vented nozzle bodies

how important are vented nozzle bodies in the hat?? I've got an old carbon hat that I can't idle down to my liking, I got the butterflies pretty tight (any tighter and they jam) I've closed the gap around the shaft to the bearings and resealed the base. When I taped the holes shut on the nozzle bodies I made the best change in idle speed, I've got the barrel valve rather rich (85% to 88% leakage) (gage says 15% or less). Since this is a puller, I need to feed the throttle to drive it out the gate so I can't have the butterflies jammed shut....thanks for any help

 

I'm just a newbie myself but it sounds like you have a vacuum leak around the hat area.

Getting air in when the butterfly's are nearly shut tells me you're getting air in from somewhere else.

 

Happens all the time. You can solder the vents closed and drill small vent holes as needed.
But the easy way to do it is take a small lengths of hose that just fits over each of the nozzles right where the air vents are. So in effect, it is just closing off the air vents. Then drill little holes in the very top part of the hose until you get the air bleeding in that you want for the proper idle. Then, you can either run with the hose on, or solder up the holes and drill a hole in the top the size you had in the hose. They have done tons of testing with dyno stuff and the air vents do very little, (if any), off idle. You will not lose performance. Just a big help in the idle performance.
(This is also very handy to do when running a stack injected deal and want to get the EGT's close to each other at idle.)

 

yes I used silcone and let it set a day, I think that the butterflies just don't fit the bores of the hat real nice but is that that bad?? And that maybe changing the nozzle bodies to nonvented would help. I can't see where there might be a leak otherwise. Don't have the problem with the Big & Ulgy hat .... thanks

 

Did you try to reseat the butterflies in there bores?

 

On carbon hats the carbon actually loses roundness over time and this problem happens. You can order new butterflies and make them fit.....it's a lil' bit of work but much cheaper than buying a new hat. This is why several of the newer hats use billet fronts.

Brandon Booher
NHRA TAD #35

 

Hey Lucky,
Most of mine have the hole welded shut.