'95 325i, Supercharger question - Page 2 - United Bimmer Community

**catalyst** · 03-21-2006, 06:29 PM

Well, i can be of no help.. but this sure sounds like a fun project

, have fun!!

**B_w.** · 03-22-2006, 01:11 AM

in all honesty i would just sell the super charger and buy a turbo. in the end you will be much more satisfied with a turbo. i bet you are not going to get that completed cheaper than it would be to buy a kit.

**Avlany** · 03-22-2006, 05:30 AM

I will

, And no, I had a turbo which is not what I need. Turbo kicks in at certain RPMs, while Super is constant power. I used to drive both and i fall in love with supercharged bimmer.

**Rooz** · 03-22-2006, 11:13 AM

Avlany was my friend of any help?

**Avlany** · 03-22-2006, 03:29 PM

He is trying to help Rooz, but I am affraid he cant. He is a very nice guy, but he is not a mechanic

.

**wutzu** · 03-26-2006, 12:54 AM

Quote:

Originally Posted by Avlany

I will

, And no, I had a turbo which is not what I need. Turbo kicks in at certain RPMs, while Super is constant power. I used to drive both and i fall in love with supercharged bimmer.

NOT QUITE

You're correct on the turbo part:

A turbo kicks in when the "boost threshold" is reached, which is a function of how big (how much boost) the turbo is, and how big the engine is (how much exhaust it's spewing out).

So for a turbo, you can have a high-boost turbo (20 Psig) that has a long lag and high threshold, or a low-boost turbo (7-8 Psig) that has a low threshold and short lag.

However, your assessment of superchargers is a bit off the mark.

A "roots" or positive displacement supercharger meters the same amount of air for every revolution, and thus provides constant boost (think PV=nRT, put the same extra volume in, it'll add up to the same extra boost) Positive displacement blowers will consequently give you the constant torque on tap that you crave.

The supercharger you're showing pictures of is a centrifugal supercharger, have the worst qualities of roots superchargers and turbochargers. They only generate significant boost at high rpms. This is because the turbo's pressure increases as a square of the RPM, which means if you set your max boost to 8 Psi at a 6k redline, then you'll only make 2 Psi at 3k. Near the redline will a centrifugal supercharger generate the amount of boost you're looking for, but SO WILL A TURBO.

EDIT: In summation: Centrifugal<Turbo<Roots

**tomctx** · 03-26-2006, 01:52 PM

The supercharger you're showing pictures of is a centrifugal supercharger, have the worst qualities of roots superchargers and turbochargers. They only generate significant boost at high rpms. This is because the turbo's pressure increases as a square of the RPM, which means if you set your max boost to 8 Psi at a 6k redline, then you'll only make 2 Psi at 3k. Near the redline will a centrifugal supercharger generate the amount of boost you're looking for, but SO WILL A TURBO.

EDIT: In summation: Centrifugal<Turbo<Roots[/QUOTE]

Let me ask a question. I was told that a centrifugal supercharger was basically a turbo driven by a belt. And some do look like a turbo. How close is that assessment?

**komodo** · 03-26-2006, 05:58 PM

Quote:

Originally Posted by wutzu

NOT QUITE

You're correct on the turbo part:

A turbo kicks in when the "boost threshold" is reached, which is a function of how big (how much boost) the turbo is, and how big the engine is (how much exhaust it's spewing out).

So for a turbo, you can have a high-boost turbo (20 Psig) that has a long lag and high threshold, or a low-boost turbo (7-8 Psig) that has a low threshold and short lag.

However, your assessment of superchargers is a bit off the mark.

A "roots" or positive displacement supercharger meters the same amount of air for every revolution, and thus provides constant boost (think PV=nRT, put the same extra volume in, it'll add up to the same extra boost) Positive displacement blowers will consequently give you the constant torque on tap that you crave.

The supercharger you're showing pictures of is a centrifugal supercharger, have the worst qualities of roots superchargers and turbochargers. They only generate significant boost at high rpms. This is because the turbo's pressure increases as a square of the RPM, which means if you set your max boost to 8 Psi at a 6k redline, then you'll only make 2 Psi at 3k. Near the redline will a centrifugal supercharger generate the amount of boost you're looking for, but SO WILL A TURBO.

EDIT: In summation: Centrifugal<Turbo<Roots

On a slightly unrelated topic, welcome to UB.

You should post up a thread in the Introductions forum saying hi and introducting yourself.