merc 5.7 cam question

[badger213]

Hi folks, I'm new to the group and have done a lot of searching for the last month for information I need, but have not found. I bought a boat at auction and am in the process of rebuilding the motor. I've never heard the boat run prior to purchase, so I'm replacing most of the internal parts ie (rings, bearings,lifters oil pump, gaskets, ect). The motor is a 5.7L Bravo SWC, serial # OM0880###. I believe it's a 2000 manufacture date with a EFI Gm Rochester TBI. I have researched doing a cam up grade and have narrowed my choice to either a Comp Cam Xr 258HR or a XR 264HR. The motor has Vortec heads and because of the limited lift on these, I was going to go with either the CCA-987-16 springs or the Beehive 26915-16 springs made by Comp Cams. I understand that the heads will have to be machined to except the newer springs. The larger cam (264) list a rise of .488 intake & .495 exhaust.
My concerns are:
1) Will I have problems with the stock ECM or ignition?
2) Do I need any other engine modifications for the cam upgrade?
3) Do I need the higher priced Beehive springs?
4) Will my stock TBI handle these improvements?
5) What engine mods can you do before you have to replace ECM/Ignition?
6) Lastly, has anybody tried either of these combinations and what kind of performance gains did you achieve?

Thanks in advance
Steve

 

[fishingman220]

Re: merc 5.7 cam question

might not make a difference, but what kind of boat and drive?

 

[badger213]

Re: merc 5.7 cam question

The boat is a 25' C-Hawk. The boat originally was equipped with Bravo transom assembly and a Bravo III outdrive. All this (with exception of motor) was missing at time of purchase. Motor was just sitting in back of boat, unsecured. Reason for rebuild! Any help with rebuild would be very much appreciated.
Steve

 

[Honest Don]

Re: merc 5.7 cam question

going with an agressive cam in a boat that size will require variable duration lifters. Because TBIs are speed density systems you will need to reprogram the computer. talk to the tech line at comp cams, they may have an efi cam that will work with your project. Also you need to be careful not to get to agressive unless you're considering exhaust mods also. Too much cam will get you in trouble with reversion... the variable duration lifters will help prevent this. I have the rhoads vmax lifters with a lunati voo doo 60103 in my 19' cuddy and it all works fine without any issues and greta low end... not the case before the lifter upgrade. There's a company out there, i wanna say Arizona Speed, but I'm not sure... someone will know. They can re-flash your ecm for you.

 

[180shabah]

Re: merc 5.7 cam question

You are going at this bass ackwards - selecting a cam then trying to figure out how much power you will get.

What is your goal for this engine? What are the speed/power requirements for the boat?

 

[badger213]

Re: merc 5.7 cam question

I'm not looking for a real Hi-performance engine. I just figured that while I have the motor torn down, I do some small mods to it and pick up another 20-30 hp from the motor. The cams that I quoted were on the recommendation of a tech at Comp Cams. I told him I wanted good idle and some performance gains. When I asked him about about whether I'd have problems with my stock ECM, he said he wasn't sure.

 

[badger213]

Re: merc 5.7 cam question

going with an agressive cam in a boat that size will require variable duration lifters. Because TBIs are speed density systems you will need to reprogram the computer. talk to the tech line at comp cams, they may have an efi cam that will work with your project. Also you need to be careful not to get to agressive unless you're considering exhaust mods also. Too much cam will get you in trouble with reversion... the variable duration lifters will help prevent this. I have the rhoads vmax lifters with a lunati voo doo 60103 in my 19' cuddy and it all works fine without any issues and greta low end... not the case before the lifter upgrade. There's a company out there, i wanna say Arizona Speed, but I'm not sure... someone will know. They can re-flash your ecm for you.

Thanx Don, Arizona speed is correct for a company that recalibrates ECUs.
A quote from their website that I thinks answers my question regarding Mercruiser ECM's and engine mods "If you are planning to make any modifications or already have, the ECU re-calibration is necessary.

I was hoping to avoid this but am not surprised. My 2005 Harley EFI needs to be remapped for every little mod you do to engine.

I still got to buy transom plates and a Bravo lll outdrive for this project and am gettting into more money then I wanted to spend on the engine mods. Guess I'll just stay stock with the rebuild....Thanks again
Steve

 

[MikDee]

Re: merc 5.7 cam question

Here's a (reasonably priced) stock factory hydraulic roller offering that is a bit hotter then the orig. equip. cam, but still works with all the stock valvetrain, & Vortec heads, and you can still use the same orig. lifters, saving some cash!
It's probably good for 20-30hp over the stock setup as well.

It was used on the 383 truck engines, and from what I read on the net, it is a great mild hop up for any small block Chevy in a boat.

http://www.gmpartsdirect.com/performance_parts/store/catalog/Product.jhtmlPRODID=2600&CATID=826.html

http://www.gmpartsdirect.com/performance_parts/store/catalog/Category.jhtmlCATID=826.html

 

[180shabah]

Re: merc 5.7 cam question

Of course you could sell the EFI setup, drop a 4bbl on it and possibly make a little money in the process.

 

[Honest Don]

Re: merc 5.7 cam question

Another option is to go with an aftermarket engine management system. The Holley Commander 950 that is used with my Stealth Ram, I believe can be adapted to any system. It cam be used with any cam you'll through at cuz it's tuneable through a laptop. It does take some time to fine tune, but it's all done via laptop, no re jetting or sending out your ecm... You make the adjustments yourself.

check Summit Racing for pricing and options, but I thinks it's around a nickel for the computer. That should be about the cost of 2 reflashes!

 

[badger213]

Re: merc 5.7 cam question

Another option is to go with an aftermarket engine management system. The Holley Commander 950 that is used with my Stealth Ram, I believe can be adapted to any system. It cam be used with any cam you'll through at cuz it's tuneable through a laptop. It does take some time to fine tune, but it's all done via laptop, no re jetting or sending out your ecm... You make the adjustments yourself.

check Summit Racing for pricing and options, but I thinks it's around a nickel for the computer. That should be about the cost of 2 reflashes!

Thanks Don, I'll look into it today!

 

[MikDee]

Re: merc 5.7 cam question

The cam I mentioned is the only factory mild hi-perf hydraulic roller cam made for the limited lift on the Vortec heads, without needing machine work, or any valvetrain changes, or upgrades. Also, it was used with the factory stock TBI on the 383. It is reasonably priced, & cost efficient because all you need is just the camshaft itself.

 

[ringmaster72]

Re: merc 5.7 cam question

The Commander 950 computer is around $1K. I had it on one of my Camaros, it is a good system, I had no problems with it. Holley has several files available on their website from various engine setups. You just plug in the file that is closest to your setup and tune from there.

 

[badger213]

Re: merc 5.7 cam question

The cam I mentioned is the only factory mild hi-perf hydraulic roller cam made for the limited lift on the Vortec heads, without needing machine work, or any valvetrain changes, or upgrades. Also, it was used with the factory stock TBI on the 383. It is reasonably priced, & cost efficient because all you need is just the camshaft itself.

Sounds real good MikDee, but do you think I can get by without reflashing ECM?

 

[MikDee]

Re: merc 5.7 cam question

Yes, That's why I put it out there!
This link describes a bit more about the 383 motor's stock configuration with TBI, and rated hp with that stock cam. It says they later changed the rocker arms to 1.6 ratio, in Part 2, but I don't know if that was with the stock springs? Or if the extra lift with stock springs, & no machining would be a problem with the 1.6 roller rockers?http://www.chevyhiperformance.com/techarticles/57841_ht_383_crate_engine_test/index.html

 

[Honest Don]

Re: merc 5.7 cam question

The Commander 950 computer is around $1K. I had it on one of my Camaros, it is a good system, I had no problems with it. Holley has several files available on their website from various engine setups. You just plug in the file that is closest to your setup and tune from there.

Woops... I was thinking of the replacement cost of the ecu! Now here's the funny thing. I got my entire Stealth Ram package for $1000 on Craigslist. Imagine that. Truly an amazing system and well worth the money!!!