rockers or cam?

[JoeGrapes]

In my 440 I have a Comp Xtreme Energy 274 cam with a lift of .488/.491 and a duration @.05 of 241 deg. I also have Crane aluminum roller rockers with 1.5 ratio. Which way would be better to increase lift? Change cam or go to 1.6 ratio rockers? Changing the rockers would be eaiser but what effect would it have on the excisting cam? How would the extra lift help? I'm using Edelbrock heads with a Performer RPM manifold. Thanks all and have a good one.

[rumblefish360]

Take the cam lift and divide it by 1.5 the multiply by 1.6 for the new lift.
Double check for clearance.
The 1.6 ratio will create a more intense cam and quicker opening valves without changing the duration.
Double check the geometry of the rocker to tip area if you go that route.

[dave571]

I'd go with a different cam.

You have a decent set of rockers already. Sure the 1.6 will have some gain, but I think a cam change will yield better results for less money.

I am currently running the 1.6/1.5 combo rockers on my 440. I did see an improvement, from my stock stamped ones. BUT it wasn't the kind of night and day thing you will see with the right cam.

[dave571]

I was just looking at the comp site.

The xe274 hydrualic is only 230/236 @ 50

The mechanical is more. 236/242

I've never run the mechanical version, but a friend had the hydrualic.

I'd definately say a more radical cam will give you more power. How radical is hard to say.

[dust]

Although the rocker change to 1.6 would probably be a little better for performance, I would change the camshaft. You already have a decent set of rockers and a shaft is cheaper.

Basically, what dave571 said...

[pishta]

rocker change would be a lot easier plus you keep the cams duration +-2 degrees. check your piston/valve clearance. This is a good case where a rocker change would be a more economical decision of you had a roller cam or some custom grind. figure the cost of a cam and lifters and intake gaskets and labor.

[BDS 871 Cuda]

Originally Posted by rumblefish360

Take the cam lift and divide it by 1.5 the multiply by 1.6 for the new lift.
Double check for clearance.
The 1.6 ratio will create a more intense cam and quicker opening valves without changing the duration.
Double check the geometry of the rocker to tip area if you go that route.

We already know the cam lift @ valve is .488 and .491 with 1.5 rockers.
Just take .488x.1= and .491x.1= valve lift with 1.6 rockers.

[BDS 871 Cuda]

I came up with .520 and .523 at the valve.
I think you might need to pull the heads to check clearance just to be safe.

[rumblefish360]

Originally Posted by BDS 871 Cuda

We already know the cam lift @ valve is .488 and .491 with 1.5 rockers.
Just take .488x.1= and .491x.1= valve lift with 1.6 rockers.

Hey BDS. I'm sorry. I missed what your saying.
However, I agree with your findings and advice on piston to valve clearance. (Should he go this route)

[DartGT66]

We once had some extra parts adn time to "play" at the track. The engine was a '75 stock short block 440 with homeported heads and MP 280/.474" cam, torker 2 intake, 3310 holley and headers. We had the stock stamped steelie rockers plus a set of 1.5 and 1.6 ratio crane rollers. During the day we run almost twenty runs with different set ups, and switching the rocker sets gained us absolutely nothing. Yes, in theory we gained lift, and more lift should equal to more power, but the timers didn't agree wiht the theory. the only way we found a marginal difference was using 1.6's on the intake and 1.5's on the exhaust. Even that gain was so small, that I'm not too sure it was because of the rockers, but after that trial we managed to get from low 12.4's to high 12.3's! So, don't expect big gains from the rockers; hope for the best and mentally prepare for the worst (waste of money).

[JoeGrapes]

Thanks for the help guys. I did have the duration wrong. It is 230/236 As for the clearance, when I put the motor together I checked and found a ton of clearance so thats not going to be a problem with the lift I'm shooting for. The more I think about it the better I like a cam change. It's a little more of a pain to do but I might be better off.