View Single Post
patkeefe patkeefe is offline
one of the great unwashed
patkeefe's Avatar
Join Date: Apr 2004
Location: Ringwood, NJ
Posts: 2,850
Here is the AFR story:
I have an IA modded fuel head. Problem with that is it went pig rich at the track, even on the street. So, I spoke to Brian Leask, and he modded a 930 WUR for my application. Still went pig rich, so we went to a RPM solenoid switch. It was still going rich at RPM's under the boost holdoff point. Then, I went to a stock late model SC fuel head, which I rebuilt (basically cleaned out and resealed) That worked better, but tended to get a bit lean at higher RPM (like 5000+). I define lean as above stoiciometric 14.5:1, but I prefer to stay in the upper 13's in cruise. Pig rich is 11:1 and below. Ideally, I would like to get into the upper 12's on boost. I fought AFR issues for two years, and most of it was all due to air leaks (thanks to rarlyl8 and beepbeep for the insight on that issue).

I spoke to Stephen at IA, and sent the head back for tweaking. I had the stock head at the track when the thing let go (the modded head is still in Kansas), so I may have been a bit lean that day, like pushing 15:1, at which point I backed it off, and readjusted my WUR to enrichen. My AFR gauge is prominently mounted, as it is about the only gauge I look at. Of course, one of these little crappy hemi's can detonate itself to bits in about 30 seconds, so operator stupidity may have entered into the picture. Our combustion chamber design lends itself to detonation issues, from what I can tell, especially running single plug as I do.
Patrick E. Keefe
78 SC
01 Boxster
Old 11-09-2008, 09:23 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #18 (permalink)