502 upgrade, anyone got a good setup?
 

Thinking about upgrading my 502's 425hp carbed, gm performance based, holly marine carbs (800) and stainless marine exhaust. Im thinking right now I want to get around 575hp, change heads/cam/intake, and want to run on 87 octane. Anyone got a good similar setup they have already done or reccomend a good head/cam/intake combination

easy..... call rmbuilder 585-654-8583

Bob Mandra:drink:

Use your heads, Crane 741 roller cam, Roller rockers, dart single plane intake, holley 800 carb. Probably be right at your goal, or close to it!

Will the 800CFM be enough for 502's running the 741?
I'm running an 850 and building a similar setup.

Are you running the TBIV ignition?

Plenty of carb for them.

I sent you a pm. Call me.

I don't know if you're running a blower, but could you put a set of rectangle port closed chamber heads from a 69-71 BBC to bump up the compression to gain some more power?

AFR 265 oval heads, Vic Junior intake, RM Builder cam and valvetrain. Easy 600+hp. An 800cfm carb is just barely big enough for this app and would need a bit of tweaking to optimize. A 950ish works better. I did a pair in a 29 Baja upgraded from 502Mag MPI. It went from 68 before to 86mph after! They made 630hp 605torque. Bob's the man!

You should have the square port heads i believe. Of course their are better choices for heads out there, but if your on a budget yours can work to meet your goal. I highly recommend sending your heads to Jimmy Valayko in grand rapids for a little magic, bob madeira cam, and you'll be a happy guy. Adding a solid 100-125HP per side in your 28 should make you grin.

I think the day's of head porting are almost done.. You could spend a week on factory iron heads and not come close to a good set of CNC'd heads right out of the box. What's it cost to send your heads out to get ported $1000? plus new springs, resurface, valve job, seals, etc.. Before you know it you're at $1500 with some dumpy old iron castings. Or you can get a brand new set of aluminum heads with all new quality parts that'll show up at your door ready to bolt on all for around 2k..

Those are nice:coolcowboy:

I agree. Also, unless they flow test them and flow test each cylinder you can lose flow, or have inconsistent flow throughout the head.

A friend of mine had a big-name guy port his heads. He wanted an aggressive head that started with an Edlebrock Victor Jr. and he had them ported from there. He paid the guy well for his efforts, got the heads back and had them flow tested. They #'s were worse after porting them than prior to porting them. He took them back 2 more times to the guy who was going to "work some magic" on them, and they never got any better.

If I ever pay someone for porting heads I would like to see the #'s before porting and after porting. It doesn't seem worth it to me, especially with the existence of CNC machines. I realize that even a CNC machine can't get in and clean up casting marks and obvious slag left behind, but that's stuff that I would take care of myself.

I agree for the most part with you guys. Going with some brand new CNC marine heads is the way to go. I had a set of square port heads redone with all new valves, inconel valves, new springs, guides, seals etc. Basically full rebuilds, all of my valves were junk. They did a little work on the bowls, and ended up costing me about 900 bucks or so.

A new set of dart CNC marine heads with inconel valves fully assembled are around 2500? So two motors thats 5k.

I was just stating that if he wants to go thru his current heads, they will support the HP he's trying to make with the right cam, and he can save himself a few grand. Of course if he wants to make 650HP out of his 502, then ya, go with some new CNC aluminum heads.

My buddy had a set of 502's, with old iron merlin square port heads(non cnc and no porting), 741 cam, HP500 intake, and 800 holley. made over 600Hp and 600FT lbs on the dyno and ran great.

Assuming all is good with the 502 what would cost be to get 550-600 hp?....and I know the phrase "if you gotta ask you cant afford it".
Lots of boats out there with twins black power, might be cheaper to get the power out of them instead of selling them and looking to buy blue motors.
Sorry for the highjack......
mike.

Call Eddie at YOUNG PERFORMANCE MARINE he would be you guy. He is great to work with and flat out knows his stuff. I've got 750 horses worth of proof as do a bunch of other guys on here. IMO

double post sorry

Can you put closed chamber heads on a factory 502 to get more out of it?

Most guys say they do not work well on boats. Not sure why?

Everyone has given good advice here. You could rebuild the heads you have and spend the money on exhaust and cam. Forget using 87 octain, I set mine up with 8.9 comp so I could use 89. Again like was said call RMbuilder for your cam.

You are trying to reach a pretty easy goal. What you are asking is not very difficult to accomplish. There really is no reason to have some super special top secret cam to make less than 1.15 hp/ci. from a BB Chev.
I also would not normally recommend spending a bunch of money porting stock heads, but in your case I would go ahead and do the chambers. I would also deck them some to bump the compression. Porting the chambers will help to remove potential hotspots that may occur with the bump in compression and increased cylinder pressures. The stock heads have a pretty sharp edge that is left when the heads are cut for the valve seats. There is also a hump right near the spark plug that is also a potential hot spot. You may also consider just a little work in the bowls. There is also a pretty good sized hump just below the seats. Porting both the chambers and the bowls should only run 400-500 per set at most.
With the combustion chamber porting, a bump in compression, a decent camshaft, good intake (Dart, Brodix, or similar single plane), you should easily be able to make your target power of 575.
Let me know if I can help in any way. Thanks
Eddie

I agree. Cam doesn't need to be top secret. But.... when I discussed the way I used my boat with rmbuilder, and what I had in mind for rotating assembly and induction, and what I expected from the engine (NA 557), Bob Madara came up with a grind to suit my needs. On the dyno the engine was within 100 RPM of the range we were looking for. It's run flawlessly for 3 seasons and I couldn't be more pleased with the results.

Eddie is right on about the cast iron GM heads. I have ported and polished a few sets (for my own use). The set I have now are large oval 820's and I cleaned mine up just as Eddie described. If you are a "gear head" or do it yourself kind of guy all you need is a good air compressor, rotory tool and standard abbrasives kit. Or you could send them to Eddie and let him do it for you.
I am however completly sold on the RMbuilder cams. I gained 5MPH going from a so called performance flat tappet cam.