Truck cam with captain's choice?

[itsathepete]

Hi all, I just acquired a new project. It's a '97 21 foot bowrider with a Volvo 5.7GS with a cracked block. It does not have vortec heads, and though I just pulled the engine out today, I haven't had a chance to see if it's a roller or flat tappet cam. As a donor, I have a 5.7 from a 1998 truck with vortec heads and roller truck cam. The engine will be completely rebuilt, but I am trying to decide what to do for the top end. I'd like to use the vortec heads and I know I will need a different intake manifold. I'd prefer a roller cam but if the cam in the marine engine is a flat tappet, will I be fine to use the truck roller cam? I don't want to have to buy a new cam if I don't need to. I know power will be essentially the same I am just not 100% sure if I can use the truck cam with the captain's choice switchable thru-hull/thru-prop exhaust. Of course, if the boat already has a roller cam, I can just use it and upgrade the valve springs on the vortec heads. If you don't think any of these options are good, I can use the cam and heads already on the boat assuming the heads aren't cracked. Let me know what you think

 

[Bondo]

Ayuh,..... Welcome Aboard,..... Go ahead, 'n rebuild yer truck motor, 'n drop it in, No problems I can see,.....

 

[itsathepete]

Ayuh,..... Welcome Aboard,..... Go ahead, 'n rebuild yer truck motor, 'n drop it in, No problems I can see,.....

Thanks Bondo. That's what I suspected. I ran the numbers on the truck cam and it didn't appear to have any valve overlap that would cause reversion problems. I just wasn't sure with the captain's choice exhaust if there would be any issues.

 

[Scott06]

Thanks Bondo. That's what I suspected. I ran the numbers on the truck cam and it didn't appear to have any valve overlap that would cause reversion problems. I just wasn't sure with the captain's choice exhaust if there would be any issues.

The truck cam and stock marine cam are usually interchangeable, unless someone swapped the truck cam out during its life.

Captains choice uses the same wet exhaust as stock just diverts it between the elbows and the transom housing wye pipe, so in terms of reversion potential it would be the same unless someone installed it with pipes going up hill.

 

[itsathepete]

Well I got the cracked block engine torn down and found out it was a rebuild. Pistons are 30 over. But it had a roller cam that judging from its size and the numbers stamped on it is the equivalent of a GM 395 cam which seems to be pretty standard for marine cams. A bit more lift and duration over stock for more low and midrange torque. The crank had standard rod and main bearings and is in excellent condition (better than the truck crank) so I can use that too. All in all good finds just a lot of cleaning to get the milkshake off the parts. Thanks for all your help.

 

[Scott06]

Well I got the cracked block engine torn down and found out it was a rebuild. Pistons are 30 over. But it had a roller cam that judging from its size and the numbers stamped on it is the equivalent of a GM 395 cam which seems to be pretty standard for marine cams. A bit more lift and duration over stock for more low and midrange torque. The crank had standard rod and main bearings and is in excellent condition (better than the truck crank) so I can use that too. All in all good finds just a lot of cleaning to get the milkshake off the parts. Thanks for all your help.

the milkshake is a PITA to clean. The PO of my boat cracked the block and used it until milkshake came out of the valve covers and all over the bilge/engine compartment. I used Bon Ami and hot water on it...

You may want to look at the lobe separation for that cam - I think it is 109 degrees https://www.summitracing.com/parts/nal-14097395
I thought 110 LSA was the minimum to avoid reversion with wet exhaust, but 109 may be close enough

@Scott Danforth or @alldodge may be able to confirm

 

[itsathepete]

Yes lobe separation is 109 degrees but it was the cam in the engine already and commonly used in marine engines. I ran the numbers on a cam program and there is no valve overlap. If the duration was longer there would be which is why larger marine cams have more lobe separation

 

[Scott06]

Yes lobe separation is 109 degrees but it was the cam in the engine already and commonly used in marine engines. I ran the numbers on a cam program and there is no valve overlap. If the duration was longer there would be which is why larger marine cams have more lobe separation

then you should be good to go

 

[itsathepete]

Hey, so just to follow up. It's been installed and running for a while now. Runs great, no problems. Been on the lake a couple times. First time was just me and bare minimum of gear and whatever little gas was left in the tank from 2 years ago. Started with very conservative base ignition timing of 6 degrees. After very thorough checking of all systems and several short runs at low and moderate speeds I hit a top speed of 58mph by GPS. Second time out with my bro and our regular lake gear and half tank of fresh 87 octane with ethanol only 54mph. Advanced the timing a few degrees and hit 56. I might try a little more timing. What do you think?

 

[Scott06]

Not sure what the original engine was in terms of initial and total timing.

I think merc vortec 5.7s will have 10 deg initial and total of 30-32 ish by 2800 or 3 k rpm.

 

[itsathepete]

Not sure what the original engine was in terms of initial and total timing.

I think merc vortec 5.7s will have 10 deg initial and total of 30-32 ish by 2800 or 3 k rpm.

Sticker on engine says 8 degrees initial timing. I started at 6 to be safe and advanced it just a little by feel. Haven't put a timing light on it since then. I'll see where it's at and might try a little more but probably won't go above 10. I also didn't check total timing but it was advancing with rpm. I'll have to check that as well.

 

[dubs283]

I also didn't check total timing but it was advancing with rpm. I'll have to check that as well.

I'd be more concerned about total advance than initial timing, especially on a fresh rebuild sbc. Most sbcs can handle up to 34 degrees total advance on a stock setup, naturally aspirated. Anything more can get terrible quickly. Old fuel mixed with 87 isn't ideal either.

If you're planning anything higher than 34 total advance you'll want to do a plug burn and jet your carburetor accordingly

 

[Scott Danforth]

I ran my SBC with vortec heads at 12 BTDC, however I had done some cam work. 10 degree on a stock motor is fine.

 

[Tail_Gunner]

Timing advance seems to be a very touchy subject most of the time, opinion oriented. Boats can be quite unique, they have a built in dyno..opinion of course yet any tune you do will become very apparent...you will have instant results right in front of you.

Over the yrs I've always used a timing tape, timing gun and a GPS device to measure this dyno. A simple explanation would be set your timing at say 8^, spool her up to plane and check your rpm&speed. Next stop 4500 rpm again rpm&speed. Pick your own points of references of courses respectfully.

I've found no gains at high rpm levels& high timing settings, but throttle response and stumbling getting up on plane can be a issue at low initial timing. Generally speaking stumbling at low rpm is a carb/metering fuel issue.

Rich mixtures require less timing.
Lean mixtures require more timing.

I once had a well respected member on this board give me a lesson on outdrives and torque. Made short a big block can eat a alpha drive in a instant, a hull leaving the water catching some air and along with the prop can create havoc. The engine will spin up instantly and when the prop re enters the water and catches...it's good by alpha...think instant high load...the same goes for a engine. Going from 5000 to 4000 rpm in a instant under high timings could easily grenade a engine...of course this will only happen at the worst possible moment that's a given.

While I haven't popped a engine I have hurt a drive or two. Not a great experience.

 

[itsathepete]

I do need to put the light on it and check current base and full advance timing. The two times on the lake were definitely not apples to apples since the weight in the boat was a lot more the second time. But we did get improvement in rpm and speed by advancing the timing a little. Probably shooting for a max of 32 degrees full advance. More testing is definitely required.

 

[itsathepete]

Checked the timing. 10 degrees initial advance. 32 total at about 3000rpm. I'm gonna leave it there