Little Motors Love Nitrous

True Happiness is the Combination of a $350 4.8L LS Motor and a ZEX Nitrous System

By Jeff Smith

This story started out as a complete accident. What eventually happened was we stuck a simple plate nitrous system on a 140,000 mile 4.8L LS truck engine and have run as quick as 11.40 at 119 mph. This has so sucked us into the quest, that our goal is now to see if we can push this underdog 3,600-pound Chevelle into the low 11’s and perhaps into the high 10’s. It has become something of a quest and like many oddball projects, the original plan was something completely different.

We originally went looking for a budget-based 5.3L motor to stuff into our ’66 Chevelle. The 5.3L LS (RPO LM7) is the most common LS truck engine on the planet and we thought we’d found a long-block with no intake or coils for only $350. But after we bought the engine and took it back to the shop, closer inspection revealed our purchase was really a 4.8L. This tiny engine only displaces 293 ci using a teacup-sized 3.78 inch bore and a short 3.26-inch stroke. Basically, this is GM’s Gen III version of the venerable 283 that can trace its lineage all the way back to 1957. Since we were stuck with this little motor, we went ahead and bolted it in the car.

The only mods we made to this little LS was a mild Comp hydraulic roller cam with 219/227 degrees of duration an 0.607/0.614 inch lift, a set of Comp beehive valve springs, an Edelbrock Performer RPM dual plane intake, a Holley 750 cfm vacuum secondary carburetor, a pair of Hooker’s cast iron exhaust manifolds, an MSD ignition controller, and a steel Champ oil pan. The Chevelle that now cradles this little junkyard orphan weighs in at 3,650 with a 180-pound driver and uses a California Performance Transmissions 200-4R trans with a somewhat tight converter. Out back is a Global West rear suspension with relocated tubular lower control arms to improve the instant center along with a BMR anti-roll bar to keep the front end square on the launch. The 12-bolt rear end carries 3.55:1 gears, a limited slip, and 30-spline Moser axles spinning a pair of Mickey Thompson ET Street 26 x 11.50 x 15 tires.

What caught our attention was how well the car ran despite its diminutive displacement and incredibly slow 60-foot times. With its tight converter, the Chevelle’s normally aspirated 60-foot times were in the 2.02-second range – slow enough to be measured with a sun dial. Yet despite that, our best 1/8th mile time was an 8.47 at 85.44 mph which equates to quarter-mile times of 13.20’s at over 105 mph. This showed us that the little 4.8 was making some decent horsepower, but it just didn’t have the torque to launch the car. While we could have put a deeper 4.10:1 gear in the car, this wasn’t what we wanted from a true street car. We knew that the easiest way to wake this baby up would be with a simple plate nitrous system and a 150 horsepower shot.

We originally bolted on a Nitrous Oxide Systems kit for our original testing almost two years ago. The original test triggered the full 150 shot right off the starting line, but all this accomplished was to put the Mickey Thompson ET Street tires up in smoke. We had been talking with our pal Jason Haines at Lingenfelter Performance Engineering (LPE) about their new digital, progressive nitrous controller so we decided to bolt that computer on and try it out. We’ll admit there were some teething pains with dialing in the computer and making all the systems work together. Most of our issues involved learning how to work with the computer’s complexities. We had to configure the computer for an eight cylinder engine and then learned that testing the unit with the engine off would only work if we disabled the fuel pressure sensor. It was stuff like this that took several hours to learn, but eventually we had the system operating as we intended. At least partially – but we’ll get to that.

What makes this controller worth the effort is it allows you to pulse both the nitrous and fuel solenoids very quickly using an LPE-supplied electronic relay. The computer allows you to set the percentage of “on” time from 0 to 100 percent, in much the same way electronic fuel injectors operate. We decided to start the nitrous at 40 percent on the starting line. The computer then allows you to create any sort of curve but we elected to ramp the percentage up with a straight linear line up to 100 percent at 1.7 seconds, which we felt would be roughly the 60-foot mark. We also received some excellent tuning advice from Steve Johnson at Induction Solutions in Florida. Our initial call was to ask how often we should change the nitrous solenoid seals (because we were pulsing them so many times) and he told us that installing a shut-off valve and a pressure gauge in the interior between the nitrous solenoid and the bottle would be the best way to improve seal life. Steve says that constant bottle pressure on the seal is what reduces its service life. He told us that the cycling of the solenoid on and off really doesn’t affect seal life nearly as much as the pressure.

With careful attention to bottle pressure, tire pressure, launch rpm and timing retard, early on we were able to lay down a really good 1.67 60-foot time that gave us an eighth-mile time of 7.26 at 96 mph. This has become our benchmark pass that we were unable to duplicate or improve upon despite several attempts. Usually, the problem was related to tire spin. This eventually demanded some work on the suspension with a set of QA1 double-adjustable shocks along with an anti-roll bar from BMR and tubular upper and lower front and rear control arms from Global West. We had previously installed a Global West rear lower control arm relocation bracket that changes the instant center on the rear suspension to plant the tires a little more aggressively. With tuning from the shocks, this helped the chassis tuning issue, but we still had issues with the nitrous.

After our one good pass with the nitrous, the car mysteriously created a delay in the nitrous trigger on the starting line. Testing the system with the engine off, the nitrous solenoids would trigger immediately and run through their intended linear progression to 100 percent on. But when hitting WOT on the starting line, there was a ½-second or so delay before the nitrous would hit. This took us several trips to the track to finally determine that we had set the low rpm trigger point on the LPE controller to 2,500 rpm. On our good pass, we had preloaded the converter with enough stall that this low rpm point was achieved on the starting line. But later we changed the starting line rpm procedure without realizing this caused the little 4.8L motor to struggle to get to 2,500 rpm off the line – creating the delay. We finally worked out the solution by reducing the controller low rpm trigger point to 1,500 rpm, but we did this only after we had decided to try a different nitrous systems.

By changing to a ZEX perimeter nitrous system, we thought we could isolate the problem of the delay.

Plus, we had a plan to eventually integrate the ZEX system with a FAST EZ-EFI 2.0 throttle body EFI system. But that’s down the road. For now, we installed the new ZEX system and were hopeful that the ZEX system would run as quick as the previous system. Our first runs at the track were less than successful and a bit perplexing. On our first run, the arming switch mysteriously turned off at 5.1 seconds into the run. Then, on our second pass, our time improved but when we looked at the data logging that is automatically recorded on the LPE controller, the data logger recorded that the nitrous turned off twice during the run. At first this was puzzling until we realized that the computer again did what we told it to do and shut-off the nitrous at 7,000 rpm. The engine had in fact buzzed to 7,200. This was very strange since we had shifted the trans into second gear at 6,500 rpm as indicated by the tach. We made a second pass, shifting exactly at 6,500 rpm and the same problem occurred. Not only was the nitrous turning off, but over-revving the engine way past the engine’s power peak. This could be one reason why the car slowed down from previous passes.

As this story is being written, we’re going to take our tachometer over to our friend Shannon RedLine GaugeWorks to test the accuracy of the tach in question. We also spoke to Kevin Dykyj at Auto Meter about tach accuracy, even though the tach we were using was not an Auto Meter. He told us that if there is some concern about an Auto Meter tach, you can send it into the company and they can test and adjust it for free as a customer service. He also mentioned that supply voltage and poor grounds are often a cause for inaccurate readings.

Our problems are typical of any performance or racing effort in that all the supporting systems have to do their job in order for the car to run properly. We had several problems unrelated to the nitrous system that caused the car to slow down. In this last case, we normally shift at 6,000 rpm but decided to raise the shift point to see if the car would run quicker. This put the engine at 7,000 when our best pass had been when we shifted at 6,000 rpm. Our higher shift point put the engine a full 1,000 rpm past where it had run well. It does not appear that we have hurt the engine but we will change the tach so that we have an accurate rpm count and double-check that with our data logger.

Despite all of our setbacks, that 11.40/119 mph dangles like carrot in front of our donkey cart efforts to improve upon that time. But this pass represents an improvement of 1.21 seconds and 10.55 mph in the 1/8th mile. Calculating the improvements in the quarter mile, these jump to a reduction in e.t.of 1.89 seconds and a gain of an impressive 13.13 mph! This is all from a simple 150 hp shot of nitrous. If we can get all of our ducks beak-to-tail, the Chevelle has proven it has the potential to run low 11-seconds. It’s entirely possible that we will have to hit this package with more nitrous to run low 11’s, but it is certainly possible. Remember, this is only a 293 cubic inch engine and well used at that! We’re going to keep hammering away at this little motor we’ll let you know how it turns out.

Cam Specs

Camshaft	Adv. Dur. (degrees)	Dur. at 0.050 (degrees)	Valve Lift	Lobe Sep. Angle (degrees)
Comp 54-456-11
Intake	268	219	0.607	112
Exhaust	276	227	0.614

Time Slips

1/8 e.t. x 1.57 = ¼ e.t. estimate
1/8 mph x 1.24 = ¼ mph estimate

Run	60-ft	330-ft e.t.	1/8 e.t.	1/8 mph	¼ e.t. (est.)	¼ mph (est.)
1)	2.02	5.587	8.478	85.44	13.29	105.95
2)	2.035	5.153	7.730	94.54	12.13	117.23
3)	1.974	5.118	7.684	95.51	12.06	118.43
4)	1.678	4.722	7.265	96.03	11.40	119.08
5)	1.735	4.922	7.710	87.61	12.10	108.63
6)	1.858	5.156	7.843	92.38	12.31	114.55
7)	1.828	5.153	7.883	90.53	12.37	112.2

1. Best run normally aspirated
2. First run with NOS nitrous, spun badly
3. Third nitrous run: tried lower tire pressure, hit nitrous on the line, spun, lifted
4. LPE nitrous controller, 40 percent starting line, best pass
5. ZEX system first run, delay eliminated, arming switch disabled at 5.1 seconds
6. Bottle pressure at 950 psi – mph improved but e.t. still slow
7. Tire spin, nitrous shut off due to over-rev twice during run

Parts List

Description	PN	Source	Price
ZEX plate nitrous, adjustable	82040	Summit Racing	605.97
ZEX bottle heater and purge kit	82001	Summit Racing	299.97
LPE nitrous controller	L460240000	LPE	649.95
LPE nitrous controller harness	L480310000	LPE	74.95
MSD LS6 ignition box	6010	Summit Racing	306.58
Induction Solutions 4” press. gauge	19708	Ind. Solutions	59.95
Induction Solutions quarter-turn valve	19705	Ind. Solutions	59.95
Comp Cams hyd. Roller camshaft	54-456-11	Summit Racing	373.97
Comp Cams beehive valve springs	26918	Summit Racing	180.97
Champ LS oil pan, steel	LS1000	Champ Oil Pans	267.59