timing hotter cam?

[rin1178]

This is my first post on iboats although I've spent hours reading other boater's questions and answers. I have found this to be a great source of information. This is my story and I will try to be brief. I live in upstate New York and do my boating on the fulton chain of lakes. I purchased my first boat 5 years ago a 1985 baja 190 sunsport with a 5.7 mercruiser(mcm 260) and an alpha 1 outdrive. I was told that the motor had recently been rebuilt using some performance parts. Just looking at the top it had and edelbrock intake and carb and a msd blaster coil. The rest of the accessories i.e. thunderbolt IV ignition, distributor, alternator, power steering are all stock. When I purchased the boat I was not very mechanically inclined so I left the service to a friend of mine who had attended MMI. He did the winterizing and necessary parts replacing (water pump, gimbal bearing, ect.) Boat season is pretty short up here and I probably only put on 50 hours per year. Boat always ran well, never started or idled well, but when she was going she was going fast. End of last season motor gave up the fight. I limped in, and after having the trailer serviced ($300), I towed it to the shop the previous owner stated had done the last rebuild. They told me they had never seen the boat before but would try to diagnose the problem. They pulled the plugs noticed that #4 electrode had been hit, looked in the plug hole with a camera and told me the piston had a missing piece. This diagnosis cost me $200 and was told it would be another $600 to pull the motor strip it down and determine what I need to fix. Then cost of parts to fix and cost of labor to reinstall motor in boat. Not wanting to put anymore money into it at the end of the season I towed it back home. Soon after I decided that I was sick of paying other people to work on my stuff and what better time to learn than now. I purchased an engine hoist, engine stand, tools, several books and started in on it. I pulled the motor striped it down and to my pleasant surprise found 8 good pistons when I pulled the heads. I had sucked in a pea sized piece of the intake valve on #4. This piece had left several very small divots on the top of the piston but no marks in the cylinder walls. I took the heads to a good machine shop and per their recommendation had all intake valves replaced. I followed the books closely, put everything back together, reinstalled motor and again to my pleasant surprise the motor runs great. By this point your probably wondering what the question is. Well in my case with more knowledge and a better understanding of how things work comes more concerns. I now believe that this motor has a slightly hotter cam in it. When setting the timing at idle the motor runs well around 14-16 degrees BTDC if I try to retard it back to the 8 degrees BTDC the stock motor calls for I have to really compensate with the idle adjustment on the carb to keep it running which is just loading it up. I've read most of the posts regarding the thunderbolt IV ignition and determined that there is no base mode for setting timing with this ignition. My first question is, with the information I've provided is my assumption of a hotter cam logical? I've been told that a hotter cam will usually have a timing that is more advanced. It also has a bit of a roll to it at idle. My second question is if I'm setting the timing a idle and it is 6-8 degrees more advanced than stock what will this do to the timing at WOT will it be to far advanced and cause a lack of power or worse? Thunderbolt IV advances timing 22-26 degrees putting my WOT timing at +/-40 degrees BTDC is this OK? Well that?s it for now, so much for being brief, I just felt like a little background might be needed. I have many other questions but I'll save them for another post Thanks for any help that you can provide I'm still learning and love it.

 

[Alpheus]

Re: timing hotter cam?

What do you mean by hotter cam? What are the specs? Is it just a mild or wild lift and duration cam? Did you degree it before you threw it in or just line up the dots on the gears and hope for the best? You want to stay away from performance cams do to water inversion. Do a search on this subject it has been covered many times. I suggest that if you want a hotter cam that you should have a closed cooling system and degree the cam for optimum performance...

 

[rin1178]

Re: timing hotter cam?

cam came in the motor when I bought the boat. seller should have been a used car saleman because he sold me. boat has had quite a bit of work done to it. block is a 4 bolt main not sure if it is original casting number came back for a 85 truck? bored .30 over. not very expirenced but learning also don't have endless funds just trying to figure out what I have and how to make it work as well as I can

 

[John_S]

Re: timing hotter cam?

Welcome to the board. BTW, I use to spend a bit of time up around 1-4th lakes. I haven't been up there in many years, though.

FYI: Some paragraph breaks makes reading a whole lot easier on the eyes.


- Yes, a high lift and long duration cam will want to run with the ignition advanced at idle. But there may be other reasons too, like vacuum leak or badly set-up carb, etc.

- Idle rpms need to be in 600-700rpm range so you don't beat the alpha drive up on shifting.

- With a SBC marine engine full advance should not be more than 34 degrees. Less may mean slightly less power. More may destroy engine. (you have probably already proved that)

- The Thunderbolt timing curves are not adjustable.

- So, if your base timing is 16 degrees and your T4 has 24 degrees advance, the total is 40 degrees. Way too much to run in your boat.

- You would probably want a module that has 16 degrees of advance, which do not believe were made. A V6 module may work but will have less advance than advertised.

- Options are: Replace cam or purchase adjustable aftermarket marine ignition.

- I vote for replacing the cam.


PS: I also think you may have some auto vs marine parts on your engine. For safety, you will want to id and replace any non-marine items. (carb, fuel pump, fuel lines)

 

[jtmarten]

Re: timing hotter cam?

You need to know the advance your TBIV module provides. You should have 35-36* total timing. Anything beyond 36* you're looking to shotgun the top of a piston.
If the cam is hotter than an RV cam, you can use Rhoades lifters. They scrub off some of the lift and duration below 2K rpm, then pump up to provide full lift/duration. It takes a bit longer to adjust the rockers with them, but they're worth it. I had a healthy cam in my jetboat's 454; 0.501/0.527 lift, 280/290 duration, 224/234 dur @ 0.050 lift, 112* or 114* lobe sep (can't remember which). No reversion problems, no lopey idle since the Rhoades did their thing.
Personally, I'll never run any engine with the mfg suggested weak initial timing. Leaves way too much power at the table.

 

[rin1178]

Re: timing hotter cam?

Thanks to all for your quick replies and my apologies for that lack of breaks in the text. Upon rereading my own post I can see what you mean.

To Alpheus I probably should have tried to gather more information about this cam while I had the motor on the stand. Never made it any farther in than removing the heads. Didn?t even take the timing cover off. I cleaned everything very well, checked the cylinder bores and pulled the oil pan for a visual inspection of the crank and bearings. Reinstalled everything using marine gaskets and proper torque specs. Figured if it worked before and it wasn?t broken now it didn?t need to be fixed. My mistake.

To John S could you elaborate a little more on the improperly adjusted carb causing the motor to run better at a more advanced position. I believe that this intake / carb setup is one of those automotive parts put onto a boat that you questioned. At least I have the stock flame arrestor on top. All vacuumed plugs are covered and I have a new carb to intake gasket I just picked up and have not installed yet. Old gasket appears OK but I just wanted to be sure.
When I removed the carb I didn?t do much to it and didn?t change any of the adjustment screws. Figured it might help me know if the motor was running the same as before rebuild. The carb was set up like I explained in my original post. With the idle screw compensating for the motor being over retarded. I could tell that the motor was running very close to before with the same symptoms low lumpy idle wanting to stall and loading the motor up with gas. I have a hell of a time in 5 mph zones sometimes have to stop take it out of gear and let the motor run at a higher RPM for a while to burn off some gas. So I advanced the timing and lowered the idle speed runs much better at idle now but creates the problem of over advancing at WOT.
Are you talking about detonation happening if you go to far advanced. Is there a magic number at which this will happen. If I can get the WOT timing down to say 36-38 degrees BTDC would I get away with it.

To Jtmarten could you tell me more about the Rhodes lifters if I?m understanding correctly at low RPM they are not fully pumped up so they don?t open the valves all the way this in turn will allow me to run closer to 8 degrees BTDC and avoid the problem of over advancing. Not real happy about taking the intake back off but sounds easier than changing the cam.

Thanks again for the help

 

[John_S]

Re: timing hotter cam?

Are you talking about detonation happening if you go to far advanced. Is there a magic number at which this will happen. If I can get the WOT timing down to say 36-38 degrees BTDC would I get away with it.

Yes, detenation... like you already had. No magic number. Merc ran the 350 MAG at 32 max (8 + 24). Now, that is probably slightly conservative, but they prefer the engines stay around a little while. If you are right on the edge, one little push (like a slightly lean condition, bad gas, etc) will put it over the cliff. But, it is whatever you want to risk. It is your motor.

Bite the bullet and pull the cam. It is probably nothing that should be in a boat with wet exhaust anyway. A new cam and lifters don't run that much and not much harder than you already have done.

If you want to know if there is a vacuum leak, put a fitting on intake and hook up a vacuum gauge. Using new gaskets doesn't mean it can't happen.

Flame arrester does not make an auto carb safe. If you are not sure, take some pictures with arrester off and post, and report any part numbers found on carb. Also, if it is an auto carb, it probably has not been jetted for a boat engine. Boats are jetted on the rich side, to keep things a little cooler, again to try to avoid detenation.

Your response seems to indicate you are looking for the easy way out. I would have thought that the book you wrote, would indicate you learned that lesson. Maybe not?

 

[jtmarten]

Re: timing hotter cam?

To Jtmarten could you tell me more about the Rhodes lifters if I?m understanding correctly at low RPM they are not fully pumped up so they don?t open the valves all the way this in turn will allow me to run closer to 8 degrees BTDC and avoid the problem of over advancing. Not real happy about taking the intake back off but sounds easier than changing the cam.

Thanks again for the help

Yes and no.

Yes - the Rhoades don't fully pump up which reduces lift and duration at lower rpms. If you don't have a reversion issue, I'd leave the cam and lifters alone.

No - the cam/lifters have nothing to do with setting timing. The best way to set timing is with an advancing timing light. Set the light at 35*, run the engine @ 3000rpm, adjust dizzy to get the balancer line at the zero mark on the timing tab. That will account for +4*/-4*/0* cam installation, dizzy/TBIV advance, and initial timing advance. Double check the timing @ 3500rpm and 4000rpm to make sure full advance is in by 3000rpm.
I'm guessing your at-idle timing will be 12*-14*.

 

[rin1178]

Re: timing hotter cam?

John S ?Your response seems to indicate you are looking for the easy way out. I would have thought that the book you wrote, would indicate you learned that lesson. Maybe not??

I?m not necessarily looking for the easy way out, just willing to entertain any viable solution to the problem. I will not argue that stock = reliable. When I purchased this boat I knew it had been modified = fast
Obviously there are down sides to this decision. In my case shorter part life. My thinking is that if I can keep the majority of the parts I have and increase reliability somewhat I?ll go with it for now. Boat gave me seasons of use and many good times in the previous years. Boating season is only about 3 months in upstate New York and we have snow on the ground for what seems like 6. A more complete rebuild or even just the cam swap would be a nice project for winter months. Boat has other problems one of which is an old, over geared, alpha 1 gen 1 outdrive running a big 14 ? 25 pitch ss prop. My assumption is that will be the next thing to give up the fight. Funds for toys are bit tight and I will probably be spending the majority of them on an outdrive. In an effort to stay on the water I have to budget my funds according to what is in need of the most immediate repair. So maybe I am looking for the ?easy way out? but just for the time being. I?m all for making things right but would rather be on the lake than in the garage. Lets face it we all bought are boats to be in them not working on them. I value your opinion and appreciate your and all others feedback. As I stated at the beginning I?m new to most all of this and these forums are a great source of info.

I?m going to

- Purchase a vacuum tester and perform appropriate tests.

- Remove and rebuild carb even if I don?t end up using it on the boat I?ll have a better understanding of it and maybe it will work on a later project.

- Take boat to the lake and take some timing readings at different RPMs. Haven?t been able to do much other than idle timing on the muffs. Water tested the boat for the first time about a week ago. Windy day rough water no tests just cruised around between 2000 - 3000 RPM for a hour then got rained on. Trying to be nice to her during break in period.

While boating is fun safety is the most important thing. Could you please tell what you know about the safety risks involved with running an automotive intake and carb on a boat. I have an edelbrock performer intake couldn?t find a single number on it. It is for a square bore carb. Numbers I found on the carb are located on the front lower left hand side 1407 2207 and on the right rear 8867 it has also been stamped as a reman. Not sure about the 2207 or 8867 but 1407 seems to indicate an edelbrock performer series 750 cfm manual choke carburetor. Not a marine series. Carb says edelbrock right on the front but has Weber cast into the right hand side of the body? Thanks again for any help you can provide and for taking the time to read this chapter of my ?book?

 

[jtmarten]

Re: timing hotter cam?

While boating is fun safety is the most important thing. Could you please tell what you know about the safety risks involved with running an automotive intake and carb on a boat. I have an edelbrock performer intake couldn?t find a single number on it. It is for a square bore carb. Numbers I found on the carb are located on the front lower left hand side 1407 2207 and on the right rear 8867 it has also been stamped as a reman. Not sure about the 2207 or 8867 but 1407 seems to indicate an edelbrock performer series 750 cfm manual choke carburetor. Not a marine series. Carb says edelbrock right on the front but has Weber cast into the right hand side of the body? Thanks again for any help you can provide and for taking the time to read this chapter of my ?book?

No issue with the intake in fresh water. In salt water the intake should have the (I believe) brass sleeves in the water passages.
I don't know that there is a difference in auto/marine Edelbrock carbs. They have no gaskets below the fuel level, so no chance to leak. The base plate may have different seals/bushings. The marine version would be setup to run a little richer too.

 

[John_S]

Re: timing hotter cam?

I am not sure of all the differences in the Edelbrock carb, but from memory when I did some part comparison, accel pump, and throttle shafts. It also needs a fitting for the fuel pump overflow tube, and the big vacuum port sealed. Even if you could convert the carb, and "possibly" be safe, you can still get a ticket.

No issue with intake manifold for the water you are in.