Williams but that could be wrong!
Randy Cuberly
Yes, Frank re-ran this testing after I published the article I mentioned above. The result is not "off the centerline" but just off perpendicular.
The testing showed that there is a sweet-spot of just a very small rotation where the "suction" suddenly jumps, by on the order of 12%-15%, and that if the hole is positioned anywhere else (downstream) there just isn't any significant difference. Only at the "sweet-spot".
It's almost impossible to find the sweet-spot my just looking at the valve body in the venturi, so, as I said, just put the hole somewhere out of sight and you get what is available.
Now one must consider the old Fox 2-hole needle valve body. The holes weren't drilled directly opposite. Kind of wonder why. Maybe Duke realized that if you put the needle valve in so that the two holes were just about out of sight and "looked" the same to the eye, maybe they would find the "sweet-spot". Maybe .... ???