Offshoreonly.com - What hydraulic roller cam to use in place of this solid roller cam in my 598's?

Quote:

Originally Posted by rob vanharten (Post 4033584)

Right now they surge from about 800 to 1400 rpm. They shift in and out of gear excellent. If I lean out the idle circuit they won't surge, but die as soon as I put them in gear. I kinda like the surge anyway. Yes big props, 37 pitch 17.5 diameter, 18 degree rake.

I have some thoughts that might help on your idle setup. As for the cams, Call Bob. He will set you up with the right cam, lifter, spring combo.

Problem with most of these HP carbs, is the idle feed restrictors (idle Jets), are simply too large. Then, they install 4 corner idle circuits on these carbs, which everyone gets excited about. However, the main reason holley developed the 4 corner idle system, was for street driven vehicles. It allowed for fuel to be pulled from the secondary side at idle. Reason is, on some street cars that never get secondary actuation with progressive linkage, the fuel can become stale in the secondary bowls. On some wild cammed N/A engines, the vacuum signal is very weak at idle, and they help there too.

The problem is, when you have a twin carb setup, you now have fuel being pulled from 8 holes at idle. Combine this, with large idle feed jets (restrictors), you have a fuel mixture that is simply to rich. Most assume that when you tune the mixture screws, you are cutting off fuel only. However, the fuel passing thru that port is already emulsified (air and fuel mix). So, while in a way you are leaning the mixture out, you are also cutting off air to the engine. Sometimes this can be tuned acceptably , sometimes it cant. I have found that on some setups, completely closing off the secondary side idle mixture screws, and working on the primary sides only can result in a cleaner idle. Another option is to install secondary throttle blade adjusting brackets, that allow you to open/close the secondary butterflies with a screw driver from the top side. This allows you to keep the primary idle speed screw setting were it needs to be, which helps maintain proper idle circuit function, and lean sneezes during transition.

You can also play with idle air bleeds, but opening the idle air bleed is more or less a band aid fix. It will lean out the mixture somewhat. Which if I recall, you don't have screw in bleeds as it is anyhow. The best result is a properly sized idle feed restriction. A friend of mine has a pair of nickerson carbs on his blown 540's. They are some of the best idling blower engines ive seen. The key is the idle feed restrictors in his metering blocks to reduce the amount of fuel drawn from the idle circuit.

Anyhow, get with Bob on those cams, you'll be happy.