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I HAVE A 1988 350 OMC COBRA, ALL FACTORY,IN A 205 FOUR WINNS, IM THINKING OF PUTTING ROLLER ROCKER ARMS ON IT. HAS ANYONE WENT TO 1.6 RATIO FROM 1.5 WITHOUT CHANGING CAMS, HOW DID IT AFFECT THE POWER AND TORQE CURVE. ALSO ANY OPPINIONS ON GAINS FROM, CARB SPACERS, THRU HULL VS OUTDRIVE EXAUST(DOING THAT ANYWAY JUST FOR SOUND OF IT). LOOKING FOR A FEW H.P. GAINS WITHOUT ANY MAJOR ENGINE WORK. I HAVE LOW HOURS AND 60 TO 70 LBS OIL PRESSURE
Bobby-I would post this under the "GearHeads" section. You might get a better response over there. just my .02 wink
I change my rockers every two years to meet smog.
I'm running a Crower special grind cam on my SBC Suburban. With the 1.5 Ratio rockers I get a lift at the valve of .447 int and exh (.298 lobe rise at the cam X the ratio). Just swapping out to the 1.6 rockers gives me .477 lift.) Because of the extra length on the stroke the duration changes slightly also.(A couple of Degrees I think) Bottom line is there is a slight but noticeable difference in performance. This is worth it to me to get a better pulling power but still have the option to go back to the smaller lift for smogging.
Hope this helps
I have a 383 with a 520 lift flat tappet cam and use 1.5 comp rockers. I was thinking of using 1.6 and have been told many times that 1.6 will ware the valve guides on a motor that gets a lot of use. On a drag motor its ok beacuse of the ammount of run time.
Ronnie
Guides will wear.....
True if you use stock length push rods. False if you resize push rods to be in the middle of the stroke for the 1.6 rockers. I use a different set of rods for each. 1 1/2 years on the motor and app 20,000 mile with know sign of premature guide wear.
GUIDES WILL WEAR? WHY? IF ITS BECAUSE OF THE EXTRA TRAVEL THE HIGHER RATIO WILL GIVE THE VALVE, WHATS THE DIFFERANCE BETWEEN THE 1.6 ROCKERS AND STOCK 1.5'S WITH A BIGGER CAM GIVING ME A EVEN MORE LIFT,(THE GENERAL OPENION FOR MORE POWER,)WHICH WOULD ALSO MEAN MORE VALVE TRAVEL, RIGHT? WOULD THIS NOT ALSO BE THE SAME TO THE GUIDE? PS. AS LONG AS I'M ON, WHAT WOULD BE A GOOD REPLACEMENT CAM FOR A STOCK 350 IN A 21 FOOT BOAT W/ THRU HULL AND K/N THAT WOULD NOT HURT LOW END AND IMPROVE POWER?
Bobby MC...You are correct any change in the vale train geometry increases the chance of valve guide wear. The reason the guides wear at all is due to side load on the valeve as it is pushed by the rocker arm. It is NOT a big issue if You make sure the rocker is pushing the valve on the center of the valve stem at it'shighest lift. I also use roller tip rockers as this helps to reduce side loading and friction. Bigger cam or different lift rockers are really one in the same. Just my Opinion.
P.S. See "BBC Valve Train Geometry" post in th e Gearhead forum
Thanks for all the advice.I might just throw on a set of 1.6's just for the heck of it, It'l only take a hour or so. along with the thru-hull exaust and the K/N filter it might be at least one of the better running stock 350's around.
RD.... If you're going to quote my Handle at least get it it right "sChell sChocked" LMAO.
BobbyMC let us know how the mods work OK>
Merry Xmas to all.