# Number of Turbos

## What you do:

Find a balance between the number of turbos and turbo impeller size.

Factors to consider:
1. HiPerMath is currently limited to a range of 0 - 2 turbos. This effects the size
of the turbo(s) you use. Two smaller turbos will spool up faster than one big turbo. Spooling
up is when the turbo impeller gains rpm (revolutions per minute). Turbos can spin up to 30,000
rpm, so the time it takes to spool up can be significant. However, two smaller turbos will be
heavier than one large turbo.

The HiPerMath equation is:

spool time in seconds = __turbo impeller size__^{2}

(exhaust psi)(100)

Exhaust psi can be assumed to be 30 psi for the above calculation.

2. Weight. The more turbos you have, the more weight is added to the total weight of
the car.

The HiPerMath equation is:

turbo weight = turbo impeller size + 50

This includes all the piping and an intercooler.