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Water pressure Merc 450R

Old 07-05-2020, 09:52 AM
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Default Water pressure Merc 450R

Hi!

If I am correct some owners of the new V8 4,6 litre 450R have experienced water pressure issues with their new engines running high. The new 450R loose water pressure earlier than 400R. I know that Nor-Tech have seen water pressure issues, and for that reason the speed potential of the new 450R suffer. One way is to add a transom water pickup, but for my part I would like to avoid that.

The 450R is a very expensive engine and it would be a mood killer to discover that extra speed is limited due to engine height....

I run my 400R propshaft 2 inches above the bottom. Top speed is 89-90 mph with a Max5 spinning at 7,060 rpms.

Thanks !


Cheeers, Toffen
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Old 07-06-2020, 08:17 AM
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Not a 450, but on my 300's I had all the side holes, except for the bottom 2 plugged. So, I'm running off the LWP, and bottom 2 side holes. My pressure did increase.
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Old 07-06-2020, 08:59 AM
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When I talked to Myrick Coil (Performance Boat Center) about this early after the 450s were released, he indicated they and Mercury were working on the issues. I haven't spoken to them since so don't know if the water pressure issues still exist or not. PBC has sold and worked on a lot of 450s since they were introduced. They may be a good place for an update. We also see them on the new NorTechs at LOTO so NT may also be able to confirm where the issue is at.
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Old 07-06-2020, 03:36 PM
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I heared That first thing they do is open up
low water pick up holes making them
quite a bit bigger also on the 400 s as they use same lower units far as I know

how much set back you have running 2” above ?
I’m at 2 1/4” whit 8.5” but that’s critical
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Old 07-06-2020, 06:47 PM
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I was told it was more of an air intake issue, hence why you see the MTI cats with the "scoop" or spoiler to increase incoming air flow. I had some water pressure issues but I believe they came out with a software uptake to adjust the air/fuel ratios. I was also told they may have a recall on the air intake to replace the intake manifolds with larger bore however, I doubt they will do this as that would be extremely costly for them. Redline is 6450ish on the 450's which I do not always hit with Bravo rev4. There should still be way more to squeeze out of my 450s. I did have water cooling issues early on but they seemed to disappear? my own personal opinion is they will probably revamp the intake manifold or intakes/scoops if they release a 500R which is feasible. That V8 supercharged is thirsty for more
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Old 07-07-2020, 06:11 AM
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There is a service bulletin to address water pressure issues on some of the first 450s. Replaces the exhaust sprayer. This was mainly on engines using either Mercury or Optimus Joystick systems.

We had a brand new Nortech delivered to a customer that was having low water pressure on the center engine. Wouldn’t get over 77mph without overheating and sending into guardian. It took plugging off all of the side intake holes to get the water pressure high enough to reach 83mph. No modifications were required to any of the 8 nosecone intakes.

MTI has Gary Stray add the intake scoops for increased speeds. They found out that by opening the top access door, they’d pick up 3mph on the 340x.
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Old 07-07-2020, 06:48 AM
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BTW, if you’re going to be running over 85mph then the SportMaster gearcase will need to be your choice. It only has a low-water pickup.
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Old 07-07-2020, 03:31 PM
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Hi!

Thanks

Bor: I have approx 10 inches setback (notch and powerlift). Running my 400R 2 inches above
Davidwademarine: I expect top speed with the 450R to be mid 90 ties with Max5 prop. Possibly higher with CNC 5 blade cleaver.

Cheeers, Toffen
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Old 07-07-2020, 05:36 PM
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Originally Posted by GatorMD View Post
I was told it was more of an air intake issue, hence why you see the MTI cats with the "scoop" or spoiler to increase incoming air flow. I had some water pressure issues but I believe they came out with a software uptake to adjust the air/fuel ratios. I was also told they may have a recall on the air intake to replace the intake manifolds with larger bore however, I doubt they will do this as that would be extremely costly for them. Redline is 6450ish on the 450's which I do not always hit with Bravo rev4. There should still be way more to squeeze out of my 450s. I did have water cooling issues early on but they seemed to disappear? my own personal opinion is they will probably revamp the intake manifold or intakes/scoops if they release a 500R which is feasible. That V8 supercharged is thirsty for more
Merc currently can not place any more HP in that little foot.
550 HP on up will explode that baby for sure.
​​​​​
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Old 07-07-2020, 08:32 PM
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I have the HD drives on mine. I am strongly considering starting to mess around with props.

I think 500hp is reasonable for the platform. Agree maybe 550 is much. But, a 500HP outboard would be perfect, at least for my application on a triple 39
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