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

Ian McCloghrie ian at codrus.com
Mon Feb 3 16:10:05 EST 2003

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.

'01 Nogaro Blue S4
'99 Mazda Miata FM2 Turbo

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