What happens when I add a second supercharger?

douglas vincent · Post by **douglas vincent** » Thu Jan 26, 2006 5:48 am

When I do the twin supercharger, I will double the airflow. I will be doing this only on my closed deck motor with SOHC heads (not the old ones).

Currently I am pushing 1.5 liter of air into my engine per revolution. With two SCs, I would be pushing 3.

Will my psi go double? I doubt it but what exactly should technically happen?

Psychoreo · Post by **Psychoreo** » Thu Jan 26, 2006 5:59 am

you'll get something along the lines of http://www.forcedairtech.com/

douglas vincent · Post by **douglas vincent** » Thu Jan 26, 2006 6:03 am

YEah, but what does it mean?

Oh yeah, and I would be cooler.

Psychoreo · Post by **Psychoreo** » Thu Jan 26, 2006 6:05 am

hell if i know, i just found that set up like a month ago and thought it might be some food for thought. but since you're doubling the input flow, i'd assume it would close to double the PSI although anytime i assume something it's wrong.

vrg3 · Post by **vrg3** » Thu Jan 26, 2006 6:16 am

How are you going to plumb the two superchargers?

azn2nr · Post by **azn2nr** » Thu Jan 26, 2006 6:19 am

one over by the battery

doug, wouldnt you be doubling the air as well as the strain on the motor???

douglas vincent · Post by **douglas vincent** » Thu Jan 26, 2006 6:31 am

Yes the strain would/will be more. But if I keep the pulley ratio 2-1, the supercharger is not pushed out of its effeciency range at any point so even though I am "straining" the motor, the power outout should overcome the parasitic loss. Look at what I am getting right now.

And yes, I DO feel the parasitic loss down low. While I do get 7 psi the moment I punch the gas pedal, anything below 3000 rpm does feel groggy. However, its still more power than I have at NA.

Kelly · Post by **Kelly** » Thu Jan 26, 2006 6:36 am

Havn't seen any twin superchargers Doug. I assume because the parisidic drag doubles too?

douglas vincent · Post by **douglas vincent** » Thu Jan 26, 2006 6:39 am

There are alot of twin superchargers, but all on V8s. But that basically means 1 supercharger per 4 cylinders. I just want 1 per 2!

douglas vincent · Post by **douglas vincent** » Thu Jan 26, 2006 6:40 am

I will admit, if I were to find a really really nice BIG new generation superchager, I would go for that instead, providing it was affordable.

vrg3 · Post by **vrg3** » Thu Jan 26, 2006 6:42 am

How are you going to plumb the two superchargers?

douglas vincent · Post by **douglas vincent** » Thu Jan 26, 2006 6:50 am

One on left, one on right side.

Air intake where ever it works. No MAF yet.

Dump into FMIC. I will have an IC modified to take two intakes into where it usually has one.

OR.....

Two smaller FMIC side by side, or one on top of the other.

The charge tubes will then lead to a Y of some sort that then has a MAF.

Then spilt to the dual throttle bodies, or single throttle body.

Splinter · Post by **Splinter** » Thu Jan 26, 2006 6:56 am

What about switching to MAP airflow?

Kelly · Post by **Kelly** » Thu Jan 26, 2006 6:59 am

douglas vincent wrote:There are alot of twin superchargers, but all on V8s. But that basically means 1 supercharger per 4 cylinders. I just want 1 per 2!

Still, twice as much drag!

douglas vincent · Post by **douglas vincent** » Thu Jan 26, 2006 7:02 am

All the more dresses for you Kelly!

douglas vincent · Post by **douglas vincent** » Thu Jan 26, 2006 7:04 am

Seriously though,

I think the parasitic drag loss is overrated/antiquatied. It does exist. That is not the question. But how much is the question. The old V8 Weiand (sp) and such blowers really sucked efficiency wise.

But the new stuff doesnt drag as much. The REALLY new stuff is awesome in efficency, but I cant afford that.

Kelly · Post by **Kelly** » Thu Jan 26, 2006 7:05 am

sthutup girlfriend.

douglas vincent · Post by **douglas vincent** » Thu Jan 26, 2006 7:06 am

Splinter,

yeah, I could/would run a 3 bar Map sensor, run it through the piggyback/standalone.

dzx · Post by **dzx** » Thu Jan 26, 2006 8:18 am

I understand the unique part but wouldn't it just be easier to go turbo?

Splinter · Post by **Splinter** » Thu Jan 26, 2006 8:46 am

Buying a WRX would be easier than upgrading a legacy.

Easier isnt the point when you're talking about upgrading cars.

rallysam · Post by **rallysam** » Thu Jan 26, 2006 3:36 pm

If life were simple, I bet it would double the absolute pressure (not double the boost). For example, if you were running 5 psi of boost with 1 SC (20psia), you'd be running 25 psi of boost (40psia) with both.

I know it ain't that simple. I don't know much about SCs, but I bet you could analyze it as 1 SC blowing a 1.1 liter engine.

I've gotta believe this is overkill. When most superchargers were born, they probably thought they would grow up to blow a 5L. They probably don't know what's going on when they blow into our little 2.2's.... let alone a 1.1. But knock yourself out. I'm all for making a crazy frankenstein project.

vrg3 · Post by **vrg3** » Thu Jan 26, 2006 4:03 pm

Don't confuse the loss due to parasitic drain with the loss due to compression inefficiency; they're two separate phenomena.

These are superchargers meant for 2.3-liter Mercedeses, right? They're positive-displacement blowers without any internal compression, right?

So plumbing two of them in parallel would ideally double the volume of flow at the inlet. But, as we've discussed before, there's a great deal of leakage around the lobes. This leakage becomes greater and greater as the pressure differential across the supercharger increases, too. That means you'll push a good deal less than 3 L/rev.

I think the leakage is also going to hurt compression efficiency. The density ratio will not increase as much as the pressure ratio.

What does it matter how much boost you see in the manifold? I don't see how we can really predict it, since it depends a lot on how well the engine copes with the increased air at its intake ports. With my meager understanding of what's going on, it wouldn't surprise me to see the boost pressure more than double.

dzx · Post by **dzx** » Thu Jan 26, 2006 8:17 pm

Splinter wrote:Buying a WRX would be easier than upgrading a legacy.

Easier isnt the point when you're talking about upgrading cars.

I'd like to know where you're getting this wrx for less cost than a legacy. Cost wise, my car will kill a wrx and is still faster. I really fail to see how buying a wrx would be easier than modding a legacy. Especially when it's very easy to change out a turbo.

Splinter · Post by **Splinter** » Thu Jan 26, 2006 10:13 pm

Saving money is easier than doing work on a car. Saving money doesnt require you do anything.

The point is, he's doing it because it's something he wants to do, not because its easy.

Same reason I integrated a computer into my dash.

dzx · Post by **dzx** » Thu Jan 26, 2006 11:36 pm

Ok, that makes no sense. You don't save money by purchasing a wrx over a legacy, even a heavily modded legacy. You do however save money by working on your own car.

Did you not see my post about my understanding him doing it to be unique or did you miss that?

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What happens when I add a second supercharger?

What happens when I add a second supercharger?