Draco1340
Registered
OK, so I intentionally want to stir the pot on this post and get some new views on the pros and cons of Dry nitrous and spray bars, but I do think they are grossly flawed and this is why.
First, I will readily admit that a bar will make more HP than a well designed fog system. If I spray 15 ounces of spray during a pass, I will definitely make more power with a bar. Fogging the box makes power by dropping the temperature (and thus the density of the total charge), and it makes power by adding 33% O2 in place of 20.9% O2. Spray bars make power using these two methods, but they also use phase change. A well designed bar can shoot liquid at or past the valve, allowing MUCH more liquid 33% O2 into the chamber. So, I readily admit that bars can make more power. Its a fact.
Here is the problem. If you have a bar, its because you want a big hit. You shouldn't waste your money on a 30 or 40 shot. You can easily fog for that small amount. Lets say you build a motor to take a 100 shot with your bar. This means you have to progressively launch the spray through your bar. You can't leave the line with a 300 shot (at least not without bars and a 10 inch slick). You can't turn it on in second gear. Hell, a 100 shot will blow you over. It needs to be progressively launched, and this is were things start to get hard on your parts. The intake valves are opening almost 100 times a second. 11k RPM /60 / 2 = 92 Hz. The nitrous solenoid operates at 25 Hz. That 1/4 the frequency of the intake valve. This means sometimes the valve opens and sees enormous amounts of liquid nitrous squirting down the pipe, and sometimes is sees almost none. During the time that you progressively ramp from say 40% to 100%, your motor is slamming back and forth between super lean and super rich. But your O2 sensor in the tail pipe is just averaging everything out between all of the cylinders and all of the firing. Most loggers (like my Innovate) only collect data at 25 Hz, so you will never see this rich lean condition.
But this is the reason why nitrous has such a bad reputation as being tough on motors. If you only shoot a 40 or 50 shot, it probably doesn't make a difference. If you don't progressively ramp your shot (like many land speed guys), you won't have a problem. But, If you have a 100 shot and you ramp the shot the whole length of the track, you will beat the hell out of your motor. Mini detonation beat the ring lands, wrist pins, and rod bearing. The extra torsional vibration on the crank from running rich / lean cracks cranks. A good fogging system isn't affected by the nitrous solenoid clacking along at 25 Hz. They cylinders see a smooth ramp of increasing N2O gas.
My Gen II motor had almost 2000 passes on stock rods, crank, pistons with a progressive 80 - 100 Shot through a fogger. When I took it apart, The rod bearings looked brand new, and the roundness of the big end was better than a tenth. The wrist pins had almost no wear at the point they contact the little end. The pistons and ring lands had no sign of detonation. People will tell you you can't run 300 hp on stock rods with spray, but it can be done. I just wouldn't do it with a spray bar.
I know this argument tends to boil down to a Chevy vs. Ford argument, but I wanted to add some engineering reasons behind fogging.
First, I will readily admit that a bar will make more HP than a well designed fog system. If I spray 15 ounces of spray during a pass, I will definitely make more power with a bar. Fogging the box makes power by dropping the temperature (and thus the density of the total charge), and it makes power by adding 33% O2 in place of 20.9% O2. Spray bars make power using these two methods, but they also use phase change. A well designed bar can shoot liquid at or past the valve, allowing MUCH more liquid 33% O2 into the chamber. So, I readily admit that bars can make more power. Its a fact.
Here is the problem. If you have a bar, its because you want a big hit. You shouldn't waste your money on a 30 or 40 shot. You can easily fog for that small amount. Lets say you build a motor to take a 100 shot with your bar. This means you have to progressively launch the spray through your bar. You can't leave the line with a 300 shot (at least not without bars and a 10 inch slick). You can't turn it on in second gear. Hell, a 100 shot will blow you over. It needs to be progressively launched, and this is were things start to get hard on your parts. The intake valves are opening almost 100 times a second. 11k RPM /60 / 2 = 92 Hz. The nitrous solenoid operates at 25 Hz. That 1/4 the frequency of the intake valve. This means sometimes the valve opens and sees enormous amounts of liquid nitrous squirting down the pipe, and sometimes is sees almost none. During the time that you progressively ramp from say 40% to 100%, your motor is slamming back and forth between super lean and super rich. But your O2 sensor in the tail pipe is just averaging everything out between all of the cylinders and all of the firing. Most loggers (like my Innovate) only collect data at 25 Hz, so you will never see this rich lean condition.
But this is the reason why nitrous has such a bad reputation as being tough on motors. If you only shoot a 40 or 50 shot, it probably doesn't make a difference. If you don't progressively ramp your shot (like many land speed guys), you won't have a problem. But, If you have a 100 shot and you ramp the shot the whole length of the track, you will beat the hell out of your motor. Mini detonation beat the ring lands, wrist pins, and rod bearing. The extra torsional vibration on the crank from running rich / lean cracks cranks. A good fogging system isn't affected by the nitrous solenoid clacking along at 25 Hz. They cylinders see a smooth ramp of increasing N2O gas.
My Gen II motor had almost 2000 passes on stock rods, crank, pistons with a progressive 80 - 100 Shot through a fogger. When I took it apart, The rod bearings looked brand new, and the roundness of the big end was better than a tenth. The wrist pins had almost no wear at the point they contact the little end. The pistons and ring lands had no sign of detonation. People will tell you you can't run 300 hp on stock rods with spray, but it can be done. I just wouldn't do it with a spray bar.
I know this argument tends to boil down to a Chevy vs. Ford argument, but I wanted to add some engineering reasons behind fogging.