Offshoreonly.com - 502 MPI build up

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Offshoreonly.com (https://www.offshoreonly.com/forums/)

- General Q & A (https://www.offshoreonly.com/forums/general-q-20/)

- - 502 MPI build up (https://www.offshoreonly.com/forums/general-q/357825-502-mpi-build-up.html)

hogie roll

11-26-2018 10:01 AM

The key differences are the heads, cam and exhaust. I believe the intake is the same.

525s have edelbrock heads. There are better aftermarket options. Cam is similar to crane 741 which is good for what you’re doing. You should skip the 525 exhaust and use the thunder n lightning.

Baja Rooster

11-26-2018 11:22 AM

If you stray very far from stock add in another $1500+ or so for redoing the oil cooler and fuel systems. I’d freshen up the short block to marine specs, have some good heads built, massage the intake system, and enjoy boating for another decade or two.

BBYSTWY

11-26-2018 11:39 AM

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

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

F-2 Speedy

11-26-2018 01:12 PM

Quote:

Originally Posted by hogie roll (Post 4660881)

I suspect you could do it much cheaper.

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

Bang Bang

11-27-2018 11:01 AM

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?

articfriends

11-27-2018 11:04 AM

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

Bang Bang

11-27-2018 11:53 AM

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

Diamond Dave

11-27-2018 12:07 PM

Quote:

Originally Posted by articfriends (Post 4661111)

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

Griff

11-27-2018 01:02 PM

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

hogie roll

11-27-2018 02:25 PM

Quote:

Originally Posted by Bang Bang (Post 4661120)

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

make sure you understand the difference between dyno trim and in your boat. Highly dependent on your exhaust manifolds and how many pumps you hang off it.

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