312 fastech motor upgrade
 

Thinking of swapping my base 7.4l mpi's out and installing 500hp efi's. anyone ever do it, any other thoughts. thanks guys

There was a time I was considering re-powering my 312.
I called the factory and spoke with them about it.
They knew of one guy who had put 500 efi's in his but I don't recall if they gave me his contact info.

Give them a call.

Local mechanic put them in a 312 about 3 years ago. Pulled 454mags that had 30P props (1.65 drives) and borrowed my 34P's. The boat owner loved it even though I thought the props were a little too big....they claimed the boat ran well past 80 but that was on the speedo. (probably was running 80 GPS)

i think 7.4's make the 312 heavy in the a$$ end, 500's would just make it even more. Neat idea though. Would probably get it out of the hole a big quicker.

The 500's can't weigh much more than the 7.4......but with 190 hp more per motor it's worth it!!! I had a 312 with 502 Mags, that boat was 8,000 dry from the factory......it can handle the weight of BBC's in the back!!

Pretty much the same block. There won't be a significant weight difference, as t500hps said.

With that, 80 mph on a 31 foot swim platform boat aint great.

I just test drove a 312 with the base 7.4MPIs at Robert's today and had this very conversation regarding the 312 and bigger motors. The original BoatTest.com report of this hull with 2 X 385 HP 454 Mags they got 72.4 MPH on GPS at 5,100 RPM with 22" props and stock Bravo 1s- 1/2 fuel 3 persons. The base 7.4 310HP model we drove today got 64 MPH GPS with 2/3 fuel and 5 persons 70 degrees outside temp. Given this - The 500s or 525s will get you well into the 80's The factory runs the props deep - switch to short lower units which will raise the props and easily get you 4 to 5 mph with that change alone. I think that with a 496HO and shorty lowers you could get 80+. And yes - I bought the boat.

Congrats...Robert is a good as they come to deal with (I bought my 382 from him)

So you think its worth doing the swap I have 400hrs and stock motors still pur but as always more power would be nice. boat is very clean just don"t know about return on $ spent down the road.

your boat will be easier to sell later...but you'll never get what you put into it. (so what's the speed increase worth to YOU?)