Fwd: Re: [BiturboS4] S4 without a turbo? (was.. something else)

[Ian McCloghrie]

On Feb 3, 2003 "California Fields" wrote:
> A Z-engineering (www.z-engineering.com[1]) supercharger for the VW GTI VR6
> (which is a N/A engine with 10:1 compression) pushes 7 psi without any mods to
> the engine and bumps horsepower from 174 to 270.  This company also makes kits
> for Audis and Porsches so you can look more into it if you want.

I'm pretty sure that the Z-engineering supercharger is a centrifugal
blower.  That means it doesn't make anywhere close to full boost until
you get very close to redline.  A turbo produces full boost over a much
wider range of operating revs, which complicates things a lot.

If the Z-eng VW kit is anything like the one that they were (very briefly)
shipping for the Miata, then I wouldn't touch it.  Non-intercooled,
some kind of hacked-up black box that fools the computer into running
more fuel through the stock injectors -- not something I'd trust.

> If I recall correctly, the HPA (www.hpamotorsports.com[2]) turbo pushes 1.0bar
> into the same engine for 310hp but the compression had to be dropped to 7.5:1
> (or so they chose). I couldn't find exact info on their site.

Going from 10:1 to 7.5:1 almost certainly means new pistons.  If you're
gonna do that, you might as well do rods as well.  Lots of money, that
probably boosts your kit cost from $10K to $15K, plus now you need a
machine shop to build the shortblock for you.

> So, unless a supercharger puts different kinds of boost into the engine, it
> seems that you can run about 0.5bar into a N/A engine with *relatively* high
> stock compression.  I'm not sure if 11:1 and 10:1 are considered enough
> different to make a big deal. Above that, though, it seems you need to drop
> the compression (and other stuff).

For reference, the biturbo S4 has a 9.5:1 compression ratio.  There's a
world of difference between 10:1 and 11:1

If you're interested in aftermarket forced induction, I'd recommend
picking up one or both of Corky Bell's books, _Maximum Boost_ (about
turbos) and _Supercharged!_ (I bet you can guess what that one's about).
They're very readable and have lots of good info about this kind of thing.

--Ian
'01 Nogaro Blue S4
'99 Mazda Miata FM2 Turbo