SBC Camshaft Specs

[Rootsy]

Well the summer boating bug has hit me and i guess i best get moving if i am gonna get anything done by the time the ice thaws... Considering camshafts, namely SBC camshafts... i know that there are marine guidelines so i don't vacuum the lake with my motor... anyone armed with these guidelines? Duration, duration @ .050, overlap and lift maximums? My motor isn't a beast.. basically a stock 350 with odds and ends, 4V, aluminum intake and rockers for a bit more lift... I have stock merc thru hull exhaust so i know i don't scavenge cylinders all that well and it's probably gonna stay that way for a bit until i can break down and pop for some exhaust. any info anyone can fire at me i'd most appreciate cause the last thing i need to do is pull plugs and drain cylinders then wonder how many rods are bent... THANKS! hope everyone is having a good winter!!!!

[Looped]

James,

Usually your best bet is to contact the actual cam manufacturer like Comp Cams, Lunati, Crane Cams etc. so that they can tell you exactly what type of cam you need and a long with what lifters and other components are a correct match with your upgrade. They will ask you what you have right now and what you are looking for as an outcome for performance. They have lots of data that has been recorded from mismatch mistakes that you don’t want to run into and plenty of good solid upgrades that will make things easier for you.

Sometimes using the best cam from one company and then the best lifters from another company just gets you in trouble, try to stick to one complete package for the best results and for longevity.

Craig

[RickSE]

Here's a good start. These are labeled as Marine cams.

http://www.cranecams.com/master/apps/chevy13.htm

I'm using the the H-272-2 in a 96 350, stock other than cam, Performer intake and Holley 650 carb. Also using Crane lifters and the suggested valve springs.

[DONZIMAN2]

You need to consider the entire top end package. True horsepower is made when your heads, cam, carb and exhaust all match. Get one of these out of sink and you will be disapointed. Make sure you look at all of the variables. The majority of perfomance is in the upper end. Not the rotating assembly. If you get a good camshaft, make sure everything else is a match. Also be careful when putting a new cam in without checking the heads ETC.. I have destroyed some of my old motors by a valve sticking when it extends beyond its previous travel point. Also make sure the valve springs are set up correctly. Do not compromise on good retainers or keepers. This is just my .02. Good luck with your project. Bob

[DONZIMAN2]

RickS, That smilin' Chevy emblem is awesome. Bob

[Rootsy]

think what i was getting at was the threshhold on duration where you begin to see reversion... motor is a 97 with a roller so i'll stay that route eh... with matching springs naturally... 300 scoots would do me fine, don't want to grenade the alpha... somewhere in the 275 neighborhood right now... i'm pretty good at putting the whole package together...

Thanks

Jamie

[Sam]

Craig (Looped) I found your comments very interesting in leu of the fact that I am building a new top half to my 350. This will include cam,heads,all new valve train, intake and carb. I'm interested in hearing more on your thoughts regarding matching parts. Am I to assume that you mean to buy a "package" from a source as oposed to piecemeal parts.
For instance I am considering Dart heads, is there a value in going with their recommended valve components other than the commercial gains to the seller.

Thanks
Sam

[SS18]

hEY SAM,
I ordered set of world heads from cp performance
Dart sportsmanII Came with manley HP stainless valve and guide ordered hardened push rods extra already have hp cam performer intake and most likely 750 rochester to be determined.Anyway world
prouducts # direct for tect support is
1-613-737-0372 good people willing to help.
they promise 60 hp to my already world product!
Jim in NJ
PS I would alomost pay anything for 5 more MPH
on this 18 classic biggrin.gif cool.gif

[Looped]

James,
The rule of thumb (if that's the right saying) that I have heard over and over again for SBC's in a "wet" exhaust marine setup is not to exceed 224/224 @ .050 duration. Sorry for the little story above but I was just trying to have you do the right combo.

Sam,
I too am undergoing the buildup of a marine engine (that has changed many times for the past half year and now I have found myself getting ride of some of the old parts that I have bought do to changing my mind too many times) and I am a bit anal about doing things. So I have read a bunch of books on sbc’s, bbc’s, marine engines and so on just so I know what the right things to do and look out for. Of course I am not doing the actual buildup (machine work) myself but I just want to know what is going on and not be blind about it. Basically, what every book that I have read has said the same thing and that is buy a complete package from a quality manufacture like in your case a complete valvetrain package. This way if you have trouble with the tuning of your upgrade you just have one company to contact and they will work with you. If you choose to mismatch parts from different companies than what you will run into is different manufacturers pointing fingers at the other parts you bought and not about the resolution.

It’s amazing what you learn about engines once you read a few of the “High Performance” type of books. It really puts you in line about how didly you know about what goes on. One thing keeps coming to mind is a few months ago I sent an email to Forrest asking him if it possible to change (machine or grind) the stroke height on a 350 crankshaft to make it down to a 3” stroke and now after reading I feel like a complete idiot. I’m not saying that reading up on engines will make you a mechanic (it wont) only hands on work will ever do that in any line of work. Theory (schooling) is only on paper and it will never be enough to equal the real world of hands on.

Oh yea Sam, for your answer is I don’t know about what the “best” package is for the Dart heads but for a mild performance upgrade you may be better off going with the Sportman II heads or the Chevy Vortec’s for much cheaper money.

Rambling on……………. biggrin.gif
Craig

[Looped]

The Mad Poddle,
I guess I forgot to mention if you know what you are doing than you know what "mismatch" parts will work well together. I am not there, nor will I probably ever will be. frown.gif

[Sam]

Craig, all I can say is dido ! I have read to the point of my eyes crossing. I to am not doing the grunt labor but since I am paying the bill I want to know what I'm buying and why. I have found a ton of info on the Web as well.

Madpoodle: I appreciate your feed back,it's info like that that you won't find in books. Thanks to all and keep it coming

Sam

[turbo2256]

Beware have had three sets of World Product factory assembled heads come through the shop were the valve seats fell out all they would warrinty were the heads you get stuck with the rest of the dammage.

[BigGrizzly]

Like Looped said it is the combination, especially in the valve train area. Example How many of you have changed the push rod length to get the proper rocker arm angle to let the ratio really vork correctly. They milled the heads, decked the block and than put in a HP cam than installed stock length pushrods with the correct installed valve hight. What is wrong with this picture? To add lift to the cam you do it one of two ways or both, add to the lobe (there is a limit here) or take off the base circle (there is a limit here too). I have 3 Ford Cleveland and all have different push rods.

The problem with flow numbers is that they are numbers. Its not just flow but how it flows at the desired RPMs. Putting World heads on a smallblock Ford in a boat is a waste. The head is a high RPM head, to take advantage of it you need to spin it at 6,000+ RPM. Now you have to worry about the outdrive bearings. The Vortec heads have a good flow but also a tremendous swirl built in to them(hence the name)which gives a broad powerband . After doing some checking for a friend on these heads, I found a guy who had the heads flowed to a really large number just to find his race car was slower. He then put the car on a rear wheel dyno and found the powerband was narrow and high. Bigger isn't always better.
Randy

[Woodsy]

When you are building a motor, you have to have a plan. What is your target HP? How much are you willing to spend to get there? There are alot of good products out there for the small block chevy. Most are designed for high rpm street use. The limiting factor on a marine engine is RPM. Anything over 5200 RPM and you are looking a seriously decreasing the life of your outdrive. Because of the RPM limit, most aftermarket heads will not be the best choice for a marine application. Madpoodle has it right with his opinion on how cylinder heads work. Bigger doesn't mean better, and lift & duration walk hand in hand. Everything is a compromise. This is why you need a plan. Bolting on a bunch of mis-matched components is the easiest way to spend some serious $$$ and be very dissapointed. Madppoodle is also correct, in that sometimes parts from different mfg's make a better engine, but I don't recommend this approach for a novice. Leave that to the professional engine builder, thats why he gets and you pay the big bucks. Back to James original question, I would not bother doing a camshaft, unless I upgraded my exhaust manifolds at the same time. All of the extra lift/duration and breathing will not help you if your exhaust is corked up. ou will get about 15-20hp just by putting on a nice set of exhaust manifolds or CMI headers. Once your motor can breathe, then play with how much air you want it pump...

Just my $1.50 worth

Woodsy biggrin.gif

[Rootsy]

Thanks for the help guys.. that's exactly what i was looking for Looped. You're all pretty correct... matching parts in an engine development is of great importance... does NO good to toss in a big bump stick if your head's ports won't efficiently let you get in what your valve will when it is at max lift... and if your exhaust side won't let it out... If your carburator is too large to atomize the fuel and your intake isn't designed for the purpose you are using it for, etc etc etc... and then there's the trade off where the port is too large and you lose too much flow stream velocity which drastically hurts your torque numbers, especially on the low end. You'd be amazed what you can accomplish with a set of stock head with just reworking the port designs. What is the shortest distance between two points? A straight line correct? Flatten out the short side radius, widen the runner floor, create a venturi in the port before the valve and well too many other things to even get into right now and..... Believe it or not but when we dyno'd the camaro motor (357 cu, 9.5:1) last year the heads flowed 111% VE on the intake side and 108% on the exhaust side and that was at 7200 RPM with a ported victor intake, joe scott reworked factory quadrajet and a set of custom step tuned headers. If anyone is familiar with NHRA Super Stock class you'll know that you have to use factory production head castings and valve sizes for the motor you are claiming, we claim the 69 350 rated at 300 hp (NHRA corrected to 315). The port volumes must remain the same as the production numbers but you can recontour as long as you fill in to retain stock volumes. We run a comp cams mechanical roller and pushrods and the rest is a jesel valvetrain. When you can get flow numbers like that with ported factory castings it makes you wonder if all these aftermarket wonder heads are worth the money on a marine engine for the rpms we turn.. but then again... it takes someone who REALLY KNOWS what they are doing to turn a factory head into something like that and well about 5000 bucks too... heads up did these heads and intake.. and 600.9 hp @ 7300 rpm and 542.7 ft-lb @ 5600 makes you a believer... and it all comes from the top end... every bit...

[Looped]

Madpoddle,
No digger taken from this end. biggrin.gif I was just making a point that you know what’s going on and I’m just stating about what I have read and slightly hacked with.

I have also heard that the Vortec heads are great out of the box but if any machining is done to them usually the outcome is worse than if they were untouched. A few people have told me that it’s best to use them “as is” and just replace the valves with a nice set of Ferrera valves. For $230 a pop your almost better off buying these than paying for head work done to your factory ones.

James,
It's funny you mentioned NHRA because I work with someones Wife that races the NHRA, his name is John Gray if you ever heard of him? He runs something like a 71 blue Nova???

[Forrest]

One thing that I didn't see mentioned in all this talk about cams and head flow is compression and displacement. Generally, more compression is necessary for long duration camshafts than with camshafts with short duration. This is because of the dynamic vs. static compression effect. Also, as noted, longer duration camshafts require longer or dryer exhausts. From what I understand, as noted above, somewhere around 224 @ 0.050" on the exhaust side is about maximum for stock exhaust systems. The Crane H-272-2 cam falls in at 228 @ 0.050 - which may be pushing it for stock exhaust manifolds and risers.

FWIW, the latest 383 stroker motors that I built (for the 27 Magnum) use the H-272-2 camshafts, 9.6:1 CR, Dart Iron Eagle heads with 200cc intake runners, 2.02/1.60" valves and 64cc chambers, 600 cfm Holleys, and Stainless Marine exhaust with 7" risers. Yea, these motors can breathe, maybe a little better that they should for 5000 RPM marine engine. But you figure, that the H-272-2 cam is actually somewhat small for this setup. The engines idle very smooth and never stall when docking (very important!), has a good enough bottom end to get that big 'ol heavy 27 footer out of the water without tabs, and great mid-range acceleration. The top end isn't too bad either! I still need to do some prop work to get it hook-up better on the top end, though.

Anyway, to make a point about that H-272-2 cam in the above setup as compared to essentially the same spec cam (still a Crane H-272-2) in my 302 Ford powered 16 Donzi, there is a world of difference. The compression on the 302 is 9.4:1, stock late '80s open-chamber heads, 450cfm Holley, Performer 289 intake, and a Kodiak exhaust system. And I'm tellin' ya, this little thing's a beast! It rumbles and shakes when it idles and the exhaust is noisier than any 383 that I ever heard. Though it doesn't usually stall, it is down-right un-pleasant when you need to idle for any length of time. But when it's time to get up and go - it'll go!

So what's the big difference? Displacement is the biggest difference. The same camshaft that is considered mild in a large displacement engine can be radical in a small displacement engine. The H-272-2 is going to be slightly more cam in a 350 cubic-inch engine with all things being equal, than if it were installed in a 383 or 400 cubic-inch engine.

[turbo2256]

Ok this seems to be getting back to what I have said in another thread. The smallest port volume for the flow produces the most power. So here are some figures for our F7TE heads

1.78 Vave Int........ 1.45 Exh
Lift CFM .......... CFM
.1 62
.2 118
.3 153
.4 178
.5 190 ............ 155
.6 Flow just starts to drop off right about here just as planned these heads are designed for max lifts of .500 to .550 or less


Peliminary results for vortec chevy heads

.3 190
.4 225
.5 242

Soon we will be running results on a E7TE head with 1.84 valves

[turbo2256]

Of flow on after market heads you will find the Ford heads mentioned above will out flow them up to about 5500 to 6000 RPM. The after market port volumes are much greater. The F7TEs being about 140 CCs the next closest are about 180 and dont realy do well untill you get over 6000 RPM were the after market take off. Our boats dont run there. You are all talking about matched parts thats what the porting done in these heads were all about low lift cams with lower duration that most street cars and boats run. As for you guys with the HP and torque computer programs there is one thing lacking in the program no place to put port volume info.

[BigGrizzly]

What the poddle says is true. What I mite add is my Corsican with CMI heeders have a much better midrange and top end than the other two makes I have. They are long tube and cost is high along with the quality. The truth is if I were to do that motor again I would do exactly the same thing. It’s not the fastest and not the prettiest but it has the sound I like and runs like I want it to. As soon as the bucks come in the Criterion gets them too.
Randy