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Re: TURBO (kinda long) (archive)
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Posted by Da Hose on June 27, 2000 at 00:45:23:

In Reply to: Re: TURBO posted by Rob S. on June 26, 2000 at 00:18:21:

As I understand it, with longer intake runners you get more torque at the bottom end. If you are going to go with forced induction, then a conversion to dual side-draft throttle bodies would probably be the best option. The injector can be placed directly behind the butterfly instead of in the head and you free up a little room underneath which might help reduce temperature vs. the 318 intake runner. I have begun collecting the parts for a turbo setup and have a 318 intake with a larger 5 series throttle body. The more I look at it, the more the dual side-draft appeals to me. Looks better too. As far as performance, if you look at the Audi S4, they have managed to get a flat torque curve at 265 ft/lbs of torque beginning at 1850 rpm all the way to redline. Granted that is a V-6, but it peaks at 250 hp. Excellent numbers. This makes me believe that getting good torque at the 2000 or so rpm mark is reasonable on a 4 cyl and when you drive em hard, you stay above 2000, so I don't think you would see much of a problem with lag. Take a look at the Vortech units again. The V9-G Trim makes up to 20 psi boost with an efficiency of 72% and the V7-YS makes 29 psi at 74% efficiency. I need to call those guys and ask what the air temp gets to. You would have to use a blow-off valve that would be running almost all the time though. Given all the complications of either method, I still think the Turbo seems to make more sense.

: Well, its complex but it basically has to do with how typical centrifugal superchragers limit boost.

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

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