Recommended RPMs at WOT - Merc 5.7L

[rmurray]

Trying to find the recommended RPMs for my 1987 Mercruiser 5.7L 260HP with Alpha One at full throttle. I'm right around 4000, but I think I should be a little higher (21' Bowrider). Thanks for the help!

 

[180shabah]

Re: Recommended RPMs at WOT - Merc 5.7L

It is either 42-4600 or 44-4800, somebody will chime in here with the exact answer. Reguardless though, 4000 is too low.

 

[Bondo]

Re: Recommended RPMs at WOT - Merc 5.7L

It is either 42-4600 or 44-4800,

Ayuh,........

About anywhere in that neighborhood will do,.......46/ 4800 is the Sweet Spot.......

 

[Don S]

Re: Recommended RPMs at WOT - Merc 5.7L

4200 to 4600 is what Service Manual #9 is showing. This manual is for the 1985-1988 5.0L and 5.7L engines.

 

[Mjust]

Re: Recommended RPMs at WOT - Merc 5.7L

Trying to find the recommended RPMs for my 1987 Mercruiser 5.7L 260HP with Alpha One at full throttle. I'm right around 4000, but I think I should be a little higher (21' Bowrider). Thanks for the help!

I have a 96 5.7L LX in a 18' open bow and have the same problem, hits 4000 and seems to hit a rev limiter. Been working with the guys on here to figure it out. I have the Alpha One Outdrive with a 1.62 Gear and a 21 Pitch prop.

 

[getsideways]

Re: Recommended RPMs at WOT - Merc 5.7L

service manual for my 1996 5.7 210 horse with 2 barrel says 4200-4600. im right at 4500 in my 210 bowrider with 4 adults and 1 child. i have a ballistic 14 3/4 x 19 stainless prop.

 

[Don S]

Re: Recommended RPMs at WOT - Merc 5.7L

Uhhhh, guys, he doesn't have a 1996 model, he has an 87.

 

[rmurray]

Re: Recommended RPMs at WOT - Merc 5.7L

I know its not a rev limiter problem. I have two props (I think an aluminum 19 and a SS 21). The 21 is what I have on there now. With the 19, I get the same speed, but exceed 5000 RPM (working too hard). I'll have to try a 20 I guess. Can I buy a prop, try it out, and return it if it isn't right?

 

[Don S]

Re: Recommended RPMs at WOT - Merc 5.7L

You don't have a rev limiter in your 87, you only have a Thunderbolt IV ignition, not the Thunderbolt V. Apples and Ornages.

Check with your local prop shop or Merc dealer for the prop trial. Usually you buy a prop. Try it, then change as needed till you get it right and don't damage the props. But you do have to buy 1 prop, and you damage it, and you own it.

 

[rmurray]

Re: Recommended RPMs at WOT - Merc 5.7L

Thanks Don. You helped me twice in one day. Kudos!

 

[badbowtie]

Re: Recommended RPMs at WOT - Merc 5.7L

On you'r 19p prop I would check it or have some one else check it if you are changing 1000 rpms with it I would say you have spun the hub in it. You should only change about 250 rpms per pitch.

 

[Springchaser]

I have a 20’ Larson laser with the 5.7 mercruiser and I run a 14.5 x 17 4 blade prop . I get up 55mph at 5500 rpm .

 

[GA_Boater]

I have a 20’ Larson laser with the 5.7 mercruiser and I run a 14.5 x 17 4 blade prop . I get up 55mph at 5500 rpm .

11 year old thread. Helpful info, but very late.

Closed.