That is 502 HO 461 hp stock crate cam. The ZZ502, Lil more duration, lift and 110 lsa might,be the premium fuel spec'd crate motor. And since GM wasn't putting this motor in chevelles, etc I don't think they were under selling the hp numbers like they were in the 70's. 30° total advance would probably not be noticed by the car show-stoplight grand prix guys buying the majority of these engines. And people spending this much for a 502 for et's would probably spend the extra coin for the extra 50 hp and the alum heads. The weak springs they put in these motors is probably in fear of cam and lifter warranty returns you have already taken care of.

That is 502 HO 461 hp stock crate cam. The ZZ502, Lil more duration, lift and 110 lsa might,be the premium fuel spec'd crate motor. And since GM wasn't putting this motor in chevelles, etc I don't think they were under selling the hp numbers like they were in the 70's. 30° total advance would probably not be noticed by the car show-stoplight grand prix guys buying the majority of these engines. And people spending this much for a 502 for et's would probably spend the extra coin for the extra 50 hp and the alum heads. The weak springs they put in these motors is probably in fear of cam and lifter warranty returns. And you have already taken care of that issue.

Big-Block: GM Performance Motor

"Crate engine" can mean many things. 502's from GM came in a variety of flavors.
I still don't know where your 502HO with 527HP/570TQ came from or what it actually started out in life.
A few rebuilds will do that. More detective work on your part seems in order.

Good luck.

You know, I really don't care anymore about the past...beginning to think it was a snow job by this shop that went out of business. The dyno numbers were written on the receipt, no dyno sheet. When we unveiled the cam it was some half assed grind that was through the heat treatment. Back to my unanswered question...is it possible to miss@4k exhausting through the transom but not the prop?
I did hear this boat was local in the 90's and the guy who sold it new said it was running with an blower at some point...that would apply to the original 454.

Yes, if the carb is jetted too lean. An a lean misfire can ruin your day/season in an instant.

Did you take my recomendation last year and ditch that Weber/Edelbrock 750 ? Or , if you kept it, did you tune it on dyno or water ?

SB/ no tune/dyno.. So I need to get it re-jetted (it idles perfect & was just rebuilt)...or buy which other carb?

figure out how to measure the afr's and then rejet as necessary.

Yup.

Out of the Box Edelbrock/Weber 750 is basically calibrated for the low performance 300/330 HP 454.

So if I had more money than time...which model marine carb would be a better match out of the box? Just weighing my options...And wouldn't a lean misfire at 4000 also misfire at 4600?

800-850 holley-quick fuel.