I've got a Blitz EBC and a Defi D mechanical boost gauge. The Defi is at 0 when the car is off, so as far as I can tell it's working properly. The Defi reads about 1.2 psi HIGHER than the Blitz EBC. I just installed an AEM 3.5 bar MAP sensor for datalogging, and also hopefully to help me figure out which boost gauge is off. Well, it's about 1 to 1.5 psi LOWER than the Defi!!! So I've got a range of 3 psi from lowest to highest

All 3 are tee'd off the same boost source (off the BOV vacuum line) and I've been careful to avoid any leaks. I just don't get it. How can I figure out which one is right? Or maybe they are all wrong

 

Well I'd say the defi would be right. Our cars max at 19-20 stock. Thats exactly what my defi said. I'd run your car stock for a while and see what each gauge says. That will tell you for sure which are accurate.

 

Weird, my Defi and Blitz DCII read exactly the same.

 

I am installing my 3 bar map sensor soon. I will compare that to my Defi D gauge and see if it also shows a difference. I would trust the 3 bar map sensor over the mechanical gauge.

 

3 Bar MAP Sensor > EBC > $7 Grainger Gauge > Defi D gauge