Technical > Spud Miller's Cave

Blower / fuel at idle

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32bantam:
Hi Spud.....I have an issue LOL...
Switched my 496 Arias Hemi from a 14/71 std helix (well worn in) to a fresh 16/71 HH retro set back to account for the front cut out. I was running the std. 14/71 at 15 to 20 % OD to make approx. 17 lbs. of boost to go 7.0.  My 14/71 std moved 500 cu.in./rev.  You don't list a 16 on your chart but it looks like each inch of rotor adds about 32 cu.in./rev....so I think my 16/71 should make 632. Now to get the new blower to move the same amount of air my old one did at 15% over....I started out with it 15% under.  Hopefully so far so good.

I started the engine and cyl #1 is VERY rich and # two is a close second (90-120 degrees). The other 6 are rich but OK (220-300 deg). It seems to clear up if I rev it.  I had the hat nozzles big in front and smaller to the rear....I switched them, front to back, and didn't make any difference.
I leaned the barrell valve A LOT and it helped. I checked the port poppet and it was at 15lbs. I changed the MSD 20 ignition box...no change. I ohm the wires and all are good. Leaked to barrell valve to get back to my starting point and the problem is back. I opened up the Shotgun blades from .014 to .019 to make sure they weren't getting sucked closed. Just made the idle higher.

So why are the front cylinders so rich? Do I have the blower spinning too slow at idle?  Maybe does not move as much air as I thought?  Too much fuel and not enough air......but I'm not sure why.
Thanks....

32bantam:
Tested the idle bypass...Good. Made sure the return hose was clear.
With the more I think about this it seems I just way overestimated the air moved by this blower at idle. When I had the barrel valve way lean for standard blower leak it is way rich.....when I leaned it to get the front cylinders to clear up .....the throttle response was good.

Frontenginedragsters:
Steve:
 Your engine just needs to get adjusted to Arizona air!!

Matt

Spud Miller:

 High helix blowers always throw all the fuel to the front at idle. The front two are OUT and the back two are burning up. For extreme cases like yours, I employ ball-check nozzle bodies on the front two hat positions. I set them to about 16 PSI and they are completely OFF at idle and on above that. Works great. In one case, we did the front four like that and the engine idled off the back 4 only. Two of those 4 were in the hat, the other two were in the back of the blower.

 Going down the track, the front two will be leanest generally, so the ports are staggered the other direction.

 Spud

32bantam:
Thanks...at least now I know what is going on.
I want to clarify....hat nozzles larger in the front?
Can I run the front four hat nozzles off the port block? The ports are set for 15 lbs. If not what do the ball check nozzle bodies look like? Do you sell them?
Thanks again...now I can sleep at night !!!!
Steve

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