Ok I Just got a 502 mercruiser carb engine for 1000 with only 300hrs on it........Ok I want to make 525hp at the prop..... YES AT THE PROP..So that means 550 to 575hp.....Reliable horse Power Guys....... Help Me what do i need.... I will put up my engine block number up tommorow...... I will run dry exhaust not wet..... I need a cam and lifters .... i dont know...... I have been told i can make my heads work just fine..just have them reworked... and not have to buy 2000 dollar set of heads.... need help!!!!!!!! call me 817-903-6661 Chris..... Nobody in Ft.Worth Tx knows **** abou building a marine engine...... 2 people do but they dont want to tell you how to do it.... they 10000 grand.... any and all help will be great.....

Put a good set of used heads on it,Change the cam and do a good intake and carb,I believe that has dished pistons so take some off the heads to get some compression.Oh and good exhaust.Those motors made I believe 425 hp stock,so you only got to make anouther150 hp You can do this pretty reasonable,lot of good used stuff out there. my 2 cents JOHN SR

Depending on the numbers will tell us your internals but the 502s should have the good gear. HP for your motor will depend on Pistons and Cam with a dry exhaust. Stock (rectangle) port heads with a good valve job will flow that much so long as your cam and intake can allow it to. John's totally right, head CCs = Compression. Depending on your heads (open vs closed) and chamber / runner size will depend on you CR. Get that all sorted and get a set of pistons to make the compression you want, then ask RMBuilder to match you a cam to your package with your target in mind. Then PRESTO! Hp at prop.

With a 502, you'll want a pretty simple set up, Holley 850DP, You can run an RPM Air Gap manifold easy, I'd recommend lightning or CMI for exhaust (that's what I'm going to) and spend your money getting the heads flowed and valve job done right. 575hp is high without getting carried away on compression but if you get a combo to work well together, it should be achievable.

Good Luck!
John (the other one)

Guys The 502 I bought turned out it was a 454 and i got my money back on it........ Sucks new $3000 was to good for 502 Mercruiser was to good to be true!!!!!!!!!!!! Still I Want to get to 85mph GPS All Day Every day even with full fuel and 3 people....... This is what i have so far....... Brand New Eddie Marine 12x17 tabs.... Full hydrolic steering From helm to drive Lathem Marine steering...... Complete bravo1 drive and transom assembly i am on the right track..... i need a complete dropin engine....... What horse power am i going to need to get 85mph gps.............

I'm running about 500hp with a Very similar set up to yours now (with a 468 and B1), best I've seen is about 75 with 3 people and fuel but that was into the wind. Mind you, my exhaust risers suck and I think it's costing me power. My new motor project is a 540 NA but I want dry exhaust and an Shorty drive (IMCO / Sportmaster).

I've always wanted to try a Blackhawk just for something different!
I'd stay the party line and try and find a good 502 long motor. Ebay usually has plenty in your price range. Then you can choose a sump, intake, cam and carb to suit how you want it to go.

Stick with it!

see when you start to build a motor you have to buy everything pullys,hoses,fuell lines,mounts,water pumps, i mean everything.... you canhave 2000 bucks tied up.... and other stuff.... ok i dont want to do a engine hatch modification..... I want it to look stock....can i put a 540 in this stinger and still be able to shut the engine hatch...... ok if i have to make a air resporator cutout thats fine..... but im thinking that a 540 when its all said and done that that might be a issue.......... Your thoughts.......

540/502/454 and all other standard deck big block Chevies
have the same external dimensions so a 540 is no bigger outside than a 454.

From my experience (i have a fresh 509" making around 525hp using most of the stock 502 internals,J&E pistons and a custom cam,) for a RELIABLE 575hp big block and the required oil system+cooling and the exhaust for that much HP your looking at $6000-7000 . Just a guess though ..

It can be done cheaper than that look in the swap and sell.You can put a nice motor together for about 3500.00 if you don't mind used parts of coarse you have to know what your buying.JOHN SR

Ok What kind of block will i need..... i am dum when it comes to buying the right parts.......... i am thinking that a 502 block will be easyer to find than a 540...... so lets go with a 502 block.... ok let me find a 502 mercrusier carb motor or a good long block.......

Thought you wanted to keep your short block intact,due to the fact that it only has 300 hours on it.Is that correct or due you want to start from scratch,I'm confused.JOHN SR