I was reading thru the SB Head flow thread(which has gone totally of the rails of what I was intended for IMO),
and there was some discussion on flow numbers being different from different benches.
I just had another chance to experience this last week.
I’m not even going to mention what kind of head it is...... cuz it doesn’t really matter.
The heads weren’t here for porting work anyway. There was an issue with how intake valve seats were cut for bigger valves, and a resulting installed height issue.
I knew the heads had been flowed and had the customer tell with cylinder had been tested, and I would test the same one.
Interestingly(to me anyway), the “big number” isn’t very much different between the two benches, although it happens at a slightly different lift.
However, the mid-lift numbers are rather different from each other.
Intake flow(same port, same head):
Lift———A———B
.200— 163—— 138
.300— 220—— 199
.400— 270—— 249
.500— 319—— 290
.600— 347—— 333
.650— 336—— 346
.700— 334—— 329
Exhaust:
Lift———A———B
.200— 124—— 101
.300— 169—— 139
.400— 210—— 177
.500— 242—— 211
.600— 265—— 237
.650— 273—— 244
.700— 275—— 253
So, if you’re only looking at the “big number”...... the intake ports are within 1cfm....... 347 vs 346.
The head didn’t get better on the one bench, or worse on the other bench....... that’s just how the benches interpret what the head is doing at the various lifts.
Which is why I always say....... you can’t compare numbers from different benches as “applies to apples”.
I’ll say it again.......Those two sets of numbers that look so different.......are the same port on the same head.
