Because nitrous oxide is known for creating big power increases, it’s the first item many people look for on a sleeper. If it’s discovered that you’re running squeeze, oftentimes the race will be called off. Thus, the trick to building a successful street sleeper involves fitting your car with nitrous--but doing it so no one can tell.

This story focuses on two ways to install a hidden nitrous system--an under-manifold system and a plate-style system--and it supplies additional nitrous tips. But because nitrous delivers such a forceful horsepower hit, be sure to upgrade your chassis and drivetrain components. Otherwise, your potent powerplant might puke your other components. (Nice alliteration, eh?)


Before


After


We used an NOS Under-Manifold Cheater System (PN 02620) that included direct-port nitrous nozzles, tubing, fittings, a distribution block, nitrous and fuel solenoids, braided stainless steel lines, activation switches, mounting brackets, a filled 10-pound nitrous bottle, and instructions. The kit is factory-set at 150 extra hp, but it can be adjusted to deliver between 100 and 250 hp.


To perform the installation, you’ll need basic items such as a drill, a 1/2-inch end wrench, a tubing bender, a tubing cutter, thread-sealer compound, a marking pen, and patience.


We installed our NOS under-manifold nitrous system on an Edelbrock Performer RPM aluminum intake manifold (PN 7101). Not only does this intake provide outstanding power output, but it also looks fairly stock, adding to the sleeper image of a car. Usually, dual-plane manifolds are easier to plumb because the underside of the intake runners (the area where the nozzles will be located) doesn’t sit flush with the edge of the port, as is common with many single-plenum manifolds.


Begin by flipping the intake manifold over so that the lifter-valley side is showing, then use a felt-tip pen to mark the nozzle locations. The nozzles should be equally centered within the base of the intake port and 5/8 inch apart from each other. Remember, each port gets one nozzle for nitrous and one for fuel.

 

Transfer the markings from Step 4 to the underside of the intake runners. Then make a horizontal marking across each line about 1/4 inch from the edge of the intake-gasket flange. Afterward, use a hammer and a punch to mark the locations to drill holes for the nozzles. Make sure the nozzles are installed so that they don’t hit anything when the manifold is installed.


Drill a 1/4-inch hole at each of the eight marked locations of the intake ports. The holes should be drilled so that the nozzles will slightly face toward each other when installed.


Use a 1/16-inch NPT tap to cut threads in each of the 1/4-inch holes. Afterward, carefully remove any debris, metal shavings, or sharp edges.


Apply some thread sealant (not Teflon tape) to the threads of the small nozzles. Then thread in and tighten the nozzles. The small openings in the two nozzles should face slightly toward each other so that when the nitrous system is activated, the nitrous and fuel are sprayed into the center of the intake port on the head. For plumbing purposes, with the base of the manifold facing up, install the nozzles in the following order (beginning at the rearend moving forward): nitrous, fuel; nitrous, fuel; fuel, nitrous; fuel, nitrous.


After nozzle installation, this is how our setup looked. Notice how the nozzle openings face slightly toward each other.


Center the distribution block on the underside of the intake manifold. Usually the block will sit directly on the outside of the heat-riser passageway. The bottom row of fittings on the block will be used for nitrous, and the top row will be used for fuel. Begin by installing the nitrous lines, starting first with the closest (shortest and hardest to bend) line. Thread on the first steel tube and tighten it finger-tight.

 

We inserted a short piece of tubing into the distribution block to serve as a template showing the level at which the to-be-bent line needs to be. In the area just past the ferrule nut, the line was bent downward until it intersected the template tubing. Afterward, a pen was used to mark where the tube needed to be bent to go to the distribution block. The lines should be bent so that they tuck up near the base of the intake to prevent any line-to-block interference when the manifold is installed.


Apply a small amount of thread sealer to the 16 compression fittings and carefully tighten them into the distribution block.


Using a tubing bender, carefully form the steel tubing so it matches the proper bend locations as indicated by the pen mark(s).


Position the newly bent line to check the accuracy of your work. If all is correct, mark the steel line in the position where it intersects the end of the fitting on the distribution block. Then measure 3/16-inch longer and make a second mark with the pen.


Use a tubing cutter to cut the steel line at the location of the second pen mark. Afterward, deburr the end of the tubing, if needed.


Install a compression nut onto the tubing end, followed by a ferrule. Then properly position the tube and tighten the factory-installed nut onto the nitrous nozzle. Afterward, tighten the new compression nut and ferrule combo onto the proper fitting on the distribution block. As you tighten, the ferrule will be automatically crimped onto the steel tube.

 

After the first nitrous line is installed, make the next one (this second line should be the next closest line). You want to install the shortest lines first because they are more difficult to bend and properly position. As the lines get longer (for farther-away ports), the plumbing gets easier. Here, another nitrous line is being marked prior to being bent.


After you’ve installed the eight nitrous lines to the lower portion of the distribution block, carefully check your work to make sure the fit is proper. It should look as shown in the photo. If all is correct with the nitrous lines, begin bending and installing the fuel lines.


The fuel lines should come off the top row of compression fittings on the distribution block. Once again, begin making the fuel lines starting with the nozzle that is closest to the distribution block. This line will be the shortest and most tricky line to make. Here, the first fuel line has been made and is ready to be threaded on.


Continue bending each fuel line (working from the next shortest and finishing with the longest) and then tighten it to the proper position. After the last line is fitted, inspect each line and give each compression nut a final tightening.


Apply some thread sealer to the two 90-degree fittings and then thread them into the sides of the distribution block. Afterward, thread on and tighten the two short runs of braided stainless steel hose (one hose per side). The hoses will run to the nitrous and fuel solenoids that are hidden where they will be least noticed.


There are two common ways to secretly mount the nitrous solenoids. Our favorite entails drilling two holes in the back of the cylinder block, installing the special NOS-supplied fittings, and mounting the solenoids near the back of the block. You can also drill two holes in the rear of the intake manifold and have the solenoids mounted somewhere near the firewall. However, when the lines exit the intake, a savvy car crafter might spot the nitrous system.

 

We’ve been told that if you mount the nitrous and fuel solenoids about 1 or 2 feet from the rear of the engine, the added distance slows the nitrous hit, making it come on less violently. For a street sleeper, this soft hit may actually be beneficial because it won’t wildly spin the rear tires. Here, this street sleeper has solenoids mounted out-of-sight under the dash.


Mount your activation switch on a cord hidden in the ashtray. Let everybody check out your car, and when it comes time to use nitrous, simply open the ashtray and pull out the switch.


Our favorite way to activate a nitrous system involves using the horn button. Unplug the horn(s) and plug your nitrous solenoid activation wires into the horn relay. The nitrous system will be in the off position until the horn relay is activated (by way of pressing the horn button).

Thanks to CC for all the hard work on this article.

PS Here is my first real contribution to the Iron Piston site and I have to say one thing. I'd do a whole lot more if I could post more than six pictures at a time. wink wink gen

 

That is an uber pimp setup, that would have taken some serious talent to do this so cleanly.

 

Certainly there's a lot of effort put into making that guide too, pictures are clean and everything.

__________________

 

Generic but a really nice guide. I think that'll be my summer project.

 

great guide, although the 1960's pictures were a tad rough on the eyes lol

 

The under manifold setup has been around for a long time.
I use to have it on my Z28 20 years ago.
I had it on my cougar 10 years ago but with a plate setup as well.

Now i just have a little top shot in my car.