STV_Keith

Thanks for the thorough reply. I'm not an engineer, but appreciate the technical info. Coming from the automotive world, I've been suprised to see how rich the engines run in the marine market. A stock 502/500hp we put a wideband on a few weeks ago idles at 11.6:1! That's super rich.

In the automotive world, 14.7 (stoich) is where they try to get the motors to idle. These days, they all do idle there, sometimes leaner.

While playing with the injection on the 500hp, we found it would idle just fine at 13.0-13.5. That 500hp was rich (never leaner than 12.0:1) all the way up until 3250rpm, where it progressed to 12.8-13.2, what I expected to see for peak aspirated performance. We leaned it out to 13.0 in the lower ranges and it picked up quite a bit of fuel mileage. At one point, 28%! It went from 2.8 to 3.5mpg. This was in a smaller, 22' Stoker.

I'm still curious as to the reason Merc runs them this fat.

Where do you plan to set your motors to run once they're broke in? If your fuel curve makes a nice, flat A/F curve that can be raised and lowered simply by adjusting fuel pressure, it sounds like you've got a pretty good tune already. Too bad you can use the wideband you have for closed loop feedback and just tell it what you want for A/F huh?

Gimme Fuel

Yea......I wish I had a newer MEFI controller to use. Running closed loop would be nice. I havent felt like re-pining all of my harnesses...haha. I imagine if I go on to adding boost, I will wind up doing that or getting completely away from the MEFI's ang going with a GM controller. I was trying to save money by adapting what I had but that faild so now I am stuck with it for a while. My friend and I have the HP Tuners software and a Mustang chassis dyno that we do a lot of tuning for GM and Ford vehicles on.

I would have to say that Precision Marine guessed the tune pretty much spot on. I can mess with the timing curve by messing with the distributor too. I have been nothing but impressed with Precision Marine and Marine Kinetics. They both worked together on the tune and the cam to make it right for the setup.

It is amazing how much more power and mileage the factory leaves out of their tuning. I think Merc leaves them fat because they know the motors are going to be abused and they don't want extra warranty claims. Just like what I have experienced with snowmobiles and such....very fat from the factory to keep them from burnin holes in the pistons. It is all about reliability.

My truck has an 8100 Vortec (496) and WOT AFR was over 15:1 stock!!!! My guess is they wanted to eek some mileage out of them, didn't work though. No wonder why they all burn the rings out and burn oil when used hard. I gained about 60 RWHP and 2 MPG on that truck.....runs awesome now and has since slowed on oil consumption. I would love to throw some Raylar parts at that thing.

articfriends

iTrader: (1)

Gimmee fuel: I run the Saginaw river ocassionally. Your ASFR's are WAY too rich for a N/A motor, we need to get together and give it a on the water tune. I have talked to Mark before, he is a nice guy. I redid my afr's on my N/A tune in about 2 sessions of river tuning 2-4 hrs each time, we set afr's at 13.5-14-1 at light throttle and at the higher rpm's we set them in the low 13's/high 12's. I built custom twin fuel rails with bigger injectors on my mpi set-up, if you go back and look at my old post from around 2004-2005 I put exstensive pics and detailed writeups on here about it. Like I said too, I bought 2 spare throttle bodys and had them bored to sell on a exchange basis, 1 is early style, one is late style. When we did our river tuning, we loaded motor hard with tall prop and tabs dragging and loaded motor light with short prop to set all the fuel tables at different map settings so it would be right no matter what. It really brought the cruising mileage up and cleaned up the transom, you got my number from my pm, if you need to try some props I have a shelf full of 24's, 26's and28's too, Smitty

STV_Keith

Smitty, does your software have you map the fuel table as RPM vs. MAP or some other reference? Is that the MEFI-burn software?

articfriends

iTrader: (1)

I have the mefi-burn program, it lets you do alot of stuff, you can work on the fuel tables in different rpm bands-ie-idle to 1200 1200-2400 etc or something close to that, Smitty