Going to turn a 500 hp EFI into 540 inches and Procharge it with 3-5lbs boost...going to try to keep everything as stock as possible....going to re-program the ecm,but need to know if injectors are going to be large enough as well as fuel rail size.

mild cam
aluminum heads
8.75:1 compression
CMI exhaust
Merc ignition
M1-SC Procharger
AW-324 Innercooler

Anybody tried this before?

I have a couple m3sc 500efi kits. I also have programmable computers and software to sell you. t500hps did the 500 to 540 conversion last winter. He will chime in I'm sure!

You will need to run at least 55lb injectors if not 72lb,you want to run injectors at around 85% duty cycle at wide open running 38lb psi,call jim at arizona speed he is a real expert with fuel injection he can lead you in right direction also he sells a computer that you can program to fine tune your combo,you will need a good a/f meter in exhaust to aid in tuning. About ten years ago i built a 509 procharger engine used 55lb injectors made about 730hp 5-6 boost used a fel-pro computer(now FAST)engine ran real well,still running .Idled nice as was real fuel efficient at cruise speed,stock injectors on the 500 are 36(i think)and will have a hard time with anything over 600hp

I had 500EFI's with 8 PSI Prochargers.....Sold the Prochargers and built 540's. 9.7 compression, Iron Eagle Heads using a big cam...looks like stock 500's but they don't sound like it.

Not sure I'd do it again! The damn computer work cost bucks, I had 50# injectors in the motors with the Prochargers and figured I'd be good with using them. Turns out they were defective and took one motor out in 2 hours. We did install 55# during the re-build. Gained about 10mph over a stock setup (I bought the boat with the Prochargers).

The cost savings for a stock build would have allowed me to run stock motors at 4,200 all day everyday (at the same speed) and put extra fuel in the tank for years. Adding Prochargers to the 540's would create a monster. I'm holding the engine back because I can't get enough air through the monoblade throttle body we added but maybe forcing air through the plenum will compensate for the restricked passages.

Good Luck and let us know what you build.

and Jryan......build something...anything, just put motors in that rig or we're gonna order you a set of new merc 4.3's!!!

3-5 pounds of boost why bother. I would build a 540 10.0 to 1 AFR head engine will have 675-700HP and be far more reliable and cheaper.

Cobra Marty has a point. But if you want a super charger, just buy a Whipple and get the whole package that works and looks great. Not guessing what psi to run, or if you recaled the computer right etc...

I remember Dave Wesseldyk (WESCO RACING) having rebuilt a pair of Merc 500EFI's last winter (with cams from RMBuilder/Bob Madara of Marine Kinetics) for a couple customers that had Dave upgrade them to 540cid. One pair were naturally aspirated and the other pair had the Vortech Superchargers.

I have always heard that you are limited as to what can be done with the Merc 500EFI intake manifold----especially on a NA engine. The NA engines in this case were given a modified throttle body, slight increase in comp ratio, and a new set of aftermarket cast iron heads with a little light clean-up massaging/blending in the bowl area just under the valve seats.

I can't remember the power output of both sets of engines from the dyno, but I do remember everyone was very pleased with the results.

I'm no builder but have some buddies that helped me put mine together last winter. Based on what I've learned from them the 500EFI plenum is going to hold the engine back to 600-650 HP at most. This was confirmed by Mark at Precision Marine in New Orleans as he did my dyno/tuning. With all accessories turning, seawater pump to wet CMI's, we made 630HP at 5,100 and 700 TQ at 4,300 with a "stock" looking 500EFI. Mark claimed I gave up 30-35HP at the top end because the plenum couldn't pass enough air. Forcing air (supercharger) should over come that. Tuning will be key, I ended up flying Mark out to do more fine tuning out on the water. She runs and SOUNDS awesome!!!

BTW: My old 8 PSI Prochargers on a totally stock 500EFI were reported to make 830HP.....Mark claimed he did some and that they were closer to 790HP but like me, he didn't like the Procharger setup.

Tyler Crockett has been developing a upper plenum for the 500 efi,you might want to call him as he has found it was a restriction too,Smitty