obnoxus

Is there a greater reversion risk with this cam? I would have to believe it is no worse then stock with how you are explaining vacuum. I run Gil magnum choice, and there switchable exh.

I am very strict with oil changes,, every 20-25 hours,, and I run Royal Purple straight 40 weight racing.

Thank you so much for all your time
Dennis

HARRISONMIRAGE

JUST INTERESTED IN HOW ADVANCED YOU WOULD INSTALL THIS CAM.I HAVE THIS CAM IN A 454 (461 .030 OVER)THAT IS USING FLAT TOP PISTONS AND VORTEC HEADS.I INSTALLED IT AT 106 AS RECOMENDED ON THE SPEC CARD.WITH IT INSTALLED THIS ADVANCED THE MOTOR CREATES A MIN OF 180 PSI CRANKING PRESSURE.THE COMPRESSION RATIO IS APROX 9:1.I'M ONLY ABLE TO RUN ABOUT 28 DEGREES TOTAL TIMMING OR THINGS GET HOT(PINGING AND BURNT PLUGS).AS TO CONSERNS ABOUT REVERSION I HAVE STAINLESS MARINE MANIFOLDS WITH SHORT RISERS INTO A CORSA SILENT CHOICE AND AFTER EXTENDED IDLING IF I PULL A RISER THERE IS VERY MINIMAL WATER DROPLETS IN THE MANIFOLD.IF I REV IT UP BEFORE SHUT DOWN THEY ARE DRY.I WOULD IMAGINE RETARDING THE CAM SHOULD TOTALY ELIMINATE THE WATER REVERSION? AND DROP MY CRANKING PRESSURE A BIT.I HAVE ABOUT 120 HOURS ON THIS SETUP NOW AND WILL NOT CHANGE IT UNTIL I HAVE TO PULL THE MOTOR FOR MAJOR SERVICE.ANY INPUT AS TO MY CAM TIMMING CHOICE WOULD BE APPRECIATED.

Dennis Moore

The set up that you have is equal in compression to a stock set up. The Vortech heads are used with flat top pistons on a 454 L29 engine. The Comp Camshaft is much larger than a stock L29 camshaft (204/209 duration with a 115 LSA). The fact that you have a relatively high cranking compression of 180 PSI means that you do not have excessive valve overlap and shouldn't have a reversion problem.

With fast burning combustion chambers 28 degrees total advance is correct. The Thunderbolt V ignition with the detonation sensor should feel any detonation and retard the timing but retarding the camshaft to have an intake centerline of 108 or 110 should help with detonation and increase top end horsepower production as well. Running the engine a little cooler (a 140 degree thermostat)should help a little.

I like your combination but it sounds like the air/fuel mixture may be a little lean. I hope that you are running a marine carburetor and not an automotive carburetor (a marine carburetor is calibrated to be richer at mid rpm and calibrated with a richer power valve circuit for wide open throttle).
Sincerely
Dennis Moore

obnoxus

Good question,,, should I keep mine at 32 degrees total timing? I would assume I should not degree the cam correct?

HARRISONMIRAGE

HOW MUCH HORSEPOWER DO YOU THINK I WOULD GAIN BY RETARDING MY CAM SHAFT TIMING TO WHAT YOU SUGEST.ALSO HOW MUCH CRANKING PRESSURE DO YOU FEEL IS TO MUCH.THE ONLY TIME I HAVE HAD REAL PROBLEMS WITH MY SET UP IS IF I OVER PROP THE BOAT (UNDER 5000 RPM)OR RUN LOW OCTANE FUEL.THIS MOTOR IS IN A 257 MIRAGE (25'7" ,24DEGREE,4000#BOAT).I HAD TO REDO THE MOTOR LAST YEAR DUE TO A BROKEN OIL PICKUP AND I HAD SOME TULIPED INTAKES BUT I THINK THIS HAPPENED PLAYING AROUND WITH TOO BIG OF A PROP AND TOO LOW OF OCTANE FUEL.WHEN TRYING THIS PROP THE BOAT CAME UP TO SPEED THEN STARTED DROPPING OFF JUST AS FAST DUE TO PREIGNITION I WOULD ASUME.IT MELTED SOME OF THE GROUND STRAPS ON THE PLUGS.AFTER THIS HAPENED I WENT BACK TO A SMALLER PROP THAT NETTED ME 5000-5100 RPM AND USED PREMIUM FUEL.I PUT APROX 80 HOURS ON IT BEFORE THE OIL PICKUP BROKE.I WOULD LIKE TO THINK THAT THE TULIPED INTAKES HAPENED IN THIS 60 SECOND PROP TEST AND NOT IN NORMAL USE.WHAT WOULD YOU DO A:RUN IT AS IS(ITS ALREADY GOT 110 HOURS WITH NO PROBLEMS) OR B:RETARD THE CAM(I REALY DON'T THINK MY WIFE WILL LIKE ME MUCH IF SHE SEE'S THE MOTOR IN THE GARAGE AGAIN)

HARRISONMIRAGE

I FORGOT TO MENTION I AM RUNNING A 750 CFM EDELBROCK MARINE CARB.WITH AN AIR GAP MANIFOLD.I AM USING THE HEAVIEST SPRINGS ON THE PRIMARY NEEDLES.ALSO I AM RUNNING A 140 THERMOSTAT WITH CLOSED COOLING.

Truckin

Again, I like your set up. I don't think that retarding your camshaft will help much at lowering your compression or increasing your horsepower but every little bit helps (maybe 3 or 4 psi and 2 or 3 horsepower gain). It depends upon how much of a high performance boater you are (if you are looking for that last little bit of performance). 180 pounds of cranking compression is just right for a high performance engine but you will have to use at least 91 octane fuel. A little richer on the secondary jet (.110 or .113), 28 degrees total advance and RV15YC4 Champion spark plugs (they have a wide heat range). Make sure the carburetor is pulling in cool air.
Sincerely Dennis Moore

Zoomnfun

Dennis you sure do great work here for everyone, THANKS!!!

Dean

cobra marty

With stock heads and stock exhaust manifolds-- The big question is how much more HP and TQ than the stock cam on the 502MPI?

Truckin

Hard to say how much more power, very few engines are torn down just for an aftermarket camshaft change (other mods are usually performed at the same time).

I have rebuilt engines to stock specs with aftermaket performance camshafts that have the stock duration specs @ .050 lift and they seem to perform a little better.

I would doubt that there would be much more than a 10-15 horsepower difference between the stock camshaft with slow opening and closing lobes and an aftermarket camshaft with fast opening and closing lobes (that have the same duration at .050 lift).

I would love to run a dyno test just changing camshafts but I don't know if the expense could be justified to the magazine staff.

Sincerely
Dennis Moore