Flathead Engine Dyno Testing - One Last Flathead

One of the most gratifying experiences street rodders can have is completing a project and having the end result meet all their expectations. That's exactly what happened with our one last Flathead; in fact, it's even better than we expected.

To recap what's been done so far, our engine is based on a '48 Mercury block that has been given traditional relief: The intake and exhaust ports have been cleaned up, cylinders have been bored to 3 5/16 inches, and it's equipped with a 4-inch stroke Merc crank that results in a displacement of 276 ci. Internally, there are no real trick pieces; the rods are stock with most of the other parts coming from the Speedway Motors catalog, including the Isky Max I cam, valve springs, stainless 1.60 intake and exhaust valves, cast pistons, bearings, gaskets, water pumps, and a variety of bits and pieces. We used lightweight lifters from Reds Headers, a modified oil pump, and a full-flow filter from Motor City, along with Total Seal rings. The heads and intake manifold are Sharp, and we also tested an Offenhauser intake from Speedway Motors. Jere Jobe rebuilt the carburetors and converted the stock distributor to electronic., and we planned on testing on MSD.

Many of the decisions about what components to use in our engine were influenced by research done by Joe Abbin of Road Runner Engineering. His computer modeling indicated that the Sharp heads, a mild relief and the Max 1 cam would provide the best results and meet our goal of a strong street engine with broad, flat horsepower and torque curves. However, we have to confess we thought Joe was being optimistic when he projected 176hp and 250 lb.-ft. of torque. So, after Tom Cox completed all of the machining operations on the block and balanced everything that moved within a gnat's eyelash, we kept our mouth shut when John Beck at Pro Machine started to put it all together. The last thing we wanted to do was forecast big numbers, only to fall short. After all, 160 or so horsepower out of a Flathead without a lot of displacement or a laundry list of exotic parts is very respectable. Keep in mind that 170hp is very impressive, and 176hp is in our wildest dreams category.

From the outset we planned on putting this engine on a dyno just for our own satisfaction, but for John, its standard procedure. Generally all of his engines are run at Eric Weinrich's facility, DYNOMotive, before delivery to customers. Not only does this process ensure each engine is tuned for peak performance, but it's properly broken-in and checked to make sure there are no fluid leaks and other problems that could cause grief on installation. As soon as John buttoned-up the engine it was strapped in place for evaluation at DYNOMotive, and at that point the anxiety level was about what you would find in an expectant father's waiting room; we were all waiting to see what our little baby would do. Things got off to a less-than-auspicious beginning, partly because yours truly screwed up the plug wires and we found that it took a little extra effort to prime the full-flow oiling system, but once those two issues were resolved the engine barked to life. After running the engine for 20 minutes to break-in the cam, the oil and filter were changed and we were ready to make our first pull. We have to admit, the first couple of runs were less than awe-inspiring, as we struggled to get 150 hp. It was starting to look like Joe really had been optimistic.

To make tuning easier, all three Strombergs were fitted with adjustable main jets from Dick Crawford, but even with a lot of fiddling, the engine wasn't responding and the consciences of opinion was that the engine was suffering from too much carburetion. The engine didn't like 3x2s. Fortunately, we had an Offenhauser 2x2 manifold on hand with carburetors already on it, so we decided to give it a try. The throttle response improved dramatically with one less carburetor, and with a little tweaking of the air/fuel ratio, the horsepower and torque numbers began to significantly grow. The third pull with this combination netted 182.8hp and 249.9 lb.-ft. of torque. Even more impressive was that from 3,000 to 4,800 rpm it averaged 169.8hp and 230.8 lb.-ft. of torque. To say we were ecstatic is an understatement.

While we were all happy with the end result, we managed to burn up a fair amount of time, so we weren't able to test any other manifold carburetor combinations or the MSD distributor we planned on trying. We had a clearance problem with an electric fan in this particular application, and only the Ford Crab Cap-style distributor would fit, so that's what we used. Normally, the MSD will fit without any problems, and by all reports is an excellent option. After reviewing all of the data, particularly the vacuum readings, it appeared our Flathead might make higher peak numbers with a little more carburetion than two 97s could provide, but the problem is that three is too many. A small, single four-barrel might actually work better if numbers were the concern, but we'll give up the slight gain that that combination may provide and stick with the traditional Strombergs for looks, if nothing else. Besides, with this combination throttle response is excellent, and on the street in the rpm band, the engine being operated in the carburetion is about as good as it's going to get.

As far as the rest of the combination goes, it certainly appears as though the combustion chamber design of the Sharp heads and the traditional relief work well together, and while the Isky 400 Jr. has the lumpy idle so many rodders are after, the performance of the milder Max 1 is hard to argue with. To wrap it all up we'll just say that one last Flathead has more than met our expectations, yet there's nothing we did that can't be easily duplicated. The engine didn't cost a small fortune and it produces horsepower and torque figures that will make for an ideal street engine; and of course that unmistakable sound coming out of the pipes is music to a rodder's ears. What else can you ask for?

How to Get a Dyno Ready
Along with running the dyno at DYNOMotive, Eric Weinrich is an expert when it comes to carburetion and ignition systems. When he's finished tuning an engine, you know it's as good as it's going to get. But, as talented as Eric is, there is something that can be done to help the process and make the best use of the dyno time available--arrive prepared. It's not uncommon for first-timers to show up for a dyno session and then waste valuable time rounding up parts, su plies, and information. To help make the most of the opportunity, here are a few simple tips:

Engine
Make sure the engine is complete with all components including:

carburetor
water pump
fuel pump (if mechanical)
flexplate or flywheel
thermostat housing
distributor or magneto
oil filter
spark plug wires
pulleys, crank, and water pump.

Materials
oil and a second filter
fuel minimum of 10 gallons
spare spark plugs
gaskets

Engine Specifications
bore and stroke
compression
cam type and specifications