502 MPI build up
 

(585) 654-8583 bob madara will answer all your questions.

You would need to budget around 35k to build a 540 or buy a 525 efi. or rebuild what you have and go boat

35k is way too much. I mean it doesn´t make sense to try to duplicate a 525 wich is appr. $15k when i have to spend a lot in my old motor. I could sell my 502 for 2k, add 13k and get a 525. Or i rebuild my 502 and try to get close to the 540hp.
540hp seems to be right for 80mls. I totaly agree.
If i put on a double 58mm trottle body, rip down the intake diverters, put in a 525 or similar cam, pistons wich add litte bit more compression rate (we have 95 fuel), a little porting, ecu reprograming, what could i expect?
What would be the next steps? Heads? 540?

forged internals, cam, heads, prochager/whipple....done

oh yea and a pile of bravos to swap the broken ones lol

Im talking about a custom built 540 and a Mercury 525 EFI not a 454 with a 525 sticker on it......you can always do it cheaper but how long will it last. good luck OP

without heads i would not get the 540hp, right?
As i asked... ( double 58mm trottle body, rip down the intake diverters, put in a 525 or similar cam, pistons wich add litte bit more compression rate (we have 95 fuel), a little porting, ecu reprograming ) what do you think i could get out of it?

I saw 560 hp in dyno trim from a 502 w modded intake, 68 mm tb, 731 cam and lots of tuning on 89 octane. Iron heads w mild porting. Tpis bores throttle body from twin 60 mm stock to 68 mm for 270$ btw

I saw the Tpis TB, thanks! Perhaps a friend can do this job for me. Did you use the original 088 heads or aftermarket?

How much did just the throttle body alter the tuning in your case I don't recall if you mentioned it specifically?

I would bet you will need at least 600hp to go from 70mph to 80mph

i don´t think i need 600hp. with a wasted 415hp plus stainless marine exhaust it made 70, for 80 i think 530 could be enough, could be 550 on the dyno with dry exhaust and no sea water pump.

I´m more and more ok with going forward with a 540 rotation kit and bigger heads. Next questions will be do i need a forged crank, how much intake volume should the heads have, any opinions wich rotation kit, wich heads would work? Saw used heads mit 345 cc but think thats too much...

I recently tested my muffled dyno headers against imco powerflows w short risers on a 500efi with bigger tb other wise stock. At 5200 the powerflows gave up 14 hp, at 5400 gave up 21 hp, gained 10 ft lbs tq in midrange below the peak. So we take 20 hp off for decent marine exhaust and another 25 or 30 for no raw water pump, pulleys, hotter intake air in boat etc that 560 quickly turns into about 500/510. Surprisingly a set of Eddie marine manifolds with 19" long risers out performed my imcos in every way, still didn't come close to muffled headers. Open header vs the power flows, we were down 31 hp at 5200 and about 38 at 5400, I cant run open headers here often as I havent built muffler stacks yet plus it inflates the numbers so much there not realistic. I actually bought a set of 1 7/8 headers for dyno to try soon to see if I can pick up torque and kill a little hp over my normal ones so I can mimic what a typical set of performance manifolds do, haven't tryed them yet.

You will need to add 15-20hp for each 1mph gain in the speed range you are in. The faster you go, the more resistance so to go from 70 to 75 mph, you would need to add about 75 hp. To go from 75 to 80mph, you will need more like another 100hp. The 502mpi is rated 415hp at the prop and would be more like 430hp on the dyno. How much true hp you need would be somewhat dependent on how tired your current engine is.

Since the collector is the most important aspect of the headers, the mufflers are an extension of it...so, it depends on the design of the mufflers.

muffled boat headers or dyno headers? Like i said, at the 530 ish hp level, imco powerflows (with water going into the exhaust stream) were down 21 hp at 5400 vs dry dyno headers w gibson 5" boat mufflers dry. As far as dry boat exhaust muffled vs wet non muffled, idk, Smitty

you should try some doug thorley tri y headers,best of both worlds.

I bought some 1 7/8 vette headers to try, thinking they will bump bump up tq close to what manifolds made and knock off some top end hp, if they dont, ill buy some other ones. Its a big pia for me to run wet exhaust, we killed a 02 sensor w the Eddie manifolds too. Trying to find something thats as close as possible to numbers manifold made.

The tpis tb leaned motor out from 4500 up, especially from 5200/5400 up, picks up about 8 to 10 on a stocker 502, closer to 15 on a modded 502 or 540. If you bolt a gen6 fa or pos hardin/rex marine fa on it kills hp. Also took map at top from 92/94 to 97 ish. The rex marine adapter killed so much fliw even wo the element on it drove tune into low 90 map and sub 500hp from the 540 ish i was at at the time. Ive seen 540s w 502 mpi intakes w stock tbs and crappy fa pick up 2 to 4 mph in a boat, guys have to look at big picture. All the cu inches, cam, heads in world cant do much if motors choked off

The old heads look too wasted to re use them. I get some Dart Pro 1 heads.
How would you go forward, with 509 or a cast 540 set. A cast 540 set would only be a few hundrets more that the stock 509, but cast....

I´m going to order the Crane 168741, will the stainless marine exhaust work without reversion or do i need another exhaust system? I had the stainless marine exhaust for 14 years of saltwater operation, the stainless steal riser are ok, i only need the lower parts. But if there could be reversion i would go with anything other. I drive switchable silencer endtips. I may not make too much noise in my harbor and due to the stellings extension box i do not have an under water exhaust through the drive.

Does Bob Madera still make a set or cams for this motors? I gave him an email but got no response.