CHEV 250/ 165HP ENGINE ROCKER RATIO

[Charger183]

I need the rocker arm ratio for this engine. Also the stock valve lift/timing. Any help is appreciated.

 

[coupedeville]

Re: CHEV 250/ 165HP ENGINE ROCKER RATIO

If memory serves, it's 1.7:1, like a big block.<br />Cam specs for what, exactly?

 

[Charger183]

Re: CHEV 250/ 165HP ENGINE ROCKER RATIO

Tnx CDV: The cam spects are for the stock marine cam in the engine. I wanted to know the overall valve lift. I had thought to change the rockers to a greater ratio but 1.7 is already the max. If I want more torque I'll have to change the cam. My boat ( 1975 Crestliner Norseman, 19' no cuddy 2000 lbs wet ) has a 15X19P prop on it now. I am told a 23P may be the one I need. If it is, the ability to add a little more midrange torque if necessary would have been nice.

 

[P.V.]

Re: CHEV 250/ 165HP ENGINE ROCKER RATIO

Say what???? Charger, you have too much time on your hands!!!! How does the engine run?? What are the Wide Open Throttle rpm's ??? Is this a OMC or Mercruiser?? Jumping from a 19 to a 23" prop would change rpms about 800 or so. That may give you more top end speed, slightly, but I would suspect much less hole shot, not counting possibly lugging the engine. THEN you'll need a new valve train after you tulip all the valves. If it runs good, rpms are in the range, go fishing and enjoy!!!

 

[Charger183]

Re: CHEV 250/ 165HP ENGINE ROCKER RATIO

P.V. Tnx for the thought. This is a Mercruiser/Chev 250/165hp. with the early 1.65 ratio outdrive. Both engine and outdrive have been totally remanufactured in 2001. The engine hits 4800/5000rpm now which is way too high. Speed is 45/47 mph but the boat is too "twitchy" during acceleration. If you hit a 2' wave with a little too much enthusiasim you head for the sky. The Michigan Wheel people say use a 23p on 20' light boats. The Norseman is not a well known model. Medium V with planing speed at 17/19mph. I think the larger pitch would allow a slower rise with a cruise much easier on the engine. COMMENTS? In the 60's/70's these engines in D altered drags made 375hp+ and enough torque to move a brige without breaking over a whole season.

 

[P.V.]

Re: CHEV 250/ 165HP ENGINE ROCKER RATIO

Charger, make the prop change and get the WOT rpm's correct. If you feel that you must develop more power,O.K by me. I would suspect that the outdrive will grenade, if you do!!!! All 165 hp's had the 1.65:1 ratio. fairly reliable and ez to work on. If someone came into my shop asking about rocker arm ratios and such, I'd give 'em the book and say have at it. Most dealers don't know and don't want/need to know!!! Do the ez things first. If the motor runs correctly, play with the props !!!!!You're not an "engineer" are you ????

 

[Doug Durako]

Re: CHEV 250/ 165HP ENGINE ROCKER RATIO

I ran the same engine/drive for years on an old, heavy, 18-foot Cobalt. Finally settled on a stainless steel 14.75 diameter X 21-pitch prop for best results and it dialed right in at about 4200 rpm and about 48 mph trimmed out with one person in the boat. Each inch of pitch you add decreases your rpm by about 200. But, remember, each half-inch you increase in diameter on the prop also decreases your rpm. The older Merc drives like the larger diameter prop----my guess is your pitch AND diameter are a bit small.

 

[Doug Durako]

Re: CHEV 250/ 165HP ENGINE ROCKER RATIO

OOOps---did not see that you have a 15-inch diameter prop----I think that is as big as you can go on this drive. I's still try a 21-pitch before going to a 23.

 

[Charger183]

Re: CHEV 250/ 165HP ENGINE ROCKER RATIO

Tnx guys: I'm looking at a 14.75 X 23P cupped Quicksilver prop on Ebay. My thinking is still that the 23 will allow a good speed at cruise at a 34/3600 rpm. (COMMENTS???) I am exclusively on Lake Erie so will have to contend with mostly 1 to 2' waves with 6 to 9' spacing on a daily basis. Hole shots are not required and I have a 4.5hp Merc to use for trolling.

 

[Bondo]

Re: CHEV 250/ 165HP ENGINE ROCKER RATIO

I Think 23"s is Too Much Prop.... you'll be lugging the motor.....<br />I'd think a 21" is where you Want to be....

 

[Charger183]

Re: CHEV 250/ 165HP ENGINE ROCKER RATIO

Tnx Bondo: I'm going to take your advice and go with a 21". Tnx all for the help.