Roller cam vs. flat tappet cam motors

[Beachcraft-24]

Looking for anyone's experience with putting a roller cam in a 350 Chevy with a Volvo outdrive. I've heard of some problems with the roller cam engines sucking water through the exhaust into the engine. Anyone's experience/input on this type of sitiuation would be appreciated. I'm planning to put in a marine cam casting # 795. The cam has .426 intake lift/.451 exhaust lift. Duration 491 intake - 205 exhaust @ .050 lift.

 

[Boomyal]

Re: Roller cam vs. flat tappet cam motors

Not an expert here, but two things are important for a marine motor. Keeping the overlap down is important for not sucking water in and choosing a grind that keeps the powerband in the low to midrange. I don't think that roller vs flat tappet is the issue. I have no real understanding of the numbers you give, but if it's a marine grind the roller setup should be great. It'll give less resistance and therefore more power within the powerband of the grind.

 

[achris]

Re: Roller cam vs. flat tappet cam motors

Carl,<br /><br />Mercruiser have been running roller cams on the V8s and V6s for quite some years now, without the water suck problem. However, the later V6s DO suck water. The reason is what my learned friend Boomyal aspired to. Too much overlap.<br /><br />Chris..........

 

[Bondo]

Re: Roller cam vs. flat tappet cam motors

Ayah....<br /> LSA Must be between 109*,+ 112*..........<br /> L obe<br /> S eperation <br /> A ngle.......<br /><br />You're Also going to need some Machine Work on the Block, for the Lifter Keepers........<br />If this motor Didn't have a roller cam to begin with...........

 

[WSUDERMAN]

Re: Roller cam vs. flat tappet cam motors

The only advantage of a Roller over a flat tappet is the rate of open & close or how steep of a cam you can run. This has a direct correlation to overlap. Because of the roller you can get a valve open & close faster - therefore increase the valve’s duration without increasing the overlap. There is a book by Denis Moore about Small blocks and marine engine mods. He talks extensively about cams & the marine environment. Very good book on Marine small blocks and mods!

 

[Wart T]

Re: Roller cam vs. flat tappet cam motors

Save your money and leave the cam stock. Most hi perf cam grinds are for the upper rpm range which most boats don't use.

 

[bomar76]

Re: Roller cam vs. flat tappet cam motors

Originally posted by oldbaldfatguy:<br /> Save your money and leave the cam stock. Most hi perf cam grinds are for the upper rpm range which most boats don't use.

Speak only for yourself.<br />That's the range we (and most of my boating friends) are in 90% of the time.<br /><br />

Originally posted by :CarlHerzberg <br /><br />Looking for anyone's experience with putting a roller cam in a 350 Chevy with a Volvo outdrive. I've heard of some problems with the roller cam engines sucking water through the exhaust into the engine. Anyone's experience/input on this type of sitiuation would be appreciated. I'm planning to put in a marine cam casting # 795. The cam has .426 intake lift/.451 exhaust lift. Duration 491 intake - 205 exhaust @ .050 lift.

Roller cams have a huge advantage in that the decrease in friction produces more HP. With a roller set up you can use much stiffer valve springs. Also, the valves will open faster allowing more duration at high RPMs and produce more power.<br /><br />I concur with the suggestion to get Dennis Moores excellent book on SBC marine engines. Lots of great cam advice there.<br /><br />I think the duration of the intake lift you listed was incorrect.<br /><br />The cam specs you posted are very close to the stock roller cam in marine 350's:<br /><br />.430" intake lift w/ 1.50:1 rocker arms<br />.450 exhast lift w/ 1.50:1 rocker arms<br />Duration 197 degrees intake @ .050" lift<br />Duration 207 degrees exhaust @ .050" lift<br /><br />THere should be NO problems with that cam at all.

 

[Beachcraft-24]

Re: Roller cam vs. flat tappet cam motors

many thanks to all who replied and yes my intake duration was listed wrong should have read 194@ .050 and yes this is stock marine cam shaft.Iam just trying to build more efficent motor .

 

[baddog00100]

Re: Roller cam vs. flat tappet cam motors

heres a problem you my find changing to a roller cam you may loose out on power getting out of the water and up on plane but your top end will be better that is one of the differences between the to

 

[bomar76]

Re: Roller cam vs. flat tappet cam motors

Originally posted by baddog00100:<br /> heres a problem you my find changing to a roller cam you may loose out on power getting out of the water and up on plane but your top end will be better that is one of the differences between the to

No truth at all to any thing said above.

 

[Wart T]

Re: Roller cam vs. flat tappet cam motors

My point was the rpm range I was referring to is above 4000. With the duration you are referring to you wont like the performance. It's fun to discuss stuff like this, but take it from someone who has seen it and done it you won't like it, and your boat will in fact be slower. Boats do not respond like automobiles do.<br />You do appear to be determined to change it, that's fine. It's certainly your boat. I don't wish to insult anyone nor rain on your fantasy parade. It's just my opinion and we all know what they say about opinions. <br /><br />It all has to work together for optimal performance. Cam, valve train, intake, exhaust, drive ratio, props, all have to be matched up. There is no magical gain to be had with slapping in a cam. If there were rest assured the manufacturers would use it.

 

[bomar76]

Re: Roller cam vs. flat tappet cam motors

Originally posted by oldbaldfatguy:<br /> My point was the rpm range I was referring to is above 4000. With the duration you are referring to you wont like the performance. It's fun to discuss stuff like this, but take it from someone who has seen it and done it you won't like it, and your boat will in fact be slower. Boats do not respond like automobiles do.

Again, speak only for yourself.....my circle of boating friends and I tend to spend a lot of time above 4 grand. Not everyone with a boat plods around in an old trihull or drown worms....some of us actually relish the performance aspect and spend a lot of time and $$$ in pursuit of more.<br /><br />A change to a stock roller cam will produce instant measurable results all trough the rpm range for the all reasons I have previously stated, and others. The cam the OP asked about is a great matchup for that engine, and is in fact almost identical to the STOCK cam in many Mercruiser 5.7's.<br /><br />While the OP is at it, I suggest he ponder a future swap to a set of Vortec heads and an aftermarket Vortec intake.....stock Vortec heads are cheap and a great way to gain HP.

 

[Wart T]

Re: Roller cam vs. flat tappet cam motors

Well it's certainly your money. You fool no one with your BS.

 

[bomar76]

Re: Roller cam vs. flat tappet cam motors

So, oldbaldfatguy ...<br /><br />It's your considered opinion that engines with roller cams experience lower performance than flat tappet engines?<br /><br />Wonder why Mercruiser states the following in their specs for the 5.7 and the 350 Horizon engines: "Advanced roller cam design that provides a lower friction coefficient, added torque, improved fuel economy, and greater horsepower for improved acceleration and top speed." ???<br /><br />Whatever....