I have 30lb SVO injectors with the engine being a 355 and having a 306 cam, LE1 with a 3 angle racing valve job done to the stock valves, longtube headers, cai, but I am still on the 48mm throttle body. I am thinking about getting a 52mm or 58mm throttle body and upgrading to 36lb SVO injectors.

Do I need to get it retuned again if I install the 36lb injectors before I install the new throttle body, if so why? I was thinking the oxygen sensors would readjust the injectors by having the computer lower the duty cycle of the 36lb injectors so it wasn't running to rich? Also would I need to retune it after I install the new throttle body or can my computer take care of that as well? Just to let you know my computer has been tuned for the 30lb SVO with the stock fuel pressure. Thanks for any help.

 

It will be so rich that you run the risk of causing damage by washing down the cylinders with fuel. At best, it will run like azz and use a ton of fuel. Don't do it. Just to illustrate, if it's 13:1 now (it will be in that range in PE mode) and you install 36# injectors, it will be ~10.5:1. At that AF ratio it will smoke like a pig.

Rich

 

The long term fuel corrections can only pul 15% of the fuel, then they bottom out. And when they are doing that, they only correct in closed loop, not in PE mode. Running a 36# injector in a setup using the correct flow constant for your 30's would require slightly greater than 15% correction, meaning you would be trusting the short terms to make the corrections - not a good idea, since its going to run rich until it goes into closed loop, and you have to hope that the PCM is already running with BLM's of 128 or greater, and that nothing else happens that requires additional fuel cuts.

Then the big problem.... when you went WOT (PE mode) the PCM would be pouring in 20% more fuel than you need, because if the BLM's are cutting fuel in closed loop, it defaults to a 128 BLM in PE mode, and would run pig rich... as Rich has already pointed out.

And, the PCM can't adjust the "duty cycle"... it uses the BLM's to adjust the pulse width.

Most tuners will do "updates" at a reduced cost. Or, changing the injector constant is so simple, its easy to do yourself.

 

I thought the same thing years ago when I went from stockers to 30 pounders. The car would barely run, and it died continually.

Save yourself some heartache and do the T/B and injectors at the same time and get it tuned together.