Update on 216 to 261 engine switch

[Alex Blair (RIP)]

Originally posted by Phil Waterman
That is until I pulled the # 4 piston and discovered that the bore and piston are scored this is the same cylinder that had the worst valve, real shame because the bores all measure up as being good.

Phil..
How bad is the #4 cylinder...Will it rebore ??

You are then it some serious money with pistons and all the rest ...Oh well if you have another ,that is the cheeper fix..
HERE IS SOME GOOD CARBURATOR INFO ON SIZING......
PRINT IT OFF AND KEEP IT..

Air-flow capacity: It is important to correctly size the carburetor to the engine's operating air-flow requirements. Too small a carburetor limits horsepower; up to some specific speed, normal torque is obtained. Beyond that point air-flow is limited by the carburetor and power drops off.

A too-large carburetor will cause starting troubles (too low vacuum signal at cranking), idle will be hard or impossible to set, and fuel/air mixture will be incorrect.

However, type of service also has a bearing on carburetor sizing; an engine that is never operated at full-load conditions is sometimes better off with a slightly-small carburetor; it will have improved low-end torque and easier starting. Passenger cars, forklifts, etc are good examples. Engines operated at or near full load, such as stationary engines, generators and the like, may produce better power with a slightly oversized carburetor.

Determining engine air-flow from the charts: The chart below gives air-flow requirements for most engine sizes. Use the next-closest value. Engine RPM should be the highest speed during actual use, such as accelerating under full load at highway speeds. Use the carburetor chart to pick the appropriately sized carburetor.

Calculating exact engine air-flow: You can easily calculate the actual engine air-flow directly. For normally-aspirated engines (ie. not turbo- or super-charged):

CID * RPM / 3456 * 0.85 = CFM required
CID is engine size, in cubic inches (CID = cubic centimeters (cc) * 0.06102), RPM is maximum engine speed. 0.85 is a close approximation of Volumetric Efficiency.

For turbocharged or supercharged engines:

CID * RPM / 3456 * %boost + 1.00 = CFM required
Normal inlet air pressure is 14.7PSI; supercharging merely increases inlet pressure. For example, 6PSI boost means 20.7PSI pressure, or 140% boost.

IMPCO Carburetor models vs. air flow
Vehicle applications


IMPCO Max.
Model CFM
50 91
50-500 108
100 170
125 202
175 210
200 276
225 329
300A-1, -20 348
300A-50, -70 432
425 460

Industrial/stationary applications

IMPCO Max.
Model CFM
50 118
50-500 124
100 197
125 235
200 345
225 380
200D 468
425 533
200T 680
600D 1600

Engine size and speed vs. air flow
NOTES: These tables assume 85% VE as mentioned in the text. To convert liters to cubic inches, multiply by 61.02. For two-cycle engines, double the CFM value found.

Engine speed, RPM 400 - 2400 RPM
CID 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
50 5 7 10 12 15 17 20 22 25 27 30
100 10 14 18 23 28 33 37 42 46 51 56
150 14 21 28 35 42 49 56 63 70 77 84
200 19 28 37 46 56 65 74 84 93 102 110
250 23 35 47 58 70 78 93 105 116 128 139
300 28 42 56 70 84 98 112 126 140 154 168
350 32 49 65 81 98 114 130 146 162 178 195
400 37 56 74 93 111 130 148 167 185 204 223
450 42 63 83 109 129 149 169 189 209 230 251

Engine speed, RPM 2600 - 4000 RPM
CID 2600 2800 3000 3200 3400 3600 3800 4000
50 32 34 37 39 42 44 47 49
100 60 65 70 75 79 84 88 93
150 91 98 104 112 118 125 132 139
200 121 130 139 148 158 167 177 185
250 151 163 174 186 198 209 220 232
300 182 196 208 224 236 250 264 278
350 212 228 244 260 276 293 309 325
400 242 261 280 298 317 335 254 372
450 272 293 314 335 357 378 399 419


Phil..
You might also want to take a boo at this link..I found it interesting..

http://www.oldchevytrucks.com/Tips/261_six.htm