I decided to take the plunge (and risk) and try out Chevy's new crate motors. First of all - they are the 572/620HP motors and NOT the 572/720HP motors. The 720s would never work. Also, they require racing fuel. The 620s run on pump gas.
I did quite a bit of research prior to making the decision and spoke with as many people as I could find that would offer a non-biased opinion of whether this would be an intelligent move or not. Since it had only been tested in an Eliminator there was not much to go on. According to Eliminator they "marinized" the motors and off they went. Supposedly the owner of the Eliminator has logged in excess of 100 hours to date. More on the marinization later ...
The second story I heard was a larger deep vee (unknown make and model) that encountered a problem within the first hour of running. From what I heard the motor is "too tight" for marine use. Something about temperatures, valve clearance, honing, etc. Not being an engine builder I have no idea what they were referring to. Anyway, Steve - the owner of Savage Marine in Lake Havasu - told me that I should have the heads worked on by an marine engine builder before running the motors. Cheap (relatively) insurance he said. Less than $2k per motor! Unfortunately, I found this out the same day I was getting ready to launch my boat in Havasu for it's first run. Having just towed the boat 300 miles and facing 85 degree weather - I didn't listen. The end result - a failure.
Two things contributed to the failure - the fact that I didn't listen to Steve and my impatience in not breaking the motors in slowly. I just had to see how fast I could go. Bummer. Anyway, 30 minutes of running and the port motor started knocking. Turns out Steve was right and turns out that my failure was identical the other guy's.
I now had one good motor and one broken motor. I took both out and dropped them off at Paul Pfaff's place. Sure enough the valve got hung up and a piston hit a spark plug, etc. Damage to two pistons and some other minor parts - nothing major. Fixed the broken motor and worked on the heads of both motors. The bill for the good motor was $1900. The broken motor was $4500! Another $1500 for the de-rigging and re-rigging, gaskets, etc. What could have cost me $3800 in head work ended up costing me $8000 because I was lazy and impatient!
As Wasabe indicated - yesterday was the second "maiden" voyage. Ran the boat up to Long Beach and back with no problem. The motors ran perfectly, however, I never exceed 4000 rpm. I also ran my original 30 pitch props so the motors would not be working as hard during the break in period. I believe the motors will need 34 pitch props once everything is ready to go.
IF the motors end up being reliable this could definitely be an alternative engine setup to consider. Paul and Gordon from Paul Pfaff Racing Engines admitted to me that the parts inside the 572 are top of the line. If you read the specs online you will see that GM did not skimp on the components.
In terms of marinization there is not a ton to do. Again, I am not an engine builder and I can only tell you bits and pieces. I know the engines come standard with marine gaskets. We changed the oil pan (larger), the fly wheel, the distributor, the steel bolts and plugs, water pump, and a bunch of other misc. parts.
The motor costs $11,800 from GM in the fully dressed version which includes the Demon carb. I spent approximately $5,000 total on parts and labor to marinize and install the motors. Call it $17,000 total per motor. This was probably $1,000+ higher per motor than was necessary since I added stainless braided hoses, custom pulleys, brackets, etc. If you add back the $2,000 per motor for the head work then you are looking at $19,000 per motor.
From what I have been told by everyone I have asked about these motors - the 620 dynos around 660HP and the 720 dynos around 760HP. Evidently, GM is conservative in their estimates. The engines seem to have a tremendous amount of torque. During my impatient stint in Havasu I ran the throttles up fairly quickly and the boat felt like it was being shot out of a cannon.
So was my plunge a good idea? The jury is still out. If the engines are reliable and perform like I hope they will - definitely yes. They sound awesome, seem to have incredible torque and power, and look as good as anything I have seen. Here are some pics ...