BJR Racing
Well-Known Member
I'm going to attempt to help people out that don't have much knowledge about cylinder heads so they don't make mistakes. Some of this info will be helpful to some, and more helpful to others. I'm going to be dealing with intake ports only for now as you only need 70% exhaust to be efficent so its easy calculations later.
cyl. head valve size port ccs airflow .100 .200 .300 .400 .500 .600
4027163 stk 1.78 120 54 104 155 182 188
3769973 gm,bb,bc 1.78 126 72 137 183 213 201
915 stk 1.88 150 85 130 177 189 190
915 bb,bc 1.88 154 65 143 180 203 212
Commando stk 2.02 190 80 115 177 219 251 290
Commando ported 2.02 196 87 142 209 250 303 316
915 ported 1.88 168 96 185 229 248 283 285
587 ported 2.02 170 94 177 223 251 287 287
302 HP ported 1.78 136 89 164 216 232 231 231
302HP gm,bb, 1.88 130 83 141 204 218 213 213
915 bc 1.88 150 85 168 201 213 216 216
915 bb,bc 1.88 153 90 181 219 228 226 226
915 bb,bc nail head 1.88 155 85 166 210 228 228 226
915 gm,bb,bc 1.88 159 91 177 219 231 232 232
587 gm,bb,bc 2.02 167 92 178 228 247 248 248
273 powerpac 1.78 134 86 138 199 223 228 225
ported
These are just some of the few heads with different modifications that most people would have, other than the commandos.
bb= bowl blend
bc= back cut
gm= gasket matched
If you will notice that the smaller valves flow very similar to the bigger counterparts that this would tell you that the valve is too big for the port, and as the air flow drops so does the velocity. Also you will notice that as the port volume increases the air flow doesn't in low lifts on some heads, which tells you that some heads are better with modification than others.
The main thing to do is to keep the velocity up and use the smallest valve that you can get away with.
Use 318 heads on 318s as the valves won't be shrouded in the cylinder as it opens. Keep in mind that the bore on a 318 is only 3.91 stock and this is the reason that the factory use a smaller valve on the engine and to keep efficiency up. Now as for the 360 and the 340s the bore is bigger and will accept a larger valve, this is why they put 1.88s in the 360 heads from the factory as the bore is 4.00 and 2.02s on the HP 340s as the bore is 4.04 stock.
Now as for testing a 318 with the 360 heads and a 1.88 valve the engine lost HP and torque, not just because of the compression but because of the port volume being too big for the little engine, and the velocity being down. Cylinder bore size creates suction, smaller bores pull less than bigger bores, this is partially why they made the ports larger for bigger engines. Thus the old saying bigger is better in the case of Cubic Inches. This is why port volumes are much bigger on big cubic inch big blocks, as the bores are in the 4.50-4.65 range. Also keep in mind that the stroke comes into play here also, so when bigger strokes are put in and the rods get shorter, thus the piston speed increases greatly. When this happens the pull is less due to the piston speed so the port volume has to be increased greatly to supply the engine at high rpms.
Example: Big block Chevys have big ports and big valves, short rods and longer strokes, compaired to the 440 dodge with a small port and valve and a longer rod and shorter stroke. Yet they run very similar. Partially because the rod angle isn't as bad as the Chevys and the rod to crank position is better on the Dodge thus the increased torque.
So in general, the idea is to keep the valve and port as small as possiable and achieve your goals. This will give you the best performance per the engine used.
Our test engine:
318 .030
KB 167s
mopar .528/284 cam
lightened rods- stock with 80 grms. removed
bob weight 1937grms.
ported 302 HP heads with 1.78/1.50 valves
block square decked so the piston is .020 out
heads ccd at 50 ccs with .040 cut off deck and intake sides
ported intake M-1 manifold
750 cfm alky carb flowed to 1030 cfms
corteco .055 gasket to achieve .035 quench
compression ratio 12.52:1
201psi cylinder pressure
heads ccd at 136 port volume
heads efficiency intake 67.8%
exhaust 65.2%
heads flow 231 @ .500 intake
180 @ .500 exhaust
hedders 1 5/8 dynomax open exhaust
corrected elevation:
29.98
75 degrees
56 dew point
3253 ft above
Atlanta, Ga. in October
3000 3500 4000 4500 5000 5500 6000 6500 7000
Brk TQ. 333 404 453 471 471 462 449 431 383
Brk HP 190 269 345 403 448 484 513 533 511
Average Tq. 419
Average HP 417
vol. eff. 84.4 97.4 108.4 115.3 117.7 116.5 113.7 108.8 102.3
int. vel. 217 254 290 326 362 398 435 471 507
exh. vel. 183 213 244 274 305 335 366 396 427
This is just something to keep your minds busy, if you have spare time.
BJR Racing
cyl. head valve size port ccs airflow .100 .200 .300 .400 .500 .600
4027163 stk 1.78 120 54 104 155 182 188
3769973 gm,bb,bc 1.78 126 72 137 183 213 201
915 stk 1.88 150 85 130 177 189 190
915 bb,bc 1.88 154 65 143 180 203 212
Commando stk 2.02 190 80 115 177 219 251 290
Commando ported 2.02 196 87 142 209 250 303 316
915 ported 1.88 168 96 185 229 248 283 285
587 ported 2.02 170 94 177 223 251 287 287
302 HP ported 1.78 136 89 164 216 232 231 231
302HP gm,bb, 1.88 130 83 141 204 218 213 213
915 bc 1.88 150 85 168 201 213 216 216
915 bb,bc 1.88 153 90 181 219 228 226 226
915 bb,bc nail head 1.88 155 85 166 210 228 228 226
915 gm,bb,bc 1.88 159 91 177 219 231 232 232
587 gm,bb,bc 2.02 167 92 178 228 247 248 248
273 powerpac 1.78 134 86 138 199 223 228 225
ported
These are just some of the few heads with different modifications that most people would have, other than the commandos.
bb= bowl blend
bc= back cut
gm= gasket matched
If you will notice that the smaller valves flow very similar to the bigger counterparts that this would tell you that the valve is too big for the port, and as the air flow drops so does the velocity. Also you will notice that as the port volume increases the air flow doesn't in low lifts on some heads, which tells you that some heads are better with modification than others.
The main thing to do is to keep the velocity up and use the smallest valve that you can get away with.
Use 318 heads on 318s as the valves won't be shrouded in the cylinder as it opens. Keep in mind that the bore on a 318 is only 3.91 stock and this is the reason that the factory use a smaller valve on the engine and to keep efficiency up. Now as for the 360 and the 340s the bore is bigger and will accept a larger valve, this is why they put 1.88s in the 360 heads from the factory as the bore is 4.00 and 2.02s on the HP 340s as the bore is 4.04 stock.
Now as for testing a 318 with the 360 heads and a 1.88 valve the engine lost HP and torque, not just because of the compression but because of the port volume being too big for the little engine, and the velocity being down. Cylinder bore size creates suction, smaller bores pull less than bigger bores, this is partially why they made the ports larger for bigger engines. Thus the old saying bigger is better in the case of Cubic Inches. This is why port volumes are much bigger on big cubic inch big blocks, as the bores are in the 4.50-4.65 range. Also keep in mind that the stroke comes into play here also, so when bigger strokes are put in and the rods get shorter, thus the piston speed increases greatly. When this happens the pull is less due to the piston speed so the port volume has to be increased greatly to supply the engine at high rpms.
Example: Big block Chevys have big ports and big valves, short rods and longer strokes, compaired to the 440 dodge with a small port and valve and a longer rod and shorter stroke. Yet they run very similar. Partially because the rod angle isn't as bad as the Chevys and the rod to crank position is better on the Dodge thus the increased torque.
So in general, the idea is to keep the valve and port as small as possiable and achieve your goals. This will give you the best performance per the engine used.
Our test engine:
318 .030
KB 167s
mopar .528/284 cam
lightened rods- stock with 80 grms. removed
bob weight 1937grms.
ported 302 HP heads with 1.78/1.50 valves
block square decked so the piston is .020 out
heads ccd at 50 ccs with .040 cut off deck and intake sides
ported intake M-1 manifold
750 cfm alky carb flowed to 1030 cfms
corteco .055 gasket to achieve .035 quench
compression ratio 12.52:1
201psi cylinder pressure
heads ccd at 136 port volume
heads efficiency intake 67.8%
exhaust 65.2%
heads flow 231 @ .500 intake
180 @ .500 exhaust
hedders 1 5/8 dynomax open exhaust
corrected elevation:
29.98
75 degrees
56 dew point
3253 ft above
Atlanta, Ga. in October
3000 3500 4000 4500 5000 5500 6000 6500 7000
Brk TQ. 333 404 453 471 471 462 449 431 383
Brk HP 190 269 345 403 448 484 513 533 511
Average Tq. 419
Average HP 417
vol. eff. 84.4 97.4 108.4 115.3 117.7 116.5 113.7 108.8 102.3
int. vel. 217 254 290 326 362 398 435 471 507
exh. vel. 183 213 244 274 305 335 366 396 427
This is just something to keep your minds busy, if you have spare time.
BJR Racing
