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Im building a 418 w 10.5:1 comp. 220 alum heads, victor jr with carb, want to make about 600rwhp and keep rpms limited to about 6500. Probly can do this with low boost, my q is run a bigger single turb or small twins. Thanks for input
 

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single!
 

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Lemme help you out a bit....your numbers of 600whp are low for a turbo 418 unless you plan on just running pump gas full time with the 10.5:1 compression

· Wa = Airflowactual (lb/min)
· HP = Horsepower Target (flywheel)
· = Air/Fuel Ratio
· = Brake Specific Fuel Consumption (lb/(Hpxhr)) ÷ 60 (to convert from hours to minutes)

· MAPreq = Manifold Absolute Pressure (psia) required to meet the horsepower target
· Wa = Airflowactual(lb/min)
· R = Gas Constant = 639.6
· Tm = Intake Manifold Temperature (degrees F)
· VE = Volumetric Efficiency
· N = Engine speed (RPM)
· Vd = engine displacement (Cubic Inches, convert from liters to CI by multiplying by 61.02, ex. 2.0 liters * 61.02 = 122 CI)


First calculate how much airflow you need the turbo to support (Wa. in lbs/min)
Wa= HP x target A/F x BSFC/60
600 x 11.5 x (0.55/60) = 63.25 lbs/min

Then calculate the amount of pressure needed to obtain the target amount of HP, minus sea level pressure (14.7psi).....(MAnifold Pressure)
MAP=Wa x R x (460 + Tm) divided by (VE x N/2 x Vd)
63.25 x 639.6 x (460 + 115) divided by (.90 x 6500/2 x 418)
= 23261452.5 divided by 1222650 = 19.025 - 14.7 = 4.32psi boost (assuming volumetric efficiency is 90%. It could be anywhere between 80-100%. Just find out what yours is and adjust the calculation)

Then add back pressure loss through the intercooler and piping which could be anywhere from 1-4lbs. Examples...(4.32+1= 5.32psi), (4.32+4=8.32psi)

So to get 600hp your going to need anywhere from 5.32-8.32psi (estimates) with a turbo that efficiently flows around 63.25 lbs/min. and having intake temperatures around 115 degrees

Now go and look at all different turbo compressor maps. Find all the turbos that are most efficient around 63 lbs/min. Then narrow it down to the one that is most efficient pushing between 5-9psi. That will allow you to make an educated selection on which turbo to go with
 

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you dont need a turbo to make 600 with a 418.

Just to give you an idea, my 428 ran 8.89/158mph with 15 psi and that was lifitng off the gas near the 1000ft. I figure it to be some where near 850-900FWHP and thats with an 88mm .96 AR T6 that everyone tells me is to small for my set up.

Im not going to bother going to a bigger single, its twins from here on out for me.
 
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