Recommended Secondary Metering For SD-455

[Brian B.]

Hello,  I'm new here and I hope this was posted in the appropriate area. 

I have a question about secondary metering  for my application.  I have a '74 SD-455 TA with TH400/3.08's/1.65 rockers/X-pipe/Flowmaster transverse system.  I'm currently running CK rods on a "J" hanger.  It's not a track car but I enjoy basic street driving with occasionally fun like 0-60 blasts etc.  Do you think I'm getting close or should I experiment with more combinations.  Thank you, Brian

[Cliff Ruggles]

I'd run smaller tipped metering rods unless the primary jet size has been increased some.  The Super Duty 455 carburetors use a pretty large bleed tube, and secondary bleed holes beside them.  They typically enjoy pretty small tipped metering rods for best results. 

Since they were emission calibrated, and somewhat lean on the primary side, it's common to find larger than stock jets in them from folks helping them out some over the years.

In any case, the best way to tune the carb, is to get it perfect on the primary side first, best throttle response, off idle smoothness, fuel economy, etc.  Then go after the huge secondaries for best performance at full throttle.  If you can find good traction, a couple of dragstrip runs will point you in the right direction......Cliff

[Brian B.]

Thank You!  I'll try some shorter tips.

[Cliff Ruggles]

Brian, for best results when tuning the secondary side of the carb, use metering rods with he same length tip, taper, included angle, etc.

For the Class racers, we often machine a full set of rods from the same cores, in .002-.003" incriments within the range they request.

Changing tip length more often than not requires a hanger change to see the full effects.  It is actually quite easy to install metering rods with smaller/shorter tips, and actually go leaner on the next run or dyno pull......Cliff

[Brian B.]

Great.  I'll experiment with DA's then try an "H" hanger followed by a "K" hanger to see what works best.  Then possibly repeat with CE's or even short tips like DM's.