Just sitting here thinking. I have the standard 8.1 375hp 496. When the time comes to re-power is there a good formula to get some decent TQ and HP out of this motor reliable. The boat is a Cruiser, not a speed boat. I know they have a HO 425hp model, but those numbers are up at a high RPM range. I'm looking for low end HP/TQ with a 3400-3500 cruise. I see Raylar makes a kit, but that's more for race boats I see. Ideas? Thanks

I had my 375HP 496 MAG dyno’d after a rebuild. Only upgrade was it was bored .030 over. I let the dyno sheet go with boat when I sold it but if memory serves it made 390-ish HP and a little over 500 ft lb torque. Pretty much stump pullers stock. The camshaft and programming are only differences between the MAG and MAG HO. 4,800 vs. 5,000 RPM max RPM range. Dyno shows they both make peak HP below those numbers. I think mine made max HP around 4,700. If you search on here I believe Bob Lloyd posted full dyno sheets between both engines stock.

Just put a Mag HO cam in it or the Raylar base cam which is very similar. The torqu curve is still below 5200 and basically 4700 and up. Matter of fact, lots of guys are propped at 4700-4800 with the Mag Ho. Either way, put in a set of roller rockers and an ECU reprogram to pick up a few more. should be 425++ and reliable.

The only other upgrades I had considered at the time was a used HO cam that was for sale on here (DonziMatt I believe), Whipple HO programming, and a set of Raylar’s roller rockers. The .030 overbore was out of necessity. I didn’t proceed with the other upgrades as at the same time I was dealing with the rebuild I ended up in the ICU for 10 days and missed being able to purchase the cam.

Talk to Larry at Raylar. The stock 496 is a stump puller. Getting big power out of the 496 is easy. I have close to 1300 hp and my torque is 825lbft at 3800 rpm to 1000+ at 5700 rpm Larry knows my engine and I run the NEW PSI block with HP3 ported heads at 109cc's and 10.6 to 1 compression with a pro charger. 83lb injectors A1000 black fuel system etc and one of Raylars Big cams. Larry knows his business. I also have a 1 of 55 intake made by Arizona Speed and Marine. Jim Shofner ASM did my tuning on the Holley HP efi. Ask Larry he is a great guy and is very knowledgeable. Tell him Trey sent you.

For what it cost to make power out of the 496 Mag/Ho you are better off to sell it and start with a nice 502. All the parts are cheaper and easier to find since they are a standard BBC motor. I've had quite a few 496's over the years and they are very reliable until you start adding power.

You can get a rebuilt 496 for 3800.00 swap cam mild head work, ecu reprogram and fly. The 496 flat kills other big blocks, LS style heads and FI. Hell the 496 came in a 525 hp motor that mercury buried because it stomped the 525 blue top and was 3x cheaper


The HP3

I did a lot of research and build mine into HP3 clones several years ago before I imploded a cast piston. Later I just went with Raylar 600's anyway but I agree with you - they were stout engines when built with good components. The only thing that I didnt like was the piston to valve clearance. I dont remember exact specs but wasnt it only like .030 (maybe even .020)?

Stage 1 Whipple tune was bob's test.

I recall way back they had their own racing division just using the HP3 Vortec engines. For testing, Merc strapped a test boat down and ran it for hours & hours on end just trying to break them.

It'd be nice to get my hands on pair.