TurbochargedBerserker Posted May 4, 2005 Report Share Posted May 4, 2005 Math: Formula 1: CR = [{(B/2)^2 * S*Pi}+Vcc+Vp+{(B/2)^2*Pi*(DH+TG)}] [{(B/2)^2*Pi*(DH+TG)}+Vcc+Vp] Where: CR= Compression Ratio B = Cylinder bore (Stock LT1 = 4.00in) S = Stroke (Stock LT1 = 3.48in) Vcc= Combustion Chamber Volume (Stock LT1 = 58cc = 3.539 in3) Vp= Piston Volume (Stock LT1 = 4.5cc = 0.274606 in3) DH = Deck Height (Stock LT1 = 0.015 in) TG = Head Gasket Crush Thickness (Stock LT1 = 0.05 in) Pi = 3.1415 Formula 2: (I prefer this one) Compression Ratio = (GV+DV+HV-VV+PV) / (GV+DV+HV-VV) GV (Head Gasket Volume) = Bore(in) X Bore(in) X 12.87 X (Head Gasket Thickness in Inches) DV (Below Deck Volume) = Bore(in) X Bore(in) X 12.87 X (Inches Below the Deck) HV (Head Volume) = CC's VV (Dish, Valve Pocket, Dome Volume) = CC's (Minus for dish or valve pockets, Plus for dome) PV (Volume displaced by Piston) = Bore X Bore X Stroke X 12.87 Some links: Smokeup's CR Calculator Smokeup's Dynamic CR calculator Link to comment Share on other sites More sharing options...
Xero Posted May 4, 2005 Report Share Posted May 4, 2005 CR = [{(B/2)^2 * S*Pi}+Vcc+Vp+{(B/2)^2*Pi*(DH+TG)}] [{(B/2)^2*Pi*(DH+TG)}+Vcc+Vp] OW MY HEAD!!!!!!! Link to comment Share on other sites More sharing options...
LSR Mike Posted May 4, 2005 Report Share Posted May 4, 2005 Try some of these LSR formulas Formulas: The horsepower needed to overcome aerodynamic drag at a given speed is: HP = k*A*Cd*v^3 Where HP is horsepower, k is the density of air, A the frontal (cross-sectional) area, Cd the coefficient of drag, and v the velocity. The density of air depends on conditions but is nominally .08 lb/ft^3. Aerodynamic drag is calculated as: F = 1/2 CDAV^2 Where: F - Aerodynamic drag force, C - Coefficient of drag, D - Density of air (nominally about 0.08 pounds per cubic foot.. yes I know that's not a technically accurate mass but it saves converting to and then back from metric), A - Frontal area, V - Velocity of object displacement, stroke & bore: pi = 3.1415927 pi/4 = 0.7853982 cylinder volume = pi/4 x bore2 x stroke stroke = displacement / (pi/4 x bore2 x number of cylinders) piston speed: piston speed in fpm = stroke in inches x rpm / 6 rpm = piston speed in fpm x 6 / stroke in inches brake horsepower: Horsepower = rpm x torque / 5252 torque = 5252 x horsepower / rpm brake specific fuel consumption = fuel pounds per hour / brake horsepower bhp loss = elevation in feet / 1000 x 0.03 x bhp at sea level indicated horsepower & torque: horsepower = mep x displacement x rpm / 792,00 torque = mep x displacement / 150.8 mep = hp x 792,000 / displacement x rpm mep = hp x 792,000 / displacement x rpm mechanical efficiency = brake output / indicated output x 100 friction output = indicated output - brake output taxable horsepower = bore2 x cylinders / 2.5 air capacity & volumetric efficiency: theoretical cfm = rpm x displacement / 3456 volumetric efficiency = actual cfm / theoretical cfm x 100 street carb cfm = rpm x displacement / 3456 x 0.85 racing carb cfm = rpm x displacement / 3456 x 1.1 weight distribution: percent of weight on wheels = weight on wheels / overweight x 100 increased weight on wheels = [ distance of cg from wheels / wheelbase x weight ] + weight center of gravity: cg location behind front wheels = rear wheel weights / overall weight x wheelbase cg location off-center to heavy side = track / 2 - [ weight on light side / overall weight ] x track cg height = [ level wheelbase x raised wheelbase x added weight on scale / distance raised ] x overall weight g force & weight transfer: drive wheel torque = flywheel torque x first gear x final drive x 0.85 wheel thrust = drive wheel torque / rolling radius g = wheel thrust / weight weight transfer = weight x cg height / wheelbase x g lateral acceleration = 1.227 x radius / time2 lateral weight transfer = weight x cg height / wheel track x g centrifugal force = weight x g shift points: rpm after shift = ratio shift into / ratio shift from x rpm before shift drive-shaft torque = flywheel torque x transmission ratio instrument error: actual mph = 3600 / seconds per mile speedo error percent = difference between actual and indicated speed / actual speed x 100 indicated distance = odometer reading at finish - odometer reading at start odometer error percent = difference between actual and indicated distances / actual distance x 100 MPH RPM gears & tires: mph = rpm x tire diameter / gear ratio x 336 rpm = mph x gear ratio x 336 / tire diameter gear ratio = rpm x tire diameter / mph x 336 tire diameter = mph x gear ratio x 336 / rpm tire size & their effect: tire diameter = 2 x selection width x aspect ratio / 2540 + rim diameter effective ratio = old tire diameter / new tire diameter x original ratio actual mph = new tire diameter / old tire diameter x actual mph Simple Conversions: 1 inch = 25.4 mm 1 mm = 0.039371 inch 1 cubic inch = 16.387 cc's 1 liter = 1000 cc's = 61.024 cubic inches Liter to cubic inch conversion: 61.026 ci/L Link to comment Share on other sites More sharing options...
misterp Posted May 4, 2005 Report Share Posted May 4, 2005 Maybe just a rough-n-dirty GenIII bore/stroke vs head CC table? Link to comment Share on other sites More sharing options...
SuperSport Posted May 4, 2005 Report Share Posted May 4, 2005 Thanks for this thread guys, I was looking for some of these formula's Link to comment Share on other sites More sharing options...
2bseen Posted May 5, 2005 Report Share Posted May 5, 2005 My head hurts just reading this. Link to comment Share on other sites More sharing options...
04CHASE Posted April 24, 2006 Report Share Posted April 24, 2006 ok i did good in all my math classes but cant seem to find the #'s i need. i plan on doing a 408 (supercharged). going to port and polish the stock heads, or maybe a cheaper aftermarket head, patriots most likely, but im open to suggetions. i just need to know what cc pistons to go with to get 10-0-1 cr . thanks in advance! Link to comment Share on other sites More sharing options...
misterp Posted April 24, 2006 Report Share Posted April 24, 2006 ok i did good in all my math classes but cant seem to find the #'s i need. i plan on doing a 408 (supercharged). going to port and polish the stock heads, or maybe a cheaper aftermarket head, patriots most likely, but im open to suggetions. i just need to know what cc pistons to go with to get 10-0-1 cr . thanks in advance! <{POST_SNAPBACK}> Using the following figures: Stroke Length = 4.000 in Bore Diameter = 4.030 in Head Combustion Chamber Volume = 72 cc Head Gasket Thickness = 0.040 in Head Gasket Bore Diameter = 4.010 in Piston Deck Height = 0.000 in Piston Dish Volume = 13 cc Nominal CR = 9.96:1 Double-check my head gasket thickness number and piston deck heights, but that should get you very close. Mr. P. Link to comment Share on other sites More sharing options...
04CHASE Posted April 24, 2006 Report Share Posted April 24, 2006 ok i did good in all my math classes but cant seem to find the #'s i need. i plan on doing a 408 (supercharged). going to port and polish the stock heads, or maybe a cheaper aftermarket head, patriots most likely, but im open to suggetions. i just need to know what cc pistons to go with to get 10-0-1 cr . thanks in advance! <{POST_SNAPBACK}> Using the following figures: Stroke Length = 4.000 in Bore Diameter = 4.030 in Head Combustion Chamber Volume = 72 cc Head Gasket Thickness = 0.040 in Head Gasket Bore Diameter = 4.010 in Piston Deck Height = 0.000 in Piston Dish Volume = 13 cc Nominal CR = 9.96:1 Double-check my head gasket thickness number and piston deck heights, but that should get you very close. Mr. P. <{POST_SNAPBACK}> thanks mr p those were the # 's i was looking for! but will the head cc chanmer volume change once the heads are ported? Link to comment Share on other sites More sharing options...
misterp Posted April 24, 2006 Report Share Posted April 24, 2006 thanks mr p those were the # 's i was looking for! but will the head cc chanmer volume change once the heads are ported? Port work has no effect; you loose head CCs if the deck surface is remachined. Every machine shop should have a burette and be able to tell you the actual measured chamber volume post-machining. Mr. P. FYI - resurfacing the deck also directly affects the intake manifold seal as well, you are making the 'V' between banks wider by the amount being removed from the deck. Surfacing to excess will require additional corrective machining to prevent vacuum leaks between the intake manifold and head. Link to comment Share on other sites More sharing options...
TurbochargedBerserker Posted April 27, 2006 Author Report Share Posted April 27, 2006 Piston deck height is -0.008 If you are using MLS gaskets, the compressed thickness is 0.058, but you need to pick a gasket to get this number locked in. Link to comment Share on other sites More sharing options...
misterp Posted April 27, 2006 Report Share Posted April 27, 2006 Piston deck height is -0.008 If you are using MLS gaskets, the compressed thickness is 0.058, but you need to pick a gasket to get this number locked in. <{POST_SNAPBACK}> I plugged in those numbers and wow that extra .010" of gasket makes more difference that I imagined, dropping the CR to 9.6:1; if using that gasket you need to reduce Piston Dish Volume to 9cc to maintain 10:1 CR (assuming 72cc head). Mr. P. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.