The reason that our Camaro friend couldn't dial out the rear brake lockup with his adjustable proportioning valve is because all adjustable prop valves are designed to allow a minimum amount of pressure to the rear brakes, even with the adjustment backed completely out. Once this minimum pressure is achieved, then you can use the valve to adjust the pressure curve needed for your application. In the Camaro's case, the rear piston was so large that the minimum pressure allowed by the prop valve was more than enough to lock up the rear brakes under hard braking. Our friend only discovered this when he started doing aggressive braking tests, because the higher braking effort by the front brakes created a greater weight transfer to the front, reducing the load on the rear tires. The larger rear calipers needed only a minimum amount of pressure to create leverage over the tires and lock them up. The fix for this Camaro was a Baer rear-brake package with a dramatically smaller rear-piston area. It balanced the system and improved the Camaro's 60-to-0 braking distance from a heavily modulated 117 feet to a much more stable 106 feet-that's almost a full car length and could make the difference between hitting something and missing it by inches. These are excellent numbers, by the way. Most street cars require at least 130 to 140 feet, depending upon the quality of the brakes and especially the tread width and traction quality of the tires.
Holley Idle Fix
Fran Blacker, Cheshire, CT: Jeff Smith's June '07 Holley Makeover answer helped me discover a serious idle problem. I have a cross-ram Hemi with black spark plugs. These are the only two Holleys I've owned. The story mentioned reducing the hole size of the idle feed restrictor in the main metering block. The holes in my Holleys were drilled to over 0.090 inch! These carbs were on a race car, and I have since found other problems. To fix these carbs, I plugged the holes with small solder balls and drilled 0.026-inch holes through the solder using a drill I bought in a hobby shop. Thanks, CC, from another Mopar whiner.
Jeff Smith: Thanks for writing, Fran. It's always nice to get feedback from our readers that information that we present in this column can help fix a problem without their resorting to buying new parts when the old parts can be repaired. We've seen this situation before, where hackers have modified their carburetors without really thinking about what they were doing. In your case, a 0.026-inch-diameter hole represents a flow area that's roughly 12 percent the size of that 0.090-inch-diameter hole. We're talking about flow area here, which affects part-throttle operation as well. For a street-driven car, establishing an accurate idle feed restrictor and idle airbleed sizes that will push the air/fuel ratio realistically between 13:1 and 14:1 will not only keep the spark plugs clean but also make the engine run much crisper and more throttle-responsive. Plus it will waste less fuel. This means you can have more fun and spend less money on gas. And that means you have more money left over to buy more speed parts and perhaps the occasional steak dinner. We like steak.
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