260 Merc 5.7 rebuild

[Arrow21pilot]

I have a 1987 Wellcraft with the Merc 260 5.7, Rochester quad that I want to replace heads and the carb. I would like to put a Holley 650 4bbl with a high rise manifold and would like to get more HP out of the engine. Anyone have a recommendation on high-performance heads?

 

[FreeBeeTony]

Re: 260 Merc 5.7 rebuild

Vortec heads w/ an Edelbrock 1409 carb and associated Vortec intake.

 

[Provo5]

Re: 260 Merc 5.7 rebuild

FYI on the carb. I had the opportunity to try both a 600 cfm and 750cfm when replacing my carb. Engine ran better with the smaller carb.

 

[Fishermark]

Re: 260 Merc 5.7 rebuild

Vortec heads w/ an Edelbrock 1409 carb and associated Vortec intake.

That's exactly what I would recommend as well. VERY good set up and VERY dependable.

 

[Arrow21pilot]

Re: 260 Merc 5.7 rebuild

Does changing to a vortec setup require me to change to a roller cam also?

 

[mkast]

Re: 260 Merc 5.7 rebuild

I would ask what shape the short-block is in?
1987 block, let's bolt a bunch of horsepower on an engine that needs an overhaul.

 

[180shabah]

Re: 260 Merc 5.7 rebuild

Vortec heads w/ an Edelbrock 1409 carb and associated Vortec intake.

This combination will give a solid 300hp at the prop, a significant gain over the 230ish you have now.

 

[Arrow21pilot]

Re: 260 Merc 5.7 rebuild

The block is in great shape. Pistons, rings look like new. I had burned valves (think due to the Rochester Quad and bad gas - looks like it was running quite lean), so I am looking to rebuild and output more HP.

 

[180shabah]

Re: 260 Merc 5.7 rebuild

How much power do you want?

Alphas are only rated to 300hp.

 

[Arrow21pilot]

Re: 260 Merc 5.7 rebuild

300 or as close as I can get! I hear the original Alpha had a 335HP matched to it, but it didn't last long with repeated bursts of speed.

 

[Fishermark]

Re: 260 Merc 5.7 rebuild

You don't need a roller cam - you do need self alighing rockers, but you don't need to change your cam.

 

[wca_tim]

Re: 260 Merc 5.7 rebuild

depending on how much money you want to spend and how good your static compression is, a little more cam would probably be worth a bit more power... One of the mild comp xm hydraulics would do nicely and won't set you back a fortune...

and on a lighter boat (if it is), an alpha drive will hold up fine a little over 300 horsepower - if it's in good shape and being maintained. it's heavy torque that will lunch it.

ditto the above on choice of carb and intake. If you're talking aobut a holley marine carb, that would be a great choice as well. I just swapped my edelbrock 750 out for a holley 750 double pumper and think i'm going to be quite pleased with the change based on initial impressions....

 

[Commissionpoint]

Re: 260 Merc 5.7 rebuild

and on a lighter boat (if it is), an alpha drive will hold up fine a little over 300 horsepower - if it's in good shape and being maintained. it's heavy torque that will lunch it.

Yeh, they tend to blow up if you beat the crap out of them with high torque all the time. Certainly a lot sooner than would a heavier Bravo. Keep the Alpha cool and it should be just fine.

 

[Arrow21pilot]

Re: 260 Merc 5.7 rebuild

So now I'm looking at an Edelbrock 1409 Carb, Edelbrock Performer High-Rise Intake Manifold and a set of Vortec Heads. I am also going to change to a new distributor with the associated electronic ignition module, since the one on it is still the original "Spark Amplifier"! I am hoping to get just north of 300 ponies out of her.

Anything else I should look into?


Thanks for all the help!

 

[FreeBeeTony]

Re: 260 Merc 5.7 rebuild

If I had to do it over again I would probably look into a different cam.......but all in all I am very happy with the performance........

Would really like to build a stroker though.......

 

[n2ostroker]

Re: 260 Merc 5.7 rebuild

My current combo is a 355cu in. 9.75:1 compression with a set of heavily ported 416 casting 305 heads, Performer RPM intake, Edelbrock 750 cfm carb, Comp Cams XM262H cam kit w/springs, stock center rise manifolds and 4"risers w thru hulls. Same 21" prop I picked up 6mph(61mph) over last year. I've got a 23" Laser 2 to try next as my rpms were around 53-5400 with the 21". Haven't touched the carb yet and it does need some work. Just got the calibration kit for this weekend.
The cam I run is about the biggest you could get away with on those heads cause of the lift on the Vortecs without machine work or changing springs. I love it. Mid range and throttle response is excellent. Slight chop at idle around 600rpm. I would go for the Performer RPM or RPM airgap over the standard performer. I tried one and on a 350 they nose over a little over 4k rpm. The RPM/airgap gives the best overall performance.
The Alpha will be fine as said above. Just don't go full throttle wave jumping beating the crap out of it. Keep the drive aligned and good lube in it.

 

[180shabah]

Re: 260 Merc 5.7 rebuild

I am hoping to get just north of 300 ponies out of her.

That combination will do it. Should put you at about 340-345hp at the crank, so 310-315hp at the prop.

 

[wca_tim]

Re: 260 Merc 5.7 rebuild

So now I'm looking at an Edelbrock 1409 Carb, Edelbrock Performer High-Rise Intake Manifold and a set of Vortec Heads. I am also going to change to a new distributor with the associated electronic ignition module, since the one on it is still the original "Spark Amplifier"! I am hoping to get just north of 300 ponies out of her.

Anything else I should look into?


Thanks for all the help!

That sounds like a great place to start. You should get a really healthy increase in usable power, seat of the pants and grin factor and still have a very mild mannered, well idling set-up. You could probably do a thunderbolt iv ignition off of ebay for a song. I bought my spare distributer and ignition module that way for 30. The Thuderbolt iv is a GREAT ignition set up. Use the spare dough to do a mild cam like the comp xm mentioned above. Dig up mkos posts regarding modifications on vortec heads, etc...

beware though... once you start... it never stops...


I'm pulling my (385) engine tomrrow... with plans for head work and more cam before running a couple of different combinations of intake and exhaust options to see which makes the most power...

 

[Mkos1980]

Re: 260 Merc 5.7 rebuild

Excellant choice on parts. I bolted Vortecs, intake and a cam to my 1990 unknown hour shortblock with 0 problems. And the Alpha is holding up too!! I personally copied CarCrafts build up using all their parts nad I could be happier. Car craft made 404HP with my identical combo (minus) headers, so I am guessing I'm in the high 300's

 

[Mkos1980]

Re: 260 Merc 5.7 rebuild

Dig up mkos posts regarding modifications on vortec heads, etc...
QUOTE]

Yup, let me know if anybody needs pics. I have a bunch on how to modify vortec heads for screw in studs and higher lift cams without ever visiting the machine shop!