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

Wobble-
Did you use a Flat tappet cam or Hydrolic cam? What was the specs for the cam that you used?

It's a custom grind Lunati/Ultradyne full hydraulic roller setup.

230*in 238* ex @.050"
114* lobe sep
.600" lift in/ex
1.7 rocker ratio

If you call Lunati, ask for Harold Brookshire formerly Ultradyne Cams. He is hard to get to. Never had any quality issues with Ultradyne, but I have seen some complaints here about Lunati quality. Mine is working fine so far.

RMbuilder here on OSO is an excellent source of info and would be worth contacting.

BTW we also gasket matched the Merlin intake to the carb base gasket. Lot of extra material there.

No problem

Anything you want to know about it I'll be more than happy to help.


Doug

me too!!!

560hp,
502 gen6
roller cam, custom
emi exhaust, similar to the revs
dart single plane intake
hp500 carb, 800cfm
ported and polished rect port gm iron heads(did it myself)

its a fun project, Doug made more HP than I did, we built at about the same time. i stuck with more stock items than he did (i think!!)

either way, 550hp is attainable!!
kevin

boatn70-

What Compression Ratio and Cam Profile are you running?

So you ported and polished your heads your self. That would be something that I would like to do. How did you learn? Also what did you use to test before and after the porting to make sure that they flowed better.

Thanks
Don

Yea Kevin, mine's all stock


Doug

Don,

i followed alot of advice and read some good articles online. as far as flow goes...i based stock numbers on the chevy hiperf website, theres a listing of their flow tests. used that as stock then did my work and had a local guy flow them to see the increase. the best way however would be to flow before and after and be able to test and adjust in between. i didnt have that luxury so i just went with it...my numbers turned out pretty good
i only had one set of heads and just started working...obviously being careful of all the "dangerous" areas!!
it was a messy but fun project, took alot of time to do it!! let me know if your gonna try, i can post some links to the info i have found (if i can find again)

kevin
boatn70

BTW, compression was at 8.8:1, block was decked at .050 and gaskets at .039. i did the comb. chamber too, to elimate any detination possibilities.

cam was 230/232 .610/.632 @.050 custom

Kevin-

Thanks for the info. If you get time please post some of the links you used. I am not planning on taking the motors of of the boat untill I get back from a boating trip to minnesota at the beginning of September, so I have lots of time for research.

Thanks again,
Don