I have a 7.4MPI with mag internals and Merlin heads, roller/rockers. Unfortunately I did not up-grade the stock injectors and detonated after 3 re-maps. I plan to up the injectors to say 40#s, re-map accordingly, install a LM-1 recording O2 sensor with fuel pressure logging for final tuning. I have the stock procharger (red regulator) set up with a red vein pump feeding the stock 7.4 mpi fuel-cool/stock pump. Do I need to change any of the fuel delivery system? Can I keep the fuel/cool? I had in excess of 60#s pressure with the smaller injectors programed @ 90% max duty cycle. What new injectors should I use and what W.O.T. pressure should I run? Thanks for your help.

I think you are fine with fuel delivery but do need an injector change. I have to go back and look at the injectors on my Modified M3 motor. Arizona Speed and Marine was a big help with the injectors and remap as well. 250 hours no motor problems.

I supported 700 plus hp with stock 42 or 43 lb injectors at 75-80 psi at 80-90% duty cycle so I'm sure you could use something that size for what your trying to do,mine were fine at 70-75 psi with less boost around 650hp. Are your injectors short and stubby (micro's or mini's they are sometimes called) or long?Here is a pic,the smaller one is a stock merc,the longer one is something I went to when I went bigger yet,Smitty

Short and stubby! WOO HOO!

Thanks for the response. It has been a year since I have had the injectors off but I think they are small. Mark @ performance said the good news is that the injectors on my set up are more popular as a stock item and therefore easy to replace. The motor ran all summer on the stock injectors, so I am probably not too far off. I thought about putting what ever volume comes with a stock Merc 500 or 525. Any body know what comes with either of these engines?

Rbeyer What injectors did you go to?

I have 42# injectors that were cleaned and flowed that I ran in my M-1 Procharged 468 which produced 638 HP with perfect A/F Ratios and EGTs.

I am selling them and could have them cleaned and flowed again prior to sale and send the data with the set.

You have the correct fuel system for your application.

Kirk