FORDMUSCLE.com FordMuscle Nav

by Chirag Asaravala. Photography by the Author and Dart Engineering.

Even though it's been over forty years since the advent of the small-block Ford "Windsor"series engines, the popularity of building-up these motors appears to be greater then ever. Sure Ford has made considerable advancements in engine technology since the old 289, 302 and 351 motors, but the complexity of the 4.6 and 5.4 engines, coupled with performance parts selection and pricing, simply prevent these motors from gaining popularity with the average garage enthusiast. There is also the fact that a Windsor motor is easier to crank big power out of. Stroker kits are cheap, as are power adders. In fact, in the last several years we're seeing virtually every Ford enthusiast build a 302 or 351 based stroker when it comes times for a new motor.

Are you choking?
With so many guys building 347's and 427's, we're unfortunately also seeing a lot of horsepower left on the table due to poorly matched cylinder heads. There is no doubt in most guys' minds that the stock cylinder heads wont cut it for a stroked small-block. However many of the aftermarket heads are also not a good choice. Many of the well known heads on the market were designed around stock displacement figures and their sub-200cc intake runners are a stretch when it comes to maximizing the potential of a stroked Ford. Add in a blower and there is no doubt that bigger gains are probable with a better matched head.

If you've been following our own blown and stroked project (see High on Carbs) you may at this point be calling us hypocrites. If so, you'd be right. After all we put ported World Windsor Jr heads (170cc intake runners and 1.94 valve) on a 331 cid motor. Then we went and added 8lbs. of boost via a Vortech supercharger. Sure the motor still cranked out 516 horse to the wheels, but we know the heads were holding us back. In fact, making our decision to seek out new heads was made even easier by the fact the 54cc combustion chamber yields a boost-unfriendly 10.5:1 compression ratio. So when the opportunity came up to evaluate Dart's new Pro-1 CNC ported heads, we didn't need to be asked twice. In this article we'll look at the technology behind the heads. In an upcoming issue we'll bolt the heads on to our supercharged 331 and see what happens.

Impressive Resume
Dart of-course is a well known name in the bow-tie world. Their Chevy stuff has routinely been in NHRA and IHRA winners circles. Believe it or not, their Honda blocks and heads are also top players in the import classes. It is only recently that they've tapped into the Ford market. Fortunately for Ford fanatics they took their Ford offerings just as seriously as they do everything else. Dart first introduced all new Ford 302 and 351 blocks, in iron and aluminum with four bolt mains and a standard or tall deck heights. These stout blocks are completely re-designed and, other than dimensional similarities, they share none of the weaknesses of the stock blocks. In fact, many power addicts who have inadvertently cracked stock castings into a pair of four cylinder engines have turned to Dart iron blocks and gone on to make four digit power figures.

The most recent contribution by Dart to the Ford crowd is a selection of cylinder heads. Their Pro-1 aluminum heads are available in "as-cast" form or CNC ported. The as-cast heads are available as either 170 or 195cc intake runners (1.94 or 2.02" valve respectively.) The CNC program takes those volumes up to 210 or 225 cc's. Dart goes with 2.05" or 2.08" valves in the CNC heads respectively. All heads are setup with 1.60" exhaust valves. Table 1 below outlines the major features of the four available heads.

Table 1: Dart Pro-1 Cylinder Heads - Key Figures
Part No.
Int. Runner Vol. (cc)
Vol. (cc)
Valve Diameter
Int/Exh (in.)

Vol. (cc)

Int. Port
Dim. (in.)
Exh. Port
Dim. (in.)
1.98x1.10 1.33x1.34
2.00x1.13 1.35x1.35
210 CNC*
2.15x1.30 1.42x1.42
225 CNC*
2.15x1.30 1.42x1.42
*Exhaust ports on CNC heads use spread-bolt/SVO header pattern.
**All heads have 0.135" raised exhaust ports.

Technology makes Power

It's what Dart puts into developing the head that makes us convinced this is the right head for big-displacement Windsors. The R&D process relies extensively on the use of a wet-flow bench, a new technology still only being used and understood in the highest levels of race engine development. Wet-flow testing is based on the principle that dry air has vastly different dynamics than wet air. Conventional thinking has always been to develop and test cylinder heads using observation and data gathered from the movement of dry air through the intake and exhaust runners. It of course stands to reason that on a live engine the cylinder head must move an atomized mixture of air and fuel. The physics of how a much denser volume moves through the runners and around the valves turns out to be significantly different than the properties of air alone. Consider that air molecules move at a much faster rate than liquid molecules. Transitions in the ports and runners may appear to move air efficiently and with minimal turbulence, but on a wet bench they may show the liquid falling out of suspension.

A liquid which has the same specific-gravity as fuel is used rather than gasoline for safety reasons. A dye is added for visibility. The mixture is injected into the port or cylinder along with the air stream. As seen in the lead image of this article, what develops is beautiful tornado-like movement in the bore and around the valves. It is the analysis of these vortices and their directions that reveal areas for improvement. The position of a spark plug, for instance, can cause fuel to drop out of suspension around the ground strap. This may result in poor plug performance and flame ignition. Changing the shape of chamber, or angle of the plug may alleviate this problem. It is in this way Dart get's one step closer to designing cylinder heads under empirical engine conditions.

The R&D team at Dart has a distinct advantage over many other cylinder head manufacturers in that their observations and improvements from the wet-flow bench can be effectively implemented into production. Many times the prototype cylinder head that comes off the production line does not meet the specifications developed in R&D. This is usually due to the inability to precisely manufacture the intended design. It's a problem in any sort of manufacturing, from automotive to electronics. Dart's Performance Technology Center in Troy, Michigan boasts some impressive equipment and capabilities. The plant produces 70,000 heads and over 5000 blocks per year. Once the cylinder head specialists finalize a port design, they use a Coordinate Measuring Machining (CMM) to precisely measure the dimensions. The resulting data is then used to create a model which can be edited via a Computer Aided Design (CAD) program. Once finalized the data can be transferred into a CNC program to precisely machine the head using one of fourteen multi-million dollar Makino A77 machining centers in the Dart facility and the Haas CNC machines for final port work. The end result is a cylinder head or engine block that has tolerances as tight as two-thousandths of an inch.


In This Article:
Heavy breathing small-block Ford engines, like our supercharged 331 project, require properly matched cylinder heads. Simply looking for big flow numbers isn't enough. We take a detailed look at how Dart Engineering used wet-flow technology to develop their new Pro-1 heads for Ford Windsor motors.

Dart's Pro-1 aluminum cylinder heads for Ford's are available in as-cast or CNC ported. Shown is their 210cc CNC head. Note the wide-pattern header flange locations. Headers are tough to find with these flanges, fortunatly FPA, the kings of specialty headers, are working on Dart pattern headers for early Mustangs.
The 210cc intake nd 76cc exhaust runner volumes should be a good match for our air hungry supercharged 331 motor. A 225cc CNC head is also available for even larger displacements.
All Dart Ford heads feature 62cc high-efficiency combustion chambers. The decks are plenty thick for milling to boost compression if desired. The 210cc features a stout 2.05" diameter intake valve.
The fully assembled heads come with high-quality valve train components. The dual springs are available in 1.437" OD or 1.550" for big solid roller cams.
Dart uses a wet-flow bench to simulate the effects of rear air and fuel passing through the head.
Dart uses Computer Aided Design (CAD) to define precisely where the CNC machine makes it's cuts.
Precise coordinates are fed into the CNC programs for state-of-the-art machining machines. Here a head receives final bowl blend on a Haas machine.
A Dart technician pulls out one of the 5000 blocks produced annually in their Michigan facility.



Flow Testing
We hauled the heads over to Rob's Auto Machine so Rob Jr. could flow test them on their Supeflow SF-600 flow bench. As usual we're testing at standard 28" pressure and using a 4" bore. A radiused fixture is used on the inlet. We didn't use a pipe on the exhaust to simulate a header primary, which would have slightly increased the exhaust flow numbers we obtained.

The initial flow numbers showed the 210cc intake to flow exceptionally well from low lifts all the way to .600" where we stopped taking readings. At .300" valve lift we measured a gusty 195cfm. For comparisons sake, the low and mid-lift numbers outflow heads like the Trick Flow Twisted Wedge, indicating this head isn't sacrificing bottom end for high lift gains. At .600" we measured 285 cfm.

The exhaust side also shows stellar flow characteristics. In fact, the exhaust number are better than the intake numbers on certain aftermarket heads, driving home our point that you must have sufficient heads on a big-inch small block Ford. At all points the ratio of exhaust-to-intake flow is 77-79%. This ratio is important to look at especially when considering cylinder heads for a blown or nitrous engine where evacuating the large volume of spent gasses is paramount for making power.

Dart Pro-1 CNC 210cc Flow Data
Flowed by Rob's Auto Machine, Hayward, CA. (510) 732-1909

Our cylinder head gurus poked and prodded the runners and bowls and determined that they may be able to pick up some flow by smoothing out a tiny groove that is a result of the CNC process. The CNC tool can only port so far into the bowl, then it needs to come in through the port side. As a result a small groove is left in the short-side radius, the hardest to access area, in both the exhaust and intake runners. The groove would likely cause air-flow in the critical short turn area to become turbulent. We carefully smoothed this out and re-flowed the head. The results were well worth the efforts, with as much as 15 cfm a .300" lift. We don't recommend that you put a grinder to your heads unless you are experienced in porting and understand that just as easily as we improved flow, it's much easier to disrupt it and hurt flow tremendously.

Looking Forward
With a near 300cfm head we're just as nervous as we are excited about the idea of upgrading our Vortech-blown 331 project. This sort of flow will surely bust the already stressed stock 5.0L roller block. Of course in our demented power-hungry minds we are secretly looking forward to splitting the motor -almost as if it were some sort of rite of passage before being allowed to make really big horsepower!



Dart Machinery
353 Oliver Street
Troy, MI 48084

Ford Powertrain Applications
7702 E. 96th St
Puyallup, WA 98371

Rob's Auto Machine
27515 Industrial Blvd.
Hayward, CA 94545
Phone (510) 732-1909

FM Tech Editor and cylinder head aficionado Jim Langley and head porter Rob Stuchlik Jr. of Robs' Auto Machine analyze the Dart 210cc head.
Dart's incredibly precise CNC machining process is especially evident when looking at the shapes and transition around the guide boss area. As with any machining process the cutting head can only reach so far into the bowl before having to come in from the port side. As a result a slight trough left behind at the cutting junction on the short side radius. We found some additional flow by smoothing this out.
Convinced he can gain some flow, Rob performs a quick smoothing of the above-mentioned CNC groove. This sort of "tampering" isn't recommended unless you really understand what you are doing, as it doesn't take more than a few rotations of a grinder to hurt flow.
While not equipped with a wet-flow bench, the dry Superflow bench at Rob's gave plenty of evidence that the Dart 210's are an ideal head for our stroked and blown project.


Tech Archives Project Cars Readers Cars Feature Cars