Merc 260 bolt ons?
 

I'm sure this question has been asked to death, but I gotta do it anyway because I'm a gearhead and I like to tinker with my stuff.

Is there anything to be gained by using "bolt on" performance parts for an 84 Merc 260? For instance, upgrading from a 3 inch riser/manifold combo to a 4, maybe installing some 1.6 roller rockers to give the stock cam more lift, or a freer flowing flame arrestor? I have noticed that most boaters either leave their boats with a stock engine or build something rediculous, not too much in the way of bolt ons, I'm wondering why that is? I really think that a couple more hp are available from this, but I'm a newbie so I could be wrong.

Any replies are appreciated, and yes I am the same idiot that asked about supercharging it last week lol.

vortec heads,rpm airgap intake holly 650 dp and a xtreme marine by comp cams..you eill be around 330 hp..

I changed the heads on mine to World Products, added the magnum iron high rise, rejetted the Quadrajet, magnum flame arrestor, added a Crane Cam, and roller rockers. I had to go 2" up on the prop pitch. Gained 4-5 m.p.h. If you are fresh water cooled I would go with aluminum heads and intake. You will probably save 100 pounds alone! I used 76cc heads as I was afraid of having too much compression and having to use 89 or 92 grade gas. As it was 1986 when I did my build I know I could get a lot more power today. I'd go to a 383 cu. in. setup with aluminum heads and intake, and a roller hydraulic cam. I would think you could make an easy 380-400 h.p. Enough to break your drive!

Cast crank, cast pistons, make it a winter project and do a 383.

Just got done with a similar one. I ended up replacing the whole engine, but the old short block to new is pretty much the same setup except for the roller cam.

I was able to buy two 350 long blocks from 97-99 pickups with spun main bearings, less than 100,000 miles either engine, for $500 total. Used those vortec heads and brackets on my engines. Went with the aluminum dual plane intakes and the mercruiser roller cams. Should be right at 300 HP I am guessing, but that is just using mercruiser numbers. Still using the same carbs, they aren't bad actually and changing out secondary rods is real easy to play with air/fuel ratio. yeah, I left HP on the table with the merc bump sticks, but I had one already and didn't want to fork out another $500 for new cams.

so you can get vortec heads for $300 or less per engine, then a new aluminum intake manifold will push almost $200, then a gasket set which is pricey for the vortecs, I think around $180ish, can't remember. About $700 an engine with a few extra parts thrown in. Wake it up with a new cam and lifters for another $100 I would guess for non roller.

my build is in the formula section, go figure huh?

Good luck, Brian

There may be different opinions on this, but mine come from experience. At the 260 (270 mag) horsepower level these heads are maxed out. I have put bigger cams on them and better induction and exhaust and have seen very little improvement in performance. The heads are just not up to the task.

That being said, throw on a pair of vortec heads and a good roller cam and results are instant. Either search them or I can tell you common combinations for small block power.

Of cousre you can also go big (AFR, Dart, etc.) and stroke to a 383, but you seem more interested in moderation and fair prices.

You won't be disapointed in a build vortec 350 and it wont cost verly much relatively speaking.

nobody directly answered your question, yet they all did. the 1.6 rockers won't magically make the stock 260 cam into a bob madera custom grind. the 4 inch risers and bigger flame arrestor won't change a thing. unless and until you go heads-cam-intake-exhaust you will see very little improvement. what you need to do first is make sure everything is right with the motor and it is putting out the 260 it is supposed to. plugs, wires, clean all the black gunk off the flame arrestor. make sure it is timed correctly.

I had a 24 Chris Craft 245 Limited years ago, stock 260 it went 42 mph gps, I used my buddys 350 from his camaro with a ZZ4 roller cam, edelbrock aluminum heads, edelbrock performer intake and a 650 Holley, boat went 53 mph gps after that, I would say that was a good gain over the 260 it was for the money spent...proven combo without going broke... the shortblock held up fine with stock internals..

Derek is correct, none of us answered directly.

Like he said, no bolt ons are really going to make a difference until you swap the heads. Stock cast iron vortec is the biggest bang for the buck, but that also requires a new intake due to bolt pattern. but you should get rid of that cast iron intake anyways. So a minimum: used gm vortec heads and intakes, which means top end gasket set. My gasket set was whole engine, so maybe heads up would be less, but it is the intake that was pricey I think.

And if you do that, you owe it to yourself to do the cam since the intake is off anyways. Once you see the price of intake gaskets for the vortec, you will not want to do the cams later.

And you are at that minimum number of $700 or more.

Are you willing to spend the $1500 ish it will take to do both motors? If the answer is yes, then do as suggested and get them running in top shape and beat on them for a bit to make sure they hold together before adding more HP.

Brian

Just put a weiand 144 blower on it. Run 5# of boost, you should get an easy 350hp and be able to run close to 60mph. All you will have to do is replace the intake and rejet the carb and plugs. You wont have to take the motor apart and it will idle like stock and run like stock till you get in it and start making boost.

Mr. Scarab, the easiest gain I made on my 85 Chris Craft 260 was to replace the standard iron intake with the intake from the Magnum. This one change alone made a huge difference in torque. Before the boat would run up to 4200 r.p.m.s and I could trim it out to 4600 r.p.m.s. After the intake swap it would run right up to 4600 r.p.m.s without trimming the drives out. I next added the Magnum flame arrestors (much taller) but this was a step backwards in performance until I put the Magnum metering rods in the secondaries. The Carb Shop in Ontario California set me up with the correct rods. This was the first steps I made in increasing the performance of my boat. The stock heads were prone to cracking exhaust seats in the mid 80s so that was the main reason I went to World Products SR Torquer heads. While I was into the engines that far I changed cams and added roller rockers. I know the ratings for the Magnum during the 80s was only 10 h.p. over the 260 motor but those had to have been the biggest, strongest h.p. I ever met! My guess is there was closer to a 30-40 h.p. difference.

Perfect inexpensive recipe....

Mid-90's 350 from a 1/2 ton truck, check out the bottom end. If it checks good, polish and put back together. The GM engine manual says that the bores should be left alone unless they are out of spec. If in spec, use new rings and put her back together.

Heads... Vortec. Even if the engine you buy has Vortecs on it, sell them and buy new over the counter pieces. You'll be better off not messing with valve jobs with these heads. Then, purchase a set of Z06 LS1 springs (yellow bee-hive) and the associated Comp retainers. If you use a 1.5 rocker, you will not have clearance issues.

Cam... GM LT4 "Hot" cam. Will work with the stock exhaust.

Intake... Edelbrock Performer RPM AirGap

Carb... Holley 750 Double Pumper or equivalent. I'm sure the QJet will work just fine.

Easy 350 HP set up.

When I blew up the 385 in my Stinger, I slapped this one together in a weekend. Fun, powerful, reliable. Ran in the mid-60's and sipped fuel. Estimated around 350 HP (a friend's made 380 with 1.6 rockers) . I think it cost me $900 to put it together.

Tom

Back in 2000, my friend and I took a brand new Rinker 232 captiva :picard1: with a 260 hp 5.7L Vortec and swapped out the intake, 2 bbl carb, and flame arrestor for an Edelbrock Performer(RPM or RPM airgap ... don't remember anymore) intake, 1" port matched 4 hole phenolic spacer, Holley 600 square bore 4150 marine carb, and K&N marine air cleaner/flame arrestor, if I remember all of this correctly. Back to back runs with ~12 hours in between start to finish, we went from 48 mph (gps) to 53 mph (gps). Was able to go from a 21p AL prop to a Merc 23p SS prop. Couldn't spin the 23p prior to the change, and after the change the 21p would just hit the rev limiter. That really "woke up" that engine. Bought all of the parts from a Chevy High Performance shop in Colorado, including the "recommended" grey GM silicone sealer, GM Vortec intake gasket set ($$ :eek:), carb, spacer and intake for right at $450 (seemed really low, but they delivered!). HP increase was estimated to be from 260hp to ~300 - 330 hp. We found out then, that a Rinker wasn't really meant to run at those speeds, but it was a fun 1 day project. :rolleyes:

If the motor checks good on a leakdown, you can do what has been suggested and BOLT ON a 177 blower. Run 3 to 4 lbs of boost, and don't run over 4800 rpm, and you can make good power without pulling the motor and going thru it.

Stock ignition, stock heads, stock cam, stock valvesprings. Stock fuel pump, stock exhaust. Bring static timing back to 4 degrees BTDC (from 8), and get somebody you trust to rejet the stock carb.

The blower/intake, the drive snout, pulleys and belts, gaskets, and a new prop are all you HAVE to buy. Anything more than that is optional.

Blowers are the best bolt-on going.

3 lbs of boost will get you to 300hp.

MC

I just finished a similar build for my ’85 Chris Craft Scorpion 230;

- 4 bolt main Vortec 350 from a 2000 Chevy Express 2500
- Stock bores, just honed
- O.E. type Mahle ring set
- Sold the Vortec heads and bought a set of 64cc RHS Torkers
- LT4 Hot Cam
- 1.6:1 Crane roller rockers
- Holley 650 (vacuum secondaries)
- GM Performance low-rise aluminum intake

After some break-in, no real tuning or much trim adjustment, I was able to turn 53 mph on the GPS at 4200 rpm with a 19” prop. That was with 3 of us onboard and some fuel and equipment.

Thanks alot guys I am kinda stuck for the time being untill I get it back to running again but that is another thread : (