Stock short block L98. Heads up have all been redone. The short block has about 100,000 miles on it. Good compression in all cylinders and 50 psi oil when warm.

Head gaskets are steel and ARP head bolts.

Do you think it will last on a 150 hp shot of nitrous?


I have seen some guys running 6psi or more on high milage blocks here, just wondering if this will hold up, with the motor tuned for the spray.

100 hp for sure

Set up right, you're motor should take a 150 shot without breaking. You may very well shorten the life of the motor some, though. How much, no-one can say. I put a 100 shot on my 305 at about 60K mi. and ran it for about a year. Probably ran 75-100 bottles through the motor. Now, 5 years later, it's still getting me to work and back every day without significant motor problems. At 130K it's not going to win many races, though, and could stand to be replaced.

The nitrous is more likely to kill your drivetrain. GM has never been very strong from the flywheel back. My stock 700r4 folded under the load shortly after I put the squeeze on. Pity the poor T-5 that gets it. Rears on these cars are nothing too tough either. Slicks are cyanide to these babies.

Pull your valve covers and re-torque your heads first. Years of heat cycling can loosen bolts a tad, and gaskets compress a bit over time too. You need the best head seal you can get to contain the added pressure you're about to put into it. Nitrous will slice through your block and head like a cutting torch if you blow a head gasket during a run. Personally, I'd pull the pan and torque the rods & mains too, but that's just me.

Do everything you can to avoid a lean condition on the spray. Good fuel pump, good fuel filter, brand name solenoids in good condition. Never use questionable solenoids. You'll lose a good motor FAST if you get lean. Learn to read plugs and do it often for the first few bottles. I always run nitrous systems a little on the fat side just to keep everything relatively cool.

Also, think about a dedicated fuel system using alcohol instead of gasoline. Alcohol burns cold and running fat won't slow you down. Running alcohol for enrichment has many advantages over gasoline. NOS can help you with jetting. You've got to run about twice as much alchohol as you do gas. You'll need a nitro/alky solenoid as well as an alcohol fuel pump.

Nitrous is a blast, but it's kinda like a land mine too. Keep a close eye on it and you'll be alright, forget about it, and you might lose parts.

Heads have been off. Fresh, ARP bolts.


I am planning on its own fuel cell and pump.

Does it matter if I use a low pressure pump (carb type) or high pressure (efi) for the fuel? As long as its jetted properly, does it matter?

Does alcohol have any effect on the O2 sensor and the cat?

Your cat? What cat? Don't worry about him, he won't be there for long.

O2 sensors also don't like alky.

Even though you've just had the heads off, I'd pick a few easy-to-access head bolts and re-check the torque. Composition head gaskets will compress quite a bit soon after installation. If they check OK, then go on with the n2o install. I've had a gasket give out during a run with less than desirable consequences. The motor was very low time when it happened. Anyway, food for thought.


I 've run high and low pressure fuel systems with nitrous and had good results with both. NOS can get you into the ballpark with jetting based on your fuel pressure and desired power gains, but you still need to watch your plugs to be on the safe side. You can fine tune the system by jacking with the fuel pressure if you put a regulator in the line (which you should).


I've not run alcohol on my iroc, so I can't speak for how the sensors and/or converter would react. Bummer if it won't work. At least with the dedicated system, you can use the best race gas available for enrichment without breaking the bank.

SO, would you recomend high or low pressure?


And the head gaskets are steel, not composite, and have less than 10 miles on them since the top end was put back together, with ARP bolts.

$hit, go for 200hp shot. By the way, my car has the original 10 bolt rear end with 3.23 and stock limited slip with 178,000 miles on it. It's still holding up.

When the new engine is ready, i'll spray 200, maybe more, see what it will handle. The new motor will handle a 250, and will likely see a lot of 200 hits, but till then the stock block has to stay together.

I run a holley blue for the spray.

It's generally cheaper and less hassle to go with a low pressure setup. A Holley blue pump is cheap and reliable, and, I assume, still comes with a little regulator. Don't go cheap on a fuel filter. Run the best fuel filter you can afford between the pump and the solenoid. A tiny bit of crap stuck in your solenoid can cause big headaches.

Consider completely assembling your system and pumping fuel through it for a couple of minutes while watching the spraybar to ensure there is nothing in the system to plug up one of those tiny little holes. You might even install the system while its still assembled. In my experience, the number one contaminant in a n2o fuel system is stray teflon tape particles left over from someones disassembling and re-assembling their system.

With a lower pressure system, I keep the fuel solenoid as close to the manifold as I can. Both solenoids open at the same time, but the nitrous, under 900lbs of pressure, will get into the motor before the fuel, under 12lbs. Of course, the difference in these times of fuel/nitrous entry, is the period where the motor runs extremely lean. Lean means heat and possibly detonation. You've never heard detonation like you can get with nitrous. I can't emphasize enough how fast a motor can melt down when things go wrong on this stuff.

One nice thing about the little blue Holley regulators is that they tend to 'creep'. Just sitting with the pump running, pressure through the regulator, to the solenoid, will creep up to full pump pressure in just a couple of minutes regardless of regulator setting. Follow me? This gives you a short burst of full pump pressure into the spraybar when the solenoid opens. This is good in that it will richen, and therefore soften, the initial hit up a bit.

I'd encourage you NOT to jet any larger than whatever NOS recommends to get your 150 shot. A 150 shot on a stone stock SBC is pushing your luck a bit anyway. A reliable 200 shot on a stock SBC is possible, but you'd better have your sh*t together, and shell out for every nitrous safety device available. You'll never find a manufacturer that will recommend this level on a stock piston/rod combination.