We cannot talk induction without including the Zex nitrous system. As you can see from the photos, there are no spray bars for either the fuel or nitrous running across the plate. The system has a perimeter feed where 12 pairs of holes (one nitrous and one fuel for each pair) spray at an angle into the plenum. This, as far as possible, is intended to optimize both the mixing of the nitrous and its complementary fuel supply and to produce better cylinder-to-cylinder distribution. If this is achieved, the system should produce good numbers along with less of the often characteristic torque surge as the engine goes up through the rpm range. In other words, it should run smoother and more consistently.
The intake manifold we are using in this instance is an Edelbrock Super Victor. Past experience has shown this to function well with the EQ23 heads.
The first job to tackle on the intake is to match the Zex plate to the plenum and smooth out the entry of the runner from the plenum. This only took about an hour to do. The next job on the intake-matching the intake port runners with the cylinder head ports-was a little more time consuming. For the most part, we only had to remove a little material, but a couple of the runners required some epoxy to get the match right on.
For carburetion, we chose a Barry Grant 750 Road Demon because we could get one with high-gain, high-atomization boosters. This is an advantage for nitrous engines, as overall fuel vaporization is far lower than in the intake of a regular, hotter-running non-nitrous engine.
As is the case with about half of my engine builds, I used one of the dynos over at T&L. The test was to be on a Saturday, and Doug Aitken, T&L's head dyno man, came in to help run the show.
Once broken in, the fuel and ignition were dialed in. The best timing on the 93-octane brew was 35 degrees total, which was all in at 2,800 rpm. The best mechanical advance curve was achieved using one light spring and one intermediate spring provided in the curve kit supplied with the Pertronix HEI distributor.
As for results on the motor, we got really close to our output target of 440 lb-ft and 470 hp by scoring 438 lb-ft at 5,200 and 466 hp at 6,300. And all that was done through a pair of 4-inch Flowmasters. Since we were so close to the target, we made a quick check to see if removing the Flowmasters helped. The result was a loss of 4 lb-ft on peak torque and 3 hp on peak power when the mufflers were removed. As for the idle quality, this was a glass-smooth 600 rpm, so we really are talking "street" here.
After everything was dialed in, it was time to test the Zex perimeter plate nitrous system. The system used was the most basic one offered by Zex.
So how much extra hp did our 150hp jetted Zex system actually make? If we look at just peak numbers, the peak hp without nitrous was 466 at 6,300 rpm. With the nitrous, it was 605 at 5,800 rpm. That's an increase of 139 hp. Peak torque with N2O was 604 lb-ft at 4,500 rpm. That's a 166 lb-ft increase. Although these are stout numbers if we consider figures other than at the peaks, the picture looks even rosier. The biggest gain came at 4,500 rpm, where the Zex system delivered a torque and hp increase of 210 lb-ft and 180 hp, respectively. Now that really is a punch in the back!
So how much did all this cost? Bearing in mind that we handled head and intake porting, which would drop the cost of this engine by about $800-$1,000, I would say that if you purchased a short-block from somewhere like T&L, you could follow our example here for about $5,300 total. That won't include the fancy timing cover and a few other upmarket parts only pertinent to our test needs. If you want that smart March belt system up front, then you would be looking at about $6,000 for a replica as per our final buildsheet. That's $10 per hp per lb-ft turnkey. That sounds like a deal!