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rudamus

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I'm sure this has been beaten to death but, im about to rebuild my 260 merc. just the top end new heads, cam, manifold, carb. i'm looking to increase the power. not much dont want to kill the outdrive. maybe 300 hp? any suggestions on camshafts? manifold, carb? the motor is a 1987 i think. alpha 1 drive.
 
Ayuh,.... Ya boatin' in Saltwater, or Fresh,..??

Get a set of Vortec heads, a matchin' intake manifold, 'n an R/V cam...
 
rudamus said:
.......... just the top end new heads, cam, manifold, carb. i'm looking to increase the power. not much dont want to kill the outdrive. maybe 300 hp? any suggestions on camshafts? manifold, carb? the motor is a 1987 i think.
Click to expand...
Have you torn this engine down yet to find out what the piston profile is? I think that you'll want to do this before you arbritrarily install different cylinder heads on it.

As Bill noted the Vortec cyinder heads are a good choice, but note that these have 64cc combustion chambers.
The wrong combination here can get you into trouble.
Example: 64cc chambers w/ flat top pistons would render a static compression ratio that would not be suitable for a cruiser size hull.

Likewise with some (not all) re-mans if you aren't up to speed on this.

I'd begin by tearing the engine down, and then post the info. You can go from there.

.
 
Rick your right. I should tear the motor down then move toward with the rebuild. Increasing the compression ratio wouldnt be good?
 
rudamus said:
Rick your right. I should tear the motor down then move toward with the rebuild. Increasing the compression ratio wouldnt be good?
Click to expand...
In order to more accurately comment, we need to know about the hull size/weight, etc.

In general, if you were to do a "quench" build, then yes..... the static C/R can be increased some.
However, if you use the full dished pistons, you'll want to remain very conservative, IMO.


.
 
RicardoMarine said:
In order to more accurately comment, we need to know about the hull size/weight, etc.

In general, if you were to do a "quench" build, then yes..... the static C/R can be increased some.
However, if you use the full dished pistons, you'll want to remain very conservative, IMO.


.
Click to expand...

21.5 weight im guessing 3000lbs+ the boat at wot does 39.5 mph with two people in it prop size is 14.25/19 @4700 rpms would like to get to 50mph if possible as far as i know its a bone stock motor outta the factory in 1987 not sure what stock is cc's of heads piston type cam lift duration. is there a standard for merc.?
 
Vortec heads, GM lt4 hot cam kit, performer rpm intake, 650 Holley or demon carb. I gained about 10 mph with this setup and it is very reliable
 
rudamus said:
its a bone stock motor outta the factory in 1987 not sure what stock is cc's of heads piston type cam lift duration. is there a standard for merc.?
Click to expand...
Yes, pretty much standard with the full dished pistons, and perhaps the 64cc chamber heads.
You may know for certain until you pull it down.

If you plan to keep the OEM exhaust system, you'll want to use a camshaft profile that is suitable for Marine regarding over-lap.
IOW, don't haphazardly use an automotive camshaft profile..... this gets people into trouble.
Talk to someone at Comp Cams, for example.


.
 
RicardoMarine said:
Yes, pretty much standard with the full dished pistons, and perhaps the 64cc chamber heads.
You may know for certain until you pull it down.

If you plan to keep the OEM exhaust system, you'll want to use a camshaft profile that is suitable for Marine regarding over-lap.
IOW, don't haphazardly use an automotive camshaft profile..... this gets people into trouble.
Talk to someone at Comp Cams, for example.


.
Click to expand...

lt4 cam works with stock exhaust and is very similar to some of the comp cams grinds. I wouldn't have mentioned it if I wasn't for sure on the reversion issue... In fact it would probably work very well with a regular performer intake that would allow reuse of the qjet carb and cut the expense and hassle of buying and tuning a Holley or demon.
 
Oooops........, I meant to say that: You may not know for certain until you pull it down!



87Concord, I'll take your word at the LT4 profile........, but in general, I'll have to stick with my statement re; the automotive profiles.


.
 
Well if you look at some of the motors used in todays boats, Maybe not so much the late ones (2006-to present) But a few years earlier some are corvette motors in boats........I would suspect they have a fairly radical cam, distributor run efi's......I believe they are 320 (+ a little) hp. A friend has one in his Ski boat....all stock...


Unless you are heading above a .600 lift cam with a hgh performance overlap and timing I think most streetable cams for auto's would be fine.

The issue is more of the boat itself, If it is a slug/barge then a real torque monster is needed. If not a slug/barge then anyhting around 320-350 hp would be ok and what ever it takes to get there so be it..........otherwise you will need a Bravo set up to handle the torque.......

The imfamous HP big blocks back in the day had this issue, it was solved by aftermarket exhaust manifolds as stock issue with these motors.......

So a LT4 hot cam is a mild cam in the big picture.......with the correct heads, head gasket and piston selection it would be a good motor.

So you could just pick up a create LT4 motor and marinize it............lol for about $4000.00

The resason the older baot motors were only ~ 260 hp is it was easy and repeatable as that is what was offered in the truck motor line........just marinize it......dependable and would last for years......there really was not a whole lot of other choices back then.

Now it is endless and a far superior and much highr power can be had with all the dependability as a stock OEM......

JMHO................
 
Let's forget the Marine or Automotive camshaft profile for a minute, and discuss street performance, of which generally includes higher Compression Ratios.
When we UP the C/R for Marine cruiser use, we drastically increase detonation potential.
We cannot simply turn a blind eye to the common causes of marine load detonation.

Being somewhat rhetorical with this; why do we think that the marine engine Total Ignition Advance is held back so much, compared to that of HP Automotive?


This (in part) is why I'm so Hell-Bent on steering people clear of the very typical SBC full dished pistons.
These will actually promote detonation if we aren't conservative with our TA.
When we hold back TA, we get a LPCP that is weak...... thus resulting in a rather weak low end torque potential.
 

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