502 with Afr heads ideal compression ratio
 

I have a 502 gen VI short block with Srp flat top pistons(believe stock from GM)
That I am going to be building with 315 AFR heads and the crane 741 cam.

I believe the compression ratio will be 8.9-1 What is an estimate HP & torque this engine will put out?

Is the compression to low? Should I be boring the block .030 with more compression? or is that not needed?

8.9-1 sounds great for reliability purposes but want to make sure it will still put out enough power.

Thanks!

If it were me 9.5-9.8:1 and a cam that wasn't designed for crap heads 20 years ago

Just get the 315 heads with smaller chambers to get the compression up a bit. Then go with a custom cam, with more lift, to take advantage of the 315's cnc flow capability.

i would go with 10-1 and a cam from bob madera,he also can get you a fair deal on the afr heads.650 hp is what i would predict.edit in,i just reread your post,imo the 305 would be a better choice for your application.

answers in red

and yet it still works today.

EFI or carb ?

Yeah it works, but the profile is way off for those heads. Why pay $450 for that when you can get something better for the same $$?

Yup what he said ^^^ and a new dist. gear lol, custom grind is the way to go with those heads, Id bet it would make another 40 hp

depends on what exhaust you are running,but lets say cmi elbow tops around 600,gil or stainless marine 580-590 that is what i am seeing on a fully dressed marine engine on my dyno,add a little more compression and play with some cams 30-50 more hp,just depends on were you want your power curve to be,the afr heads flow real well and don't need a lot of cam to make good power

i agree with above,i used to do my own cam selection but now i use the experience &knowledge of bob madera.

In drag racing there is B&M, ..... in the marine industry we have BM, happy holidays Bob, I think Chads engines are still in Joplin.

I think the 305cc runner would be better suited to a marine 509, however, I believe the Full CNC 315cc version, which is simply a cnc ported 305 casting, will still make more power than the 305cc as cast head in this application. I dont think its a question of will the 315cc CNC head make more power, but more of a question, is the extra power it will make, worth the extra cost for the cnc porting.

My general opinion would be to go with a smaller dome profile, with a smaller chamber head to get you a respectable static compression. If you are going for a max effort 93 octane build, then I'd say, yea, go 10:1 static. But, if this is a pleasure boat that you want lots of hours, ability to run a bit lesser octane, and have a little safety factor, I personally would build it around 9.25:1.

I feel that most pleasure marine bbc engines, operating at 6000RPM or below, don't have enough camshaft in them to warrant the use of 10:1 compression. Building a setup like this, with a cam duration that may peak at say 5700-5800RPM, coupled to 10:1, questionable fuel quality these days, really lessens the safety margins. I personally wouldnt want a marine pleasure engine to have 190psi cranking psi on the starter with a modest duration cam, thats gonna run the crap gas we get nowdays.. 30 years ago, when we only had crap Iron GM heads to work with, jacking the compression up was one of the only ways to increase output. Today, custom cam profiles, cnc cylinder heads, efficient chamber styles, piston crowns, various exhaust and intake systems, there's lots of ways to meet your goals, SAFELY. Making a big dyno number is one thing, making it stay together for 300 hours of hard wot running, is another.

FWIW, I've seen many well thought out marine builds making 1.3HP per ci, with 9.25 static compression. Last year my buddy brian built a set of 540's that were flat top setups, around 9.25, that made 690HP at 6000RPM with one of bob's cams. Best bet would be to call Bob , and discuss these options with him. He will be able to tell you how much power to expect, what parts to choose, etc. He's been involved with more than enough "502" builds over the years. Just my opinion.

So you wouldn't slap an 8-71 on a 502 with iron heads and 185lbs cranking compression?
Wonder why it won't stay together???? Lol

I would, but only if I can lock the timing at 36*, run a 195* water stat, NGK-5 projected tip plugs, and eyeball the porecelin for a nice light tan color on the plugs. Should be fine for the next poker run. For something like that, I'd recommend a 174 B&M blower, 7-8lbs of boost should be ideal. :poopoo:

If you really want to take advantage of the 315 head spend some money on the valve train spin the motor 6500rpm and I'll bet it will make over 700hp. The head is capable of 700hp either have to rpm the smaller motor or use more cubic inches with less rpm to get there...

Those are the orange and black ones? If so- they're sexy pieces.

yes