ATK rebuild purchase

I have a 91 Sport Nautique that needs new engine.. I've had good luck with Summit Racing for automotive situations, so I thought I would look into an ATK rebuild but I want the GT-40 heads. Engine with STD heads can ship right away but GT-40 is 4-6 weeks. Anyone have an opinion on this? Maybe another vendor? Extra 45 HP worth it? Any suggestions are appreciated. I am in Cincinnati.

I appreciate it. What difference does the "P" make?

In the marine world not much, slight bump in compression and good for another ~10hp. The plug angle is different on the P's making them more costly mod for the car world due to headers getting in the way. The non p's are more desirable to the auto industry, the P's more desirable to the marine world.

Standard which is left hand rotation is all 89+ CC's.

Leon - certainly the question is related to how you use the boat and what YOU want it to do.    I would question how much extra work is involved, and what it is?    seems like this should be a pretty direct bolt on intake as long as you get the right one.    Warranty might be a question also, I looked at that motor when I was searching and seem to remember that it came with an intake?     If it comes with the intake assembled, I would question the warranty issues you may create by swapping parts.     One other note,    I did not order the ATK due to the fact that they are using a high volume oil pump.    if you are going to run a DUI distributor, make sure you use the bronze gear and do the oil passage mod that DUI recommends.   It sounds like your cam gear will thank you .

No intake provided.

High volume oil pump? Sh1t I better check on this.i don't think mine does but I didn't ask, in past with other builders I had to specify whether i wanted a high volume pump. FwIW I'm ~50 hours into my motor with a DUI and no problems knock on wood.

I never thought two seconds about the oil pump being hi volume. We just swapped the DUI over from the old motor.

Longblocks don't usually come with pans installed. You'll want to match the pump pickup to the pan anyways. I'd plan on a new pump and pickup (match the old if reusing your pan). Avoid a HV pump on a Ford, especially a tame one.

Compensate for the wrong oil pump by using the wrong oil? Sheesh.

Obviously. Choose oil weight based on the set clearances and rebuilders recommendation. Not based on the HV pump.

Unfortunately a warranty is piece of paper one can wipe their a$$ with.

I have zero issue with using a High Volume Oil Pump. Many of the major rebuilders installed them in every engine in the 1990's through 2003 or so. Then they started learning about wasted horsepower and used more stock oil pumps, it is not a lot but it is a waste of free horsepower. I doubt if it exceeds 5 Horsepower on a stock 351W. On a Pro Stock Warren Johnson engine back in the late 90's they picked up 30 HP by shutting off the oil pump completely during the actual drag race. When they floored it coming off the line the oil pump was shut down till they let off at the end of the 1/4 mile 7 seconds later.   That was on a 1,000 HP 500 inch drag engine.
On these Low RPM boat engines I don't think you are wasting much horsepower switching to a HV pump. All owners are happier if they have solid oil pressure at idle so many production engine rebuilders used the HV pumps as the standard and sold it as an upgrade over factory. Were they needed? Nope, but they did not do any damage other than a minor amount of efficiency lost. I would run the HV pump and never lose any sleep over it in your new engine and I see no reason to run any oil thicker than 30W in these boats.   With 30W your engine should hold a steady 30-40 PSI at idle and it only has to have 10 psi at idle. (but I would hate to have that low of oil pressure)
Running 20-50W in engines designed for 30W loads the engine oil pump as much as installing a HV pump so why bark at a HV install and then use 20-50 with a stock Oil Pump?

I understand and the same concern applies to switching from 30W to 20-50W. It is hard to pump thick oil, adds load to the same drive.   I run 10-30 and don't worry about it but each can run what they wish.
I can share Melling Oil pumps sells thousands of the HV pumps each year. If 5% failed they would have warnings out but I have not seen them yet.