C2-Hydraulic roller cam revisited

[Robert M.]

About a month ago I posted about hydraulic roller cams as I had recently bought a 67 L36 convertible that the previous owner had installed a Crane hydraulic roller cam kit. I just got all the specs on the cam and would like the experts to tell me what I actually have. I am sure Duke,Joe and Clem can fill in the blanks. Here are the specs:
Cam lift-.325 int. .339 exhaust. Valve lift- .553 int. .576 exh., Lobe ctrs. 105 int. 115 exh., Adv. Dur.-276 int. 284 exhaust, .050 Dur. 214 int. 222 exh.
Thanks in advance for explanation of the above numbers.

[Mark #28455]

likely Crane # 139001

This cam is a decent street cam, advertised min RPM 1200, Max RPM 5000, valve float 5600 RPM. "excellent low end torque and HP, good idle, daily usage, 2600 - 3000 RPM cruise.

However, they also sell essentially the same cam with the lobes spread out by an additional 4 degrees as part 139351 which would likely run better with a stock exhaust and extend the powerband by an additional 300 RPM or so. Either is still a decent choice for a street motor.

Mark

[Robert M.]

Re: likely Crane # 139001

Thanks Mark, That is exactly the part number. The car runs great but I was just curious as to what this particular cam was. I had asked in my previous posting about what amount of legitimate power and torque increase ther is. Any ideas?

[Duke W.]

Re: C2-Hydraulic roller cam revisited

Typical aftermarket cam - too much overlap.

Compare to the typical OE LS-X roller cams than have duration in the same ballpark, but the LSAs are way out at 119-121 degrees instead of 110. The exhaust is phased earlier and the inlet later. That's why they idle smooth and make stump pulling off idle torque and higher specific peak power output at higher mean piston speeds than vintage engines. They have significantly less overlap, but close the inlet valve later, and the exhaust opening point is tuned to the exhaust/inlet flow ratio.

Overlap and exhaust back pressure (with or without headers) is like mixing ammonia and bleach - don't try this at home.

If your primary engine judging criterion is a "big cam idle" the aftermarket has hundreds or choices, but if you want broad torque bandwidth and high top end power, you have to design your own cam, which is what I am doing.

The LS7 cam has durations at .050" lifter rise of 211/230 with POMLs of 124/117 for an LSA of 120.5. The exhaust duration is longer with a relatively early opening because the E/I flow ratio is about 0.65, and the cam is considered about 3.5 deg. retarded, which is best for a long stroke engine.

Now if you pocket port 461 heads you end up with an E/I flow ratio of about 0.80, so less exhaust duration than inlet works best, and because it's a short stroke engine it's best to advance the cam if you want the peak power range sweetspot upper boundary to be no more than 6500. So swap the durations and POMLs and you will be on the right track for a 327. Retard it to "straight up" (POMLs and LSA all equal) for a 350 and another four degrees for a 3.75" stroke SB. You end up with a butter smooth idle with more low end torque and more top end power than a high overlap SHP cam.

Duke

Duke

[Duke W.]

Re: C2-Hydraulic roller cam revisited PS

For reference the OE L-36 cam has durations at .050" of 214/218 POMLs of 110/120 for a LSA of 115 with gross lobe lifts of .271/.282.

So this roller cam has a lot more effective overlap, which will hurt low end torque, and the inlet valve effectively closes earlier, which limits top end power.

Because roller cams can have more aggressive dynamics, "area under the curve" (lift vs. crank angle) is greater so the mid range should be strong, but I doubt if torque bandwidth is impressive. Also, more valve spring or lighter valves is necessary or else limiting speed could be less than OE.

The L-36 cam has about 3.4 sq-in-degrees of effective overlap. By comparison LS7 is a meager 1.9 (327/300 is 0.9). Based on similar roller cams I've modeled I would hazard a guess that your roller cam has about double the effective overlap of the OE L-36 cam, which is more than L-72.

Another thing to consider is that one way to make the mid range and upper end of an engine "feel strong" is to kill the bottom end torque with excessive overlap.

Chassis dynos tell all, but you have to start the run at 1500 or less. Most dyno operators start the pulls at 2500-3000 (unless you ask them to pull from a lower RPM), so most guys with big cams don't know how weak their engines are down low.

Duke

[Mark #28455]

compared to stock BB cams

350 HP 396 -- 214/218 degrees at .050, 115 lobe centerline
375 HP 396 -- 242/242 degrees at .050, 114 lobe centerline per GM perf parts.

Crane cam:

214/222 at .050, 110 lobe centerline (cam owned by poster)
214/222 at .050, 114 lobe centerline (cam I mentioned)

Duke, I agree that the 110 lobe centerline cam will not run as well with a stock exhaust system, but shouldn't the second cam behave very similarly to the LS5 type cam and certainly better than the street mechanical cam?

Mark

[Duke W.]

Re: compared to stock BB cams

What you listed as 375HP 396 is actually the L-72 cam that was also used on L-78 and L-71 (without the rear journal groove).

Of course, it's a mechanical lifter cam and .012" of the duration at .050" is clearance ramp. The duration at .050" lobe lift ABOVE the top of the ramp (with lash set correctly) is 231/231, which is what you use to compare to a hydraulic lifter cam that converts nearly all lifter rise above the base circle to valve lift.

The less overlap, the better. IMO a roller with durations of 214/222 should have an inlet centerline of about 110 and a LSA of 116 to 120 to further reduce overlap and delay closing of the inlet valve. This would be with OE machined heads. With pocket ported heads the whole valve timing scheme needs to be changed to reflect the new relative E/I flow numbers, which would require valve timing that does not exist in aftermarket cams, so you have to design your own.

Duke

[Mark #28455]

is a ram type intake needed?

I understand that the earlier opening exhaust will help scavenge the cylinder as the cylinder pressure will be a little higher to get the charge moving out of the cylinder faster, and the earlier closing of the exhaust valve will decrease intake/exhaust overlap and keep the exhaust from diluting the fresh intake charge.
But, I was under the impression that the late closing intake timing worked best on an engine with a ram type intake manifold to allow continued cylinder filling (like the stock late model LS engines). Does the vintage 2 plane BB intake allow the late closing intake valve to work to maximum benefit?

Thanks in advance,
Mark

[Joe L.]

Re: compared to stock BB cams

Duke-----

The 375 HP 396 (except 1965) IS the L-78. The L-78 was "de-rated" for use in 1966 and later Chevelles and Camaros. Actually, it was just rated at a lower RPM.

Also, I think that it could be said that the L-72, L-71, and LS-6 used the L-78 cam rather than the other way around. That's because the first use of the 3863143 cam was for the 1965 L-78. That use continued for 1966-1970 L-78's installed in Chevelles and Camaros (technically, though, the 3863143 changed to the 3904362 for all 1967 and later SHP big blocks).

[Duke W.]

Re: is a ram type intake needed?

All manifolds are "ram type" to one degree or another. Any duct with non-steady flow offers opportunities for "tuning" by harnessing inertia pressure and wave dynamics.

Most OE SB manifolds runners are about 4-5" in length and combine with the head inlet port length of about 5" to form an overall inlet tract length of about 9-10", which is a good length to enhance power bandwidth on engines tuned for a peak power in the range of 6500-7000, but is a little short for milder engines that peak at lower revs due to shorter cams. The FI manifold runner is about 6" long and is "just right" for the mechanical lifter cams, but until the OE heads are massaged, FI won't make much more power than its carbureted cousins. Once the head restriction is removed it's no contest at the top end though FI losses the bottom end torque battle.

If maximum inlet inertia tuning is desired in the mid range to enhance peak torque as opposed to peak power, longer runners are required. The 350 TPI engine from the eighties was an example of using long runners to enhance peak torque as opposed to peak power.

As the "tune speed" is increased, total inlet tract length must be reduced. On F1 engines it made as short as possible because at the revs they turn, aspiration efficiency is ultimately limited by the speed of sound, which is the speed that pressure waves travel in the inlet tract to initite flow.

Duke