FoxGT

I really don't understand the adjusting boost for driving... If you're not on the throttle there is no boost. I could keep my car in 2nd gear @ 60mph turning around 5krpm & still see no boost if i'm keeping it steady.

Having high psi is not a problem for any type of supercharger or turbo. positive displacements can't do much while the throttle plate is mostly closed due to lack of air. Centrifugals have to have higher rpm to produce enough air to pressurize the intake. Turbos have to have exhaust gasses to spin the turbine fast enough for the impeller to move enough air to create it.

I've built roots, centri, & turbo kits. Neither have a problem with drivability while you're not in the throttle. My experience with twin screw is limited. Never built kits, had a little bit of experience by working on cars with them, thats it.

natbel08

another vote for turbo if you have the money

boss_dude_429

ok this is a complicated question to answer but i'm gonna narrow it down for you if you decide super then get a ROOTS, "key word there", like a 4-71 or a magna charger, or turbo it, cetrafugal s/c's just plain suck, worst form of FI period, i think we can all agree on that one, now back to the topic at hand, a roots blower, which is what i run, make boost at IDLE no lag at all, the turbo can make boost with higher cr pistons than a roots, roots must have 8.5 and below, the tubos must use a waste gate and the like, but most serious roots and all turbos use a blow off valve, me personally i'm a dyed-in-the-wool 8-71 fan, a REAL 8-71, original detriot diesel one, is MAZZIVE like a foot tall, without a manifold or carbs and air filter, and 3-foot long without the pullies and belts and another foot wide, the turbo can give you the knock your socks off sleeper just blew him away thingy, me i like people not to mess with me unless they're a real challenge, but hey thats me, listen im not a REAL expert but i know a thing or 2 so if you need anymore info PM me i'm happy to share

FoxGT

I definitely don't agree with centrifugals sucking. I think centrifugals are great superchargers. The compressors are more efficient at high rpm.

You can run them on higher than 8.5:1 cr. I've built kits that have ran on 9:1 & 9.5:1 on pump gas. the 9:1 setup was ran at 10psi on 91 octane.

Roots superchargers do not use a bov. Some designs use a butterfly style bypass valve to equalize the pressure before & after the supercharger while under cruise conditions so the rotors will freewheel at cruise so there is very little loss in fuel economy. They're able to do this because the roots type supercharger doesn't compress air in the case, it just moves air & it's compressed in the lower intake (in a top mount setup). The other types of compressors can't do that & the bypass valve (or bov)'s purpose is only to vent the air out when the throttle plate closes to prevent it from trying to spin the impeller backwards.
Same applys for centrifugal superchargers & turbos. On any setup it's a good idea to run a bypass or bov, but if you're not running an intercooled setup & have relatively short intake plumbing then it's not as big of a deal. If you run an intercooled setup or have quite a bit of intake plumbing then it's a big deal. Imagine you're pushing 12psi with the throttle plate open, then you let off, the plate closes. When that happens pressure before the throttle plate shoots up extremely high so it pushes against the impeller, If you have lots of intake volume then it will keep pushing until all of it has went back out through the compressor. On turbocharged cars it actually causes the turbo to spin backwards, for centri s/c it can cause the belt to wear fast; both cases it's very bad on the bearings of the turbo/sc.

As with turbos though you need to get a roots sized for what you're aiming for, you can go too small & you can go too big which will cause a drop in efficiency. Also as far as money goes If you have the money to spend & do decide to go with a roots look for the 4 lobe 160 degree lobe design, they're quite a bit more efficient & are still good at higher pr's. The older 3 lobe 60 degree like to stay around 1.6 pr on the stock case.

For the record, vnt turbos don't use a wastegate.

rob.d

I say go for more CID. You can never go wrongwith more dispacement. A pro engine builder once said "Supercharger's and Turbo's are for people who don't know how to build engines". I have to admit that I love the look of a huge supercharger sticking out the hood of an old muscle car. I just don't have the same feeling for the turbo's. Anytime I here turbo I think of school buses and ricers. I know that they are very efficent and make big power, but they usually kill the one thing that I lovethe most about our V-8's, and that is the exhaust note. To each thier own.

2000AZ5.0GT

No sh*t your not a real expert, your absolutely wrong. You think a centrifigal sucks? take a ride in my car, 550rwhp, and you will be saying something completely different, especially in a street car. I can guarantee you have no clue what you are talking about

FoxGT

Turbo's don't kill the v8 note at all. The only thing a turbo will do to your exhaust sound is make it quieter. If you've heard one that sounds ricey I wouldn't blame the turbo I would blame the exhaust setup they're running after the turbo. You have to think though, most people that run a turbo on their car want people to hear it, they don't set it up to be quiet. There are quite a few things you can do to make the turbo next to impossible to hear.

Not trying to convince you that you should go turbo or anything. I've built quite a few kits & like s/c's just as much as turbos. They both have their upsides, but as far as exhaust note the only major difference is how quiet the exhaust is with a turbo whereas superchargers from my experience seem to make it a bit louder under boost. Then again i'm not really a big fan of a really loud car. I like it to be louder than stock, but not by much.

doogyhap

I went PD supercharger to avoid messing with the exhaust. I did not want to deal with possible exhaust leaks or excessive heat problems. I know that is probably easier to deal with than a belt problem. I have never had a turbo, so I cannot make an honest comparison, but the individuals that have them love them.

ESG-642T

Turbo:

If you can read compressor maps , build your engine, and properly size your turbo you can almost catch a positive displacement (on the dyno) and still have power up with the centri's (on the dyno)

FoxGT

Well if it wasn't for the hp loss from the belt I prefer 100% positive displacement superchargers. They're way more fun to drive imo. For the cars I actually intend on going out to find a race I prefer turbo, for a daily driver car with things like a/c, stereo, ect... I prefer a roots s/c. A car you're building all out you kinda gotta cut down weight like losing the a/c, no big stereo, ect... Heck I have manual windows & manual locks in my turbo notch I took out the front bumper & cut into the headlight bracket just for room to fit my intercooler, I'd never do that to a nice daily driver car.
I'm confused... what do you mean by almost catch a pos displacement supercharger?