articfriends

iTrader: (1)

Ive ran a boost referenced voltage booster in my own boat before on a Aeromotive elimiator pump, Im sure it could be done. I have several customers who didnt have quite enough fuel from a stock pump on dyno and it was marginally ok in their boat, once leaned out . I highly recommend a fuel pressure gauge at helm,

SB

iTrader: (1)

How much debris do you typically see in the filter baskets ?

SB

iTrader: (1)

Found a 502 with max power 5600rpm I had run into pipemax:

@ 5800 RPM
- Induction System Tuned Lengths = ( Cylinder Head Port + Manifold Runner )

1st Harmonic= 35.485' (usually this Length is never used)
2nd Harmonic= 20.140' (some Sprint Engines and Factory OEM's w/Injectors)
3rd Harmonic= 14.061' (ProStock or Comp SheetMetal Intake)
4th Harmonic= 11.067' (Single-plane Intakes , less Torque)
5th Harmonic= 8.979' (Torque is reduced, even though Tuned Length)
6th Harmonic= 7.554' (Torque is reduced, even though Tuned Length)
7th Harmonic= 6.520' (Torque is greatly reduced, even though Tuned Length)
8th Harmonic= 5.734' (Torque is greatly reduced, even though Tuned Length)
Note> 2nd and 3rd Harmonics typically create the most Peak Torque
4th Harmonic is used to package Induction System underneath Hood
Plenum Runner Minimum Recommended Entry Area = 2.865 to 3.223 Sq.Inch
Plenum Runner Average Recommended Entry Area = 3.294 Sq.Inch
Plenum Runner Maximum Recommended Entry Area = 3.365to 3.981 Sq.Inch
Minimum Plenum Volume CC = 1113.7 [typically for Single-Plane Intakes]
Minimum Plenum Volume CID= 68.0 [typically forSingle-Plane Intakes]
Maximum Plenum Volume CC = 8229.2 [typically for Tunnel Ram Intakes]
Maximum Plenum Volume CID= 502.2 [typically forTunnel Ram Intakes]

articfriends

iTrader: (1)

occasionally little paint chips, I see white beach sand looking "sediment/deposits" from evaporated gas with ethanol more than anything but surprisingly not as much as you'd think.

sutphen 30

I had my injectors out a couple of years ago,now I did my fuel system over and used really good filters,any way,after 12yrs in service,,they were still perfect.also,the baskets were clean.I really thought I was gonna find a ton of crap in there.
they're back in the engines and running great.
maybe my boat being a trailer queen has something to o w/ it,,always going to high volume gas stations.

smokediver

I recently went the 540 route from a 502 mag mpi. I went the carb route though. I was able to reuse my serpentine setup but had the headache of figuring out fuel delivery as there is no fuel pump boss on the seawater pump. And I had to run larger diameter fuel line. The motor dyno’d out at 712 turning all the accys on dyno headers. The Eddie marine exhaust knocked it down a full 50 horsepower… for fuel I went with a Weldon pump through the carb to a return regulator and back to the fuel fill. Vapor lock in south Florida is real !

mkr3686

As someone who had 502Mag MPI for 20 years in my 99 Velocity 280, I can say this is a very nice and accurate write up. I've done everything listed above and will re-mention and add the following.

1.) Biggest improvement is a good labbed prop with the right size/pitch for the boat.
2.) Properly tuned engine with all maintenance performed (plugs, wires, cap/rotor, timing set properly, etc)

In my opinion though, not a lot can be done to make any dramatic improvements in speed with this engine. I rebuilt mine bored 30 over with competition heads and an HP 500 equivalent cam, plus stainless marine exhaust manifolds and while the motor dynoed an extra 100+ HP with a stock 4 bbl Carb and Edelbrock manifold, once I put the engine back in the boat with the EFI and Stock MPI intake manifold I saw maybe 1 MPH more on the top end. The engine just felt too restricted and couldn't breathe well on the top end. I was about to try and have it re-tuned and mess some more with timing but had a decent offer and sold it. Realistically though, a super charger would be the best way to increase performance as long as the engine is solid.

articfriends

iTrader: (1)

Yes, in stock form its hard to gain much with MPI intake, BUT with intake modded, t body bored, properly tuned a MPI can make respectable power
Here are several examples of motors I dynoed and built or dynoed and tuned that others built:
!. My 272 Baja ran 60-63 GPS for the 6 weeks it was still stock when I bought it new, over course of time I made more and more boosted hp using a MPI intake. When I moved on to my 33 Scarab, I took the original 4.470 bore 502, re-ringed it with the .004 over srp pistons, Iron mag heads w some bowl and chamber work, a used 500 efi 731 cam, modded MPI intake with bored tb. Sort of a "economy" build. Tiuned on my Dyno that made around 560 hp in open header, glory trim. Installed in boat with Gil exhaust then tuned on water, the 272 that ran between 60 to 63 w stock mag, ran 68 to 70 GPS when i sold it depending on load.
2. Jeff Hoekstras 280 Power quest ran 66 to 68 with a 4.500 bore 502 w stock cam, stock heads, exhaust. Re-ringed, A mild cam provided by Valeko, a set of Promax 317 heads, MPI intake modded by me, bored out TB, made 611 hp in open header "glory pull" trim after tuning on my dyno. Made 580 ish hp on my dyno with EMI manifolds. We tuned it in the boat and saw 77/78 GPS with a 1/2 tank gas, 3 guys. He went on to run 81 on radar at LOTO at shootout 2 years ago, 1/4 tank gas, by himself.
3. Jason scott, aka, "racin jason" built a 4.500 bore, 9.6-1 502, dart 325s, highly modded mpi intake, bored out TB, made 630 hp/640 ft lbs of tq on my dyno tuned with mufflers on (lost power w open headers)
Tuned in boat (2001 280 powerquest) we were almost touching 80 mph, at LOTO 2 months ago he ran 83/84 on low gas then 85 on sunday (took hatch off and parts off boat LOL)
4. I built a piar of .030 over 454s with modded intakes, BOB m cams, bored out T bodys, iron factory heads I ported on, made 550 + nout of both motors before bolting his whipple sidemounts on, made 785 hp with whipple 2.3s w 9 lbs of boost, lowered boost and made 725, in a 322 Baja, runs between 90 nand 92 mph
There IS room for improvement on the MPI intakes, Flame arrestors and camshafts selection, heads or head work and TUNING are needed to get good results

CarreraHector

Hey Smitty do you have a shop? Sounds like you know your 502 MPI's like the back of your hands my friend. I'm looking for someone to rebuild both of mine and are more power as they have 600+ hours on them.

snapmorgan

iTrader: (2)

I toasted a 454 mag mpi in one of my boats and decided to build a mild 540 for it. After tuning, it made 565hp with the stock intake. I got one of the extrude honed intakes from ASM and had the throttle body bored out, made over 600 with no changes. I know that i left 30hp on the table by using the MPI setup, but it is what I had at the time and it worked great. I was also able to find a slightly larger oil cooler that fit in the stock location that had 1/2"npt fittings. Made all new oil lines with -8 hose. Worked out well.