Been reading that marine version of the slant 6 is not like a daily driver. Equated to running 90mph all day up hill pulling a trailer. Seems a bit exaggerated but I get the hint.

Camshafts seem to be the biggest difference in the use of an engine. I measured my 68-74 engine with a 72-73 head and its cam lobes. I am not sure where this engine came from on my boat. The lobe height is 0.26 for both intake and exhaust.

This doesn't seem right. Very, very conservative. The lobes are very peaked with steep ramp up and down. Both looking the same contour. No wear to speak of that I can see.

Is this maybe correct? Or is there something better for my application?

Stock SL6 cams were different over the years and used different lifts that were in the .365 to .415 range.
Example: Lift for the 170 intake is shown as .375. and early 225 was .395
170 exhaust lift is listed at .365 and the 225 at .395.
By 1965 the service manual lists both 170 and 225 intake lift as .375
The later '71-'80 cam has the most lift at .414 (244° duration intake and exhaust)

You may want to custom grind a cam for you marine engine and use a cam design that makes max torque in the boat's primary operation RPM range.
DD

https://www.dutra.org/pictures/engine/s ... -specs.jpg

Thanks Doug.

I don't know the timing and duration of this cam, so at this point I can only go by lobe height. The lobe height I have is either severely warn down, or it is ground to that low a height for a reason.

What effect does the lobe height of only 0.26 have on this engine. I know it only opens the valve so far, and only about 2/3 that of a street cam. But does that increase torque some how?

I have attached a couple of photos. It doesn't look that worn out does it? What about how the geometry of the lobe? How does that compare to other cams people see for their slant 6 for street use. The lifters do not have any concave to them, but I guess they could have been replaced when the head was off by previous owner.

I sent an email off to Comp cam to see what they have to say about a marine grind.

I've heard among many engines that "marine grind" vs "car grind" doesn't really mean much except for those that rotate opposite normal. I'd send it to either Oregon cams or (maybe) Delta Cams (I don't know much about Delta besides that they exist)
You're not gonna get much out of Comp especially since it isn't a damn Chevy..... Nowadays it has to be a damn LS to get their attention (where is the middle finger icon?)

D

The D’s have it. Don and Doc are right on track.
If you were working a SBC in your boat, Comp would possibly be a source of cam selection information.

Post your key engine build parameters: target static and dynamic compression ratios, fuel choice, premium or regular, the controls that you have over the ignition curve here at .org, as well as the rpm zone where you want power, and you will get some ideas

_________________
Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

DusterIdiot, thank you for clarifying. I didn't think of rocker involvement. That makes sense now. The cam didn't look at all worn down by nearly 3/16".

Dadtruck, I would love to post my goals when it comes to torque and hp, comp ratios, etc. But honestly I don't know myself just yet. I have never had this boat in the water, so I don't even know what it did before I decided to rebuild the engine. When I saw my compression numbers I knew it needed a rebuild. I had it running for 5 minutes with water flowing, that was it. Then the diodes in the alternator burned up and started melting the coils. I knew also, based on taking boat and trailer to weigh scales, that my boat was somewhere between 750-1000 pounds overweight somewhere. I found the flotation foam under the floor, soaked. So I knew I had to pull up the floor too.

I don't have a budget or spare $ to rebuild, so this is gonna take time. That said, I knew I can freshen up the existing engine. I may have to look at adding performance later. But if there is something that needs to be done now, then I want to add the performance part now. So I know that the engine at some point was bored out 0.30 over. But I don't know if it was done right. And I don't know if the piston to cylinder wall clearance is within spec. So if its not broke or worn out its not being replaced.

So if I have to bore out the cylinders, which would require new pistons, then I would go to 60 over. And while its at the machine shop, I would take some off the deck and head.

My compression ratio would be in the 9+:1 area, but still wanting to keep using 87 octane gas. Pump gas here maxes out at 91. 87 and 89 both have ethanol in it. The places I would take the boat, I don't know the gas, so better be able to stick with 87 with 10% ethanol.

I don't know how well the boat drives, and right now, by at least the serial number of the driveline, it was geared for an 8 cylinder engine before. But the gears may have been changed, so may have the prop. Both of which are like equating to transmission gear ratio (stern drive) and the differential and tires to that of the diameter and pitch of the prop.

Perhaps I will stick with a budget build for now. Then once I am in the water, I can see how it performs, with regard to torque, RPM range, etc, then look at making adjustments from there. At this point I don't even know how I plan on using this boat. Its a cabin cruiser so not planning on water skiing behind it, but maybe a tube??? Others have had their similar boat, outfitted with an outboard motor and getting 35ish mph. I am connecting with other owners to see what they are getting with regard to numbers. As far as I am aware though, I have the only Lonestar Cabin Cruiser that has a 225 Slanty in it. Ive seen some Mercs and the sell sheet from 1969 listed it as having your choice of Volvo Penta, Mercury (ford), or OMC (chevy) engines, as well as Chrysler power plant. Strange too, because Chrysler Marine bought Lonestar boats in 1965. My 66 was their first Chrysler badged year.

I wouldn't necessarily go right to 60-over. That makes zero sense unless to make it "right to the edge" of what would be allowed in some racing rule book. or it actually needs that much to restore the tolerances.
All else being equal, going 20-over or 30-over or 40 or 60, isn't gonna mean a hill of beans. I would go to the least O/S that will clean it up, and restore tolerances. If it'll clean up at 20 or 30, you still have the option of 40 or 60 if something goes "oops" later.

I would venture to guess that many of the hopups guys around here do to their car and pick up truck engines, would be a good start.
Increase the compression (head/block shave)
(remember; currently available head gaskets are thicker than what that engine would have had in it when new..... you gotta shave something (head or block) by the difference there, just to keep status quo (how it ran before it got tired)
At a minimum I would measure it out and see where you are for compression ratio as it is. and at a minimum, "blueprint" it.... in other words, published specs for every /6 I have ever seen says that the 225 was an 8.4:1 engine. Most anyone here will tell you that build tolerances what they were, engines that truly were even "that" good from new, are few and far between. I'd be willing to bet you are at least a full point lower. meaning that engine never did make even its "rated" power. even a "stock" rebuild to restore all your clearances with a compression increase, will show a noticeable difference in how it runs.

and don't do the job twice. Unless you are on some sort of "time crunch" to "get it done NOW" and just gotta have it up and going (are you a charter boat capt., and youre losing money with it being down?) Otherwise, to "just get it running for now" and then going back in for the redo, will be what is called "spending good money after bad" You're far better off to do whatever it takes to do it RIGHT, and get it to where you want it to be// and only tear it down ONCE. it will be cheaper in the end.
Bore it, replace pistons and rings as needed to the new bore size, shave the block and head, (but measure along the way/ so you know where it stands), get that cam reground, a good valve job, and possibly recurve the ignition (yeah I know ignition systems in marine land, do have different standards just like all marine electric/electronics do vs automotive. but to get the most out of the advance mechanism shouldn't break any rules)