Rhoads Lifters On Solid Lifter Cam - Setting Valve Lash

Thanks, Wyrmrider! Much appreciated. Yes, I know Mike Jones from another forum. He's one of the best and I plan on running some things by him.

I already have my cams for both engines. I worked out the specs using Isky's cam lobe profile listing and checking my choices against a Dyno 2003 program a buddy gave me back in 2003. It doesn't make recommendations. Only predictions based upon what you spec. Probably not spot on as to TQ and HP values, but should be close enough. The main value of such programs I believe is in comparing trends as you manipulate valve timing events and engine specs.

With the 292, I need to build it primarily for torque. Even if using the best parts you can get, its wise to keep piston speed below 4,000 ft./min. The longer the stroke, the lower the revs. With the 292's long stroke (4.120") that works out to 5,800 RPMs. But...... The 292's have harmonics issues that begin around 5,500 RPMs. Spin them faster than that and they will soon start slinging flywheels and having issues with torsional dampners (AKA 'harmonic balancers'), crankshaft and main bearings. So I need to limit RPMs to 5,300 or less in order to keep this engine together. Its going in a driver. Not a drag car that will only see short 1/4 mile runs of less than 15 seconds duration down a drag strip. If anything, it needs to be built for endurance racing, as I intend to use it to tow a boat and trailer up in the Texas hill country.

I have the flow numbers for a reworked lump ported head with larger 1.94" / 1.60" valves. This will actually flow more air than I need. The issue with these 9-port heads with siamesed intake port is not flow...... Its velocity. You can't optimize velocity through the intake ports like you can a 12-port head. So you cut the head bolt boss out of the siamesed intake ports, increase valve size and do the lump port mods and live with the slower port velocity. Also...... No need to lift the valves over 0.500". They will flow all you need and lifting the valves higher doesn't make any more power, it just beats up the valve train.

So I took those parameters (5,300 RPMs max and 0.500" max. valve lift) and set out to design a cam that would have the broadest, flatest powerband and the most average power within that RPM range rather than one having higher HP and TQ peaks but less average power and a narrower power band. Took my time and went through quite a few designs until I had what I was looking for. Then I contacted Isky and had them grind the cam.

The Rhoads lifters will be an experiment. I want to see if I can use the variable valve timing aspect to broaden the powerband even more and pick up more low and midrange power, as well.

I ran the same cam specs through the Dyno 2003 program after entering engine specs for my '78 Chrysler 360 engine and the predictors indicate a broad powerband with similar RPMs at which HP and TQ peaks will occur. Power band will not be quite as flat from off idle to peak, but power at peak will be higher. That's likely a function of shorter stroke length, better breathing and more displacement. The 360 will go in my '62 Dodge Lancer and that will be my daily driver when the old girl is roadworthy again. So I had Isky grind me a cam with similar valve timing events as the 292 cam only using MOPAR specific lobes to take advantage of the larger .904" lifters.

With these cams, IVC is 56 degrees, so I need 9.25:1 static compression ratio to come up with 7.79:1 DCR. That should work well with 91 octane gas.

Now with dish top pistons, the dished area is usually too far below the deck to really have any quench. Only the flat top portion of the piston that isn't dished really has any quench if its within 0.050" or less of the flat surface of the cylinder head (closed chamber design) when piston is at TDC. Some guys will adjust that distance using compressed thickness of the head gasket and set quench distance as close as 0.040". Which is as close as you would want to be in order not to have the piston hit the head once the engine is running and at operating temps. Just to be safe, I shoot for 0.045" quench distance. Are you sure your quench distance is 0.025"? That's awfully close.

Best regards,

Harry