Thermal loads are
why 1.5 times the existing power level is the practical limit. It's related to the 34% oxgen atmosphere that nitrous gives. In practice, its like a blow torch, and even if you use Heanium coated forged pistons, over that level, the engine will run into detonation. First the spark plugs, then the top of the piston or ring lands. It's 'MC Hammer' time then. There is not much of a treashold.
From Hot Rods tech articles:
One point often overlooked with nitrous and blowers is the massive torque gain realized through either power enhancer. While a budget nitrous kit might only add 125 peak horsepower, it will be worth a 50 percent power increase at peak torque. If the engine makes 300 lb-ft of peak torque, the nitrous will instantly make that jump to 450 lb-ft or more. You’ll feel that!
The common by-product of cylinder pressure is detonation. Detonation starts on any sharp edge or crevice and, with enough pressure (and heat), this will be the result. Also, while moving the top ring upward on the piston makes better power, it reduces the mass of aluminum that absorbs pounding and heat and can mean piston or ring-land failure. Serious nitrous engines should have the top ring lowered on the piston to help the piston dissipate heat and keep the rings cooler. Hedgecock adds that thin-wall piston wristpins will fail in nitrous engines and should not be used. Gianino uses tapered-wall, tool-steel pins.
The increase in torque and power was noted in Hot Rods landmark December 2002 artical on page 66. It covered a 359 cube SBC with a 750 cfm carb in three stages of trim. Bore was 4.04, stroke 3.5, comp ratio 9.74, running 35 BTDC with a dual plane and 91 octane (US mon+ron/2). I must stress, this was a nitrous cam engine. If you use a non nitrous cam, the power on nitrous may be less.
Stage 1:
Dual Plane, 235/240 at 50 thou nitrous cam
445.8 lb-ft at 4500 rpm.
461.4 bhp at 6300 rpm.
Stage 2
Single plane, 114 octane
454.8lb-ft at 4500 rpm
457.6 bhp at 6400 rpm
Stage 3
Single plane #7530 Weiand G-team manifold, 114 octane, 28 BTDC, 8 Nossle Fogger with 28 N20 jets, and 32 gasoline. 900-925 psi N20, 6 psi gasoline auxilary supply to fogger nossels
670.1 lb-ft at 5300 rpm
679.0 bhp at
5400 rpm, not 6400 rpm.
1.47 times stock power, with an 18% drop in peak rpm. 1000 rpm less!
This is info 21 st century style. According to my reference material which was repeated in three of David Vizards 1980's books on Mini A-series, Ford Pinto SOHC, and SmallBlock Chev's, there is a reduction on the power peak speed, with a huge increase in power. The n20 kicks in as a violent increase in torque at whatever rpm it is invoked. You may bend rods below 2500 rpm, or take 1.5 seconds off your quarter mile time.
A nitrous engine will
need taller rear end gears, but will have a lower engine speed through the traps if the advantage is taken of the idealized rpm.
Example is the stage 1 engine with 461 hp at 6400 rpm, red lining through the traps at perhaps 6900 rpm in 4000 pound 67 Chevy Imapala with 26 inch slicks.
Gears are 4.56:1, quarter mile 12.0 secs at 114 mph.
With the Stage 3 engine with 679 hp at 5400 rpm in that same Chev, ideal change-up is about 5800 rpm. So doing the idealised Moroso dreamwheel, you'd be looking at 10.5 sec quarter at 130 mph. The ideal gear ratio? 3.42:1!
See? The bearing loads will be huge, but the engine will be under less stress even at 10.5secs, as the engine is down 1100 rpm and optimised to produce power down low.
We have had good luck with our system and a lot of fun.
