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...\

: Out of curiosity... Why are you leaning away from supercharing if you're looking for low end torque? Turbos are generally considered pretty mushy on the low end because you have to wait for the turbo(s) to spool up, while a supercharger is giving you boost all the time. Don't have any personal experince turbo-ing an 02, but if you haven't, you may want to check out Top End's turbo, intercooled, fuel-injected, 220 rear wheel horsepower 02.

: Scott.

: http://www.racetep.com/car.html

: : I am beginning to think twice about my leanings toward supercharging my 2002. So, I'd like to hear about people who have turbo'd and intercooled a 2002. Also, what are good sources of manifolds/etc. The goal is to produce a car with as much low-end torque as possible.

Follow Ups:

OOPS. Powerdynes cant beat 9psi, not vortechs. Rob S. 00:21 6/26/2000 (0)

[ Follow Ups ] [ 2002 Message Board ] [ Msg. Board FAQ ]

Questions, comments, or problems, please visit the Roadfly help desk.