mcr vyper

Hello,
We have a 2002 Powerquest Vyper and we are having our 496 Mag Ho's rebuilt. They are replacing with steel crank, forged pistons, new roller rockers, oil pump, valves, head work. Also replacing the exhaust header to CMI Etop headers.

This is were i am not sure what direction to go. Do we keep the cam stock, or one step up from stock? I don't want to go with too big of a cam. If we go with a bigger cam we have to get the ECM's re mapped. The person doing the work has a dyno and will remap the ECM's when running on the dyno.

I still want the reliability of a stock engine but more performance,

Still up in the air about changing from a stock cam and remapping the ECM's.

Anyone already go through this ? Please provide pros and cons.
Any issues afterwards?

Any help and insight would be appreciated.
Thank you,

BUP

iTrader: (9)

the stock engine with stock PCM 555 tune and all that believe it or not is calibrated from how the engine was set up. This includes harmonics within the engine and fuel dampening - along with induction / air in / air out and so on.

For you to really see gains - for one is you will need O2 sensors and a good tuner - tuning this on the water. You want to get it tuned where the boat mostly will live in per the water temps, air temps , altitude , load , correct prop, timing, fuel pressure, and the fuel being used. Anyways just a jist of info here

BUP

iTrader: (9)

And for the record - there is 4 people only that I know of who can retune 555 's and I am one of them. 2 of them tune thru the mail only. IMO that always leaves a lot on the table and a lot of liability when one is doing a ground up efi build.

Possible might be best going to a stand alone EFI / ECM set up or a carb set up .

Ryan00TJ

iTrader: (8)

Test ran the new Raylar goodies

Some info above of my 496HO build.
Good call on upgrading to a forged rotating assembly. Don't forget to add fuel injector cleaning service to your list during rebuild. I would not drop back in 18yr old used injectors.

Keeping the stock heads you will not get above 475hp. They suck. Period! 275cfm @ .500 lift. The stock intake unmodified is the same. You cannot go above .540" lift cam on the stock heads anyway. Raylar's 203 cam is a step up from the 496HO cam. It's as big as you can go on stock heads. It's good for 20hp on a good day. Just a few more degrees duration and .020" more lift than HO cam. You will also need to upgrade the valvesprings to run the 203 cam.

It needs a little larger hole drilled in the TB plate and it idles just like a stock cam with a tad more lope. My setup runs awesome but the stock heads limit everything.

I'm also curious as to who you are using to tune the PCM555?

BUP

iTrader: (9)

My guess would be Alexi @ Boostpower possible is doing the work ? He is one whom can retune 555 s.- (one of the 4). He likes to mod the 496's. He is really good at what he does if in fact the builder the OP is using. Anyways hopefully you are using his services to get the 555 dialed in correctly.

mcr vyper

Going to using Ateco engine and dyno shop in Ingleside IL. They also do all their own machine work in house, block, heads ect. Engines are out going to meet up with them in the next few weeks to go over everything. Just looking for some info from people that already been through all this.

Ryan00TJ

iTrader: (8)

I installed the Raylar 203 cam, 80mm CoolGap intake, roller rockers myself. Parts were like new, bought cheap. I would have been very disappointed with power result if I had to pay a shop. The stock heads/intake really choke this engine.

If you have the budget, replace the stock heads with Raylar's 315cc CNC aluminum heads, Raylar ported 90mm stock intakes, Raylar 203 cams, roller rockers. The heads have smaller cc that yields 10-1 compression vs stock 9-1. The 203 cam is very easy on the valvetrain. Should never require replacing valvesprings as bigger cams will. The above setup in marine trim makes 525-550hp and idles like stock. Whipple Superchargers has tunes for the 525 setups.

OR

Save the above $12k and go with a stock rebuild.

It gets really $$$$ to make more power out of the 496.

Vortec 8100 / 8.1L / 496MAG Mercury Marine Performance Parts Upgrade - Raylar Big Power