I am planning on converting my 406/Vortec from carb to Super Ram. I have searched here and on some other sites to figure out what sized injectors to use, and I have found some conflicting information. Basically it seems that too small is bad and too big is worse. I was further confounded by the low/high impedance injectors. I would like to use the stock 90-92 ECM with custom prom, so I think I it will work out OK as long as I use the correct injectors. I think I need 34LB high impedance but I am not sure.

The second issue is; can the stock TPI air clearner/inlet assy flow enough air to keep pace with the 58mm/1000CFM throttle body? I measured the size of the outlet from the air cleaner/inlet at 3".

This vehicle is for street use now, and possibly some road course work later. The local road course (VIR) has a 4000' back stretch!

I am on OLD carb guy, and converting from carb to custom EFI is showing me that I should have paid more attention in school.

 

What size cam are you running with your 406 for a better estimate of injectors. I would think somewhere between 30-36 would be good(now it depends on the cam though). The stock assembly will hurt airflow so an aftermarket or custom piece would be a lot better. You'll like the benefits from carb to EFI I know where you come from. My father knows just about everything about carbs and I know more about EFI than he does. Just shows you how times have changed.

 

I was over 90% on the duty cycle using 30lb injectors on a miniram 383, now with 36lb injectors, I'm at 74%, both shifting at 6500 rpm and fuel pressure at 45psi.

You should be fine with the 36lb'ers and will have more room if you need it with increased fuel pressure.

 

Cam details; ComCams 12-000-5
INT lift .477 Duration@.050 224
EXH lift .490 (.508 w/1.6) Duration@.050 236
Installed @ 108.0 C/L
Lobe seperation 113.0

 

I'm running 32s on my 383 so I would say 36s would leave you with room to grow.