Zex Perimeter Feed Plate Nitrous System
Is it over engineered for the job or is it’s complexity performance justified?
By
Robert McDonald
When it comes to nitrous injection and plate systems I kind of figured I had tested just about every style on the market and a fair few that are not (home made stuff). And when it comes to being different I would have to say that the Zex perimeter plate system introduced a couple of years back was about as different from mainstream plate systems as it gets. Although I have done a few nitrous engines in the last couple of years I had yet to actually dyno a Zex system. On Saturday the 6th of October 2007 that all came to an end. The Zex plate system was put to the test on a GFN test engine to see just what it would do.
Other than being a motor with good tough parts in it there was nothing exceptional about this 460 hp dyno mule so the results we see here should be about what you can expect of any similar motor.
Before talking results here we need to delve into the justification for what is essentially a much more complex plate than the normally used multiple spray bars. Is this peripheral feed plate an over engineered gimmick or does it actually add function?
The first point to take into consideration here is that when the nitrous is triggered it exits at the point of injection at a very low temperature. Typically after about 2 seconds the discharge temperature is below -120F. At this super cool temperature almost none of the fuel is vaporized sufficiently well for optimal combustion. This being the case using the high pressure of the nitrous (700-900 psi) to break up the fuel is a very positive move. An example of what better atomization and mixing of the nitrous and fuel is worth can be appreciated from the results of a GFN staff test of some years back. This involved a back to back comparison of a spray bar system with four fuel and nitrous holes versus one with ten fuel and nitrous holes. The area of the small holes was only about 20% more than the larger holes but the overall flow was, in each case, controlled by the jet in both the fuel and nitrous lines. For just about the same flow of fuel and nitrous the ten hole system was, on the kits 150 hp jets, over 15 hp up on peak and as much as 25 up at 1000 rpm below peak. Think about it. All that extra power was due solely to better mixing and atomizing of the two constituents involved.
Seen here is the underside of the plate. From this view it can be seenhow much more complex the ZEX peripheral feed plate is to manufacture.
Another factor also creeps in here. Because of inconsistencies in mixing of the nitrous and a factor called thermo-hydraulic resonance, which happens only in nitrous systems having a blind ended tube on the nitrous section, torque surging can result. This means that it is not possible to get two matching runs on the dyno as the surges occur differently each time. This is not so good if you are bracket racing a nitrous motor. Come to think of it, surging is not good regardless.
A close up shows the placement and angle of the nitrous/fuel feed holes. By having the nitrous spray into the fuel and into the prevailing air stream in the vicinity of each runner the fuel/air/nitrous is more evenly mixed and better atomized.
In theory the Zex perimeter plate should produce good results from the possibility of better mixing. In addition to that there should be minimal torque surging because there are no cavities from blind ended tubes in the system. If it does not do this then it looks like a lot of fancy engineering that achieves no more than a much simpler spray bar system might produce. Well now is the time to find out just how far theory translates into practice.
The GFN test engine, a 355 inch small block Chevy, I would say, is somewhat typical of a moderate budget bracket motor. Equipped with a hydraulic roller, mildly ported heads and a single 4 barrel carb on a single plane race manifold this engine put out right on 462 hp. The plan was to calibrate the Zex system with the jets intended to produce a 150 hp increase and see what this did to the power curve. The following chart shows the results.
The columns in red are for the engines Normally Aspirated (N/A) output. The numbers in blue are those generated when the nitrous is activated. The two columns on the right show the torque difference (TQ Diff.) and HP difference (HP Diff.) Peaks are highlighted in yellow.
On the dyno the nitrous button was pushed as the engine, at full load, wide open throttle, hit the 3500 rpm point. With the system pre-purged the nitrous hit relatively quick and power built smoothly between 3500 and 4000 where it was ‘all in’. From there on the system ran so smoothly it was hard to believe the nitrous was actually on. The only give away was the torque readout showing numbers in the high 500 and low 600 range. A good analogy was that we had gone from testing a 355 inch small block to a 500 inch big block. Although peak power only went up by 143 hp the power increase lower down was as much as 186 hp. As for torque this took a giant leap. At 4400 rpm the test motor hit 610 lbs-ft. That’s a number typical of a good (and I mean good) 500 inch street big block Chevy. That’s an increase in peak of 172 lbs-ft. But more to the point is the fact that there was that 186 hp increase in output at 4400 rpm along with a 225 lbs-ft increase in torque at 4300 rpm. These are stout numbers by any standard and, with a little more exhaust duration, I am sure the top end numbers would have been improved measurably.
In all I was impressed with the system. At this point in time I would give the Zex plate system a GFN five star award. I say ‘at this time’ because nitrous systems re-act differently from motor to motor and a sweet running system on a motor that is nitrous orientated can deliver a lot better than one which is not. The good results from this one test has prompted me to, down the road, do further testing on a variety of engines. At this point I see no reason why the system should not deliver very positive results on any engine as I hope time will tell.
GFN rating - Five Star
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