Max RPM for a Chevy SM 350

[Ol Yeller]

I'm just looking for an opinion here. I have a pretty big heavy boat with a Chevy 350SB. I have a 2 to 1 belt drive and a 3 blade composite prop that I can adjust the pitch on. Right now I have the prop pitched so that at WOT I hit 5200 rpms. I'm thinking about reducing my prop pitch so that at WOT I'll be hitting 5500 rpms. Of course I only need to hit these revs on land. I would like to do this in order to break loose from the dirt a little easier, and 5500 rpms is well within the specs of my cam. What do you think? Am I going to destroy my engine doing this?

 

[Whitebear]

Whats your max HP RPM?
Whats your max Torque RPM?

I'd bet you could prop it down to around 4700 RPM WOT and you'd make that mill last a lot longer. Theres not much gain in over running your max HP rpm, just makes a lot more noise.

Of course I don't know your engine, but just because the cam is good for that RPM, if the rest of the engine isn't built for it, you'll find it doesn't last long.

Scotty

 

[Ol Yeller]

Thanks Scotty,

I've had it pitched so that at WOT was 4700 rpms and I couldn't run dry at all. When I pitched to run at 5200rpms it does all right. I'm not concerned about noise because I hit those revs only for a few seconds. I don't know what my torque or HP is. If running my engine at 5500 rpms means it's only going to last me 9 years and not 10 I can live with that.

 

[Whitebear]

Your lack of dry running ability "might" not be an engine & prop issue. Theres some disccussion here on jacks and hull shapes and how to set them up. Might be worth reading through. If it isn't ballanced and shaped right there isn't enough HP in the world to make it move very far.

A good stout SBC should move a boatload of people, dogs, coolers, ice and gass without a lot of punishment with that belt redrive.

Scotty

 

[c chardt]

Most of the stock gm engines they say are good up to 6000.rpm but not for long periods. I have mine set up to turn 4600. and the other day I was running dry and looked at the tack and it was at 5500. but they will run for quite a while at that rpm but I would suggest a 7 or 8 qt oil pan if you have to run that rpm for more than a minute because you will pump the oil pan dry quick been down that road before and cost me my motor

 

[Whitebear]

I just called my boy back there in Pam Bay. He has a Corvette SBC setup w/ 1.5 belt redrive and a 3 blade sensenich on an old .090 thick Hamant hull and he said he has his propped to 4100 WOT and he breaks dry ground at 3000 RPM out on Sarno grade. (lose sand and small gravel.)

He said by all means get the big deep oil pan, says its a must.

This kinda confirms what I was getting at about your hull and it "might"not be your motor and prop.

Scotty

 

[bondsman]

who ever got to read my other post before i deleated sorry for sounding dumb i am just verry tierd.

 

[marshmaster pat]

Billalvord - I would be careful about grabbing less pitch and turning it up to 5500. Exceeding the max RPM limit on the prop will probably not gain you too much. Not sure which brand blade you are turning, some people say theirs keep producing more.

Those Power Shift are great but I have miss pitched PS Signature series on a Lycoming and the engine would rev up to about 3300. Just made lots of wild sounds, but didn't really seem to gain much once it peaked over 3000.

Now the early Power Shift Plus stubbies that were originally made for Aircraft engines seemed to gain more thrust with the extra 200 RPMs, but I don't think the Signature does as well with extra RPMs.

Let people know what you have and someone may be able to give you some clues from experience.

 

[Airboatcapt2]

What model and length prop are you running? Also What is your engine H.P?

 

[SAFARI RICK]

I have a similar set up- 350 w/gear box running a warp drive. Was haveing the same problem and solved it by setting the jacks to bow the hull alittle more and it made a world of diffence running dry. Go slow when setting jacks only altittle at a time too much and you'll wear your poly out quick. Just my 2 cents. SAFARI RICK

 

[Ol Yeller]

Thanks for all the help concerning my 350SB max rpms. My prop is a Sensenich 3 blade wide at 78". I don't know my horse power as I've never dynamode my engine. I would estimate it's about 370 hp with the cam, solid lifters, high compression etc. Did I mention my boat is heavy. It's 16' long, seats 5, and has all stainless rigging. Don't get me wrong it runs dry. Just not real good. And I'm careful about where I park because this boat is just too heavy to start pushing around. I might look into those jacks though. I know my hull is a slightly concave from previous dry running. Thanks again. Bill