502+250 Supercharger=questions
 

I HAVE A STOCK 502 MAG(GEN V) WITH LESS THAN 200HRS IN A 29FT PROFILE(APPROX 4200 LBS).IT HAS SILENT CHOICE WITH STOCK MANIFOLDS AND RISERS.
MY UNDERSTANDING IS THAT THIS ENGINE HAS FORGED PISTONS AND CRANK WITH 8.75:1 COMPRESSION.
I ALSO HAVE A B&M 250 SUPERCHARGER THAT I AM PLANNING ON PUTTING ON IT.
I'D LIKE TO MAKE MORE/RELIABLE POWER.
I'M LOOKING TO MAKE MORE TORQUE THAN TOP END HORSEPOWER.
I ONLY PLAN ON ABOUT 5000RPM MAX AND APPROX 5LBS OF BOOST ON 93 OCT FUEL.
I HAVE A FEW QUESTIONS AND WOULD APPRECIATE ANY RECOMMENDATIONS.

1)WHAT CARB/SIZE SHOULD I RUN?DUAL CARBS?(I'D PREFER TO RUN A SINGLE).

2)WHAT CAMSHAFT?SPECS?I WANT TO STICK WITH A FLAT TAPPET HYDRAULIC AS I CAN'T AFFORD TO SWAP TO HYD ROLLER.

3)TIMING/ADVANCE CURVE? DIFFERENT MODULE?

4)SHOULD I CHANGE THE HEAD GASKETS TO SOMETHING BETTER,THICKER TO REDUCE COMPRESSION?

5)AND LAST BUT NOT LEAST WHAT KIND OF POWER SOULD I EXPECT OUT OF THIS COMBINATION?

I KNOW I NEED TO UPGRADE TO EXHAUST,IF ANYONE HAS A GOOD USED SETUP FOR SALE(GIL,IMCO,STAINLESS MARINE,ETC.)PLEASE LET ME KNOW.THANKS FOR ALL YOUR HELP!!!

Jeff, do a search on "Blowing Motors". A lot of the questions you asked have already been addressed.
I run a B&M 250 with a single 1050 Dominator (Nickerson setup), Superchiller, 496 Stroker. I am seeing 72-75 mph. This is installed in a 1989 27' Actvator. My prop is very deep (propshaft is 7.25" below keel). I also run a 26" Bravo 4 blade. Boat weighs in around 4000 lbs. I always run with a full tank of gas and 2 people

THANKS FOR THE ADVICE RLW. I'LL TRY THE SEARCH.
I MADE A MISTAKE WHEN I POSTED THESE QUESTIONS.
MY ENGINE IS A MARK IV.
THANKS AGIAN

My motor is a Gen V 502. (HP465) Same bottom end as yours. 250 blower with 1050 Dom. on top. 5lbs boost. Blower/ carb was originally a Nickerson package. Ran way to rich all the time. Sent carb out to have it worked over and boost referenced at another shop. Ran like an EFI motor afterwards.
I have a Hyd roller cam, (.234/.242, .610/.632) silent choice, Merc/Gil exhaust.
Swap out the V8 ignition module to a V6 Module and set timing right around 28-29* at 3500rpm. I use the standard Felpro marine head gaskets. Prem gas only. Very reliable and safe.

Motor was dynoed this spring@ 624hp

Use the Felpro loc ring gasket - do not go with the thicker gasket, as it opens up the quench height too much.

If you don't go with a chiller, then stick with 5 pounds boost.

If you don't go with a roller, then plan on 112-114 lobe centers and 240/245 @ .050 duration with lift numbers in the .540-.550" range.

A 950cfm 4150HP, a 1050cfm 4500, or two 600cfm 4150's will be your choices.

Use replacement exhaust manifolds (Gil, etc..).

31-32 degrees total timing.

Nickerson is "supposed" to be the man on the carbs.

Rumrunner, your PM box is full.

short version

624.9hp @5500
torque peaked at 655.3 ft/lbs @ 4600

Standard ol' Bravo1, 1.5. never a hint of problems do to the 400hrs of blower power, (underwater boulders are a different thing, new drive this July) :rolleyes: Boat has never been nailed out of the hole and driven with a light hand.
'94 27' fever, 4950 lbs dry
Jerry

nice to hear a friend has reliable&powerful&cool engines.

but this is not fair!! someone asked a question about 250 blower for 502 cu.in. SOMEBODY from the board said that they are too small for that cu.in. how come it makes 620+ :( :( .because I was planning to get 250's that time....and after that thread I gave up...

NO, they are not too small. Just the smallest that you would run on a 502. Ideally, the larger is best. But at a cost of space. That is the trade off. I "believe" that the Merc. 600SC was based on the 502 with a 250, or a 256 blower. If it was good enough for them, then...........

But to conterdict myself, I know of a local guy running a 174 with a single 750/800 carb on a 502. Been a turn key motor for at least 6 yrs I know of. So reliable that when I asked him if he was running a t-stat in it, he said he didn't know, cause he has never even changed spark plugs. Puts gas in it and goes!

The Merc. 600's used the B&M 420 Mega Blower. The new 575 sc's use the Weiand 256 blower.

Be safe.
Mark

Thanks, I stand corrected.
Actually, I have heard both, 250 and 420, that was the reason for the "believe"