PaulW

I don't think a roots blower would work well, it really needs to be intercooled (as I think all will), so mounting and plumbing could prove difficult.

Secondly, the roots blower adds a lot of low end torque, which I really don't think we (or should I say I) need.

I guess after looking at how I use my car, how I want it to last, and how hard the install would be, I'm thinking of a centrifugal blower.

A centrifugal blower makes no real power until about half way through the rev range, and then it's small.

It's a fan, so it follows the fan (pump) laws. Fan head (pressure it develops) is proportional to speed squared. So if you set it up for max output at 6200 RPM (redline), at half that (3100 RPM), the output would be 1/4 the pressure. At below that, it would almost be negligble.

However, I think that would work well for my A8 and driving style.

First off, I really want the power on a race track or maybe in a street application when I'm going to be above 3500 RPM. That's when the power will pour on. On the track, you never upshift unless you are at redline. That's when it would be working its best.

During normal driving (which I do most of), it will have little or no effect.

And because it's a centrifugal fan, it won't really change any of the low end characteristics of motor HP/Torque from the factory.

I'm thinking the engine controls will be easier that way.

So with that laid out, I'm going to see what would be required to achieve 375 HP, 400 HP and 425 HP.....then see if I can find a centrifugal blower that has compressor flow map that matches the application. This WILL HAVE to be intercooled, I don't see anyway around it. BTW, a centrifugal compressor also has the lowest added heat, another benefit with our high compression ratio motors.

I've already started the calcs.....it's very cool!

ohbw

Just curious, Paul: why have you settled on supercharging over turbo?

skiracer

Almost ;-) I'm not familiar with the centrifugal blowers, how big are they? What kind of horsepower do they require to drive them (parasitic losses)? Fitting an intercooler and the associated large plumbing into the front end of an A8 has got to be challenging (although I know Louis and others have done it with turbos). The performance you are describing fits the description of a turbo- no low end help but lots at the top end. Would you rather look into the turbo solution? What would be the advantage of the centrifugal blower over a turbo setup? It would be a tradeoff between mounting/running a belt to the compressor and messing with the exhaust system and heat issues.

PaulW

I'm just investigating.....in my mind, a supercharger is simplier to design and install than a turbo....Luiz's is great, but it requires tear down of a lot of parts to get those manifolds in there, the kit price was something like 7K for me! Plus I had to do the install, and I don't think it had the intercooler.

First off, we're not going to do anything with a high pressure system, it's just not going to work in the summer with a 10.8:1 or 11:1 compression ratio.

Secondly, I would like something easy to install. I could custom fabricate a few parts to mount it and that's all that would be required, plus the supercharger to intercooler to inlet piping, easy to do.

And with a modest increase in power, and that the supercharger is upstream of the MAF, I'm thinking the electronics changes are going to be minimal.

Plus I'm on a budget.....I can get an intercooler from a 91 200q used for about $150, and if I can find a manufacturer of a centrifugal blower that matches our design requirements, there is a chance I could get a used blower.

I could possibly build a system for 3K and then test it.

Interesting side note: Almost everything I have read states that the supercharger really doesn't do too much to the tranny, and a centrifugal one would even have less effect....a tranny breaks because of torque, not HP....and this thing will come in when the tranny is spinning already, so the torque number changes will be low.

pw

PaulW

The centrifugal blower requires the least amount of energy to drive them versus a roots or twin screw.....they also add the least amount of heat.

It could be mounted like the Russian guy did....here's a picture of the ProCharger:

<img src="http://www.procharger.com/SPORT_COMPACT/images/FX35_uh_lg.jpg">

It's slick how they now put the pass through pulley so it can be mounted on the back of the bracket.....

Here's the russian design.....I would hope mine looked more like the one above....but if it works, it works! You can see the bypass valve on the unit (blue hose short circuiting back to atmosphere, used during high engine vacuum conditions)

<img src="http://www.tuning-club.ru/images/a842_1_1.jpg"><ul><li><a href="http://www.tuning-club.ru/kits/audi_42k1.htm">More pictures of the 32 valve here</a></li></ul>

D3AeighT

I'm sure you've seen this page...<ul><li><a href="http://www.fiautosports.com/centrifugalchargers.html">http://www.fiautosports.com/centrifugalchargers.html</a</li></ul>

PaulW

Hadn't seen it, but it just restates what I had stated above, thanks for the link!

obLu

They're cheaper/easier to install, and easier to do the ecu tuning on. Big question though is where you going to find the room?

Usually the centrifugal kits do away with the stock airbox, put the blower there and then run a straight pipe down to the bottom of the bumper for the intake.

I haven't pulled the airbox off an A8, is there enough clearance there?

PaulW

Will have to do the calcs first, then based on the wanted pressure ratio and required airflow, find a suitable blower.

Once that is determined, see if it can be shoe horned it!

Heck, I put a dash out of a 2000 A8 in my car with a Nav Plus, with the help of Tozo and his machine tools, this should be a cake walk! ;-)

No, not really, but I'm thinking how many V8 owners out there want a kit that works well? I imagine at least 5!!!

D3AeighT

<ul><li><a href="http://www.carhaven.com/audi/2003_audi_s8.html">http://www.carhaven.com/audi/2003_audi_s8.html</a</li></ul>