"Safe" nitrous levels?

[DK832]

I know the title is self-contradictory but bear with me!

I have a 351W built on the FRPP Sportsman 9.5" 2-bolt block. Pistons and rods are forged BUT the cranck is stock besides being polished, chamfered etc. Desktop Dyno estimates a little short of 400HP on the current setup (see my garage for more details).

I'm putting together a Edelbrock RPM Air Gap manifold with Fogger direct port nitrous and 900 CFM Holley ProJection unit on top. I have read what I could dig up on the capabilities of both block and crank and it looks like it's the crank that's the limiting factor? On the G-Tech I can see that power drops off from about 5800 rpm, so I never rev above 6500. Seems to be the commonly accepted limit for the stock crank?

But what about max HP? What is considered max for the stock crank? For the Sportsman block? I'm jetting the N2O for 175 HP but hope to go higher once it's dialed in.
Any thoughts or hints appreciated!

 

[brianj5600]

If everything is right, 300 should be ok. I get scared much over 200 because when things go wrong, they go very wrong.

 

[10secgoal]

I think 200 would be plenty safe. Paul was making somewhere over 600hp with a stock crank and block. Block left early, but they always do.Crank should be fine. I'm going for 600+ with stock crank, and yours is beefier than mine.

 

[86bluecobra]

yep i would say stay in the 200-250 range and you will have plenty of fun times ahead of you.

 

[351w_swap]

I can't believe there are so many of you using or considering using nitrous. I know that I am a lead foot and being that your are looking to cheater juice for more power i assume that you are too. Why would you want to put nitrous on a motor? It will increase the wear and decrease the life. I am simply too scared to touch the stuff; I would not only blow myself up but I would take anything within 50 feet with me. Good luck in your N02 foray.

 

[86bluecobra]

It is safe. I love my kit. For the amount i use it i doubt i am putting much wear on the engine. After all it's not like i'm using the power all the time. There is no real concern with blowing yourself up either. The kits are safe.

 

[351carlo]

I can't believe there are so many of you using or considering using nitrous. I know that I am a lead foot and being that your are looking to cheater juice for more power i assume that you are too. Why would you want to put nitrous on a motor? It will increase the wear and decrease the life. I am simply too scared to touch the stuff; I would not only blow myself up but I would take anything within 50 feet with me. Good luck in your N02 foray.

I'm going to be blunt and say if you don't have any experience and you don't know what you're talking about, please don't chime in with your two cents.

Nitrous is one of the most common, if not the most common form of power adder in most drag racing classes which use them. Please do your homework before adding such false statements. It's also no more of a cheater than higher octane gas, therefore it's not a cheater at all.

It's also N2O not N02; N02 wouldn't be very happy inside a motor, probably killing everyone who inhaled the exhaust if it even is combustible... I don't know. It is highly poisonous though (NO2, not N20).

I also suggest you stop watching the Fast and The Furious.... Nitrous oxide is NOT a flammable gas. It is an OXIDIZER, and will not just blow up and burn as suggested in the movies. I take a torch to my bottle often, and have no worries doing so. I'm also not of an average education, so please don't question that.

Wear and tear to a motor are simply due to the extreme power boosts that can occur, and the increased pressure from combustion inside the cylinders. A properly prepped motor can take repeated use and not show a bit of difference between another power adding method or a higher compression motor.

As for the original posters initial question, personally I would start with a 100 or 125 shot and work your way upwards. Many things should be changed when using nitrous quantities in excess of 150-175 to optimize the effects. Your suspension may no longer be adequate and you may end up not gaining enough traction resulting in lower ET's. It's best to slowly come up to the amount you are comfortable at, instead of risking everything. Make sure you're running the recommended safety systems, and I also recommend a window switch. I'll list more below. I would start at 100 and work my way up with 50 shot size increments. If you must, starting at 150 isn't too bad either. Try the 250 but I would probably stop there for a while.

You're going to want to start with a smaller shot and make sure you're running the right A/F ratio on the nitrous. If the Holley system has a wideband and a log, I suggest reading that. If not pulling the plugs and reading them after every pass in the beginning is a MUST. Do not blow up the motor. It is not nitrous oxide that blows up the motor, it is inexperience and improper mixtures/error on our part.

As far as system, I would recommend running the following:
Digital Window Switch (standard is fine, but I like my digital)
Fuel Pressure Safety Switch (Hobb's switch) - if running a separate fuel system for the nitrous side, make sure to have dual hobb's switches. This way if one pump fails, you won't keep running the nitrous. (Imagine your carburetor's pump failing, then the only fuel would be the nitrous system and the car would go lean... opposite applies)
WOT Switch to ensure you're ready to go
Standard arming switch

Best of luck with it, you should have a lot of fun.

 

[mustangdave]

Good points: you must have more fuel and retard timing. Personally, I wouldn't go over 150 with a stock crank.
More importantly, why are u winding your engine to 6500 when it's max power is at 5800?!?! Your just losing time there and hurting the engine.

 

[HookandLadder]

351carlo and Dave are correct. I have a simular setup with a fogger and have run 350-400 through the motor. Dart block 333......but I have forged everything. I would not push above a total of 550 total HP at the flywheel with a stock crank unless it has been gone through meticulously by a shop. Buck up for a new crank....worth it considering you have most of the rest of the motor up to spec. As far as safety stuff let me reinterate:

Window switch with a manual trans
Hobbs switch....aka fuel pressure switch
Increased fuel supply
Retarder for the timing
WOT switch

If you don't run these....not today....not tomorrow....but eventually BFK for the motor.

 

[351carlo]

Thanks for filling in my blanks guys. I got typing and missed a few things for sure.

OK! Just some more key aspects...

Personally I'll run a stock crank on a 200 shot all day long, so long as it's been magnafluxed and the rotating assembly has been properly balanced. Then again a good 4MA Cleveland crank isn't very weak, so I have an advantage.

I run an MSD Digital 6 + which automatically retards the timing when the window switch turns on the nitrous. That way I'm running full timing on motor and only taking it out when it needs to.

I run an Aeromotive S/S pump, regulated to 6 PSI. It flowed plenty for the old motor on a 125 shot, but the new motor has a separate fuel system.

Also if you're running pump gas on motor and have compression of more than 9.5, I suggest running 100 octane or better. Tell me your compression and I'll give you better advice on what fuel system to choose. Also how much you spray depends on whether it is necessary to have a second fuel system.


and DEFINITELY shift where you have max power. If the car's not making more power at 6500 all you're doing is putting load on it where it shouldn't be and slowing yourself down. Get to the track and shift it, guarantee shifting it at 5800 will result in better times. If not you need to get everything together and order the right torque converter/gears/tires for your combination. Max power is your shift point.

 

[86bluecobra]

I have the digital 6 box. Love it for automatic timing retard when on sauce. As for a window switch yes it is a very good idea. I do not run one. The reason you want to run one is so that the nitrous will shut off before you hit your rev limitor and you load up with a nitrous fuel mixture once the spark comes back. That could be very bad. I have my rev limitor set for 7 grand and i shift around 6200 so i don't worry bout it but as stated i guess it is only a matter of time. I like the point about starting with a smaller shot and working up since you need to get used to it.
something not stated is that for every 100hp shot you need to go 1 step colder plugs. On my 150 shot i run 2 steps colder to be on the safe side. Retard the timing 2 degrees for every 50 hp shot is a safe measurment.

 

[DK832]

Thanks for all the input, much appreciated!

To correct myself: I do shift earlier than 6.500 when drag racing, but when road racing turns and other things get in the way of shifting at the optimum time! Limiter is thus at 6.500 and I've bumped that a few times. Just heard that that's considered the rpm limit for a stock crank.

The engine is done by Joe Boghosian Racing (Fresno, CA) and is 10:1 compression. He used to do Indy engines for Mario Andrettti, now mostly does Top Fuel Hydros and tractor pulling + the occational engine for friends. Real solid engine.

I am building the N2O system with:
Arming switch
Jacobs Nitrous Mastermind (RPM window, timing retard, progressive "hit")
Fuel pressure safety switch
WOT microswitch

Fuel system is upgraded to a 150 gph @ 20 psi electrical Aeromotive pump (TBI pressure needed), regulated down to 6-7 psi for the N2O.

Just finished the rear end up so it now has 5 leafs, SPAX adj. gas shocs, PU bushings and HD shackles, Competition Engineering Slide-a-Links, Detroit Truetrac diff. So traction should be available when dialed in I hope.

It sounds like I should be ok with the smallest jets I have (175)? I'll probably leave them in for this season, learn to drive with N2O and get the rest of the car dialed in.

Another ignorant question: do you get off the nitrous when shifting gears? Can't figure out whether going on and off the nitrous or having x HP extra on the rearend when shifting hurts traction the most? The tranny is a JW Performance C4 and should be good for the HP either way.

 

[86bluecobra]

If you are running a race built c-4 it should shift insantly. Thus your pedal on the floor while shifting so the nitrous will be on the entire time. With my 5 speed i chicken out and let off the gas while i shift so the nitrous dies for the split second the shift takes.

 

[HookandLadder]

Make sure you use quality relays on the nitrous solenoids with the Jacobs box.
Ask me how I know this!!

 

[DK832]

Make sure you use quality relays on the nitrous solenoids with the Jacobs box.
Ask me how I know this!!

Do I even want to know? It sounds like a really expensive lesson....

 

[351carlo]

The reason high quality solenoids MUST be used on any progressive style box is that a solenoid works in 2 modes, OPEN and CLOSED.

In order to give it any sense of regulation or to progressively increase it, it will send out pulses to open and close the solenoid very quickly in a short amount of time. By doing this, it acts as if it were just partially open, allowing a progressive increase by opening it more and more.

This means the solenoid is rapidly going cycling from open to close in a very short time span. You don't want to have junk solenoids get stuck open during this, or closed.

 

[HookandLadder]

To add to that...................YES!! It can be very expensive. Just for the record, it wasn't a junk relay, but the chances certainly increase with a cheap one.

 

[67coupe351w]

I don't know alot about nitrous but this thread is pretty informative.

Something not covered regarding the window switch and WOT switch. How are they used in conjunction? Am i correct in assuming that the window switch turns the nitrous on at 1 rpm and off at a 2nd rpm? If so, how does the WOT switch play in?

Thanks

 

[351carlo]

Good Question!

How the system works depends on exactly how it is wired, but they're both switches and both have to be activated for it to work.

Imagine you're at 4500 rpm, generally an RPM where anyone would be spraying. Well at 4500 RPM you might be decelerating, obviously you don't want nitrous here. So in order for the nitrous oxide to come on, you must be above the lower limit, and have you foot all the way to the floor (Activating the WOT switch).

So take my car for example, both fuel pressure switches must have good readings, my WOT switch must be activated (foot to the floor), it must be between 4000 and 6800 RPM's and my system must be armed with the toggle switch.

When all of this occurs and a positive signal is sent to the solenoids, a positive signal is also sent to my MSD Digital 6 + and the timing is retarded according to the shot size.

Between gears you can keep on spraying in that Auto car. All of us do. Your torque converter will near instantaneously have load right back on that motor and there is no problem at all.

 

[86bluecobra]

I spray from a launch. I usally launch at 2500 rpm because we don't have all that great of a track. Basically its a airport we use twice a year. I get a 1.78 sixty foot launching on the juice from that rpm. I have never been told that it was a bad thing to use nitrous at a low rpm. It sure does get to red line quickly on the juice.