ok, for a long time I was told that nitrous on a cast piston motor meant death. Suprisingly, here many people seem to be doing just this quite successfully. I read that one guy went through 50lbs of nitrous with a 135 wet shot, but did his motor then blow up? What kind of durability issues when adding this type of power adder? Are cast pistons really that bad if detonation is avoided? I am looking at a 50hp first stage and a 75 shot 2nd stage wet system for my stock, cast piston 8.5:1 compression 455 in my daily driver... but if its gonna kill it quickly I may take a different track. Any experiences? I want to know as much as I can about this type of power adder before I go spending money.

 

I know a guy who had a 350 with cast crank, rods, and pistons 2-bolt main. All the parts were put together right and with good ARP hardware. He sprayed a 200 shot down it for 5 years on a weekly basis, plus put a ton of street miles on the motor. It was in the mid/low 10's. Wanna know what gave out and led to the demise of this motor? Not the pistons, the cast crank snapped in half.

Its not that cast pistons and nitrous dont mix, its cast pistons and detonation that dont mix. Forged pistons are simply more forgiving to misuse. The key to longevity is making sure its tuned properly.

 

frickin AWESOME!

 

I ran 35 10lb bottles through my stock 305 TPI bottom end with no problems at a Nitrous Express 150hp jetting. 4degrees base timing and pump 93 octane usually.

Also ran a lot of bottles at the 75hp and 100hp level with the stock 6degrees base timing and pump gas.


Goodluck.

 

We have ran lots of cars with cast pistons.AS stated above its all in the tune up.Use the needed saftey features such as a window switch and you will be able to spray your car time and time again with out any problems.
Dave

 

so i need an rpm operated switch and a conservative tune? I'm probably just going to run 75 hp pills what should I do about spark plugs?

 

odddoylerules,
Go to the NOS official website and look in the technical setion. There is a chart in there that shows what they recomend for the different power levels. That chart will answer any question you can think of regarding how big you can go before you will need "forged items". Anyway if you cant find the chart let me know and i will dig up the link.

Later
Matt

 

Heres the link for the chart i was talking about.

http://www.holley.com/HiOctn/ProdLin.../InstlReq.html

I dont know if this will show up as a link that you can just click on and it will go to the site if not that is the correct address so just cut and paste into your browser.

Later
Matt

 

I've run countless lbs through my stk bottom end / stk head '92 305 @ approx 150 hp for 8 years & the motor now has > 180K miles on it. I believe that the '90 - '92 F-body V8s have hypereutectic pistons, which make them a bit more resilient, as well. Here are some rules of thumb for running nitrous:

Don’t let the afr run lean - use a fuel pressure switch that monitors fuel pressure AFTER the fuel solenoid to enable the nitrous solenoid - this assures that nitrous is injected only when the fuel pressure at the nozzle is above a safe set point - this will prevent catastrophic failure in the event of low fuel level, defective fuel pump, clogged fuel filter, defective fuel solenoid, etc. – install a dash mounted fuel pressure gauge that measures the pressure at the inlet of the fuel solenoid – this will let you see the exact pressure drop through the lines when the system is enabled.

Upgrade your fuel pump to meet the needs of the nitrous system – here’s some data regarding fuel pumps (I’m using the Bosch in-tank 61805 in my ’92 Z28 & the Walbro GSS307M in my ’84 Berlinetta):

TPIS Bosch in-tank 61805 67 gph @ 50 psig
(Bosch 61805 rated for up to 550 hp)
GM LB9 pump 24 gph @ 50 psig
GM L98 pump 28 gph @ 50 psig
GM BGN / Cyclone pump 41 gph @ 50 psig
GM LT1 pump 33 gph @ 50 psig
Vortec in line pump 45 gph @ 70 psig
ATI in line pump 67 gph @ 70 psig
Walbro GSS307M (< 60 psi)
54 gph @ 50 psig @ 12 VDC (9.4 amps)
64 gph @ 50 psig @ 13.5 VDC (9.8 amps
Walbro GSS340M (> 60 psig)

Run a bit more rich with nitrous than when running normally aspirated - 11.8:1 afr range with nitrous; 12.8:1 range normally aspirated. A wide band oxygen sensor and EGT sensor are helpful to tune the system.

Retard the timing approx 3 deg / 100 hp, use 1 step colder plugs for every 100 - 150 hp, & don't gap the plugs greater than 0.040". Use an aftermarket ignition system - MSD, Jacobs, etc. - the stock ign can't even ignite a fairly lean mixture (12.8:1) above 4500 rpm @ WOT, normally aspirated.

The system should not be allowed to function unless the ignition switch is on, an “arm” switch is enabled, a WOT detect switch is enabled, and the line lock (if you have one) is disabled. Also, don't enable the system below 2500 rpm, or above a few hundred rpm below the rev limiter set point - use rpm activated switches to create an rpm "window" where the system will function:

[2500 rpm < Enable NOS System < (rev limiter – 200 rpm)]

The mass flow rate delivered by the nitrous system is constant, and independent of engine rpm. This causes cylinder pressure to increase dramatically at lower engine rpms when the system is enabled – if the system is enabled at low engine rpms, the result could be a blown head gasket – or worse.

Use high octane fuel - 100 octane for greater than 100 hp – & use only unleaded fuel if you have any oxygen sensors in the exhaust system. Use a scanner, like an AutoXray, to monitor knock counts.

Install a pressure gauge on the nitrous bottle – or even better yet, mount it on the dash with a hose connecting it to the inlet of the nitrous solenoid – after the nitrous filter – this will give you the static bottle pressure as well as indicate the pressure drop across the lines / filter when the system is enabled & let you know if the filter needs to be changed. If you are running in cool climates, or are making back to back runs, you will need a bottle heater to bring the pressure up to approx 950 psig for each run. As nitrous is allowed to escape from the bottle, the bottle temperature drops, and as a result, the bottle pressure drops. Also, if the bottle pressure is too high, the system may run too lean, causing engine failure, or the nitrous solenoid may not be able to open against the high pressure. If you install a bottle heater, be careful to not leave it turned on too long. Put a big light on the dash to remind you that it’s on, or use a timer to turn it off after a predetermined amount of time – you don’t really want to test the operation of the high pressure release valve….

I have found that a nitrous purge system is not necessary on my Z28 system. A purge system uses a second nitrous solenoid to purge the gaseous nitrous from the line between the bottle and the nitrous solenoid feeding the engine. This allows the line to be filled with liquid nitrous to prevent an over rich condition – and consequent bog when the system is first enabled. It looks cool to spray a plume of nitrous in the air, but it wastes a lot of nitrous, and I have not had a bog problem without using the purge system.

When having your bottle filled, make sure it is cold – ice it down in a bucket or have the filler put it in a freezer prior to filling it. This will allow the bottle to be filled completely.

If you plan on running at a track that conducts tech inspections, you will need a vent pipe that connects the high pressure pop off valve to the outside of the chassis, and you may also be required to have a drive shaft safety loop in place. Also, when mounting the bottle, make sure that the outlet points down, as the liquid pick up tube is bent toward that edge of the tank. Also, the nitrous and fuel solenoids have different pressure ratings, so be sure to install the correct solenoids on their respective nitrous / fuel systems.

I have an Excel spread sheet that I received from someone on this web site a while back that contains a formula to calculate fuel jet diameter based on nitrous jet size, nitrous pressure, and fuel pressure. I have found the formula to be on the conservative (rich) side in calculating fuel jet diameters.......Here's the formula:

Fuel Jet Diameter =ROUND(POWER(B5*B5/((5.8/3.4*9.65/POWER(B$1/B$2,0.5)*0.9)),0.5),0)

B1 = Nitrous Pressure
B2 = Fuel Pressure
B5 = Nitrous Jet Diameter in thousandths of an inch
(Fuel Jet Diameter calculated is in thousandths of an inch)

 

WOW!?

 

well let me see?
I got my FPSS mounted right after the shrader valve and before my fuel selenoid, (NX says to mount the FPSS right on the shrader valve)
Im running ACCEL header plugs gapped at 45 I think, my electric nitrous pressure gauge is checking pressure right at the bottle, Im using the stock fuel pump........I guess Im just doing it all wrong? to late now...theres no turning back. I havent retarded the timing.

but everything else Im doing....what little is left...LOL!

I havent tried it yet as I still have to mount the MSD box, window switch and wire everything up.

 

wow, i really appreciate all the useful information you guys have provided for me. I never expected this kind of response. special thanks go out to the guy that talked of using a fuel pressure switch as a safety. All the information you gave will go a long way towards creating a nitrous system that will operate safely on my cast piston motor. Thanks again guys.

 

Tim, what you said, does that apply to a dry kit too?

LB9GTA

 

some excellent info in this thread, definately put it on the bottle!

start out small and pull timing until you get comfortable.

HOSE IT HEAVY!

 

Yes, the difference with a dry system is the absense of the fuel solenoid - additional fuel is supplied by the fuel injectors. In this case reference the pressure switch that enables the nitrous solenoid to fuel rail pressure.