Hi All-

So my father and I have been having a discussion for the last week or so about the best way to rebuild the Gen IV 502 mag's in my 1991 formula 311.

Here are my requirments:
Would like to see at least 550HP-575HP
Can not turn more than 5500RPM
Needs to run on Pump Gas 91 octane
Would Like to use Stock Heads

Here is my idea:
Cams (Crane 741),
Intake (Merlin single plane)
850 Holley
Ported stock heads.
Revolution Marine Manifolds
Stock Compression 8:75to1
Turn it at 5200-5500RPM

Will this build 550HP? What Ideas do you all have?Any help would be great.
Thanks
Don

Lchornet-

Thanks for the help!
I am trying to keep the cost to a reasonable amount, or as reasonable as boating can be.
Being only 24 years old I only have so much money to play with so If I could find a way to use my stock heads I think I would "hopefully come out ahead.
I agree with you that bumping the compression ratio would be a great idea but in Cape Coral,FL it is almost impossible to find any marina with octane levels greater than 91. So I think this would be out of the question unless there is a way to find 93 octane fuel....

Thanks Again
Don

I am sure that I have 502's. 1991 was the first year they produced the 502 mag's. They were rated at 390hp @ 5100RPM.

Its doable, but you'll need to bump the CR. 9.5:1 would be a min. My last one got right around 565hp, 630# tq. w/ the 741 cam. You can run 91oct. I did. Just be gentle with the timing and jet a tad rich. I ran merlin 315 runner heads with just a bowl port and 3 angle valve job. Demon carb Merlin intake and MSD. Good machine work/parts and assembly are a must to make it live.
I'm in Ft Myers so if you need more info contact me, I'll be glad to help.

Dan

I think the (731) cam would be a better choice unless you want to turn them higher than 5500 and use more compression.
The Teague 509 620hp has a cam that is slightly larger than the (731) and makes power at 5600 - 5800.

Hey guys this is great info. So If I wanted to bump the compression a little to 9.5 to 1 what would be the best way todo it? What pistons do you all recomend?

As for the cam, 731 versus 741, in comparison where do these cams make the best power. It wouldn't make sense to run more cam than I need so if I could run the 731 I would be better off.

One other question, right now in stock configuration the Gen IV's run Flat Tappet cams while the 731/741 are roller. Can I run a roller cam in a Gen IV or would I be better running a similar profile Flat Tappet cam? What would need to be changed to run a roller cam?

Your question was 'Best Way'...

If you keep compression at 8.75 to 9.0:1, Run Canfields 310 cc w/CNC chambers and hard anodizing for corrosion protection, a custom cam and retro fit hydr. roller lifters, a good flowing intake, and roller rockers, you can burn 87 octane, and see between 550-600hp, depending on quality of exhaust and max. rpm you wish to run, and how much in the way of lift and duration you desire (and back to the exhaust thing again, to avoid reversion). About 4000 bucks. And it will live a long life.

I started with Gen 6, decked the block for quench(CR went to 9.0:1 w/.028"Cometic head gaskets), balanced and checked specs, and I'm expecting to see about 590-600hp, sometime this week. I have CMI e-tops exhaust, polished.

You may wish to do a search on a good, bigger oil pan and bigger oil cooler, now, because running more hp makes more heat.

Consult CStraub; he did my cam.

I did pretty much what you're looking for this spring.. I have 40 hours on it so far and it runs excellent!!!

I've gotten up to 79 mph in my little Checkmate so far.

Doug

502 Build and dyno results

This is my Gen 4 motor and heads 9.4-1

RPM TRQ HP BSFC
3000 533 304 .64
3100 544 321 .62
3200 552 336 .59
3300 558 351 .60
3400 559 362 .59
3500 557 371 .59
3600 556 381 .58
3700 554 391 .59
3800 557 403 .56
3900 555 411 .57
4000 552 421 .57
4100 554 433 .56
4200 560 448 .56
4300 563 461 .56
4400 572 479 .56
4500 579 496 .55
4600 580 508 .55
4700 581 520 .56
4800 575 526 .57
4900 574 535 .54
5000 572 544 .56
5100 570 553 .56
5200 564 559 .55
5300 558 563 .54
5400 553 569 .55
5500 555 581 .56
5600 544 580 .56

509 gen4 block & heads. This is the boat setup (fat & 35 degrees)

850 hp holley, merlin single plane marine, ultradyne cam. ported heads, port matched, ceramic coated forged pistons.

Doug-

Thanks for all of your information. This is a great help. I might be emailing you in the furture about specific part numbers that you are using.

Thanks,
Don