5.0 Mustang & Super FordsHow To Engine
347c.i. Small Block Engine - An Easy 500
Coast High Performance's budget 347 makes a quarter ton of power on the Westech water brake
In our July issue ("Half-Price Hardware," p. 50) we detailed the building of a 347 small-block by Coast High Performance. It was labeled a budget engine because it didn't go all-out for an aftermarket block or killer reciprocating parts and was fairly bursting with offshore-sourced parts. The goal was to replicate what many a hobby racer seeks-affordable thrust that works.
While we did a fair job of laying out the costs and hardware, this month we'll see if the combination works. And it does-so you don't have to turn pages as if this were a suspense story. That means it met the goal of 500 hp. Along the way, we did some interesting intake tests, so of course you'll want to check out the whole story.
The Parts List
In case you missed July's article, a quick review of the budget 347's hardware is in order. It begins in 1972 when the stock 302 block was cast with more meat than the later Fox Mustang 5.0 H.O. engines offered. Two-bolt castings, these late-'60s, early '70s blocks, especially the so-called Mexican blocks, are as solid a foundation as you'll get before stepping up to a Dart or Man-O-War block. This one was prepped with a 4.040-inch bore and a SCAT 3.400-stroke cast-steel crankshaft.
Because Coast High Performance and Probe Precision Products are basically one and the same company, many Probe parts were used. This includes the forged, non-finished connecting rods. They carry 31/48-inch ARP bolts and can be thought of as good sportsman-type pieces. Probe calls them machine-beam rods.
Likewise, Probe pistons were a given. Because high compression is a sure path to power-and doesn't cost that much to build into an engine-this time Coast reached for 12.5:1 compression slugs. They are SRS-series forged pistons with a 9cc universal dome that works with most inline heads-Brodix, Edelbrock, all the Chinese copycat heads, Roush, Darts, AFR, in other words, all the usual suspects-but not the all-out canted-valve racing heads from Neal, Blue Thunder, or Yates, nor the slightly different Twisted Wedge or Edelbrock Victor castings. They will, however, work with a Victor Jr. head.
That's a good thing, as this engine wears Procomp heads that are strikingly similar to the American Edelbrock Victor Jr. head. These Procomps sport 215cc intake runners and a 2.055x1.600-inch stainless steel valve package. Coast had Troy Bowen at Ford Performance Solutions set up the heads, meaning Troy final-adjusted the CNC porting job, did a valve job, set the spring heights, and all that.
Camming is another low-cost path to power, and Coast went plenty big using an Isky custom grind measuring 263/272 degrees of duration at 0.050-inch of lift, and 0.592/0.608-inch of valve lift with the expected 1.6:1 Probe roller rocker arms. The lobe centers are a close 110 degrees, so this cam has a fair bit of overlap and promotes high rpm.
If there is a downside, it's that with the older block, a flat-tappet mechanical cam is almost required. This can be touchy to break in with modern oils, and a flat-tappet cam requires stout valvesprings. In fact, it seems that given a ton of spring pressure to control the valves at high rpm, the chances of flattening a cam lobe are high, yet if the valve spring pressures are reduced to promote cam longevity, the valves float. The answer is a mechanical-roller cam, but that would be more money, so the flat-tappet got the nod.
Part of an effort to promote lobe life by Isky is its EDM lifters. These feature a small hole in their faces to increase oiling at the cam/lifter interface. The valvesprings measured 130 to 135 pounds on the seat, and in general Coast figured this engine is safe to as much as 7,800 rpm.
Oiling is wet-sump via a modest Elgin pump and a beefy Probe heavy-duty oil-pump drive. The pan is a standard deep sump from Canton.
Coast also crowned the budget 347 with something new to the U.S. scene, a Parker Funnelweb intake supplied by Procomp. This is a tall, single-plane intake with a seemingly built-in carb spacer. It looked rather racy and promised to make good power, but obviously a tall hoodscoop or bulge would be required to get it into a Mustang.
Because the Funnelweb was new to us, too, we decided to try a few manifolds as a comparison. An Edelbrock Victor Jr. intake seemed the logical choice because it too is an rpm-oriented single-plane and one that fits under many hoods. We also tried an Edelbrock RPM Air-Gap to illustrate how a dual-plane intake would "rock the curve" in favor of lower-rpm torque. Frankly, we didn't expect the RPM Air-Gap to do anything but choke at high rpm, but luckily we actually do these tests, otherwise we'd never learn just how ignorant we can be.
Running this engine on the dyno was a refreshing, low-key effort. Carburetion is typically a snap on the dyno-nothing broke, the engine had already been run in by Coast High Performance on its hot test stand that isn't a dyno, but it's able to run the engine and break in the cam/lifters. Generally, it was a simple case of bolting up the engine and making power.
As delivered by Coast, the engine lacked only exhaust and carburetion. The exhaust was handled by our usual Hooker long-tube headers, short collectors, and, at least to start, a pair of mufflers. The carburetion was via a 750-cfm Speed Demon. This is the most affordable Demon carburetor at $435 list, and it lacks the more fully contoured carburetor top of the slightly more expensive Mighty Demon. No matter, it ran fine and fits in with this engine's budget philosophy.
With the Hookers and Speed Demon in place, our first steps were to set the timing and verify the air/fuel mixture before leaning hard on the loud lever. The fuel was easy, as the Speed Demon proved spot-on with a 12.7:1 A/F ratio. The ignition timing was almost as easy, hunting between 30 and 38 degrees-none of which made much difference-and we ended up where we always do, 32 degrees of total timing.
At this point, simply making a full pass netted 503 hp, so our initial goal was met without really trying. Nice. Backing it up we saw 510 hp as the oil warmed up, so labeling this a 500hp engine is an easy call.
What did catch our attention was a lack of torque. Steve Brule at Westech figured the engine would generate approximately 440 lb-ft at its peak, yet we were seeing just 415 lb-ft. The dyno said the Brake Mean Effective Pressure (a calculated number quantifying cylinder pressure) was also down and remained low for the rest of our time on the dyno. We never did find a fault with the engine and concluded it was simply a characteristic of this particular combination.
Next we removed the mufflers, as we've occasionally seen some improvement without them at this power level. Also, this engine could well be run unmuffled at the strip, so we wanted to make sure there wasn't another 20 hp being corked up.
We needn't have worried. Removing the mufflers helped nicely up to 4,200 rpm, but after that the open headers roared out just a couple more horses. Even at the peak, the unmuffled gain was just 2 hp, 508 versus 510 hp. We didn't think the power gained at the bottom would offset the power lost at the top, but when changes are close and move around like this, it helps to average the power or torque across the working powerband and see who wins given a run through one gear, so to speak. In this case we have to give it to the open exhaust, as it came out ahead by the slimmest of margins:
Being practical about it, this would be impossible to see in a car, so there's little to fear from a proper set of mufflers. We left the mufflers off for the remainder of the day's testing.
Next we switched from the Parker Funnelweb to an Edelbrock Victor Jr. Now, before saying we should have used a Super Victor 8.2 instead of the Jr., we would have loved to, but the Jr. was the most equivalent manifold we had available. It's also one of the most popular and best known of the Ford Edelbrock single-planes, so it would do a fine job of helping place the poorly known Funnelweb in the intake pantheon.
All hands were curious going into this comparison, but just glancing at the two you had to think the Funnelweb was looking strong. It is statuesque, with straight runners and a huge plenum area. It fairly shouts "high rpm" just sitting there, and so far we had to say the results were great. We also all agreed it would take some creative bodywork to get the thing to fit under even a high-rise hood, and a scoop seems probable.
With absolutely no changes to the timing or air/fuel ratio-the distributor need not be moved during the swap and the carburetor adjustments needed no attention-the Victor Jr. came up surprisingly short of the Funnelweb on the top end. With power peaking at 482 hp, the Victor Jr. was 30 hp down from the Funnelweb's official 510hp peak. The Victor Jr.'s peak was narrower and dropped off sharply, too. At first we thought something was amiss with the dyno or test procedure, but double-checking and rerunning the tests showed the results were correct.
Is the Funnelweb's taller profile and larger plenum that much better? To help find out, we slid a 2-inch spacer between the Speed Demon and Victor Jr. This did help about 5 or 6 hp through the midrange, and carried the Victor Jr.'s low-end superiority up 500 rpm to 5,000 rpm, but as power built to the peak, the story was substantially the same as without the spacer. The spacer stopped the Victor Jr.'s top-end bleeding by 2 to 8 hp, but against a 30hp deficit that's not much, and the best gains were over a small rpm range. Too little too late, in other words.
Looking at the fuel curves, we could see the Victor Jr. uses less and less fuel as it stretches its power peak. This is a textbook example of air and fuel consumption, as the fuel use dropped precisely with the power drop. This is the carburetor telling us that less air is flowing through it, and therefore it is doling out less fuel. As an eyewitness to the laws of physics, the carburetor is a master of such observations-the Victor Jr. simply wasn't passing the same mass of air as the Funnelweb.
This can really be seen at the top end, where the Victor Jr. signs off with a definite drop. At 5,500 rpm it's as if the Victor Jr.'s horsepower curve was put over someone's knee and bent downward. It makes a hair more power than the Funnelweb below 5,500 rpm and a little better with the 2-inch spacer, but above 5,500 rpm there's definitely a deficit. By 6,200 rpm the Victor Jr. is 9 hp behind, and the gap widens from there until it hits the 30hp loss at the peak. The Victor Jr. also dies at 7,300 rpm with more vengeance than the Funnelweb.
While the power was falling off before then anyway, we could hear the valves floating at 7,500 rpm on these last few runs. The Westech crew figures this is mainly from the valvesprings retaining heat from the repeated high-rpm operation; in any case it illustrates how such a large flat-tappet cam and sane spring pressures are at their limit. Luckily the valve float was only at the highest rpm and would not be a factor in the remainder of our tests because we didn't have to rev it that high.
With the Victor Jr. documented, it was time to move down to the dual-plane RPM Air-Gap. Again, this intake is obviously designed for street operation and was never intended to rev close to 7,500 rpm. Our goal in trying it was simply to show how much torque this engine could put out at streetable rpm levels in the hopes of better illustrating the engine's personality. We fully expected it to make great torque and die on top.
Weren't we in for a surprise. The RPM Air-Gap did make a pile of torque, but it lost much less horsepower to the Victor Jr. than expected. That got us to comparing the RPM with the Funnelweb, of all things, and we were lightly shocked to see the following numbers when averaging the data
Remember, these average numbers don't show the rpm peaks, and the Funnelweb makes its power much higher than the RPM Air-Gap. To illustrate that, here's a chart showing the gains/losses of the Victor Jr. and RPM Air-Gap compared to the Funnelweb:
Clearly, the RPM Air-Gap is a different sort of beast. While it's hopeless as a high-rpm racing intake, the RPM Air-Gap has the advantage of making substantially more power down low. So, for anyone on the street, the RPM Air-Gap looks good because it produces generous low-rpm power and doesn't lose that much horsepower at high street rpm. Just don't put it up against the single-planes at the track.
The Bottom Line
Coast High Performance made 500 hp and more with its budget 347. It isn't necessarily the most driveable around-town engine when making this much horsepower with its Funnelweb intake, and it isn't the sort of engine that will pound out its maximum power endlessly without maintenance to its valvesprings. Congress won't send you a letter appreciating your help in reducing our country's foreign debt and, generally speaking, we don't expect this engine to hold onto its ring seal for 100,000 miles thanks to the stroker architecture. But it easily makes the 500hp mark and would prove an exciting prime mover in a bracket racer, Saturday Night Shaker, or other special-use Mustang.
Furthermore, our experience with the dual-plane Edelbrock RPM Air-Gap intake shows this engine could be made plenty civil on the street with an, uh, acceptable loss of top-end rush, we suppose. Of course, for street use less cam and the dual-plane intake would be best.
As for the manifolds, the Victor Jr. loses bottom-end and doesn't gain enough top-end power to make up the difference in this group of manifolds. The RPM Air-Gap does gain the bottom and doesn't lose that much top, just 11 hp shy of the Victor Jr. at 7,000 rpm, so it would make a powerful street-prowling intake. And the new Funnelweb has the sparkling top end to make up for its bottom-end loss. And to think-we haven't even hit the spray. Yet.
|Edelbrock Victor Jr.|
|Victor Jr. w/Spacer||Edelbrock RPM Air-Gap|