I have often heard it said that significant things happen in threes. I'm 90 percent sure it's coincidental, but the other 10 percent-well, not so sure. It's a Monday morning and I get a call from DSS Racing's Tom Naegele. Tom wants to know if I would like to put the latest iteration of its new line of small-block Chevy pistons through some kind of torture test. "Sure," I replied. "When I have a suitable block, I will give you a call." Later in the day I don't get one, but I do get three e-mails asking if the Zex perimeter feed plate nitrous system is any good. My response? "Don't know-haven't tried it yet."
Well, later in the day I call what is rapidly becoming my favorite core supplier, AAEQ. During my conversation with AAEQ's Eric Haugland about a late-model short-block for piston testing, the subject of porting its highly successful iron EQ23 heads crops up along with-you guessed it-its use with nitrous. Bingo-we have a plan for a street nitrous-injected 350 using DSS's new pistons, a Zex nitrous kit, and a set of ported EQ23 iron heads.
After talking to all parties concerned, we decided on a basic spec and targets to shoot for. First, this was to be an honest-to-goodness street motor, not something thinly disguised as such. How honest? A steady (no lope) idle of no more than 650 rpm, plus the ability to pull right off idle in high gear. It must be capable of decent mileage and have enough oomph to push a typical automatic-equipped 3,200-pound car on slicks under the 13-second barrier without the nitrous and into the 11s through the mufflers with the nitrous.
First, the heads. The results to date with the EQ23 heads have been stellar, to say the least. The heads looked like they were very porter friendly to the extent that even a first-timer could get results. From that you might mistakenly assume they must not be that good in terms of flow to start with if even a basic porting job bumps flow up significantly. Actually, it's the other way around. Because the port shape is so good, the out-of-the-box flow is hindered to a far greater extent by minor casting flaws than would be the case for a fundamentally poor port design.
As far as the cam and valvetrain are concerned, we decided to partially bias the cam spec toward serving the engine's needs when the nitrous is in operation. A cam favoring output when the nitrous is in use needs to be on a wider lobe centerline angle and be more advanced in the engine. This meant using a cam on a 110 LCA angle instead of the 108 known to be optimal for an engine of this spec but without nitrous. This cam would be installed 6 degrees advanced instead of 4. The earlier opening of the exhaust valve allows the cylinder much needed extra time to blow down before the piston reaches BDC. This extends the useful rpm range at the top end.
Along with this, the reduced overlap resulting from the wider LCA will allow the engine to idle more slowly and smoothly. That same reduction in overlap will also improve low-speed driveability about town. All the advantages of a nitrous-biased cam spec sound good, but there are some negatives in terms of reduced torque and hp while the nitrous isn't in operation. For us, a torque reduction of some 10-15 lb-ft can be expected along with about the same in top end power. When the nitrous is on, the useable high-end rpm is 300-500 more, and the power at this higher rpm is up to 30 hp more.
The late-model (1993) roller-cammed short-block was stripped to the bare block and, together with our DSS pistons, taken over to T&L Engines in Stanfield, North Carolina. Here, we asked T&L boss Lloyd McLeary to furnish a cost-effective, nitrous-capable, balanced rotating assembly for our build that incorporates our DSS test pistons. We also needed to prep the block as per their budget custom crate motors. Normally they would supply a short-block built up with the customer's choice of cam installed and timed in. In this instance, we planned on doing the assembly in our studio/workshop, as it was far more convenient for the photography required. What we got back from T&L a couple of weeks later was a bored block, honed/decked deck plate, align-honed mains, detailed casting, and finally, a primered and finished block in engine enamel. Along with this was a Scat one-piece rear main seal cast steel crank (PN 10526) and a set of Scat's least expensive race rods (these are proving really tough pieces for something as light as they are; PN 2-ICR6000-7/16). Along with this, a Professional Products SFI certified race crank damper (PN 9000) was used. Lloyd also recommended an ARP crank bolt to maximize the crank and damper interaction.
The cam chosen for the job was a Comp XR282HR Xtreme Energy hydraulic roller. This had 282 degrees of off-the-seat duration on the intake and 288 on the exhaust. Duration at 0.050 was 230/236. Timed in at 6 degrees of advance, this cam makes a great middle-of-the-road choice between no nitrous and all nitrous cam. Normally, this would be driven by a simple double-row roller chain with a multi-keyway sprocket to get the timing required. In our case, a fully adjustable Comp timing set was used so we could make cam timing adjustments and cam changes in a speedy fashion.
The Cylinder Heads
The Engine Quest EQ23 heads we intended to use are the 50cc chamber race heads that have been doing very well in IMCA oval track racing to the extent they have won a number of championships. The fact that a lot of these oval tracks have a tight turn and a long straight means the heads have to be able to pull off a corner at relatively low rpm and wind all the way up to over 7,500 rpm toward the end of the straight. With a Comp Xtreme Energy hydraulic roller of 288 and 294 degrees of of-the-seat duration on a 108 LCA, from a 10.3:1 CR we have seen open exhaust 350, 470hp, and 445 lb-ft of torque with out-of-the-box EQ23s. The plan here is to drop 8 degrees of duration and spread the LCA by 2 degrees, add a pair of Flowmaster mufflers, and then see if the head porting will bring back the output to about where we were with the bigger cam and open exhaust but with far more streetablility.
To establish the viability of successfully porting these heads with no previous experience, I had mechanical engineering/motorsports student Dusty Kennett port the heads. The only instructions were to skinny the guide bosses, blend the cast surfaces smoothly into the machined ones, and smooth out the rest of the port with coarse (80-grit) emery rolls. It took Dusty about 20 hours of cautious work the first time around, but the results were well worth it, as can be seen from the nearby flow tests. For the record, an experienced head porter could probably get this done in less than eight hours.
Intake flow improved from about 0.200 inch up, and at the intake valve lift our valvetrain would deliver (0.544 inch), the flow was about 8 cfm up on that produced by the as-cast port at 0.700-inch lift. The exhaust really picked up from 0.100-inch lift on up. This makes the head very nitrous friendly, as any nitrous application needs far more exhaust flow than does a regular nitrous application. As far as port velocity is concerned, these nominally 200cc intake and 60cc exhaust ports only increase in volume by 4cc and 3cc, respectively. For rockers, we used a set of Comp 1.6 aluminum roller items. If the motor spec had been for a non-nitrous application, there would have been a ratio split between intake and exhaust on this engine. Instead of 1.6s all around, it would have been 1.5:1 on the exhaust. This would have improved low-speed torque to the tune of 10 or so lb-ft and given an even slower idle capability.
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!