Table Of Contents
Introduction Typical custom 2275cc engine
Overview General information
Engine Origin & HP Serial number cross referance iwth rated HP
Reduction Thrust Typical reduction drive thrust
Engine Displacement Displacement of bore & stroke combinations
Deck volume Volume of deck height & bore combinations
Compression Ratio Compression using vol, deck, disp combinations
Volumetric EfficiencyApproximate engine efficiency
Engine CFM Carburetor intake CFM
Engine Limits Recommended settings and limits
Maintenance Recomended service periods
Fastener Torque Nut & bolts torque specs
Conversion Tables Common specifications

Introduction

An air cooled VW engine rotates about 205 million times in 1000hrs of flight. If the engine is not treated with care during each of those rotations, it won't see the expected longevity and we may not keep the airplane in the air. This document provides common formulas, tables, and data needed to estimate realistic performance and safely operate the engine.

Other Links
MS Excel spread sheet to calculate engine horse power is imagehere.
An example of a highly modified 200hp 2275cc build specification is imagehere.
Dyno data: 82mm stroke x 90mm bore 2000cc, 100hp@4000rpm is imagehere.

Custom Engine

This is the specification for a proven moderate 220hp@5000rpm 2276cc using a stroke of 82mm and 94mm bore. This particular engine has been replicated many times by sand rail operators. I estimate that using a stock cam and a more conservative carburetor could result in 140hp@4000rpm.

Of course this type of power from a VW requires extreme detail to cooling issues such as a full flow large oil cooler, 10mm oil galleys, etc.

      1.  82x94 (2276cc) medium state of tune. 8 to 1 compression
      2.  Pistons - 94mm Cima 
      3.  Rods - 82mm welded stroker stock relieved VW 
      4.  Flywheel - 14+lb 
      5.  Cam - 120 (295dur x .495lift w/ 1.25 rockers)
      6.  Rocker - Solid shaft 
      7.  Pushrods - 3/8 thin-wall chromoly 
      8.  studs - 8 mm chromoly head 
      9.  Heads - 040 stock VW castings, un-shrouded chambers w/ hemicut
      10. Valves - 40x37.5  fully ported (as big as you can go without welding)
                   competition valve job, stainless steel valves, dual springs, titanium 
                   retainers, tapered intake guides, intake guide bosses NOT removed
      13. Intake manifolds - match-ported all the way up
      14. Carburetor - 48 Dellortos or 48 IDFs will work fine too
          IDF manifolds are the 1st choice. The best ones are from Gene Berg, but they  
          are a pain to install because they are shorter. Other manufactures that are 
          slightly taller than the Bergs are easier to install, but they have a 
          tendency to break at the flanges. Installation is easier if you use 11mm nuts 
          with thick washers.
      17. Muffler - 2-1/2" turbo
      18. Exhaust header - 1-5/8" 
          
      
image image

Cylinder, bearing, and distributor arrangement.

image

Horse Power

The horsepower rating of a normally aspirated VW engine at least 1300cc or larger can accurately be calculated for a specific rpm. The specifications of most VW conversion manufactures was plotted on a horsepower vs. displacement chart and it was found that a straight line coincidence exists.

The formula is not applicable if a turbocharger, a PSRU, or custom cam is used. The formulas used here can only be used for a single rpm, plus or minus one or two hundred rpm difference. Additionally, differences in propellers, carburetors, exhaust systems, fuel type, and accessories did not cause a deviation of more than 10%.

3400 rpm
HP = Disp(cc) / 30
or
Disp(cc) = HP x 30

For 5000 rpm we must use a offset straight line equation:

5000 rpm
HP = .085 x Disp(cc) - 63.17
or
Disp(cc) = 11.7 x HP + 756

These HP estimates are applicable for both full VW and 1/2 VW engines. As an example, the power at 3400 rpm for a "1600cc" is calculated to be (1585/30) 53 hp. The data for this conversion is 48-58hp.

Examples (full vw):
44hp = 77mm bore x 69mm stroke (1300cc) @ 3400 rpm
50hp = 83mm bore x 69mm stroke (1500cc) @ 3400 rpm
53hp = 85.5mm bore x 69mm stroke (1600cc) @ 3400 rpm
64hp = 92mm bore x 69mm stroke (1915cc) @ 3400 rpm
72hp = 92mm bore x 82mm stroke (2180cc) @ 3400 rpm
76hp = 94mm bore x 86mm stroke (2280cc) @ 3400 rpm


Examples (1/2 vw):
28hp = 88mm bore x 69mm stroke (840cc) @ 3400 rpm
32hp = 92mm bore x 69mm stroke (920cc) @ 3400 rpm
37hp = 92mm bore x 78mm stroke (1040cc) @ 3400 rpm
40hp = 92mm bore x 82mm stroke (1140cc) @ 3400 rpm
45hp = 94mm bore x 86mm stroke (1200cc) @ 3400 rpm


image

Approximate BHP horsepower at 5000 rpm.


image

Horsepower and torque chart.


image

Horsepower and weight chart.

Engine Origin & Stock Rated HP


TYPE - 1 (Beetle) TYPE - 2 (Transporter)
YEAR START ENGINE CAPACITY RATED HP YEAR START ENGINE CAPACITY RATED HP
1978 AJ-0-119-668 1600cc 48 1978 GE-0-007-083 2000cc 70
1977 AJ-0-095-936 1600cc 48 1977 GE-0-000-001 2000cc 70
1976 AJ-0-012-406 1600cc 48 1976 GD-0-000-001 2000cc 70
1975 AJ-0-000-001 1600cc 48 1975 ED-0-000-640 1800cc 70
1974 AK-0-239-365 1600cc 48 1974 CB-0-101-139 1800cc 66
1973 AK-0-000-001 1600cc 48 1973 CD-0-000-001 1800cc 62
1972 AE-0-558-001 1600cc 60 1972 CB-0-000-001 1700cc 66
1971 AE-0-000-001 1600cc 60 1971 AE-0-000-001 1600cc 57
1970 B-6-000-001 1600cc 57 1970 B-5-116-437 1600cc 57
1969 H-5-414-586 1600cc 57 1969 B-5-050-174 1600cc 57
1968 H-5-000-001 1500cc 53 1968 B-5-000-000 1600cc 57
1967 H-0-204-001 1500cc 53 1967 H-0-183-373 1500cc 53
1966 F-0-000-001 1300cc 50 1966 H-0-000-001 1500cc 53
1965 8-796-623 1200cc 40 1965 8-713-768 1200cc 40
1964 7-893-119 1200cc 40 1964 7-143-543 1200cc 40
1963 6-935-204 1200cc 40 1963 6-914-251 1200cc 40
1962 5-985-948 1200cc 40 1962 5-979-934 1200cc 40
1961 5-000-001 1200cc 40 1961 5-000-001 1200cc 40
1960 3-072-320 1200cc 40 1960 3-400-000 1200cc 40
Engines earlier than 1960 are different than those discussed on this website and therefore will not be included in this table.


Typical Reduction Drive Thrust


Thrust - 2200(cc)@3800(rpm)
ConfigurationThrust
1:1 with 62 inch prop215 lbs
1.6:1 72 inch prop350 lbs.
2:1 84 inch prop450 lbs.


Note: A 1600(cc) VW engine is rated at 81(ft/lb) at 2400(rpm).

4 Cylinder Engine Displacement


VW Engine Displacement
Bore →
Stroke ↓
77 83 85.5 87 88 90 90.5 92 94 96.5 101.6 103 105
64mm 1192 1385 1470 1522 1557 1776 1647 1702 1777 1872 2075 2133 2217
69mm 1286 1493 1585 1640 1680 1756 1775 1835 1915 2018 2238 2300 2390
71mm 1322 1537 1630 1690 1727 1807 1827 1890 1970 2077 2300 2365 2550
74mm 1378 1602 1700 1760 1800 1883 1905 1968 2055 2165 2400 2465 2563
78mm 1460 1688 1790 1855 1897 1985 2007 2075 2165 2280 2530 2600 2700
80mm 1490 1731 1837 1900 1945 2036 2060 2127 2220 2340 2595 2665 2770
82mm 1527 1775 1883 1950 1995 2087 2110 2180 2275 2400 2660 2733 2840
84mm 1565 1818 1930 1997 2045 2138 2160 2235 2330 2457 2725 2800 2910
86mm 1602 1861 1975 2045 2093 2188 2213 2287 2387 2515 2790 2865 2980
88mm 1639 1905 2020 2093 2140 2239 2265 2340 2443 2575 2855 2933 3050
90mm 1676 1948 2067 2140 2239 2290 2315 2393 2500 2633 2920 3000 3117

Engine Displacement

Bore 2 x Stroke x .0031416  =  (cc)  

Formula: Engine Displacement (CC's)
Displacement(cc) = BORE(mm) x BORE(mm) x STROKE(mm) x .0031416

Example: 87(mm) x 87(mm) x 69(mm) x .0031416 = 1641(cc)

To get the volume for one (1) cylinder in (cc), divide by four (4).

Example: 1641(cc) / 4 = 410.25(cc)

2 Cylinder (1/2 VW) Engine Displacement

Examples (1/2 vw):
28hp = 88mm bore x 69mm stroke (840cc) @ 3400 rpm
32hp = 92mm bore x 69mm stroke (920cc) @ 3400 rpm
37hp = 92mm bore x 78mm stroke (1040cc) @ 3400 rpm
40hp = 92mm bore x 82mm stroke (1140cc) @ 3400 rpm
45hp = 94mm bore x 86mm stroke (1200cc) @ 3400 rpm


1/2 VW Engine Displacement
Bore →
Stroke ↓
77 83 85.5 87 88 90 90.5 92 94 96.5 101.6 103 105
64mm 596 693 735 761 779 888 824 851 889 936 1038 1067 1109
69mm 643 747 793 820 840 878 888 918 958 1009 1119 1150 1195
71mm 661 769 815 845 864 904 914 945 985 1039 1150 1183 1275
74mm 689 801 850 880 900 942 953 984 1028 1083 1200 1233 1282
78mm 730 844 895 928 949 993 1004 1038 1083 1140 1265 1300 1350
80mm 745 866 919 950 973 1018 1030 1064 1110 1170 1298 1333 1385
82mm 764 888 942 975 998 1044 1055 1090 1138 1200 1330 1367 1420
84mm 783 909 965 999 1023 1069 1080 1118 1165 1229 1363 1400 1455
86mm 801 931 988 1023 1047 1094 1107 1144 1194 1258 1395 1433 1490
88mm 820 953 1010 1047 1070 1120 1133 1170 1222 1288 1428 1467 1525
90mm 838 974 1034 1070 1120 1145 1158 1197 1250 1317 1460 1500 1559

1/2 VW Engine Displacement

Bore 2 x Stroke x .0015708  =  (cc)  

Formula: Engine Displacement (CC's)
Displacement(cc) = BORE(mm) x BORE(mm) x STROKE(mm) x .0015708

Example: 87(mm) x 87(mm) x 69(mm) x .0015708 = 820(cc)

To get the volume for one (1) cylinder in (cc), divide by two (2).

Example: 1641(cc) / 2 = 410(cc)

Deck Volume


image

Measuring deck height.

DECK HEIGHT(mm)
PISTON SIZE(mm)
85.5 87 88 90.5 92 94
Deck Volume(cc)
.030" 4.36 4.51 4.62 4.88 5.04 5.27
.035" 5.16 5.34 5.47 5.78 5.97 6.24
.040" 5.79 6.00 6.13 6.49 6.71 7.00
.045" 6.71 6.54 7.11 7.52 7.77 8.11
.050" 7.28 6.95 7.72 8.16 8.43 8.80
.055" 8.03 8.31 8.51 9.00 9.30 9.71
.060" 8.72 9.03 9.24 9.77 10.09 10.54
.065" 9.46 9.80 10.03 10.60 10.96 11.44
.070" 10.15 10.51 10.75 11.37 11.76 12.27
.075" 10.90 11.28 11.55 12.21 12.62 13.17
.080" 11.64 12.06 12.34 13.05 13.48 14.08
.085" 12.33 12.77 13.06 13.82 14.28 14.91

Deck Volume

Bore 2 * Height * .01996  =  (cc)  

Formula: Deck Volume(cc)
BORE(mm) x BORE(mm) x DECK HEIGHT(in) x .01996 = Deck Volume

Example: 87(mm) X 87(mm) x .060"(in) x .01996 = 9.06(cc)

BORE(in) x BORE(in) x DECK HEIGHT(in) x 12.87 = Deck Volume

Example: 3.425(in) x 3.425(in) x .060(in) x 12.87 = 9.06(cc)

Compression Ratio (CR)

image

Measuring head volume.

O pinions on CR differ, but most agree that higher CR generally yields higher horsepower (HP). If it was safe to run high CRs while maintaining the engine's longevity, EVERYONE WOULD BE DOING IT - and there would be little debate.

The 1945 original VW engine had a 5.8:1 ratio. From 1950 to 1991 the compression ratio was incrementally increased from 6.1:1 to 7.0:1.

High compression engines will typically run significantly higher operating temps. High temps can spell disaster in a hurry especially if you live in warmer climates. High CR engines usually require higher octane fuel to prevent pre-ignition (knocking and pinging).

What is debated, is the safe compression ratio to run. Gene Berg, Hummel Engines, Aerovee, and other respected folks recommend between 7.0:1 to 8.0:1. That should enable it to survive on the low-grade pump gas that is available today while still giving good usable power without overheating. Some folks are flying VW's at 8.5:1 by using aviation or premium gas.

Deck Height: With the piston at TDC, the distance between the top of the piston and base of the head.

1 Cyl Volume: Total engine displacment divided by number of cylinders.

Head Volume: Head volume is measured by placing a Plexiglass sheet over the head and measuring the amount of fluid that is required to fill the combustion chamber of the head.

Compression Ratio Formula:
[HEAD(cc) + DECK(cc) + 1 CYL_VOLUME]  /  [HEAD(cc) + DECK(cc)] = CR

Example: [50(cc) + 9.06(cc) + 410.25(cc)]  /  [50(cc) + 9.06(cc)]  =  7.95 OR 7.95:1

Compression Ratio


[ HEAD(cc) + DECK(cc) + CYL_VOL(cc) ]
------------------------------------------------------------------------------  = 
          [ HEAD(cc) + DECK(cc) ]

Note: cyl_vol is for single cylinder.


Volumetric Efficiency

The actual amount of air an engine ingests compared to the theoretical maximum is called volumetric efficiency (VE). It is the ratio (or percentage) of the quantity of air that is trapped by the cylinder during induction over the swept volume of the cylinder under static conditions.

If the engine were perfect it would have 100% efficiency but factors such manifold pressure drop and friction cause less than the ideal amount of air to be drawn in to the cylinders. High performance engines may reach close to 90% or higher, but most engines will be 70-80%.

A carburated engine normally has a volumetric efficiency of 0.70 to 0.80, but the electronics can raise this figure as high as 2.0. A diesel engine (2 cycle or 4 cycle) normally has a volumetric efficiency of 0.90. A turbo can raise the volumetric efficiency to between 1.5 and 3.0. If you don’t know this value for your turbo, it is best to use 3.0.

Typical volumetric efficiency:
 stock engine = .75 (75%)
 modified street engine = .85 (85%)
 racing engine = .90 (90%)

We general assume that aircraft engines have the same attention to detail as a modified street engine so ve=.85 is reasonable.

The formula for volumetric efficiency is... VE = (56633.7 * CFM) / (CC * RPM)

Example: (56633.7 * 100cfm)  /  (2175cc + 3800rpm)  =  .69ve

Note: The formula for US units is... VE = (3456 * CFM) / (CID * RPM)

Volumetric Efficiency


(56633 * CFM ) /  (CC  *  RPM ) = 


Engine CFM

An engine will not run efficiently if the components are not matched to the overall requirements of an engine. A very good approximation of the cubic feet per minute (CFM) that a carburetor should be rated can be found by using a engines maximum rated HP. The rule of thumb for gasoline engines is 150cfm for each 100hp. (diesel is 160cfm per 100hp)

A slightly more accurate way to determine the proper cfm rating of a carb is to calculate the airflow that will be sucked in using engine displacement and rpm. This method is shown below.

Formula

The formula to determine airflow for a 4 cycle engine is rpm multiplied by displacement divided by 2 (because the engine displaces half its overall capacity each intake stroke). The resulting number is then converted from cubic inches into cubic feet by dividing by 1,728 (cubic inches per cubic foot).

There is one additional factor for real world performance. Since there is resistance in the intake manifold, the engine can not suck the optimum air volume. This loss due to manifold friction is called volumetric efficiency (ve).

CFM = DISP(cc) * RPM * VE / 56633

Note: For US units use CFM = DISP(in) * RPM * VE / 3456

Example 1:
    What is the cfm for a 2000cc VW at 4000rpm and volumetric efficiency of 75%?
  Answer:
    CFM = DISP(cc) * RPM * VE / 56633
    106(cfm) = 2000(cc) * 4000(rpm) *.75 / 56633
  

Cubic Feet Minute (CFM)


   CC  * RPM  * VE  / 56633   =  
Typical VE values
stock engine      = .75 (75%)
modified street engine = .85 (85%)
racing engine       = .90 (90%)


Engine Limits


Engine Limits
Description Limit
Idle speed 700-800 rpm
RPM Green 2000 - 3700
Yellow 3700-4000
Red 4000
75% 3500
Takeoff 4000 5min
Firing order 1 - 4 - 3 - 2
Point gap .016"in - .020"in
0.40mm - 0.50mm
Plug gap .028"(0.70mm)
Dwell angle° New:   44° - 50°
Used:  42° - 58°
Fuel Auto or Avgas
Oil (psi) Green 20-100psi
Red +100psi
~10psi for each 1000rpm
Oil °F Green 180°-220°F
Yellow 220°-250°F
Red  +250°F
CHT °F - sensor in head
(for spark plug sensor add 50°F - see note)
Green 340°-370°F
Yellow 370°-400°F
takeoff 400°F 5min
Red 400°F
EGT°F Green 1200°-1400°F
Yellow 1400°-1500°F
Red 1500°F
Takeoff 1450°F 5min
O2 sensor .45v ideal
lean .3-.4v
rich .5-.9v)
Oil capacity filter   3.00 quarts 30W
no filter 2.75 quarts 30W

Note: Volkswagen did not provide CHT for auto engines. But it did instrument it's industrial engines and measured CHT for its EFI systems. The measurement point recommended (and used) by Volkswagen is a specially cast lug on later model heads. They provided a Service Note explaining how to attach the CHT sensor to the lower exhaust stud on early model heads. Testing has shown that CHT measured at the spark plug can show as much as 100 ºF too low.

Maintenance


image

Part wear limits.

Maintenance
Description Time
Starting
Below (40°F) engine must be pre-heated prior to starting.
na
Oil & filter change
Use diesel grade oil, racing oil, "SB", "SC", "SD", "SE", or "SF" oil.
Detergent oil is ok if it has been used the entire life of the engine.
NEVER use aviation oil. It is designed to deposit carbon on internal surfaces. The VW oil passages are very small in relation to a certified aircraft engine.
no filter 50hrs
filter   100hrs
Valve adjust 50 hrs
Magnetos 50 hrs
Cylinder head torque 100 hrs
Spark plug clean & gap
Champion REL37B, REL38B or REJ38 .016
Bosch W8AC .028
Bosch W8AC with mag .016
Autolite MP4163
100hr
Compression 100hr
Exhaust cracks 100hr
Exhaust nuts & gaskets 100hr
Intake cracks 100hr
Intake nuts & gaskets 100hr
Ignition harness 100hr
Coil - cracks 100hr
Replace points & condenser 100hr
Replace Distributor Pints 100hr
Lube distributor cam/lobe 100hr
Case nut torque 100hr
Prop & hub 100hr
Case nut torque 250hr
Oil cooler seals & nuts 250hr
Main oil seal (flywheel) 500hr
Head and cylinder removal & inspection500hr
Note: Annual is the same as 100hr


Fastener Torque Specification


FASTENER ft. lbs. mkg
Connecting Rod Nuts 22-25 3.0-3.5
Oil Drain Plug 25 3.5
Crankcase Nuts (12mm) 18 2.5
Oil Pump Nuts 14 2.0
Crankcase Nuts (8mm) 14 2.0
Sump Screen Nuts 5 0.7
Cylinder Head Nuts (10mm) 23 3.2
Spark Plugs 22-29 3.0-4.0
Cylinder Head Nuts (8mm) 18 2.5
Generator Pulley Nut 40-47 5.5-6.5
Rocker Shaft Nuts 14-18 2.0-2.5
Fan Nut 40-47 5.5-6.5
Crankshaft To Flywheel Bolt 253 35.0
Crankshaft Pulley Bolt 29-36 4.0-5.0


Conversion Tables

How to Convert Metric Thread to SAE Thread

Manufacturers name screws according to their diameter, pitch and length. In 1916, the Society of Automotive Engineers, or SAE, emerged to oversee the development of standards for the transportation industry, including component parts such as bolts. Today, SAE threads represent a major system for classifying screw and bolt sizes. However, the metric system represents an international standard. Metric screws are named according to the diameter of the shank in millimeters; the pitch, or the distance between threads; and the length of the screw or bolt. Although no metric screw is exactly like an SAE screw, you can calculate the closest equivalent by converting these measurements to inches and threads per inch (TPI).

Converting the Diameter

  1. Look at the first number in the screw or bolt's name to determine the diameter. For example, an M8 screw has an 8mm diameter.
  2. Divide this number by 25.4. The answer is the diameter in inches. The 8mm screw has a diameter of approximately 0.315 inches.
  3. Multiply the diameter by 64 to calculate how many sixty-fourths of an inch the screw measures. A 0.315 inch shank equals 20.16/64 inch.
  4. Round the numerator to the nearest whole number, 20. 16/64 is not a standard screw size, but 20/64 is.
  5. Reduce the fraction to lowest terms, if necessary. A 20/64 inch screw is commonly called 5/16 inch.

Converting the Pitch

  1. Look at the second number in the screw or bolt's name to determine the pitch. For example, an M8 x 1.25 screw has 1.25 millimeters between the crest of one thread and the crest of the next.
  2. Divide 1 by the pitch of the metric screw to determine the number of threads per millimeter. A pitch of 1.25 equals 0.8 threads per millimeter.
  3. Multiply this number by 25.4. The answer is the number of threads per inch.0.8 threads per millimeter equals 20.32 threads per inch.
  4. Round the answer to the nearest whole number. For example, no screw has 20.32 TPI, but many screws have 20 TPI.
  5. Consult a chart of SAE screw and bolt sizes to determine the actual TPI of the nearest screw size. For instance, a 5/16 inch SAE screw usually has 24 TPI rather than 20.

Converting the Length

  1. Look at the last number in the screw or bolt's name to determine the length. For example, an M8 x 1.25 x 12 screw is 12mm long.
  2. Divide this number by 25.4. The answer is the length in inches. The 12mm screw measures approximately 0.472 inches.
  3. Multiply the length by 4 to calculate how many fourths of an inch the screw measures. A 0.472 inch screw equals 1.888/4 inch.
  4. Round the numerator to the nearest whole number. 1.888/4 is not a standard screw size, but 2/4 (1/2) is.
  5. Reduce the fraction to lowest terms, if necessary. A 2/4 inch screw is more accurately called 1/2 inch.
image

Metric conversion table.

image

Force conversion table.

Socket Conversion Table


Socket Conversions
USMetric
9/32" ~= 7mm
5/16" = 8mm Good fit
7/16" = 11mm
1/2" = 13mm Sometimes 1/2" fits better than 13mm!
9/16" ~= 14mm Not a good fit
19/32" = 15mm
5/8" = 16mm
11/16" = 17mm
3/4" = 19mm
25/32" = 20mm
13/16" = 21mm Spark plugs
7/8" = 22mm
15/16" = 24mm
1 1/16" = 27mm
1 3/16" = 30mm
1+1/4" = 32mm
1+7/16" = 36mm