Max RPM Mercruiser 170 and 470 differance

[jimmer400]

I have a 1986 Mercruiser 170 in my 21ft Sea Ray Seville. I all so have an older (1980 t0 1982) Mercruiser 470 in my garage. The max operating range is different on the two motors. (170 4200-4600 RPM) (470 3800-4200RPM) I plan on going though The older 470 this winter and installing it in the spring. What is different about the two motors? Will I have to re-prop? What can i do to the 470 to bring up the max operating range. I have learned a lot from this site and I know about the 470 issues. Any help would greatly appreciated.

 

[180shabah]

Re: Max RPM Mercruiser 170 and 470 differance

I don't know much about those particular engines, but I would look at differences in the valverain.

 

[ErieRon]

Re: Max RPM Mercruiser 170 and 470 differance

I have a 1986 Mercruiser 170 in my 21ft Sea Ray Seville. I all so have an older (1980 t0 1982) Mercruiser 470 in my garage. The max operating range is different on the two motors. (170 4200-4600 RPM) (470 3800-4200RPM) I plan on going though The older 470 this winter and installing it in the spring. What is different about the two motors? Will I have to re-prop? What can i do to the 470 to bring up the max operating range. I have learned a lot from this site and I know about the 470 issues. Any help would greatly appreciated.

There's not a whole lot of difference between those two engines. You can download manuals #3 & #8 here to find the nuances; http://forums.iboats.com/showthread.php?p=1693398#post 1693398

Sometime in the nineties (I think), Merc. changed the prop spec for the 470 from 14" to 14.5 ". When that happened, the "new" WOT for the 470 went to 4200-4600.

Hope this helps.

 

[180shabah]

Re: Max RPM Mercruiser 170 and 470 differance

there was no 470 in the nineties..

 

[ErieRon]

Re: Max RPM Mercruiser 170 and 470 differance

No, there wasn't, but they made the prop change around then for previous years. I have an '84, and when I replaced my prop in 1999 they said it was NLA and the 14.5 X 19 was the replacement, and to expect a higher WOT. There was even a little spec sheet that came with the prop to that affect.

 

[180shabah]

Re: Max RPM Mercruiser 170 and 470 differance

OK, but we are getting off topic. prop design has nothing to do with an engine rated WOT range. This determined by things like the balance of the rotating assy, cam profile and valve springs used.