Am I allowed more RPM ?

[HPLou]

Good day,
I am confused when reading some messages about Mercruiser 305 RPM's.
There must be different engine version then mine !

I have a 1980 Merc 898 s/n 5452697, on the engine there is a sticker that reads MAX RPM 3800-4200.

I read posts about 305 RPM's up to 49-5000.

When talking to mecanics they all say 4200 seems to be low. I went to the boat show few months ago and had a talk with the rep at the Merc Kiosque.
He confirmed that I must follow the specs written on the engine (3800-4200)
and not exceeed it (for sure he works for Mercruiser)

Presently, at Max RPM my engine does 4550-4600 RPM but never run full throttle, I'm scared the engine will blow up (if I'm out of specs).

Can someone that knows this engine better then me confirmed max RPM ?

Thanks

Louis

 

[ziggy]

Re: Am I allowed more RPM ?

MAX RPM 3800-4200.

that is correct per service manual #4......

 

[MikDee]

Re: Am I allowed more RPM ?

Most of the Mercruiser V8's specs per the Clymer manual show 4200-4600rpm, basically a Chevy 305V8, is a 350V8 with the same stroke, just a smaller piston bore, I seriously doubt the engines gonna blow up, But, they might figure it develops maximum marine horsepower at that rpm with only a 2bbl carb.
All I know is, I had a (similar vintage) 79' SeaRay 20' bowrider with a Mercruiser 228hp 305/4bbl carb, and I believe it was rated to be run between 4200-4600rpm, just like the 350/260hp.

 

[ziggy]

Re: Am I allowed more RPM ?

Most of the Mercruiser V8's specs per the Clymer manual show 4200-4600rpm,

mercruiser service manual #4, MCM 898. s/n 4887830-6218461

the 4200-4600 is correct for the MCM 228 (305), and the MCM 260 (350), the MCM 898 is 3800-4200........

 

[Malibud]

Re: Am I allowed more RPM ?

What is the max rpm for an OMC stringer 350?

 

[chiefalen]

Re: Am I allowed more RPM ?

4200-4600

 

[MikDee]

Re: Am I allowed more RPM ?

mercruiser service manual #4, MCM 898. s/n 4887830-6218461

the 4200-4600 is correct for the MCM 228 (305), and the MCM 260 (350), the MCM 898 is 3800-4200........

Ah Yes, probably because the 898 is a 305 with only a 2 barrel carb., and reaches it's peak hp at that rpm, IMO the only difference between this and the 228hp version is a 4barrel carb., But the full specs remain to be checked out.

 

[HPLou]

Re: Am I allowed more RPM ?

so I am out of specs then. My engine must not exceed 4200 RPM.

Last summer I had installed a 14-19 #4878120-19 Black Max prop. The MAX RPM was 3900 and top speed on GPS 38-39MPH. The boat felt loaded & lazy.

I replaced it with a 14-1/2-17 and the RPM is now 4600, top speed 44-45MPH on GPS and I can feel the torque. The engine seems to breed much better.

I certainly don't want to go back to my used 14-19 prop But if I must do it, I will.

I am not looking for Top Speed at all. Most important is torque for skiing. For that need, I am satisfaid with the present prop installed (14-1/2-17)

What would be the effect on the engine if I keep this prop but never reach Max RPM ?

HPLou

 

[f_inscreenname]

Re: Am I allowed more RPM ?

IMHO it all comes down to how much time you spend over 4200? If it's not much anyway then don't worry about it. If you are, you just need the right prop.

Also think about it. You went up in RPM and speed with a prop change, and with a bigger in diameter prop. Something's not right about that.

 

[Bondo]

Re: Am I allowed more RPM ?

I replaced it with a 14-1/2-17 and the RPM is now 4600, top speed 44-45MPH on GPS and I can feel the torque. The engine seems to breed much better.

Ayuh,....... Leave it Alone,....... You'll be Fine.......

 

[MikDee]

Re: Am I allowed more RPM ?

Ayuh,....... Leave it Alone,....... You'll be Fine.......

Ditto!

So you're probably putting out more power then stock, I doubt the 305 is not built just as sturdy as the 350, IMO you'll be just fine unless you start pushing 5k, or more.

 

[Don S]

Re: Am I allowed more RPM ?

I can feel the torque. The engine seems to breed much better.

I would leave it alone for awhile. You can always sell the off spring,.......... Or maybe one of the offspring will grow up to be a 5.7 with an Alpha I drive.

 

[Coors]

Re: Am I allowed more RPM ?

I want one of the babies, but not the runt of the litter.

 

[nailem]

Re: Am I allowed more RPM ?

i was reading in the prop forum that diameter is not as important as pitch. also that a stainless prop is like adding degree compared to a aluminum prop. so would it be a perfect prop to find a 14.5 x 17 stainless would be like a 14.5 x 18. im not sure if thats correct but that is the way they made it sound.