IRONMAN

would a 136931 crane or a 136941 be better on a 572 or 598 BBC with dart rectangle heads 325 or 340cc?

PatriYacht

Do you mean 731 or 741 cam? I'm using the 139651 cam in my 540's. They seem to work great. Even idle good at 800 rpm.

jdnca1

You need a Big duration cam for big cubes, Go as large as you can with Hyd roller.

For example I run a 280/[email protected] 115CL solid roller on my 632". It idles fine. The old cam was 272/278 114CL installed 2 degrees RETARDED, the motor obviously wanted more. Picked up 40HP by inc 10 degrees.

I don't know what CR you plan to run, but the larger duration will help you bleed down cylinder pressures which big inch motors will build.

MINIMUM crane 741 and I would talk to them about something even bigger....IE custom grind.

Steve Tanzy @Erson is the best in my opinion, Gordon @Comp is very good to talk with as well. I would get their opinions.

You'll need the 340 heads, minimum if you want to make power. I run fully ported and polished Dart 360's.

IRONMAN

Thats what I meant the -731 or -741 sorry, brain fade. I want to be able to run it for at least 500-600 hours so I want something fairly easy on the valvetrain. Thanks guys.

Dave F

I put a 254/264 114 .642/.641 w/1.8 rockers in my 598. It dyno'd at 730hp, nat asp and 1125hp blown.

When you get into the large duration cams the hp/torque peaks later, the more rpms you need to run for the motor to perform. The more duration, the more spring pressure, the more spring press, the harder on your valve train.
Hyd. rollers don't like to be held at 6000 rpms for extended periods of time. In my opinion I don't like to spin hyd. rollers more than 5500. It's too hard on the lifters.
That's why I cam'd it to run around 5500. If you're not gonna run the motor more than 5500 then put a cam in that will perform in that rpm range.

In my opinion the 741 cam is alittle too small. I'd use the the next one up, minimum, it's a 244/256 114 .632/.632. Dont go above the 256/264 114 .632/.632 though.

DAVE

KAAMA

iTrader: (1)

I think he's definately in the ball park!

Dennis Moore

If you want to run it 500 or 600 hours then you need a much milder camshaft. Running a high duration camshaft is fine but run a camshaft that has much less valve lift.

The horsepower difference between .540 lift and .630 lift is minor but the valve spring tension required for the .630 lift is considerably more. You can regain some of that horsepower by increasing the size of the intake valve and grinding around the valve seats and valve pockets (the exhaust is relatively unaffected by lowering the valve lift).

The camshaft lobe base circle is made smaller when lift is increased, forcing the lifter to climb a steeper opening ramp with a high lift camshaft. By keeping the lift to a moderate amount, the lobe can retain some size and the roller on the lifter will last longer.

Most performance camshafts (with high lift) need to have all of the rocker arms backed off every winter (or during long periods of storage) so the valve springs won't take a set. Remember, whenever the engine is not running, there are always some springs that are compressed (when the valves are open). Every time you take it out of extended storage you will need to readjust the rocker arms/valves/lifters.

The secret to valvetrain durability is to run a camshaft that requires less spring tension. Comp Cams has a line of camshafts called the Xtreme Energy Hydraulic Roller. They are an excellent design and have much lower lift numbers than all of the other camshaft manufacturers.

I would suggest that you call Comp Cams and ask about the XR288HR (236/242 intake/exhaust duration, .521/.541 intake/exhaust lift). Have it custom ground on a 112 degree lobe separation angle and two degrees advance (110 degree intake lobe centerline)This camshaft should last you for 500 hours without the need to constantly readjust and maintain the valve train.

Some may suggest that this camshaft is a little small but with only 2 degrees advance on the intake lobe centerline and a wide 112 degree lobe separation angle it should work fine.

Sincerely
Dennis Moore

IRONMAN

5500 - 5600 rpm max and close to 700HP with a normal idle, 800rpm's is what I would be looking for. I have been running the -731 crane in the 509 with excellent results for 300 hours now and would like similar reliability with the 572 or 598 that is the next project. Thanks for the input.

Infomaniac

I have a custom grind that I use that makes very good power in big CID engines.

Mid 640 lift 250ish 260ish @.050 hydraulic roller.

Run 150 on the seat with good oil pressure.

Can even run a solid roller on it with .005 lash.

Very easy on springs.