New to oso forum,Just removed and broke down my 502 mag mpi motors,only had 200 hrs on them but not enough power.Looking to build natural aspirated motors. Can I use stock rectangle port heads to obtain this amount of Hp?I think 119cc chambers what would be a good piston?Im going full roller crane 741 cam ect. motors going in36 outlaw. Thanks

sutphen30,any ideas on pistons and comp ratio?you suggest isky springs,should I stay away from the crane?are those valves available in inconel?

Crack,

Nothing wrong with your stock flattops in 200 hours unless you been running gravel thru it.

Stay away from crane springs. Comp 929 are better than Cranes. Isky toolroom springs are expensive.

Youll need adjustable rocker studs and some rocker arms (harland sharp same price as Crane and last longer).

Ferrea makes inconel valves, but you don;t need them uless you plan to supercharge.

thanks for reply i have been reading your replys on other threads glad you responded.The stock pistons Im told had metric rings and were responsible for the engines using alot of oil.If I can use pistons over what would comp ratio be,and what rings could I use to upgrade and reduce oil consumption?Im happy to re use any thing I can,any advice on heads or porting to obtain 575hp?am I being realistic,as long as we get close to target hp not looking to split hairs.Looking to gain 10+mph to cruise speed and be as reliable as possible,doing the poker run gig.I have gil long turn exhaust late stlye hp 500 should be okay on reversion?


when in doubt rip it out!

Nothing wrong with a 502 using oil. The 502's ran typical forged piston wall-to-slug clearances which are a little loose versus a station wagon motor. The oil rings used a looser tension than a grocery motor as well.

Anybody's good performance ring pack will serve you just fine. I would stick with standard or low tension oil control rings. Oil is cheap, and you need to be checking it twice a day anyhow. If you have no room in the boat for a few quart bottled of oil, then throw something out and make room for it. Cylinder prep for the rings is important and make sure to get the recommended hone spec for the rings you choose.

CR will be somewhere around 8.5:1 - different on all motors cause the deck height varies a bit (yours is probably a -.023 deck or so).

Pocket port the heads, do a little unshrouding in the combustion chamber, gasket match the intakes, use a small flap wheel on the short side radius without changing its shape, and leave the longside radius alone.
3 angle valve job with .080+ seat on the exhaust side.

Hi perf valves versus factory stainless will give you as much as 10hp at 5200 but dont expect more.

741 cam with above mods (plus maybe a carb spacer) will put you in the 540hp range.

If you want more, it will take more cam and more money on heads.

If you do not plan to supercharge, then have the block decked to zero deck. That will give you a decent bump in CR and improve your squish.

stock pistons 8.5 cr will this be enough squish/ if I change deck height ,or pistons up 1 point 9.5 do I gain ?
Also 502 standard bore or 30 over 509 any gains?if standard bore gets me to my goal and block needs just to be honed I will go with that.What about the mods you talked about in the heads dollar wise?Whats your feeling on selling stock heads and buying complete merlins?wasting money?complete meaning,pocket port and gasket matched.Harland sharp,can they be obtained from jegs or summit/Rockers.this way I can obtain my 575 easier.Sorry for the essay,want to do it once !

Arright.
CR is (swept volume + combustion volume)divided by(combustion volume).

Swept volume is (bore area)x(stroke)
Combustion chamber volume is (deck ht x bore area) + (gasket thk x bore area) + (head volume) + (piston dish or minus piston dome).

4.470 bore
.023 deck
.038 gasket
flattop pistons (4 cc eyebrows)
119cc head
8.39:1 CR

Same setup with zero deck
8.72:1 CR

Back to stock deck
flattops
bore to 4.500
8.48:1 CR

4.500 bore
flattops
zero deck
8.82:1 CR

Stock bore
flattops
zero deck
111cc heads
9.22:1

Stock bore
17cc pop up pistons
.023 deck
119cc heads
9.71:1 CR

Stock bore
17cc pop ups
zero deck
119cc heads
10.18:1 CR

Gains hp wise to go to .030"
Yes. About 7 horsepower.
And you will have to rebalance the rotating assembly.
(but you will have to do that with pop ups, too)

Your stock heads are worth maybe $400 for the pair? I haven't checked the dragrace forum out, but they may pay more for them than boat guys - then again, there may be somebody wanting to replace peanut heads on a 330 (but these wouldn;t be their best choice).

Wasting money? On heads? Head money is generally money well spent if it is for quality parts.

H/S rockers can be found most everywhere.

this one would be about 8.5 just a typo Im sure

also the stock 502 mag pistons have a very slight dome to compensate for the eybrows I think and come out to around -3 not +4cc which is why stock compression is 8.6 -8.7 depending on the deck/heads

mine measured in at 8.78:1 with 4.47 bore, the block decked to .020, .039 gaskets and polished/cleaned up combustion chambers which brought them to about 120cc

If he builds a 540, he'd be there, but I don't think so with a 509. The 741 will be a little too big so the power will come in too high, the stock heads have a really crummy exhaust port, and he's missing 30 cubes.

Look at those new AFR heads. There is post in this forum regarding a recent dyno session. The power increase was very impressive. With the same cam the guy made some 50 hp more than me.

Okay ,merlin cast iron with pocket port gasket match intake with inconel valves ,harland sharp rockers,741 roller cam and lifters,merlin single plane or victor jr 870 carb ,msd ignition,gil headers and 8.75 cr + 550-575 hp?

What do think?would you put bigger valves on intake,or leave them alone,are we talkin 315 head 119 cc?

I appreciate all who responded!! My budget was roughly $4,000 per side those afr heads sound great but I didnot get a quote.Im guessing $3,000.00 per pair though.

Any idea how much to re work stock heads ?