Re: TURBO (archive)

: Well, its complex but it basically has to do with how typical centrifugal superchragers limit boost. They do it by limiting maximum boost on the supercharger itself, whereas with turbos, they limit the exhaust pressure (with a wastgate) or the output pressure (blow-off valve). So a turbo system that is limited to 11psi may actually be capable of producing 30 or more psi at theorhetical engine speeds, etc. Such pressures would normally pop a given motor like a can of soda, but they limit boost with the wastegate so that the turbo can only spin so fast. What all this boils down to is that for a given supercharger to give 10psi at 6000rpm, at 3000rpm it gives only 5psi, and at 2000 rpm, probably only one. A properly sized turbo can give you full available boost as low as 3000 rpm, meaning that at 2000rpm, you can have more boost, probably as much as 60-80% of full boost, assuming the turbo is sized correctly. Its all about time (or rpms) to boost, and according to what I've read, turbos are better at this. This is in direct contradiction to something I said in a previous post, which was that superchargers give more boost sooner, which is simply untrue.
: UNLESS! you get a supercharger that is capable of 25 or more psi, and run it through a wastegate-style pressure relief valve to limit boost to the 6-9psi target typical street runners are looking for. I am currently looking into this option. Please note that Vortech superchargers, due to the limitations of their internal drive belts, cannot produce more than 9psi of boost in any event. Paxton/vortech/etc.s are the only options, which require oil lines/ etc. and I'm just thinking that all the complexity makes me want to choose the most-travelled path.
: I'm thinking a t-3/4 Garret turbo hybrid, blowing into and intercooler, which feeds into a ported 318i manifold running custom fuel/spark from SDS and MSD with all the knock-sensing bells and whistles is going to be my choice.
: HOWEVER, if Weber 38/38 people can show me a blow-through turbo setup that is quick and dirty and RELIABLE, I would much rather spend the $2k FI/spark budget on bodywork...\

I think you need to go back and read a little looks like some of your info is a little old....

I purchased a used Lysholm supercharger (off a Mazda Millenium) that is a twin screw posititve displacement type that produces a near linear constant 14psi (on a 2.3 liter motor) from about 1500rpm on up (and yes it will produce boost at idle too --but not quite 14psi). There are no oil lines to plump and no lubrication required. This is a different type of supercharger than say a Paxton/Vortech or Roots. The twin screws are actually meshed to each other and push air through them from one end of the supercharger to the other --a pretty cool setup! It is setup stock as a suck through system (throttle body on one end) --no carb here only efi. And it is fairly compact too.

These are expensive new due to the precise machining of the screws (which is a work of art). Look around you should be able to find one in the wrecking yard for under $700 in good shape.

This would be better for your project......

Also think about the power drain from your engine from running a supercharger that is way bigger than you need --also the waste of good boost pressure.

Also turbos don't quite work that way --having maxmimum boost at 3000 doesn't necessarly mean you will get 1/2 of that at 2000rpm --it depends upon the engine design (pistons/cam/intake & exahust manifolds, bore x stroke --you get the picture) You can't think simply in rpms.....

(3) turbocharged cars now
(1) supercharged almost done

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