I was talking to a guy at the racetrack last night and he was talking good stuff. Based on his combo, 350 30 over 9 to 1 compression and a 234 intake 246 exhaust cam and Long tubes ina Camaro, he said with 12 pounds of boost, 700rwhp was possible and close to 900 rwhp with 16lbs. I know boost can get some nice numbers, but is this possible? Any real numbers out there with these boost numbers and similiar combos?

 

My buddy's C5 has about 9 lbs of boost and he dynoed at 450 at the rear wheels.

 

Forced induction can make some serious power. A friend of mine has a 5.0 mustang with a 221/225 duration, .499/.510 lift, 112 lobe seperation, some really nice heads and an intake, headers as well. He's running about 10 pounds of boost from a vortech s/c and running well over 400 hp.

He had the car on the dyno and it wasn't tuned properly and he made 400 at 5000 rpm's. He spins the car to 6000 but since the wide band wasn't working that day he let off so as to not blow anything up. With his tune nailed down I'm sure he's making close to 500. Now that's a Ford 5.0, just imagine what more displacement and a little more boost would do. :reddevil

 

Ok. so here's the theory if you're interested. We live under 14.2 PSI of pressure, or 1 atmosphere or 1 bar. That is the ambient pressure going into a wide open manifold if the car is normally aspriated. On a boost gauge this would show as zero boost. Imagine then the car creates 300 hp under these conditions. (The modifications don't matter to boost theory. Things like compression, stroke, cubic inches, etc. only make a difference to the builder not the compressor we are using.) Theoretically if you add to the car 14.2 psi of additional boost, whether it be a supercharger or turbocharger the power ouptut will increase by 2. Thus 600 horses could be made. I say theorectically b/c power adders cause parisitic drag. Superchargers while operating actually eat between 60 and 100 hp while creating that sort of boost, while turbos take between 10 and 20 to create those numbers. That is power you pay for (i.e. your fuel consumption would be for increased by that much) but you wouldn't see it at the wheels. So, to calculate the maximum power for a particular engine boost combo use a proportion. 14.2/300 = 28.4/x in this case x=600 but if you change the second boost number to 26.2 or 12 psi of boost, you'd get 14.2/300=26.2/x in this case x=553 hp Remember now to subtract the parasitic loss from the ower adder. Use 10 for turbos and 60 for superchargers at these boost levels. They decrease as you lighten the boost though. Follow this theory and you can make a pretty safe estimation of what the power would be. A well built small block with 14 pounds of boost could make between 700 and 800 hp depending on the type of machine producing boost. Move that number to 19 and see the numbers jump substantially.
I used to go to the tractor pulls and guys would run what they call smokers. Diesel tractors with such low compression that they would hardly run (probably made around 60 hp), then 4 turbos later and up to 200 lbs of boost the thing sounded like a jet taking off and made in the range of 3000+hp. I am not sure the theory holds true when you get this much boost, but they used 15 gallons of fuel in 300 ft.
Have a nice day.
Shanon

 

Theory is interesting, here's the math.
345 hp stock X 16% loss due to drivetrain = 55 loss
290 hp at the rears stock.
14.2/290=23.2/x = 473 hp (the 23.2 is equivalent to 9 psi, read why above.)
473 hp, then subtract rougly 30 hp parisitic loss estimate for power adder = 443 hp at the rears. Pretty close. See, it does work.
Shanon

EDIT clarification


[Modified by fueljeta, 10:26 AM 3/16/2003]

 

I was looking at the combo he was talking about and making 900 RWHP. No way can that be done with the combo spoken of. IMHO.
Hey thanks for the writ eup, that helps dispel allot of myths of supercharging etc.

 

i'll have to demur. 700rwhp is considerable, and not achievable on pump gas with an engine like this. even with race gas, we're talking about a considerable effort in matching the combination of heads, cam, exhaust, fuel system, tuning, and a shortblock that can handle it.

the formula put forth ignores any thermodynamic effect, which is considerable. 14.7psi on a bone stock engine won't get you even close to 600hp, too much is lost in heat. (increase pressure, hold volume constant, and increase temperature, pV=NkT tells you the number of molecules drops, since the temps rise disproportionately from both the efficiency level of the impeller, and from the heat transfered directly from the case. fewer molecules = less hp.)



[Modified by MSR, 11:50 PM 3/16/2003]

 

Its actually 14.7 PSI for the atmosphere and 14.5 PSI for BAR, anyways, what you said is all theory because boost is measure of pressure (e.g. PSI or BAR) and what really counts is the amount of air that you put into the engine, (i.e. air flow or volume) this one in term determines what the HP will be given that there is a good tune.
So why doesnt boost/pressure is a good measure, do you ask? Because its just the intensity of the air at that particular location. (e.g. you have a 195cc heads, and then you decide get better flowing heads and you buy a set of 225cc heads, well you crank your engine and the boost gage will show less boost but in fact your engine is performing better. Remember, to have a lot of pressure it is best to be in an enclosed area and not in high flowing area.
Therefore BOOST doesnt mean nothing because different compressors provide different boost levels at different flow #s. Oh and BTW it is not so linear like you did above 1 bar doesnt double the power (per say)

Later