At Raylar we are always trying to find better ways to extract HP and Torque out of the good ol' Merc 496.
We just finished a lot of dyno testing on two Merc 496's we did for a customers Formula 330ss. They started life as stock 496 HO's . We redid the blocks with all new forged internals and our standard build specs and set them up with +.010" over size pistons and our 4.50" stroke forged crankshafts to give a 513 cubic inch size. We really have done a lot of camshaft re-engineering and we came up with a new secret weapon stick for the engine and equipped the engines with our standard BCK103 kits with heads, intake, etc and a set of CMI E-top headers. With our reprogram of the ECM's and resetting the rev-limit to 5400rpms we clamped them on our dyno and started testing.

Well, all I can say is we were pleased and amazed at the results of this combination and new camshaft weapon!

These engines idle nicely at 650 rpms like regular Raylar HO525's but thats where the comparison stops.
On two pulls he torque numbers climbed to just kissed 600ft/lbs at 3300 rpms, peaked at 4200 rpms at 647ft/lbs and carried nearly 600ft/lbs at 5200 rpms while making 591HP at 5300rpms and they were still building HP at 5300 so I think if we had re-tweaked the rev-limiters to 5500rpms these sweet mills will touch 600HP at 5400rpms! All on 89 pump gas without a ton of timing advance-max 31 degrees! I think with a few more degrees of advance we would have seen even better numbers but we had to get the engines to the customers shop for installation in his boat and he wants to be sure he can run 87-89 octance fuel all the time even in summer high air temps. +110 degrees!
The torque curve alone on these mills totally justify our camshaft work and bore stroke configuration. As some of you may know the stock 496 block is limited to about 4.280" bore size because of its thinner bore walls that are not siamesed like the 502 and aftermarket blocks so getting addtional cubic inches is a problem and additional stroke is part of the answer to a point.
The crazy oversquare stroke to bore ratio on this tall deck engine and obviously our high velocity, small valve BigPower aluminum heads and our long runner CoolGap intake does not hurt either.

It is my firm belief that on recreational high performance boat engines that this big flat torque is the "Bomb"!

I attached the one of the dyno sheets so interested OSO'sers and 496 owners can study the results.

This gives 496 owners some more lower rpm reliable high torque possibilities for their engines.

Sometimes you are lucky and good and you take five steps forward and only one back when you think outside the box.

What do you guys think?

Best Regards,
Ray @ Raylar

How much to turn a stock 496 HO into one of these and does it still retain all the Merc Smartcraft capabilities?

Nice!! So have you been able to test this new cam on a HO600? I have that package now and will always entertain a way to sneak out some more HP.

Nice Job!! Numbers look good.

Impressive results....how did the boat perform?

Good job Ray. That will be a great package for your customers. With that torque curve those engines will feel great from the drivers seat.

Ray, That looks like a great combination. Nice dyno results! I have not had the opportunity to tear into one of these 496s. Did you have to clearance for the increase in stroke and what did you end up with on your compression height?
Depending on deck height, stroke and rod length, I have seen piston stability decrease at bottom dead center. I always have CP, adjust piston design to correct this. NOT SAYING THIS IS OR COULD BE A ISSUE. Was just wondering about your thoughts on this.
Thanks for the dyno sheets, it's nice to see data on this forum and not quoted or projected results.
Mark

x2. Looks like another excellent upgrade for the 496 and good use of the original accessories. I agree with Mark, it's nice to see a posted dyno sheet of an engine run in the same configuration it will see in the boat with REAL HP numbers. Looks like you left a bit on the table too, 600hp is only a bit of tuning away. Good work! Now get a price together for that kit quick!

+1 how much?

Very nice piece Ray. You are the man with the 496's.

Quick question for ya.....to what do you attribute the .6 -.7 difference in afr's from bank to bank? That's not something I have normally seen(have seen it though) in NA engines, especially in ones with longer intake runners. It pretty much always shows up to some extent in SC engines, especially ones with Whipples that are spinning slowly. Just curious.
Thanks,
Eddie