Baseline head air flow test

[Joe R.]

I'm having my 3873858 heads (L-72) air flow tested this week for baselining purposes before switching to the 1.88 " exhaust valves. I will probably do it again after changing the valves. My question is, should I have all cylinders tested or not? The machinist is recommended doing two cylinders, one with a short runner and one with a long runner because it gets expensive to be more thorough. What do you guys think?

Thanks,
Joe

[Duke W.]

Re: Baseline head air flow test

Do as your machinist recommends. There is always some cylinder to cylinder variation, but if the porting and valve seat work is reasonably consistent, the difference is not significant.

You definitely want to do an "after" test after all the work is done to see the improvement in flow, which is an indication of how well the work was done.

Suggest you use valve lifts of .050, .100, .200, .300, .400, and .500".

Going over .500" is of no value because the maximum valve lift with the OE cam is no more than this. You could also skip the .200, and .300 readings if you want to save money because the flow between .100 and .400 is very nearly linear.

Whatever you decide use the same lift values for both the before and after work tests.

I assume you are going to do the recommended pocket porting/port matching, multiangle valve work with the back cut off the tops of the valves in addition to installing the larger exhaust valves.

Duke

[Joe R.]

Re: Baseline head air flow test

Duke,

Thanks for your help. I passed your suggestions on to the machinist. I have already asked him to CC all the chambers as well.

Joe