Engine height Merc 450R

[Toffen]

Hi!

If I am correct owners of the new V8 4,6 litre 450R have experienced water pressure issues with their new engines. 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

[CUDA]

Would more off-set help?

Got any pictures ?

[Toffen]

Hi!

I have not yet ordered a 450R, but are a little alert about the water pressure issues if running high (which is essencial to get speed out of the huge lower unit). I have mounted my 400R on a stainless marine jackplate with 5 inches setback and added a noth to my transpom of about 5 inches.

Cheeers, Toffen

[FUJIMO]

...same old rule applies. mount it as high as it will go and still have good water pressure(and nowadays, so that no alarms are set off). make up for any slippage you might have after that, with the correct prop with the appropriate number of blades to get the job done.

[Toffen]

Hi,

In theory The lower unit of the 400R is the same of 450R. If the 450R is more sensitive to running high than the 400R, you loose speed. I use a Max5 prop now on my boat. Possibly a CNC 5 blade cleaver will offset for the lower engine height with lower slip percentage. However, my boat needs bowlift ... and a CNC cleaver will hold the bow less ..

Cheeers, Toffen

[CUDA]

Yeah cleaver's don't have bow lift so add more set back then you get to raise the motor more.win/win.

What about weight difference between them, looks like the 450 is a extra 100 lb.that will change the teeter-totter.

Excuse me balance point.

[engineermike]

I think the 400r and 450 are very similar weights.

it is baffling though that the 300r, 400r, and 450r seem to require different heights while the housings are supposedly identical.

[CUDA]

May as well go all the way...
Looks like 100lbs vs

https://portaproducts.com/porta-brac...series/#photos

[FUJIMO]

...yes, the porta is the universal antidote...

[Toffen]

I think the 400r and 450 are very similar weights.

it is baffling though that the 300r, 400r, and 450r seem to require different heights while the housings are supposedly identical.

Hi,

Yes, thats strange. I will ask Wildman about his experience with 300R, 400R and 450R on his boats. It seems to that 450R loose waterpressure when higher than 1-1,5 inch above the bottom, and its a 1-3 mph on the last inch.

Cheeers, Toffen

[perfmarine1]

400 is inline 6- 450 is V8 water capacity would probably be more on V 8 block so they may need a little more flow

400- 668lbs 450-689lbs

[racer]

Another possibility is that the different blocks of the inline 6 and V8 restrict the flow differently making for the same amount of water to have different psi. One may need more volume while the other needs pressure.

[FUJIMO]

Another possibility is that the different blocks of the inline 6 and V8 restrict the flow differently making for the same amount of water to have different psi. One may need more volume while the other needs pressure.

...or...maybe...crabbing comes into account...a lot of variables on the install/hull, etc...just guessing...

[Brad Zastrow]

Dave Z and I setup his Doug Wright with 300R's and we found the sweet spot to be 2.25" above the bottom. Any higher and the engine went into limp mode for overheat.

[Mini Max]

Limp no more. Reggie mentored me on getting water to the 400R's. We opened and profiled the water intake to the Sportmaster gear case.
Problem now is the next boat gets twin 450's with HD gear cases and I have been told water pressure is a big issue.