The Boost Gauge is Dead To Me!
Would you believe this? I’ve got an engine on my Dyno and I’ve made four pulls. The first was naturally aspirated and the remaining three were ran with exactly the same twin turbo setup, running exactly the same 20 lbs of boost. The engine made 580 hp without turbos. The three pulls at 20 lbs ranged from 1,044 to 1463 hp. That’s a 419 hp difference at the same boost.
Knowledgeable engine builders talk boost like it’s the ultimate gauge of an engine’s capability. Well, I’m calling BS on Boost. If you want to compare muscle, you need to compare MAD (Manifold Air Density). Have a look at my iDash screen shots below and you’ll see what I mean!
Air temperature in the intake manifold is the culprit here. Boost gauges don’t measure that. In these examples we start with 20 lbs boost and no intercooling, running racing gas, then we add state of the art air to air intercooling and finally, ice water cooled intercooling. All are tested at the same boost, but at different manifold air temperatures producing wildly different horsepower results. But there’s more.
Comparing the same engine at the same boost, but at different altitudes, is just as bogus. The power will drop as you gain altitude even though the boost is the same. And, testing in the same location and at the same boost will result in a power loss approaching 5% as the humidity goes from 0% to 100%! So, air pressure, temperature and humidity all influence air density delivered into the intake manifold. And manifold air density determines power potential.
Have a look and tell me if you would like for me to explain more on why I consider the Boost Gauge to be Stone Age…MAD is the ultimate goal of all forced induction systems. As you add manifold air density you can add more fuel…that equals more power and that’s what life is all about! MAD is a new and infinitely more accurate way to compare your forced induction system with any other, anywhere on the planet.
The iDash forced induction screen, one of many screens available, can display boost, MAP, IMAN temp, Density Boost, MAD and much more, you choose during setup and change readings or position any time you want.
Because, MAD
100% is the air density reading at sea level on a standard, SAE J-607, day. The conditions on a J-607 day are; 60 F, 29.92 Inhg or 14.7 lbs air pressure and 0% relative humidity. In the Dyno cell we are higher and warmer with mild humidity present. So we have less than 100% MAD. We are starting with a 93% MAD at full power and producing 580 hp observed. All the runs are actual observed power produced.
Now we twin turbo with no intercooling boosting the MAD by 79% with state of the art compressor efficiency raising the intake manifold air temp (IMAN temp) to 262F. Boost is 20 Psig and power is 1,044 hp. Density ratio is the increase in ambient MAD. MAD is now a 166.
