1987 260 mercruiser info needed

I have a 1987 BAJA FORCE 265 with twin mercruiser 260's. I am looking for motor spec and can't seem to find any for that year. I am interested in the camshaft technical data (lift, duration, roller/flat tappet) and cylinder head tech data (combustion chamber size and valve sizes). I may want to do some updates but do not want to rebuild the lower end. At the moment I'm just trying to get a baseline so I know where I am so I know where I can go. I want to use the carbs that came with the boat( Q-JETs) and change the intakes to an edelbrock performer.

Aslo, what is the difference between the standard 350 and the 350 magnum? Any help or information would be helpful.

[birdog]

Order a copy of Dennis Moores small block chevy book from
Barnes & Noble on line. It will tell ya all you want to know.
I did my 86 260s years ago but i can't remember all the specs.
350s are pretty "bulletproof"......

[ChristianGott]

Mag 350 vs 260:

cam lobe lift: Mag 350: intake-.287, exh-.300
260 : intake-.263, exh-.269
crank and main bearings: same
heads: same
lifters: hydraulic
rocker arm ratio: 1.5 to 1
valve spring free length: Mag 350: 2.03
260 : 1.91
installed : Mag 350: 1.70
: 260 : 1.72


It looks like the Mag 350, 260 differences are a cam and lifters thing...a typical first step hop-up..i don't know about carbs, but I would bet that the Mag runs richer (bigger jets), especially in the typically lean rpm range before the secondaries open...

not a pro...just reading up on it , too
hope it helps as a starting point.

Moore's book is a great help and I highly recommend it. I've heard from some hotboaters that some of the info may not be completely accurate and the cam specs on the 5.7L and Mag were at the top of the list. I don't know if this is truth or not. I can definetly tell you that comp cams XM 258(?) is a stronger than stock cam for the 5.7. Unfortunately, I threw away my '92 5.7 stock cam before I measured the lobes.

5.7 and Mag both use 76cc crate motor heads (non-swirl), 0.025 deck height, and 4 valve relief, slight dish pistons, and small valves (1.94/1.5).

Mag uses the Z-28 cast iron hi-rise manifold, which is available from GM Performance Parts (and is better for a RWC boat than a Performer!, IMO), and a roller cam. The 5.7's use a flat hydraulic cam. (Actually, some 5.7 BIIs may have used the roller as well)

Merc set up the 5.7 and 350 Mag Qjets differently on both the primary and secondary sides. The Mag uses the smallest primary jet (069) and a 039 rod (I think) whereas the 5.7 uses a 070/042 set up (the 305 used a 070/041, which is richer - go figure). The Mag used CH secondary rods which are short tips and the 5.7 and 305 used CL rods, which are Long tips.

My 2 cents? Go with a Comp Cams XM 262(?) roller cam, Iron Eagle 72cc heads, the Z-28 cast iron manifold and use the CH or CP secondary rods and your 260 should be over 300, maybe even 320 (if the short block is sound)

Good luck

Oops, lt me try that again. All the Merc Qjets that I have seen have been set up like this:

For the 5.7L: 068/041 primary & CL secondary

For the 350 Mag: 069/036primary and CH secondary

Thanks for your help!!!!!!!!