how high do you rev your 350ci chevy engines?

[ratman]

i just bought scarabj's 71 18, im junking the merc ign in favor of a crane hi6 set up with a msd blaster coil. cant tkae the 4800rpm red line in the stock ign. was wondering how high you guys are revving your 350 ci powered boats? thx rm

[Rootsy]

the ignition isn't limiting the rpm of that motor... the valvetrain, or more importantly the camshaft profile is setting the max RPM of the motor... basically the horsepower peak.

my mouse makes peak HP around 5700 rpm... i prop it to run 5500ish namely to take it easy on the drive...

[ratman]

roots, it hits the rev limit at 4800 its a 99 merc 260hp set up. im running a 19 pitch and it blows out coming on plane and hits the rev limiter in a hurry as soon as it gets on plane, i located a 23 pitch do you think thats too much? what drive and pitchh are you running? thx rm

[onesubdrvr]

My motor makes peak hp at 5500, and that's where I'm trying to run it (still propping)

BUT, like Jamies, my motor is more suited for it, roller everything, beefed up valve springs, etc.

On a stock motor, I'd stay with the stock limiter.

Wayne

[blackhawk]

I would guess on a STOCK 260 hp motor, I would say 5000 rpm would be max, maybe lower. Some 350s had a operating range of 4400-4600 but I'm not sure which ones.

[mrfixxall]

roots, it hits the rev limit at 4800 its a 99 merc 260hp set up. im running a 19 pitch and it blows out coming on plane and hits the rev limiter in a hurry as soon as it gets on plane, i located a 23 pitch do you think thats too much? what drive and pitchh are you running? thx rm


Does the prop have holes in it at the lower part of the prop? if so try pluging the holes and see if stops itfrom blowing out...

You shouldnt be running a 260 past 4800 rpm...

i run mine at 6000 to 6200 with a stock ultra 24 on a volvo 1.61 ratio.

I run 5600 to 5800 on a labbed finished ultra 24, and the same with my stock 26 ultra..

[ratman]

the 76 18 we had when i was a kid was a bone stock volvo pkg with 270 drive it revved 5800 out of the box and 5600 with a nybral cupped prop. why should the 260 sbc only be good for 5k?

[blackhawk]

ratman what happened to the hammond challenger? Did you buy that boat too?

[onesubdrvr]

the 76 18 we had when i was a kid was a bone stock volvo pkg with 270 drive it revved 5800 out of the box and 5600 with a nybral cupped prop. why should the 260 sbc only be good for 5k?
There were a number of different engines in use then, to include a 320hp chris craft engine, I'm SURE the rpm range was higher on that engine as well.

Wayne

[Rootsy]

you can spin it as high as you want for as long as you want until #1 the valves float or #2 the rods exit stage south... the prop you run is the lever that throttles the max rpm at WOT...

merc, etc specs the WOT of their motors, again based upon the camshaft, etc which dictates where the motor makes PEAK horsepower, this is where you want to prop the boat, so that at WOT the motor only turns that high... durability wise the motor will handle more rpm... but it does no good you have dimishing hp and torque output the higher you rev it...

now take my 350... the camshaft, cylinder heads, etc (the whole combo) makes peak horsepower at 5700 rpm on the dyno. therefore i want to prop the boat ideally so that at WOT it spins that rpm... BUT on a stock lower end that is unbalanced, etc you begin to get into some harmonics that put undue stress on rods, cranks, etc... therefore i add an inch of pitch and bring the RPM down... it labors the engine a bit but it makes it easier on both the motor and sterndrive... and i don't hold it there for extended periods either...

it is going to do you no good to spin the motor where you say you want to... you'll be way off of the torque peak and all you are gong to be doing is over revving the motor and the sterndrive... you want to prop it so that it will rev @ the range mercruiser has set for the motor...

as for me... 410ish hp, down to 400 at 5500 i run a 25 pitch 4 blade at 5200 - 5300 and a 23 pitch 4 blade (identical to the 25) prop at 5500-5600ish on a 1.47 ratio alpha SS...

in my 16.. with a 250 hp 350 rated 4400 - 4600 rpm i spun a 19 P prop 4400 - 4500 rpm... stock 350 mag mpi 300 hp 18 with a 1.5 ratio alpha will turn a 23P prop 4800 - 5000ish rpm, rule of thumb with a 3 blade such as a turbo or mirage...

just my take on it...

[ratman]

the guy with the challeger backed out of our deal. the boat had transum floor and stringer work also, so i bought scarabj's 18 instead. i'll run the snot out of it til it pukes then build a 383 roller for it.

[ratman]

im gonna swap ignitions this week and put a 23p on and see what she does and take it from there.

[Just Say N20]

The 260 hp Mercruiser engine, at least the two I have owned had an operating range of 4,200 - 4,600 according to Mercury. I imagine it has to do with a durability issue, as well as what ignition technology they were using on the engines.

I put a 110 to 125 Nitrous kit on one of them, and it would BRIEFLY run up to 5,300, but only for 6 or 7 seconds. I never had any problems with it.

I believe that if you ran the 260 over 4,600 for any period of time you will have problems. The valve train they used didn't have the grunt to operate at high rpms.

[blackhawk]

im gonna swap ignitions this week and put a 23p on and see what she does and take it from there.

A 23 will pull your rpm down to about 4600 on a 260hp motor. I had a 23 on my Donzi "copy" with 320 pshp and it would pull it 5000 rpm at about 67 mph. I would guess a 260 hp 350 would like a 21 at 4800-5000.

[MOP]

RPM is not everything, my 383 with a 21 went from 63 at 5500 to almost 66 with a 4B 23 @5150. Like Jamie says there are several factors and many times guys go thr wrong way and don`t get where they should. Jamie also brought up the out drive, they do not last long spun over 5K. You say you will run the snot out of it, hmm and maybe spent a goodly part of the summer on the beach.

Phil

[Woodsy]

I wouldn't spin a drive much over 5500 RPM. The drive towers will start flexing.... then kaboom!

Woodsy

[Cuda]

4800 should be your top rpm, otherwise, go ahead and build the 383 now, because it won't be long until you need it if you are going to spin it higher. A 23 pitch should get you in the ballpark, maybe a 21. I have a 21 cleaver if you're interested.

[ratman]

You say you will run the snot out of it, hmm and maybe spent a goodly part of the summer on the beach mop, i should have my new blower motors in my cigarette with in a few weeks so if i puke the stock 350 its no biggie. but ive worked for gm for years and i never ran across a 350 that would hang a 5500 rpms, the 350 is a great lil moptor and will such a mild cam the vlve train shoud hang together. is seems to me that our 76 donzi with the 350 that revved 5600/5800 nver had any issues, i find it hard to believe that 5800 was the torque peak of that engine

[ratman]

cuda, did you get you donzi with the starter problem repaired? thx for the offer on the 21p but dont think the cleaver is the best prop for this boat, im picking up a 23p from lucky strike why a ride over to the miami boat show. you heading down to mia for the show? take care , ratman

[blackhawk]

Unless that's where the power is why would you want to spin the motor that high? A stock 260hp motor makes it's hp at 4600-4800 rpm. If you spin a 21 pitch at 4800 rpm for 60 mph you would need to go down 17-18 pitch to be at 5800 rpm but your speed will be the same(or less because the motor makes less power there). So, what's the point of spinning the motor that high unless the power is there? If the speed is the same I will ALWAYS take the lower rpm setup. Easier on the motor and the drive. Just my $.02

[dick grande]

ratman dude,

I say drive it like you stole it! No issues man, it will hang together for shore, i rev my baja like 6400 and i get crazy mad acceleration. it sounds geeked to! PPL luv it. don't listen to these fogeys they don't have no gonads.

peace out

[blackhawk]

ratman dude,
I say drive it like you stole it! No issues man, it will hang together for shore, i rev my baja like 6400 and i get crazy mad acceleration. it sounds geeked to! PPL luv it. don't listen to these fogeys they don't have no gonads.
peace out

You know now that I think about it I'd bypass the rev limiter and put a 13p prop on it and rev it to about 7000 rpm. Should still give you some good top speed, accelerate like a mofo and sound sweet! :biggrin:

[Cuda]

ratman dude,
I say drive it like you stole it! No issues man, it will hang together for shore, i rev my baja like 6400 and i get crazy mad acceleration. it sounds geeked to! PPL luv it. don't listen to these fogeys they don't have no gonads.
peace out

What kind of special outdrive do you have that will survive at 6400?

[Cuda]

cuda, did you get you donzi with the starter problem repaired? thx for the offer on the 21p but dont think the cleaver is the best prop for this boat, im picking up a 23p from lucky strike why a ride over to the miami boat show. you heading down to mia for the show? take care , ratman
Leaving in the morning. You should drag the 18 down and make the lunch run to Key Largo with us on Saturday. :)

[joseph m. hahnl]

WHAT THE: some where some one got lost. last I knew he was saying it was hitting the rev limiter out of the hole with the 19. 19 is way to small. i run the stock mirage 21 on my 350 mag 4800 58 to 60.

so here's my question if i proped up say to a 23 0r 25 is my rpm going to drop
or will it still hav e the hp to spin it at 4800?

joe

[Cuda]

You know now that I think about it I'd bypass the rev limiter and put a 13p prop on it and rev it to about 7000 rpm. Should still give you some good top speed, accelerate like a mofo and sound sweet! :biggrin:
Does anyone make a scatter shield for an oil pan?

[KRAVEN]

Running 25p labbed Mirage plus,scorpion 377 5000/5100 Bravo1XZ 1.5/1rev limiter 5200.

[dick grande]

What kind of special outdrive do you have that will survive at 6400?

bra, i'm hangin an alfa 1 off the back its da bomb. the guy who whipped it before me had the guts frozen and shot makes it super tuff. its got abec 23 bearings too which are kick ass. told me it was good for 8g but i can't get my baha over 6400 it wants to mis and stall and i don know why.

[Woodsy]

Joe...

Your RPM will drop approximately 200RPM for every 1" of pitch increase.

Woodsy