Cam Upgrade

[haulnazz15]

I have been looking at upgrading the cam in my 351W as I rebuild it from the bottom up. I know about the effects of reversion, and I cannot use anything but the standard 3" risers due to space limitations above the engine. I'm not looking for a big loping idle, just something to replace the stock cam (which I believe is a hydaulic flat-tappet) since I am getting new valves/lifters/etc for the heads.

I understand much about engine specs, but absolutely nothing when it comes to cam specs and their application in a boat. The valves will be something like 1.9/1.6 Intake/Exhaust on the D00E heads. Any recommendations for something that will have a max RPM of 4600?

I can't have anything with more than 500 lift at .050 due to valve clearance. Appreciate the help as this is the las piece of the puzzle before we get it all ordered and built. Not looking for high speed runs, just overall good performance, hopefully better than stock.

 

[Bondo]

Re: Cam Upgrade

Ayuh,... If you search the online motor Parts Houses,...
You'll find BaZillions of cam choices,...
Pick a Manufacturer, then search their Marine/ RV cam listings...

 

[Alpheus]

Re: Cam Upgrade

I have been doing allot of research on different cam applications for marine use and keep coming up with the same answers. Yes a hotter cam will give you better HP but you have to deal with possible side effects, IE reversion,reliability,vacuum,timing,springs,etc. I have found by reading many articles that you can get almost the same HP increase by just porting and polishing your heads and intake and using the stock marine cam. It has 0 side effects as mentioned above and best of all its practically free. Many people are just looking to free up the HP in there stock engines rather than bolting on upgrades that could hinder the the reliability and lifespan...

 

[haulnazz15]

Re: Cam Upgrade

Well it has whatever cam came stock in the 351W when they installed it in the boat in 1976! I have looked under marine applications for a few cam suppliers (lunati, comp, etc), many of them don't have a whole lot of options for the 351W-marine. I was looking more along the lines of what would be acceptable duration etc. for a marine cam. I don't know what the stock duration is, nor do I know much about the intake degree centerline. I would assume somewhere around 110 is acceptable.

Like I said, I'm not looking to build a fire-breathing animal here, but if I'm going through all of the trouble of putting new pistons/rods/bearings in the lower end, and valve job plus new valves, springs, lifters, and push rods; why would I leave one remaining old part (the stock cam) in place?

I simply want to get the most from my engine build in terms of torque/hp without sacrificing anything on the longevity of the engine.

 

[haulnazz15]

Re: Cam Upgrade

Well, from the CompCams downloadable cam suggestion tool, I came up with a 35-255-5 cam. It calculated the numbers somewhere around 242HP/315TQ at the upper end of 4600rpm. Seems a little low on the HP, but it doesn't allow for overbore calc, or specific intake manifold/marine exhaust specs. Hopefully with the Edelbrock RPM manifold and the 4bbl Edelbrock carb w/9.0:1 compression (up from 8.0:1 stock) I can eek out closer to 300 ponies.

 

[vip-vindicator]

Re: Cam Upgrade

ive use a company called cam technique for race cams all custom ground to match my specs and not at all expencive. ill try to find the info on them and send it to you.

 

[Don S]

Re: Cam Upgrade

Before this thread goes to far with race car cam specs and such. Read this thread, http://forums.iboats.com/showthread.php?t=369284 , well, not all of it. but posts #168 to the end #183. I think you will see some of the problems that can happen with getting the wrong cam in a marine engine.

 

[TimeBandit]

Re: Cam Upgrade

I'm doing similar upgrades to my 77 Cobalt's 351 before spring. Not a complete rebuild but a swap to ported D0 heads, TorkerII intake, mild cam, and thru-hull exhaust. Shooting for around 300 h.p. also.

You may know this already but, be sure and put a "straight-up" timing (chain/gear) set in it, as post-71 Ford (carbureted) engines had the cam timing retarded 4 to 8* for emmissions reasons. Not sure that the marine engines were cam-timed the same as automotive, but my guess is that they were. A good aftermarket multi-keyway roller-timing set will do. I don't think the pre-71 stock timing set is available any more.

I'll be using a Crane cam which worked well for me in the past that should be mild enough to not cause reversion issues, but will still have a slight lope at idle (the thru-hull addition requires a lopey idle IMHO). I don't have the exact specs in front of me right now.

To be safe, stay below .230* of duration @ .050" lift and 112* or wider lobe seperation. Or less than .220* @ .050" with 110* lobe sep. I prefer a little more duration and wider lobe seperation, as I think 110* seperation is pushing it for pleasure/ski/cruiser boat use (which is what most current "street/strip" cams have) The key is in the actual intake and exhaust valve opening overlap. Duration and lobe seperation both effect the overlap.

I'd love to see pics of your Mark Twain if you have them.

.

 

[dan t.]

Re: Cam Upgrade

C heck out Comp Cams site ,see if they make the xe250h grind for your motor,also the 252h grind will give you smooth idle with exelent bottom end torque

 

[haulnazz15]

Re: Cam Upgrade

Well, the Comp Cams software suggested the 35-255-5 which is a XE254H grind. Specs look like 210/214 lift at .050 and 254/258 duration. .478/.485 is the valve lift. Lobe centerline is at 114 I believe, so there shouldn't be any issue with idle. It doesn't seem like it would be too bad, but like I mentioned, I don't know much about cam specs in terms of marine applications.

TimeBandit, I don't have any pics of the MarkTwain except on the trailer a few years ago, kinda big pics but here they are!

This was with the engine removed and new SeaCast transom in place.

 

[havasuboatman]

Re: Cam Upgrade

Dude, stick with the factory cam spec's. Clean up the ports DO NOT USE GLASSBEAD BLASTER on the manifold. The valve sizes you mentioned are stock (ie: small) You are using the old heads, right? You get even a little too much overlap and your motor will be nothing but headache ever after. Your not building a motor for a racer here. (it's for the Mark Twain, right?)
That hull is not a performance hull. Once you get to a certian speed, your boat is going to start porpoising, any horsepower you have beyond what it takes to hit that speed, is money pissed away.
Short of putting 24" Dana tabs on the back of that thing and "stepping" the hull, NOTHING is gonna' make that boat set any speed records. It will, however make it chine walk, and VERY hard to control on the water.

 

[TimeBandit]

Re: Cam Upgrade

"210/214 lift at .050"

210/214 is actually the duration at .050" lift.
The cam will be plenty mild for your application, and have a boost in power over the stock cam.

I don't see any hyd flat-tappet XE cams with wider than 110* lobe seperation, so I'd stay away from them for your marine app. If you look in the sb Chevy listings there is a large Extreme Marine line. The XM256H grind looks like what you would want. Comp will have no problem grinding a Ford cam core to those specs. It will cost a little more than a shelf cam, but not much. With your 1.6" rocker arm ratio (sbc is 1.5") the lift will be... .477 / .493" .

You have a very cool boat there.

Here's mine. http://s165.photobucket.com/albums/u67/fordified1/77 Cobalt/

 

[TimeBandit]

Re: Cam Upgrade

Dude, stick with the factory cam spec's. Clean up the ports DO NOT USE GLASSBEAD BLASTER on the manifold. The valve sizes you mentioned are stock (ie: small) You are using the old heads, right?

No he's upgrading to 1970 (pre-smog) heads and the sizes he listed are larger than stock. The 70 351W heads give a 1 point boost in compression and have better ports chambers than the 76 heads. 1.94/1.6 is the largest valves that fit in them and is a very common upgrade. I think the original valves were 1.88 / 1.5 or thereabouts.

Cam tech has come a long way since 1976 so there's no good reason to use a stock cam when rebuilding. And why NOT boost the power? It will pull skiers up easier, get on plane quicker and require less throttle to maintain cruising speed. Nobody said he's building a race engine. Far from it.

 

[haulnazz15]

Re: Cam Upgrade

Havasu, I'm not looking for more top end speed, so it really doesn't enter into the equation. It ran right up near 50mph (stock pitot-speedo) with the stock 233HP, I mainly want the power and torque for the holeshot and cruise. I won't be adding trim tabs as this boat planes out in 3 seconds as it is fully loaded, it's a great boat to ski behind. The only goal is to get the most power out of my rebuild. I'm not doing any headwork aside from maybe port-matching and new springs/lifters/valves/etc. I'm trying to set it up for 9.0:1 compression if I can work that out, up from the stock 8.0:1.

I don't intend on bead-blasting anything. It's a fresh-water only boat so I don't think going with an aluminum Edelbrock Performer intake should pose any corrosion problems.

TB, I always loved the Cobalts, we looked at one (78 20' open-bow) before we picked on the 'Twain. Both looked remarkably similar, but the Cobalt's hull is a bit deeper, but both are built solid as a rock. Yours looks in great shape like mine, looks like an 18' model?

I actually intend to build a bench and sun pad like yours on mine instead of the doghouse with 2-seats like my current configuration.

 

[haulnazz15]

Re: Cam Upgrade

Before this thread goes to far with race car cam specs and such. Read this thread, http://forums.iboats.com/showthread.php?t=369284 , well, not all of it. but posts #168 to the end #183. I think you will see some of the problems that can happen with getting the wrong cam in a marine engine.

Don, just letting you know that I did read through that mess of arguments, lol. However, I still couldn't conclude that there was a specific line at which you don't want to cross regarding cam lift/duration. Other than too much is bad, and I understand what reversion is and how it works, just that I don't know at what level it becomes an issue. Is the 210/214 too much? I have no idea what the stock 351W grind is, so I have nothing to compare it to.

 

[TimeBandit]

Re: Cam Upgrade

TB, I always loved the Cobalts, we looked at one (78 20' open-bow) before we picked on the 'Twain. Both looked remarkably similar, but the Cobalt's hull is a bit deeper, but both are built solid as a rock. Yours looks in great shape like mine, looks like an 18' model?

I actually intend to build a bench and sun pad like yours on mine instead of the doghouse with 2-seats like my current configuration.

We like the bench as it easily sits 4 people, my teenage daughter likes the sun pad. My Cobalt is 19'. We bought the deep-V to replace my old Galaxy tri-hull (which I miss) because my wife has a bad back so a smooth ride in chop was important. Were looking for an open bow, but couldn't pass up this boat because of the condition and only 325 hours on the clock. Only drawback is it's an OMC electric shift, but I've gone through it and replaced the shift-wires (rotten insulation) and re-sealed it, so I think it's good to go for a while.

 

[Tail_Gunner]

Re: Cam Upgrade

"210/214 lift at .050"

210/214 is actually the duration at .050" lift.
The cam will be plenty mild for your application, and have a boost in power over the stock cam.

I don't see any hyd flat-tappet XE cams with wider than 110* lobe seperation, so I'd stay away from them for your marine app. If you look in the sb Chevy listings there is a large Extreme Marine line. The XM256H grind looks like what you would want. Comp will have no problem grinding a Ford cam core to those specs. It will cost a little more than a shelf cam, but not much. With your 1.6" rocker arm ratio (sbc is 1.5") the lift will be... .477 / .493" .

You have a very cool boat there.

Here's mine. http://s165.photobucket.com/albums/u67/fordified1/77 Cobalt/

The above advice is very sound if you must journey there.....been there doing that.

 

[havasuboatman]

Re: Cam Upgrade

Havasu, I'm not looking for more top end speed, so it really doesn't enter into the equation. It ran right up near 50mph (stock pitot-speedo) with the stock 233HP, I mainly want the power and torque for the holeshot and cruise. I won't be adding trim tabs as this boat planes out in 3 seconds as it is fully loaded, it's a great boat to ski behind. The only goal is to get the most power out of my rebuild. I'm not doing any headwork aside from maybe port-matching and new springs/lifters/valves/etc. I'm trying to set it up for 9.0:1 compression if I can work that out, up from the stock 8.0:1.

I don't intend on bead-blasting anything. It's a fresh-water only boat so I don't think going with an aluminum Edelbrock Performer intake should pose any corrosion problems.

TB, I always loved the Cobalts, we looked at one (78 20' open-bow) before we picked on the 'Twain. Both looked remarkably similar, but the Cobalt's hull is a bit deeper, but both are built solid as a rock. Yours looks in great shape like mine, looks like an 18' model?

I actually intend to build a bench and sun pad like yours on mine instead of the doghouse with 2-seats like my current configuration.

That is exactly my point. You have a 3 second hole shot that's not fast enough? I would have guessed about 50 for that boat.
Getting the most power out of your rebuild should be secondary to getting the most reliability. The more performance parts you stuff into a motor the shorter it's life span is, the more fuel it wastes, and the less reliable it is.
You said yourself what a good performer it was before.
Anyway, I was only trying to point out that you were spending alot more money than you needed to.
Most people think that boats are like cars when it comes to horsepower. Think about this: Have you EVER run a car WOT for 30 minutes? 20? 10? Foot to the floor wide open.
"Why not boost the power"? Time bandit, I love it when you guys come into my shop. I bet you have a 10 inch lift kit on your truck too.

 

[TimeBandit]

Re: Cam Upgrade

That is exactly my point. You have a 3 second hole shot that's not fast enough? I would have guessed about 50 for that boat.
Getting the most power out of your rebuild should be secondary to getting the most reliability. The more performance parts you stuff into a motor the shorter it's life span is, the more fuel it wastes, and the less reliable it is.
You said yourself what a good performer it was before.

Time bandit, I love it when you guys come into my shop. I bet you have a 10 inch lift kit on your truck too.

If you don't understand that bumping the compression up from 8:1 to 9:1 and a modern cam profile to replace the junk mid-seventies smogger crap increases fuel effeciency AND performance without effecting longevity, then you don't have any business giving out advice.

You don't have a clue what kind of guy I am, so don't even go there. Know this though.... I would not have any reason to come to your shop, or anyone elses, unless it was after closing to shoot the breeze, or throw back a cold one. So please get off my case, and let haulinazz build his boat the way he wants... It is HIS boat after all.

.

 

[haulnazz15]

Re: Cam Upgrade

havasu, while I do appreciate your input, I would like you to explain to me how stronger pistons/rods with all new bearings, and a new top end with a slightly upgraded cam is going to affect the reliability of the engine. It doesn't make any sense; it's like saying that we should have never started designing improvements to any engine design since the 60's because it would just result in shorter engine lifespan and less efficiency.

Example: My old 98 F150 w/5.4L had 230HP, my 08 F150 w/5.4L has 300HP. Well they didn't add displacement, there's no forced induction . . . sooo, it has to be with improvements to the original parts list (honestly it's due in part to a 3rd valve per cylinder).

In any case, you don't seem to understand where I'm coming from. I'm not trying to build a fire-breathing monster capable of planing out in 1 second and hitting speeds of 60+. The ONLY reason I know the boat does 50mph is because my father and I did it ONE TIME back when we first got the boat and tried it out. My goal is to build a good strong engine that performs as good or better than the old one. The intake/carb upgrade should be worth it alone, but why reuse the old cam and have it be the one remaining item in the engine block that didn't get replaced?