Help with cam ID on my 70 LS-5

[Mark E.]

Re: Help with cam ID on my 70 LS-5

Thanks for the insights, Duke.

By efficiency, I was thinking (but with no data) that a roller has less friction, maybe translating to better economy.

Isn't there a hydraulic roller cam kit (cam, lifters, push rods, springs, etc.) in the market that is proven to work well together in a street, oval port, big-block? A recipe if you will, that avoids the R&D you warn about. For example, what do you think about the roller cam Chevrolet Performance uses in their oval port big-block crate engines?

I appreciate what you're saying about how porting heads may be more effective. But isn't "head massaging" only as good as the person doing it, with a risk of butchering the heads if done poorly (sort of like plastic surgery- it depends on the skill of the surgeon and risks irreversible damage)? That's why I'm attracted to "bolt-in" mods like valve train hardware that doesn't alter the heads or intake.

But if you're saying there is no proven recipe for using a roller cam, I appreciate the warning.

EDIT: My apologies- I just searched "roller cam" in the Forum and discovered this stuff has been thoroughly discussed already. It looks like Duke and Joe have been very patient as this continues to come up over the years...

[Joe L.]

Re: Help with cam ID on my 70 LS-5

Another data point: My 1970 LS5 was rebuilt (really just overhauled- same pistons, rods, crank, valves) years ago by the PO, and although I wasn't given any documentation, I was told a Crane cam with specs virtually identical to the OE high-lift hydraulic cam was installed. It idles smoothly with 16-17" hg vacuum at 750 RPM.

I'm not a cam expert, but as Joe suggests, if I did replace it I would research a modern hydraulic roller. I've read that a roller provides significantly more HP, torque, efficiency and reliability, with no downside other than maybe cost. It's perhaps one of the few mods that really works and is invisible during judging.

Does anyone have experience with a roller cam upgrade they can share? Does this require any special machining on the block?

Mark------

No block machining is necessary if a retrofit hydraulic roller cam and kit is used.

GM, Ford, and Chrysler have not used a flat tappet cam in an OHV engine in about 20 years. Do you suppose they've got something figured out? Certainly, the cost of roller cams and lifters is MUCH greater but they still use them exclusively. OEM roller cam set-ups are not that much different than retro-fit. Roller cams have proven highly reliable over I'm sure BILLIONS of miles since their introduction.

[Duke W.]

Re: Help with cam ID on my 70 LS-5

By efficiency, I was thinking (but with no data) that a roller has less friction, maybe translating to better economy.

Isn't there a hydraulic roller cam kit (cam, lifters, push rods, springs, etc.) in the market that is proven to work well together in a street, oval port, big-block? A recipe if you will, that avoids the R&D you warn about. For example, what do you think about the roller cam Chevrolet Performance uses in their oval port big-block crate engines?

But isn't "head massaging" only as good as the person doing it, with a risk of butchering the heads if done poorly (sort of like plastic surgery- it depends on the skill of the surgeon and risks irreversible damage)?

Roller cams in conjuction with roller trunnion rocker arms do offer less friction, but it would likely not be measurable in terms of fuel consumption on a vintage engine. Modern Corvette engines have lower internal friction than vintage, but it comes from a number of small details that add up.

Roller cams have more aggressive dynamics, which require stiffer springs than flat tappet cams. The LS valvetrain is considerably stiffer than vintage engines to accommodate the more aggressive dynamics and stiffer springs without excess false motion. I'm not sure what changes have been made to modern big blocks to stiffen up the valve train for roller cams, but I'm sure the valvetrains are stiffer.

Anytime you hand over your engine to some "engine builder" you are taking a risk. The archives are full of horror stories, even for "stock" rebuilds". Head massaging does not require the removal of much metal. It's not "race porting", so the risk of destroying a head is low, and the procedures have been in publication for decades.

It comes down to a matter of philosophy and economics. People talk about "upgrades", many of which I consider downgrades. For example, electronic switches to replace the ignition points. Now you have replaced a simple mechanical device with a "black box" that can fail suddenly without warning. Points do fail, but usually give ample warning. One of the beauties of vintage engines is their simplicity.

The same goes for roller tip rocker arms, which offer little return for the cost. With a roller cam you take a chance on altering idle behavior, which offen means a loss of low end torque. Most guys don't know how to select a roller cam that has similar idle behavior and low end torque characteristics as the OE cam. Massaged heads with the OE cam will not alter idle behavior or affect low end torque, but offers higher top end power and a broader peak power bandwidth, which has been well proven over the years with dyno tests on engine restoration projects where I was involved in a engine system engineering capacity.

Duke

[Mark E.]

Re: Help with cam ID on my 70 LS-5

Thanks Duke and Joe. Isn't this a great country? We have the right to our opinion and the freedom to express it. I actually appreciate the logic of each opinion which makes this discussion fascinating.