ok, in the endless pursuit of more forward Gs, time to upgrade to the 2.1 + more injector while engine is rebuilt.

some say don't do 850's on the primary, some say no problema.

i'm considering these:
http://www.ebay.com/itm/4-Siemens-De...item3cb364afbc

why, thinking tuning would be much simpler than having primary different than secondary.

seller claims these have superior flow characteristics than old design.

i personally dont see idle/response issues specially w/ the fresh rebuilt. i've been running 720's w/the Rtek 1.8 with the idle resistor almost maxed. my multimeter says injector pulse width is over 5ms @ 1000rpm. so going to 850's on a fresh motor (more vacuum) i'd expect pulse width not change much from current. seems to me there will be plenty of room for fine adjusment.

thoughts,experiences, suggestions appreciated.

 

Assuming those fit correctly, the issue is that the Rtek 2.1 has presets for 720s but not 850s. So you will be fiddling with fuel correction and such.

Also, make sure you don't get confused with the advice about 850 primaries on FD's. When people do that, they are usually swapping in the OEM side feed 850 (originally designed for the secondary position) and put it into the primary. They don't work well in the primary position on your typical FD running Power FC management.

 

There isnt much adjustment available at idle unfortunately. I'm running 4x750 and my variable resistor is at nearly 4 volts to get a smooth idle. I've tried running the N390 afm (cosmo 13b-re) and it wouldn't even try to idle regardless where the variable resister is set. You might have better luck leaning out larger injectors than bumping up the DC on smaller ones, but I doubt it, the variable resistor is pretty limited, and almost worthless in my experience.

 

ahh! so guess I'm wrong assuming I can initially address the low-rpm/high-vac range of the fuel map!?

 

I'm running an Rtek 2.x with 720's in both primary and secondary holes, no idle problems at all. This is on an S5T2 (N370 ECU).

 

You can address those areas of the map just fine, just so long as "low rpm" doesn't include idle. Idle is separate and cannot be tuned. It can be messed with by adjusting the variable resister value, turning the screw on the bac and perhaps the TB, but all those things combined font provide enough adjustment range to qualify as "tuning idle" in my book.

That being said, I dont see why you would have a problem getting 850's to run on the stock afm.