Has anyone experimented with the actual engine run differences between remote needles feeding into a spraybar vs needles right-up-front-where-they-belong? (That is, I’m ignoring sprinklers / spigots)

At a recent combat match, I noticed the combat guys are universally using remote NVs. Being an old school guy, it took a while to figure out the obvious. Makes sense to use a remote for any profile mounted engine, as the needle can be placed to avoid breakage. And, it is nice have a little more distance to the prop (Yeah, I got one of those knuckle scars)

When the EVO came out, some changed, some said it was unnecessary. The LA s I’ve seen have been mostly up front. It seems logical that where the metering actually takes place should be immaterial if the spraybar is in the same place. But is that true?
   I know there are some strong prejudices on the subject. Any data?

    Larry Fulwider

My experience is very limited, but there is a slight lag in the adjustments taking effect.  Sure nice not to buzz my fingers in the prop, though. 

My experience is very limited, but there is a slight lag in the adjustments taking effect.  Sure nice not to buzz my fingers in the prop, though.  

My first few bench runs with an LA 46 still had the remote needle. Next day runs on the bench were with a regular needle, as I had to swap NVAs to fit the plane it was going into. I don't specifically remember any troublesome lag, or any lag at all. I was needling up and down, obviously.
         But, I'll bet you are right, and I was focused on other things. That seems an almost guaranteed difference with the distance involved.

Searching further, I've read some complaints of hard starting because of "retreating fuel" issue that Geoff mentioned, albeit his was due to a leak.

I think I'll try one on a plane here in a few weeks, and report back of any issues I find. Ya notice, no one has responded, "Don't ever use a remote NVA!"

Also, Ray Copeland mentioned last weekend that he runs several remotes, and so far hasn't had any issues.

     Larry Fulwider

Opinion only... Remote NVA's always suffer from varying fuel feed during maneuvers because the acceleration in either the 'up' or 'down' directions, independent of the attitude of the airframe, pulls the fuel in the line toward or away from the venturi.  This causes small variations in fuel feed and changes the run.  The effect is masked in a conventional setup because the metering orifice is located right at the venturi throat, where  manifold vacuum is maximum.  With the metering hole 2 inches or so away, momentum affects the fuel in the line between the metering hole and the venturi.  All of this goes for suction fuel feed only.  With a bladder fed combat setup the engine runs wide open all the time, so not much variation occurs.  You can play with this by running the fuel line up to the venturi on the same side of the engine as the fuel inlet, run some test flights and evaluate the run.  Then wrap the feed line over the other side of the engine, behind the venturi , making a tight U turn to attach to the inlet fitting.  Puts the weight of the fuel in the line on the other side of the engine.  I have been able to find noticeable differences just by re routing the fuel line.  On other guys airplanes only.  I never thought that a remote NVA could improve the run.

The engine shut off ruling affecting Slow Combat pretty much dictated a remote needle valve assembly starting in 1999.  Using OS FP RC Needle Assemblies proved totally reliable.  Those familiar with slow combat will know that these are suction fuel systems in a most demanding performance environment.  Unfortunately the shut off rule pretty much ended slow combat and AMA Combat for that matter after the 1999 Nationals.

Need to use a quality needle valve assembly like the OS FP RC Series use.  Not the LA Series that are prone to leakage and broken integral mount/spray bar.  Those who say it doesn't work or can't work satisfactorily probably never tried it.

If it was only the slow NV response, I'd be in favor of using remote NV's, but it isn't, for suction/muffler pressure fuel systems.

High pressure bladder fuel systems used on combat models fix all the problems, that is, if they don't leak. It's a different ballgame, and they work fine.    Steve