Camshaft experts

[Buttanic]

I am rebuilding a 350 Chevy for my 22 foot straight inboard fisherman. I know some cams can increase the chances of sucking water into engine on I/O's because of the underwater discharge but what about wet exhaust with above water discharge. My discharge is about 6 inches above the waterline. Does anyone have any recommendations on duration, lobe seperation and overlap. I want a cam that gives good performance and economy at cruising RPM (2500 to 3000).

 

[KaGee]

Re: Camshaft experts

Oh no! You just opened the can-o-worms! <br />Get ready for the fur to fly! <br /><br />The question most will want to know: is the motor originally from your's/another boat?

 

[Bondo]

Re: Camshaft experts

I want a cam that gives good performance and economy at cruising RPM (2500 to 3000).

Regardless of Where the Exhaust Dumps....... <br />It's Still "Wet", at the end of the Risers.... <br />That's where the Reversion takes place.......<br /><br />For what you're looking for,<br />You'll be hard pressed to find a Better Grind than the OEM, or RV/ Marine/ Truck grind.......

 

[f_inscreenname]

Re: Camshaft experts

Just installed a duel plane cam from Crane called there “power max” line. It is a cam for exhaust restricted motors (all marine motors are restricted). It opens the exhaust valve more and longer allowing the motor breath better. I got a better idle, more torque throughout the power ban and drastically better gas mileage. I use a pretty wild cam, lots of lift and duration. I am sure mine would be to much for you but as wild as it is it will not open up things to much or long for water invasion.

 

[deputydawg]

Re: Camshaft experts

Increase the chances of sucking water into the engine? This would mean your duration was so radical that the valve was still open after the exhaust stroke was complete and the piston was starting it's downward stroke. This would cause such an overlap on the intake side that it wouldn't work. Unless I am missing something, and correct me if I am, but a larger cam should not suck water. Your 4 cycles, intake-compression-power-exhaust each on it's own stroke just won't work if they overlap.<br />On our top fuel drag racers we didn't have that much duration or lift. We did have to cover our headers after a run, but this was to keep cold air from rushing into the header hitting a hot valve. This is a fast way to crystalize or tulip a valve.<br />If you want overall power and economy improvement our of a 350 look for something with around .204 to .214 duration intake side, .214 to .234 exhaust and .420 to .488 list intake and .442 to .510 lift exhaust side.<br />The smaller cam is only one size above stock. This one will give you good response, smooth idle, good economy. It will of course use a little more fuel, but it should use the fuel more effectively.<br />Keep in mind that with a larger cam you will increase you HP output slightly. A good question for everyone here would be will this effect the gear ratio you need to run?

 

[Buttanic]

Re: Camshaft experts

Deputydawg,what do you think about this cam<br />228 degrees @ .050 .474 lift intake<br />230 degrees @ .050 .480 lift exhaust<br />LSA 108<br />Intake centerline 108<br />Overlap 12 degrees<br />This is a cam I have that was in my 2 barrel dirt track car that had to pull 15 inches vacuum at 1000 rpm. It had a smooth idle. By concern is that when I engage the clutch at idle the engine may want to die because of weak torque at idle

 

[snapperbait]

Re: Camshaft experts

IMO, thats a wee bit too much of a cam, Buttanic... <br /><br />Assuming you plan on using stock heads, low octane fuel friendly compression (8.5 or 9 : 1), and fairly restrictive exhaust in a fairly heavy boat at 2500-3000rpm, the cam you propose won't build enuff low end torque... <br /><br />Marine application... Build torque first.. Horsepower will follow.. <br /><br />I believe you'd be better off to drop it down to something in the neighborhood of 210* intake, 216* exhaust (at .050") .440", .454" lift... Maybe even smaller..

 

[deputydawg]

Re: Camshaft experts

I would definately worry about the low RPM, low speed take off. That is slightly smaller than the cam I used in my stock car for dirt track, but if you are like me your stock car never got below 2500 to 3000 RPM's once the green flag came out. I may be wrong but my opinion is you would probably be better with a stock or RV cam. I put a very mild Rv type cam in my 4x4 and it was amazing for that application. I think you will be limiting your power range on the tach with that big of a cam, like you said low torque when you enguage the drive. If you could put in a clutch or a high stall torque converter to get the rpm's up, go for it. Since you can't I personally would shy away from it.<br />Of course everyone probably has their own opinion on this.<br />My biggest money maker in my shop was building hot rod engines mostly for high school kids and race car owners both dirt and strip. The most common mistake everyone has is too big of a cam for their application. Go with a milder cam, for more power work with ignition componants, carb changes etc.

 

[cc lancer]

Re: Camshaft experts

Increase the chances of sucking water into the engine? This would mean your duration was so radical that the valve was still open after the exhaust stroke was complete and the piston was starting it's downward stroke. This would cause such an overlap on the intake side that it wouldn't work. Unless I am missing something, and correct me if I am, but a larger cam should not suck water. Your 4 cycles, intake-compression-power-exhaust each on it's own stroke just won't work if they overlap<br />Thank you for that comment!!!

 

[Buttanic]

Re: Camshaft experts

Thanks Deputydawg and Snapperbait. I also felt it would be too big but wanted a few other opinions.<br />I have a stock Mercruiser 260 cam that I will probably end up using.

 

[deputydawg]

Re: Camshaft experts

BUT everyone here would have to admit it would sound awsome with the wild cam! Call me odd but when I fire up either my stock car or my drag racer with the stroker, just listening to them thump and feeling the vibration is almost as good as sex!<br /><br />Almost.

 

[f_inscreenname]

Re: Camshaft experts

Lift - Intake 467 / exhaust 494<br />adv duration intake 278 / exhaust 290<br />@.050 intake 222 / exhaust 234<br /> I run a 19’ speed boat with a 360ci Mopar. Like I said it may be a little wild for you but you can see the differences between the intake and the exhaust. Motor breaths and runs better. They only cost on average about $55.00 more then the run of the mill cam. If you are going to build a motor do yourself a favor and at least look at them. http://www.americanspeedcenter.net/Crane.asp <br /> I didn't buy mine from this web site I bought from Summit. Had a sale at the time.