350 Mag performance upgrade suggestions

bmanafort · 02-22-2005, 01:44 PM

I own a 02' 29 foot lightning with twin 350 mags (300 horse). Are there any reliable bolt on accessories to boost horsepower and keep reliability?

SeaRay Jim · 02-22-2005, 03:11 PM

Unless you consider heads etc. bolt on, or if SC is an option, the 350 MAG is the same as any 5.7 but with a better fuel system which gives it the extra HP.

My guess is to get anything substantial you'll have to tear it down to some degree and at least do some head work, new cam etc.

bobl · 02-22-2005, 08:09 PM

If you're willing to ditch the factory EFI and go with an aftermarket system or carb you can get another 75 HP (per engine) or so naturally aspirated. Otherwise leave it alone. More than that, put a pair of Whipples on it.

Hydrocruiser · 02-22-2005, 08:16 PM

Quote:

Originally Posted by bobl

If you're willing to ditch the factory EFI and go with an aftermarket system or carb you can get another 75 HP (per engine) or so naturally aspirated. Otherwise leave it alone. More than that, put a pair of Whipples on it.

Whipples and headers.

Dangerous Dave · 02-23-2005, 09:04 AM

Start by doing yourself a favor and replacing your stock exhaust with Stainless Marine. I just put some on my 28 Cig and I really like it. It's lighter, looks better, sounds better, and makes more horsepower. They have a 5 year warranty and it will cost you less than 4g's

dykstra · 02-23-2005, 09:44 AM

sc's, cmi"s

Harper220 · 02-23-2005, 10:20 AM

Agree with everything said above or you might consider swapping for a pair of 496 HO's if your wallet will allow it... Then you'd have big block torque, a lot more hp and excellent dependability...

Badtoon · 02-23-2005, 11:09 AM

I would do some checking with Mercury because I was told by a boat builder that the 350 MPI's were listed at 300 but are actually 275 and that Mercury has upgraded it's brain on the new engines so they are 300 HP. May be worth checking into nay be a cheap 50 HP.

justinVIP · 02-23-2005, 12:39 PM

Where would you check into this extra 50 HP from the 'brain box'. I know that snowmobiles are totally different, but you can have the ECU reprogrammed by racers(who send them to the manufacturer) for an extra 15hp or so. On a sled, this is a huge difference. The problem that you run into on a sled, is that by reproming the ECU, you also are running a risk of less engine life, or restricted to diff. fuel, or just making the motor good for short runs/bursts. I would think that if it was that easy, to just send in the ECU(or whatever it's called in a boat), and gain 50 HP, everyone would be doing it. Someone please prove me wrong...I would do this in a heartbeat if it was possible! Someone on here has to know where or if something like this can be done, and if it is safe. Thanks, J.

justinVIP · 02-23-2005, 01:13 PM

I just got off the phone with a large aftermarket retailer in CA, and he said that you could gain about 15% more HP by remaping a stock ECM on a 2003 350 mag mpi. He made it sound like it there was really no big gain to be had by just doing that. I think he was contradicting himself because to me, 45HP for $400 is pretty cheap??? Is he blowing smoke?