patrick22309

Am I too easy on my motor? 1989 260/Alpha 20ft Stingray (light hull). I cruise around about 3300 rpm and all the other guys I boat with say the SBC can run 4000 RPM all day long. The engine runs great, hours???? 300+, 40-45psi oil off idle, small puff of smoke when you first start it, but uses no oil. I would like to rag on it but want to use the engine one more season. How much abuse can these marine SBC handle? Can I safely cruise at 4000rpm for extended periods of time or am I asking for it?

Scott72

Patrick,
I don't think you can ever be too easy on a motor, but you could cruise a little higher than 3300. My last boat had a 350 Mag and I found the boat liked 3400 - 3500. Boat had over 400 hours on it, burned no oil and had perfect compression. I don't know if I'd run 4000 for huge periods of time, but I'd often run it up there for 10 minutes plus. But, you GPH will be pretty bad up there. 350's seem to be able to take a lot of abuse.

BTW: My boat was in a fire last season and was totaled, but I pulled the motor and now my buddy is running it in a 19 footer. Still runs great.

Iggy

I have a SBC 350MAG/270hp with over 400 hours. Mine too blows blue at first start, bad valve guides/seals.
I run/cruise at 3500, 4000 probably wouldn't hurt it but I wouldn't do it for extended periods.
I'm not sure about yours but my max rpm is 4600 and running at 4000 is close to max.
Running it at a high cruise uses more fuel and puts more strain on it. 3500 is my "sweet spot" (best range) for fuel consumption and we know fuel isn't cheap. Running at high cruise on mine really makes a difference in fuel usage.
I don't know how much longer mine's going to last but I can't afford to rebuild now, so I'll throttle back and "cruise".

traviss

my 350 mag I ran WOT all the time 4600rpm... Never worried about hurting it... thats not much for a SBC... On my new motor (383)cruise is about 4000 and WOT is around 5500 rpm.. long as you have good oil pressure and cool oil they will last forever untill the gas runs out LOL!

TomZ

iTrader: (2)

When I first picked up my boat, the engine was pretty toast but I ran it anyway due to lack of having something better to put back in it (can't be without a boat for the season). Anyway, that motor was dumping water into the oil due to a crack that I could not fix. I ran the piss out of it anyway (put it in the water, warm it up, and then 4600 RPM all day long... well maybe not all day but you get the point) and it still ran OK. I was changing the oil everytime I went out (cheap old Trak Auto 30 wt... five bucks to fill it back up) but it still had water in it... not a good thing. Well, it lasted the rest of the season like that. Same 260 Merc that you have in yours.

I'm in the same situation as Traviss as well, 4k RPM is where she starts to wake up and it should spin to the upper 5k range at full tilt. Will I run it WFO all day? No, but I cruise at 4k RPM right now though I think that it's a bit under-propped. I would like to cruise in the upper 3k RPM range.

I would bump your cruise speed up a bit if for any reason just to blow it out some (maybe make a few WFO passes with it). Generally, I have a feeling as to when I've been too hard on an engine. Keep track of how warm she's getting and the ol pressure and you'll be OK.

Have fun with it!

Tom
"Wetscape Navigator"

ripride1

I had twin 350 MPI's. The motors were bullet proof and ran like a top.

Never was a big fan of WOT for extented time until I did my first Thousand Island Poker Run. 4950 RPMs for 20 -30 miles at a time. 156 mile run and we didnt use 110 gals of fuel and not a drop of oil. I thought the gauge broke. Ran the boat for a few seasons and it was still right up to spec. It made a believer out of me.

I now run twin 502 MPI's. Same poker run uses about 160 gals of fuel and 3-4 qts of oil. The worst thing is doing the exact same speed on GPS it just costs alot more.

Good luck and have faith in small blocks. Its tough to hurt them.

patrick22309

Thanks all!

We went out last evening and ran about 15 miles down the potomac and back @3500/45mph both directions and it was a smooth ride. Running @4000 jumped to 50+ but it just sounds to wound up for extended runs for me. I jacked it a couple times to hit 60mph @4600 and it didn't skip a beat but it sounds very abusive unless I am racing someone. I think 3500 is going to work fine and I still look fast catching and passing most boats at cruise speed. I am running a cheap steletto 21 prop, the speeds will probably be better when I get my mirage 21.

jdnca1

You can turn 5000 all day..or more likely until your gas tank is dry. Small blocks are near bullet proof.

Cord

iTrader: (2)

I once ran my 454 mag up the Mississippi river wide open until I was almost out of gas. I believe that it took me a little over 2-1/2 hours to do it. The only times I ever lifted was to go through two locks, and even then I never had to wait as they were open to me. That motor at WFO would turn 5200, but it had forged pistons. That's one of the critical elements to turning the high r's. BTW-when the motor was torn down this past year, the dealer said that it actually looked really good! Not bad for a engine with 500+ hours that got it's oil changed once per season!