Up until now what we've looked at has been directly related to improving the wet flow characteristics of the head. Some additional refinements that appear to have been done to the exhaust are also worth talking about. One of the criteria for an exhaust port is to have the exhaust flow out freely, but with the least tendency to reverse flow. By paying attention to this aspect, the heads will not only make more low speed torque, but they will also tolerate a bigger cam before the low speed output becomes unacceptable.
By rounding off the corners (as indicated by arrow #6), the flow is increased without the need for a bigger port. In addition to this, attention was given to the short side turn in an effort to get the flow to stick to the surface longer as it goes around the turn into the main body of the port. The significance here is that the short side is always the first site for reversion. By having the flow stick to the short side turn more effectively, the tendency to reverse flow at low rpm when the piston is around TDC is cut. Result: more bottom end torque.
Not only are the exhaust ports different, but so is the header flange surface. Changes were made here for installation convenience reasons. First off (and probably most importantly) was the new wider flange that allows the drilling of the Stahl-style header bolt pattern used for those bigger tube headers. Another factor not so easily seen is the thicker deck to accommodate the high stresses seen with heavy nitrous loads and big boost numbers.
Visually, we now know what we are dealing with. Now it's time to look at how such differences affect flow bench results. To establish this, a calibration test was first made on T&L's flow bench and then an example of both the original and new Dart Pro 1 heads were flow tested. The chart shows the results (step #15, see next page). As can be seen, there was very little difference in actual flow between the original Pro 1 (dark blue curves) and the Platinum Pro 1 (red curves). What we do see here is the elimination of the tip-over that so often occurs in the 0.550- to 0.600-lift range. This is due to the minor chamber reshaping at the point indicated by arrow #4 (step #9). Other than that, a conventional flow test reveals very little difference between these heads.
Where the difference did show up is in the swirl and mixture distribution as revealed by Dart's wet flow bench. At the time this feature was done, Dart's setup was not really geared to photographing exactly what goes on, as testing is done in very low light conditions. Essentially this involves a marker dye in the test fluid. This, when irradiated by an ultra violet light, causes the dye to become luminescent. This makes it easy to see what's going on with the naked eye, but it's not easy to capture on film.
It's now time to actually test the concept of wet flow testing. Our 383 T&L test engine, equipped with a Comp Cams single pattern 288 Xtreme Energy flat-tappet hydraulic cam and an Edelbrock Performer Air Gap intake produced the before and after results shown in step #14. Even with the original Dart Pro 1s, the T&L 383 made more low speed torque than the dyno could handle in the range below 3000 rpm-hence the graph curves starting at 3000. Although the Platinum heads produced a few lb-ft more at the bottom end of the range tested, the true gains showed up from about the 3700-rpm point. From there on up the gains were truly outstanding.
Peak torque with the original heads was already an impressive number, but the Platinum Pros bumped the figure up by 14 lb-ft. Likewise, peak power rose by 22 hp and the biggest power gain, seen at 5800 rpm, was over 26 hp. Remember that the flow difference between these two head styles is, within the lift range used (0.536), non-existent. This means that all the extra output we see here is the result of fuel/air mixture management within the intake tract.
So, is wet flow testing is worthwhile? The results speak for themselves.
This view of the old exhaust port clearly shows the relatively sharp edges of the guide boss. These are very much rounded on the Platinum Pro 1 heads.
Checking out the exhaust short side turn on the Platinum Pro 1 heads reveals a finish and form about what you would expect of a fully reworked race port.