ASK RAY By Ray Bohacz
HESITATING CHALLENGER
Q:
CAMSHAFT CONFUSION
Q:
I have read two articles lately on engine builds: One was the Ford 351 Cleveland build in HMM (“Overachiever,” February 2022, # 222) and the other was a big-block Mopar in Hot Rod magazine. Both engines were built using flat-tappet camshafts, and neither build was cheap. My question is, why use a flat-tappet camshaft instead of a roller? The last engine that I built with a flat-tappet cam was 20 years ago. After replacing two cam-and-lifter sets, I read that the modern oils lacked the high zinc and phosphate levels that were in older oils. When I replaced the third cam and lifters, I started using Shell Rotella diesel oil. The third cam has lasted approximately 20,000 miles. All the engines that I built after that have roller cams and lifters. From what I understand, a roller cam is superior and the best way to build an engine. Am I wasting money by using a roller cam? Lee Waddington Robinson, Illinois
I have a 1973 Dodge Challenger with a modified 318 engine backed by an A904 automatic transmission. The engine uses a Quick Fuel carburetor (QFTSS680VS), Edelbrock medium-height manifold, headers, a mild cam (I don’t know the specs), and an MSD distributor (MSD8504). The engine produces 14 inches of vacuum at 900 rpm and 18.5 inches at 1,800 rpm. The air/fuel ratio is 12:1, and the engine produces 313 hp and 351.2 lb-ft of torque. There is a full stream of fuel when operating the throttle by hand. When I accelerate just beyond idle, I have to “feather” the gas pedal to keep the car running. If I accelerate too fast, the car will actually stall. After I get past that point it runs fine. I have had this problem since I installed the engine. Any ideas for a cure? Ken Durst Via email
A:
In most instances, a driveability issue such as the one you are experiencing is due to a lean condition off idle. There are other areas that can evoke the same effect, such as not enough ignition advance or a PCV valve with the wrong flow rate or response. You make no mention of the engine popping through the carburetor, but that would just confirm that there was not enough fuel if it did. I agree with you that a modern I will assume that there are no air leaks hydraulic roller is a better choice than even a modern flat-tappet design. The lobe and that the float level is set properly, profile can be optimized in many ways and along with the mixture screws, especially the reduction in friction is always good. if that carburetor has a four-corner There is an issue that needs to be idle circuit. checked when a roller grind is installed, Often, the accelerator pump linkage is and that is cam thrust and movement. in the wrong hole, or the accelerator pump The tapered lobe of a flat tappet lifter is cam is not aggressive enough. The pump designed to hold the cam in place. Control- cams can be changed on many Holley ling cam thrust is not a big deal but it does carburetors, and since a Quick Fuel carbuneed to be checked and addressed. retor shares many of the design elements Other than the cost of the cam and roller with a Holley, you should check these lifters, I cannot think of any reason why areas. The accelerator pump stroke may those engines were built using a flat not have enough volume. I would also disconnect the PCV valve tappet. I am not familiar with those two from the vacuum hose and plug the hose engine builds.
A:
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HEMMINGS MUSCLE MACHINES
with a bolt. Leave the valve out of the engine. Re-adjust the idle mixture and take it for a ride. If it runs much better after doing that, the PCV is wrong for the vacuum profile of the engine. I would then spend the money for the M/E Wagner tunable PCV and your issues will be over. If this test makes things better, but not by 100 percent, then put 4 or 5 degrees more advance in it with the PCV still disabled and see if the engine likes it. Follow these steps and you will have the engine running like a top!
CARB CLEANER OR STARTING FLUID?
Q:
Hi Ray! I love your column — it’s the first thing I turn to. I have a 1969 Chevelle 396 with a Rochester carb. I’ve had lots of trouble with fuel evaporating during the summer months. After a spin on a hot day, once I shut off the engine, you can sometimes hear the fuel gurgling like a coffee pot! It had an electric pump in the rear, feeding the mechanical pump, but as you’ve pointed out before, it can’t pump past the mechanical. I disabled the mechanical pump and just used the electrical one and voilà, problem solved. My question is, I’ve used starting fluid (ethyl ether) in the past with success. Are there any pros or cons of starting fluid versus carb cleaner? Thanks for everything! Kevin Konieczny Denver, Colorado
A:
Thanks so much for reading my ramblings first! I am glad I was able to help you with the fuel delivery issue. Starting fluid is very volatile and it is very hard on an engine, while carburetor cleaner is much gentler during combustion. That is why I do not suggest starting fluid. Starting fluid is chemically designed to allow an engine to run under extremely cold conditions since it will vaporize, where carburetor cleaner will not. So, when it is minus 50 degrees F and you need to get the old truck started to
