Stewolds

Does anyone make a cam that has a somewhat normal idle, but really let's loose above 2000 RPM?

Charlie Jones

Your best bet would be a "variable duration" lifter.
Rhodes lifters are variable duration , as well as "Hi Vac" lifters sold by Crane Cams.
These lifters have a high leakdown rate which limits lift and duration during low RPM operation . As engine speed increases above 3500 RPM the time for the lifter to "leak down" is shortened to the point where the lifter provides full lift and duration .
This allows for a smooth idle , as well as good manifold vacuum , when used with a "radical" cam.

Fun71

I think a roller cam may do what you are looking for.

Charlie Jones

Why ??

captjim

Roller cams allow for a MUCH faster ramp.

Stewolds, there are a ton of cams that idle smoothly and will make power from 2,000-5,000 rpm. It really depends, as always, on the rest of the combination.

Lee_A

Jim is correct. In general, a HFT vs. a HR with the same duration @ .050", the HR will have about 10 degrees more duration @ .200" (there ARE some big exceptions!) and will have more lift. Solid rollers will typically have even more duration as the lifts increase, more overall lift, and will cause the valve to dwell in the upper lift area for longer.


To look at it another way, you need a certain volume of air to make a certain amount of power. A roller will need less duration than a HFT, to allow that amount of air.


With less duration (and the proper event timing) you will create more manifold vacuum, and that will lead to a motor that sounds "milder."

BlackGold

Exactly. But just in case anyone thinks you have to pay the bucks to go with roller lifters/cam, there are plenty of modern grinds out there for flat tappet lifters (hydraulic or solid) that use more lift so they can have less duration, while equaling or exceeding the performance -- and manners -- of the older grinds.

joe_padavano

Actually, Rhodes Lifters are just "leaky" hydraulic lifters. They have an oversized orifice so that at slow engine speeds the oil bleeds out and the lifter "collapses" a little, increasing valvetrain lash. At higher engine speeds the oil can't leak out fast enough and the lifter acts like a normal one.

This effectively reduces the lift of the cam at low speeds (since it is eaten up in the lifter). Of course, it also increases the clatter of the valvetrain at low speeds. This was an old trick with solid lifter cams - loosen the lash to help a radical cam live on the street, then tighten it at the track.

olds 307 and 403

I basically asked for the same thing from Mark, Cutlassefi, near stock idle, good manners but a good improvement over stock with a hydraulic flat tappet cam.

Stewolds

Hey Jim,

I am looking at making a "Sleeper" out of a plain Jane '70 Cutlass S. 350 auto with A/C and PB. I want it to idle like a stock 350, but come alive when you hit the gas! What recommendations do you guys have for motor and rear end gearing? I would love to re-create the W-31 specs, but can you do that with AC AND PB?

Fun71

That's not hard to do with the right combination of parts.

The W-31 is ancient technology. It was high compression with a very long duration camshaft and it didn't make enough vacuum for power brakes. It was definitely NOT the same idle quality as your "stock 350". My impression is that modern cam grinds can do as well or better power-wise while maintaining driveability.

cutlassefi

If you're looking for a sleeper cam, then put something on wide lobe separation. From there you want to see how much actual compression you have. That'll dictate how much exhaust lobe to put in it in order to get the horsepower you want at the peak.

captjim

I had a 9 to 1 355, mild port work, Performer, 210/216 Engle cam, 3.42 gears, small tube headers, built for torque and throttle response. It ran high 13s, was reliable and fun to drive.

coppercutlass

I had a pretty mild build (350) that ran 13.7's with a really mild towing cam 260 h , 9 to 1 compression and a 3.73 gear pretty much making good use of stock parts that worked wel together . But the car was lightened up.

Same car with a (350) much bigger cam more compression all a lil more on everything build wise ., 3.90 gear is now running 12.45 @107 in the 1/4 mile.

Im sure if i had a very quiet exhaust my current combo would work for a sleeper but there is no way to take the lope out.

Sleeper by todays standards is hard to define. My car is more " race " build but its very reliable on the street and regularly makes long trips. Now the sad part is i running just as fast as what modern base muscle cars are running. Thats not your roushes L'series or hell cats. On the street its easy to east up modern muscle cars. Most guys dont know how to drive. But at the strip a few years ago i ran against a mustang that all it had was slicks and we both clicked of identical 12.6 runs. Im running sightly faster now but so are the mustangs.

Just some food for thought.