i have done some searching on this forum and i can't seem to find much about people who use nitrous on their street rx7s.

a friend of mine got a s4 NA for free and we were wanting to see how much power it could make with nitrous on a nearly stock setup, and how big of a wet shot it could handle before exploding.
this would be done with the strongest clutch we can find, at least a walbro fuel pump in the tank, and the base timing knocked back about 5 degrees. we'd like to leave the engine as stock as possible: stock intake manifolds, stock ports, etc.

i think this thing will handle a lot of power. we arent going to be running it at the track of course, as X part in the NA drivetrain will inevitably snap, just putting it in 4th gear on the dyno. i'm thinking something in the NA drivetrain will break before the engine.

anyone care to chime in on this? think it'll handle a 250 shot?

 

I want to try it myself... perhaps along with water/meth. I found this today, hope it helps.

http://www.turborx7.com/nitrous.htm

I thought it an interesting read.

 

ah thanks for the link. very good read.

 

That guy is an idiot. Ignore everything he said.

So you think a 250 shot is possible? I will agree. Been there, done that. So let's dicuss.

There is essentially no difference to the internal components in the short block of a stock 146 hp engine compared to that of a 500 hp turbo engine. The rotors, seals, gears, e-shaft all remain pretty much unchanged (save maybe hardened gears for a high-rpm motor)... so its not really a question of can the engine handle it, its a question of whether or not whats bolted to said engine can handle it.

The N/A car has a few obstacles to overcome in handling large nitrous shots.
1. The auxilary ports MUST be open during nitrous injection! Failing this, nitrous backfire will occur.
2. If placing a single fogger in front of the throttle plates, removing the second set of secondary butterflies (TB Mod) is also a good way to reduce the risk of backfire.

To overcome both of these issues, the simplest and most effective way to install the system is to remove the auxilary port sleeves and actuators. Remove the actuator sleeve rod and install Pineapply racing or similar sleeve inserts. Replace the modified sleeves into the engine, securing them with Loctite GREEN Bearing retainer, leaving them in the open position. Press sleeves into the actuator rod holes in the lower intake manifold. Tap these freshly installed sleeves to 1/16" NPT. Install two ANNULAR DISCHARGE fogger nozzles. Annular discharge foggers spray directly out the end, as opposed to at the standard 90 degree angle. This location basically provides a straight shot of the fuel/nitrous mix into the auxilary and secondary ports.

3. The fuel system. The fuel pump will definitely need to be upgraded, but you already mentioned that. A walbro is a start, depends how much you really want to spray.

4. The clutch. You already mentioned it, but it should be restated for anyone reading this in the future. A puck disk with a heavy pressure plate will be your best bet. Even better, add a lightweight flywheel. The easier it is for an enginge to accelerate, the less chance of nitrous backfire.
I STRONGLY recommend using a clutch with a splined hub because of... #5.

5. The transmission. The N/A transmission likes to eat itself when large amounts of torque are crammed through it. Luckily, N/A tranmissions are cheap and readily available, but do not be surprised if you lose a trans.

5. Porting. Although for larger horsepower shots, you will see significant gains by going with a nitrous-specific port design, it is not required.

6. Intake manifolds. The UIM and LIM have a lot of twists and turns that can collect fuel and cause nitrous backfire. This will happen even with a dry system. Installing the above mentioned annular discharge system is your best bet, although you will lose significant low end torque.

7. Tires. Ramming a 250 shot at your tires in 4th gear at 4000 rpm is an extra 330 ft lbs of torque. The stock 185's will not hold traction, or anything close to it. Also, without a progressive control, good luck ever using 250 in anything but 3rd, 4th. and 5th on street tires. Even 3rd will give you traction issues.

8. Ignition. A 250 shot should be retarded 11-12 degrees from the stock timing. Non-nitrous driving power and economy will suffer. If you use a retard box, you will need 3, one for the leading and two for each trailing. Run 9's or colder in the leading. Consider disconnecting the trailing all together. Spray over 4000 rpm, and keep off the rev limiter!!!

9. Exhaust system. Don't even think about trying a 250 shot with the stock exhaust system. 2.5" straight pipe minimum, even mated to the stock exhaust manifold, and a catback.


Its a lot to think about, but you're almost tripling the stock power levels. Its not going to be drop dead simple . For the cheapest set-up possible, $250 for clutch, $150 for home-made exhaust, $100 for fuel pump, and $600 for the nitrous system puts you right around $1000. Now, add tires, and stock up the transmissions.

 

sean, that's some great info.

based on what you said, i think we'll attempt to run a 200 shot with the annular discharge nozzles and the pineapple inserts

 

Have fun

Make sure to use high octane fuel.