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what is max hp.rated for 270 stern drive

T

tmcboat

Regular Contributor
Hi All,
I am planning on installing a ford 351w rated at 250hp. Volvo says max hp 260 . Is this engine hp or shaft hp? How many hp. could I go over without back pressure issue? Was the 280 exhaust port made larger to reduce back pressure?
thanks,
Tmcboat
 
Did some research on back pressure when my 350/260Hp merc did not get up to desired RPMs with my 280 drive.
Per Merc manual ( and a 350 cid is a 350 cid regardless of who makes it for a given HP) minimum exhaust diameter for a single exhaust is 4", 3" for duals. By measurement and calculation, the dimensions of the ports in the 280 "Y" pipe ( one large hole, two small holes) are about half the total area of a single 4" hole. The 270 may be somewhat smaller.

See below for my detailed research and eventual solution. Per notice from Comcast, this link is shortlived. Will be migrating to another site this fall.

https://home.comcast.net/~rfierro/s...t/&PHPSESSID=e9200284a128af346a04f1e16e9829db
 
Last edited:
Thanks,
but what do I do- I think the exhaust port of the 270 is smaller than a 280-- possibly I could straight pipe- 2 pipes off the 3 inch risers through the hull below water level $$$$ ? the noise would be extremely loud and the exhaust fumes could back draft into the boat. your thoughts please.
Thank,
Tmcboat
 
You could go with transom mounted mufflers, or what some of the off shore boat guys do is use 3" or 4" diesel elbows to direct the exhaust down into the water to keep the boats quiet in areas with noise restrictions. I have had Thru Transom exhaust on all of my boats, and never had an issue with exhaust fumes in the cockpit. My boats have all been "Sport" boats, so I'm not sure if you have a cabin cruiser etc...

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tmcboat said:
Thanks,
but what do I do- I think the exhaust port of the 270 is smaller than a 280-- possibly I could straight pipe- 2 pipes off the 3 inch risers through the hull below water level $$$$ ? the noise would be extremely loud and the exhaust fumes could back draft into the boat. your thoughts please.
Thank,
Tmcboat
Click to expand...

When I did my project and used fiberglass "shorty" mufflers I ended up with a boat that at idle was a bit louder than the underwater 270/280 exhaust but much quieter while on a plane. No problem with exhaust fumes in cockpit except slightly while trolling with a breeze from behind. In my case, the only way to meet noise regs in NJ was to use mufflers
 
tmcboat said:
Hi All,
I am planning on installing a ford 351w rated at 250hp. Volvo says max hp 260 . Is this engine hp or shaft hp? How many hp. could I go over without back pressure issue? Was the 280 exhaust port made larger to reduce back pressure?
thanks,
Tmcboat
Click to expand...

I have first hand knowledge (from Volvo Penta) re; horse power capability.
Putting exhaust gas restrictions aside for the moment (270 vs 280), the 270 Drive will more than handle a 5.8L Ford marine engine!

Keep the PDS bearings and the transmission main drive gear bearings fresh.... along with all other maintenance items....... and that drive will go for years and years!


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murfman said:
Rick, how much HP can a AQ take? specifically the SP.
Click to expand...

The AQ series "SP" drives are later (after the AQ 290 series).

I can't tell you what the HP capability would be, but I can tell you a few true stories.

When I was beginning my restoration, I picked up two NOS 250 drives. NOS = new old stock.
These drives were years old, but had never seen the water. The were New... not remanufactured!

I was a bit concerned in that the 250 main drive gear male yoke splined shafts were smaller than anything later.
I called Volvo Penta and spoke with a Tech person and I explained my concern.
This person assured me that the 250 would handle power bursts up to 500 HP.

I was a bit doubtful, and called back one week later, and spoke with a different Tech person.
This person told me the same thing.

I ran the 250's for the first two seasons. No issues at all.
Prior to the following season, I had picked up two 275A transmissions, and two later C style Duo Prop lower units.
The 250's were sold.

Back to the SP drives.
Anything after the 250, the main drive gear male yoke shafts and splines became larger.
All of them (250 on) use the same main drive gear bearings........ 30207 and 31307 (31307 being the bearing right next to the actual gear).

The A and later main drive and driven gears received a better and stonger hypoid gear tooth cut.
The even later SP-C and DP-C driven gear bearings also become slightly larger.

Several years ago, I received two 280 transmissions for an over-haul (California customer).
The owner had been using these behind two 450 hp BBC.
I gave them both a good inspection of all parts, each received new 30207 and 31307 bearings, new seals and were shipped back to him.
No issues to date that I am aware of.



The one thing that would be important for me, would be the condition of the two main drive gear bearings...... (the 30207 and 31307).
On a 270 up to the A transmission, these can be checked without the need to re-set the rolling torque value.
( the A and later use a "pretension" or "crush" sleeve for this)


So.... regarding the 351W and the 270 drive...... if the maintenance has been done, there should be no problems!



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