You need another known point to get the slope correct....although the stock calibration should be close. Ie, put 50psi on the gauge and read the voltage, then you can fairly accurately use just the voltage to get pressure.

 

not hijacking your thread here , but my frish rebuilt 408 with ~300 miles on it has 40+ pis on cold idel after reaching tempreture , and after I drive for 5 minutes or so the idle pressure is arround 18-20 psi

I contacted TSP bout this , they said you should change the oring , almost all problems are from it espeicaly if there is no debres in the oil filter you should change the O ring and check pressure after that

they said 18-20 psi on 650rpm idle wont hurt the motor , BUT its not normal , and Im going to change the O-ring tomorow and see what happens

 

Id start with checking the oring. If the oring is pinched it will aerate the oil with air therefore lowering your oil pressure. 20 at idle doesnt seem too bad to me as long as youre getting 50+ at WOT. Porting the oil pump and shimming the relief valve spring will really help as long as there isnt a bearing issue.

 

I've never understood how that o-ring gets messed up. It almost seems like you have to be either blind/drunk and extreme forceful to actually damage that thing...

 

You would be surprised!!! I just took one apart and they used the wrong O ring. It was also not seated properly in the bore.

 

I think a lot of people forget to throw a little oil on the inlet of the pump and lube up the oring good before seating the pickup tube in the pump. Also, over my years of being on this site of come to realize there are a lot of people with wrenches in their hands that shouldnt.

And well **** happens, Ive seen pinched orings from factory assembled motors...

 

No way!

 

Well maybe I will drop the pan to check the O-ring. Maybe while the pan is off I will check the bearings out.

 

I used an odd double o-ring on mine, was a size longer than the original square cut and had room to compress a little bit. Tightened it up and got a boost in idle oil pressure, from 40# to 50#.

 

whats this o ring part number? where did you get the o ring?