Supercharger vs. Turbo

[2crunk]

Originally Posted by duplox

what do they run? as in boost? they'll run whatever you set them up to. They are a positive displacement compressor, which means every revolution, no matter how fast or slow, they'll move the same volume of air. So how much boost is a function of the displacement of the blower per revolution times the gear reduction of the drive of the blower, over the displacement of the motor per crank revolution. So basically, by changing the gearing on the blower you'll get whatever boost you want. The Cobra mustangs and Lightning trucks use whipple superchargers, which are similar to roots. They're also positive displacement. There are several types of positive displacement superchargers, pistons are a positive displacement compressor, vane type superchargers are positive displacement.. there are even Wankel style superchargers(rotary engines that are spun by another engine to compress air). Positive displacement types have no 'lag' whatsoever. Roots types aren't terribly efficient, some of the others are better choices. Whipple chargers are some of the best, and I believe vane types are also very good. Wankels are decent but no one makes them anymore(they were used long ago.. like 5 decades ago..) Piston types arent very efficient and arent practical. They're almost as big as a piston engine, so whats the point? I think Roots types are used in professional drag racing because they're simple and they move huge ammounts of air for their size. And considering how big they are, you get an idea of how much power these motors make! I'm not sure where you would get a roots or any other positive displacement type supercharger for a 4cyl, most superchargers, especially roots/whipple, are focused at the v8 market, while most turbos are focused at the 4cyl market. In my opinion, the situation is very backwards.. v8s should be sporting the turbos with their ability to provide big flat torque curves, plus v8s don't really need to worry about low end torque before the turbo spools, they've got that covered... And the 4cyl will really get a benefit out of a positive displacement type blower, since it'll provide boost at any RPM, so it'll give them a boost in low end torque, but still feed them way up at 7500, 8000, or whatever RPM they'll spin to. 8cyls don't need to rev that high to make their power, they're better suited staying around 6500, and thats perfect to take advantage of a turbo's efficiency... The 4cyl needs the RPMs to make its power, and a positive displacement supercharger will both boost its power up top, and help it out down low where it isnt so strong.
I suppose if you wanted a positive displacement for a small motor, you could buy a whipple charger and gear it down a bunch. I'm not sure if it'll work too well though. The ones for the mustang and Lightning are designed for 8psi on 5.4L, so you'd have to gear it down a LOT to get it to work on a 4cyl. It might not work, and if it does, it'd probably be pretty inefficient.

This might be a really ignorant question but, to have roots blowers would i need to have a supercharger, sounds like i would, but i'm new to mustangs and V-8's. Also, i heard of a stock 4.6L (i'm guessing Cobra, magazine article didn't say) achieving unbelievable 1/4 mile times with only a smaller blower pulley....again, is this only with a supercharger or would my '03 GT have this as well.

[duplox]

First off, sorry about all the 4cyl references, I'm also a regular on the Turbo/Supercharger/NOS part of the Honda/Acura section of this forum, and forgot this post was on the Mustang part... And no, I don't own a honda/acura, let alone trying to get power out of one with a blower or NOS. I'm just big into forced induction, mainly turbos, so I go there to exercise my blower knowledge(and keep the ricers from fuckin up their mom's civic...) and to offer advice to help them in their fruitless struggle to make power from a 2 liter inline four in a front wheel drive car(after all, we need SOME competition from the ricer community!). But I really don't think any honda is gonna come close to touching the twin turbo'd 351c in my '69 stang...

A roots blower IS a supercharger.. if thats what your asking. Usually they go on top of big v8s, with either a single or dual carbs sittin on top of that. The common GMC 6-71, 8-71, 10, 12... etc are roots blowers. These are the ones that you always see on hot rods and drag cars.

Starting from the top, you have your air scoop, it houses the filters and directs air into the carbs, which are directly below it. They are the ones with the small hard lines running around them(fuel lines, those are holley double pumper carbs). Then under those, that huge chrome thing, that is a roots supercharger. Probably a 6 or 8-71. That looks like a big block chevy to me, probably a 454. BDS(Blower Drive Service, www.blowerdriveservice.com) is the company that made that blower. That is obviously way to huge for a 4cyl. The way a positive displacement blower works, like a roots supercharger, is that on every engine revolution it moves more air than the engine displaces. Its simple ratio math.. if it displaces say 700 cubic inches of air for every time a 454ci big block chevy turns over twice(since its a four stroke like most automobile engines, each piston only intakes air every other crank revolution), it would be 700ci/454ci.. pressure ratio would be about 1.5. To figure out what that'd be in PSI, the formula is simple.. ambient air pressure times pressure ratio, minus ambient air pressure.. so 1.5 x 14.7(pressure @ sea level) - 14.7. That comes to about 7.4psi. If you put a smaller gear on the input of the supercharger, the internals of the supercharger will turn faster.. this means the blower will displace more air per engine revolution. Say you changed the gears to increase the displacement per 2 engine revolutions to 1000ci. That would increase the pressure ratio to 2.2, or 17psi. This is why putting a smaller gear on the supercharger will increase boost pressure. That is why when they put on a smaller blower pulley on a 4.6 cobra, they ran faster.. they simply increased the boost. This would only work with a supercharger, obviously. But you can get small gains(nothing near what increasing boost would get you) by installing underdrive pullies on your non-supercharged GT. What this does is make the gears on your alternator and water pump bigger, so these units don't spin as fast. As a result, it takes less effort to spin them, and when talking about engines, effort is horsepower. However, there is a compromise, since the water pump will not move as much water and the alternator won't make as much power. Generally, most auto manufacturers will overshoot on the size of the pullies, making them smaller than they need to be to provide sufficient cooling/charging. This is so they aren't in risk of either causing the motor to overheat(underdriven water pump) or incapable of maintaining the charge on the battery(underdriven alternator). So there are many aftermarket kits available to underdrive your water pump and alternator. But you have to be careful, keep an eye on your voltage guage(if you have one, if not, install one if you install underdrive pullies) and water temp guage. Water temp typically isn't a problem, but if you're driving along on a hot day(so the electric fans are going full tilt) and blasting the radio and A/C, your alternator may not be able to keep up. Your battery will lose its charge while your driving, resulting in a stalled engine and a call to the tow truck or a friend with jumper cables.
If you are looking to supercharge, obviously a GMC 6-71 or whatever roots supercharger isn't really an option, I dont know of anyone who makes a manifold for a 4.6 to fit a GMC blower(although if you really wanted one, I'm sure someone could make you one.. hell, I could make you one!). And it would require a rather large hole in your hood. Passing emissions would be a massive chore as well! However, Vortech makes a couple centrifugal supercharger kits for the 4.6(my friend has one on his 2001GT, its pretty quick! I think he runs somewhere around a 13 sec 1/4 with 8psi, but I think he should be running quicker... I think he has trouble hooking on launch). If you wanted a positive displacement supercharger, I believe Whipple makes a Lysholm type(aka whipple-type, they've really been the ones who popularized Lysholm types as of late, so their name as been stuck on as the type of compressor, even though technically its a Lysholm screw type...). I know they make one for the 4.6/5.4, since they manufacture the one in the Lightning, but I'm not sure if it'll clear a stock GT hood. Probably can be done, if not, I'm sure with a cowl hood they will. They are much lower profile than a Roots type.

[flex339]

One of my favorite quotes was "It's not turbo lag. It's foreplay."

[duplox]

HAHA I've never heard that.. thats great!

[Los]

If you want 1/4 or just a drag setup, go with a supercharger (roots/centi). If you want to whip rice, go with a turbo; but they're friggin massive with all the plumbing.

[duplox]

yeah, its a bitch to route all the turbo piping. I started off using stock cast iron exhaust manifolds with custom extensions for my twin turbo system, but right now I'm in the process of making custom headers. The turbos were originally in my fender wells with the stock exhaust setup because I had NO room up front in my '69. I've since pulled the motor in the car, relocated the radiator to in front of the radiator support(gave me about 4 inches up front), and I'm in the process of installing a remote electric water pump to get rid of that bulk up front. I'm relocating the alternator to sit further back using a serpentine pulley setup from a '94-'95 mustang gt and a custom bracket.. Then I get to install a remote oil filter to give the headers room to go foward, the battery is already in the trunk.. so after alll of this I have a bit over a foot in front of my motor to fit both turbos. I'm also going to notch my shock towers to get more room around the headers so I can use larger radius bends for better flow. Should be a nice setup, better than in the fenderwells!

[MrBB]

Originally Posted by 2crunk

I'm sure i will have crappy gas mileage, but if i was worried about gas mileage i would have bought a KIA. lol....But thanx for the info.

Correct me if I am wrong, but wouldn't a supercharger give you better gas mileage? (assuming your foot isnt in it) If you compress the air in the chamber don't you get more bang-for-your-buck in terms of detonation of the fuel because the explosion is more violent?

[Cobra01TT]

No, because a supercharger creates parasitic drag on the engine, like A/C. A turbo uses the heat from exhaust gasses to spin, which is already spent anyways. Most people with turbo mustangs that I've talked to said that they got a small boost in gas milage with it, if they didn't step on it all the time.

[Hypsi87]

Turbo lag is a result of torque converter selection,cubic inch,a/f raito and turbo size. Turbochargers are excelent for drag racing (espically behind an automatic.) You just have to learn how to build boost at the line (Transbrake)

[SVTcobra306]

Hypsi said it. Not ALL turbos have lag. Look at my '89 Daytona. It has a 2.5 liter 4 cylinder. Zero lag with the stock tiny mitsu turbo. I mean zero. It will build 12 psi with the tranny in neutral and the wastegate unplugged!

a Garrett T-03 (same as a T-3 but built for a chrysler) with a .48 exhaust housing has very very little lag on the same motor. Most of the "fast" turbododges I know of run a 2.5 with a hybrid and .63 housings.

Single turbos driven by 8 cylinders have proven the most efficient moslty because you can spool a massive turbo with 8 cylinders and flow a lot of CFM.

Centrifugal superchargers have been used widely on 'stangs because it isn't far from a bolt-on affair. Some of them are bolt-on, the ones that don't require oil line plumbing.

The problem with running a turbo is the fact that Ford EEC electronics have no provision in them whatsoever for timing retard and fuel enrichment under boost. Yes, the pressure regulator will up the PSI, to a point, but you still need some kind of FMU and boost retard...

[thunderbird muscle]

I like superchargers they just seem to sream muscle to me, but to each his own. Also depends on what it is going on.

[duplox]

Sure, if you size your turbo small enough, you can essentially eliminate lag, but your top/mid range HP will suffer horribly... its not a worthy tradeoff. If you size your turbo so you have no lag whatsoever you're giving away HP. If you select a turbo with a small enough housing to give boost around 1500rpm, you will not make power much above 4000rpm.. your exhaust pressures will be extremely high, your compressor's efficiency will be in the crapper, and your compressor might not even be able to keep the boost up. Let me put it this way... all true *performance* turbocharged engines have turbo lag. If you want a bit more passing power out of your daily driver, sure throw a small turbo on there and run 5psi. If you want to make power, put a larger turbo on. You wont regret it. You won't have as much power below 2500 or 3000rpm, but in the split second it'll take you to go from 3000 to 6500, you'll forget all about it. If the turbo on your dodge will spool 12psi in neutral, it is severely undersized. If I were turbocharging a car(and I am.. my '69) I would never ever consider a turbo anywhere near that small. The turbo shouldn't make any kind of boost without a load on the engine, certainly not 12psi.
As for what transmission, if you're drag racing, go with an auto. That way you can load up the engine and build boost on the line.. just revving it up with the clutch in will not(or rather I should say, should not!) build boost. If you're doin any kind of track racing or for a street car, I'd say go with a manual. That way its a bit easier to keep the turbo in the rpm range where it makes boost, plus you get more power to the ground. And its more fun!

[SVTcobra306]

I'm not saying that pathetic mitsu is good, just that it is possible to not have lag.

Anyway, properly sized twins on a V-8 doesn't produce really noticable lag since there is some low end torque present already, so that's a moot point. I think it would get along well with a twin .60/.63 setup....(turbo t-bird t-3's, I believe)

[duplox]

Yeah, I pulled my t3's from a turbo t-bird with a standard trans. The auto's had I think .60/.48 or something like that. A bit too restrictive, though those would probably work nice on a higher revving 302 running high boost. I cant wait to get my car together, it should move quite well. I'm expecting to run 10s, although I wouldn't be heartbroken with 11s. If I can manage a bit more than 15psi, and I should with all the prep I'm doing to avoid detonation(I won't get into that, it'd take pages, but pretty much anything you can think of, I'm doing.), I might be able to get into single digits(and promptly get kicked off the track!). Should keep the civics in line at the very least!
I know the mitsu isn't exactly a performance vehicle, I wasn't saying it was your fault or anything... Most manufacturers put quite undersized turbos on their cheap sports cars. Many sort of casual performance buyers don't like lag, so they put small turbos on to avoid this. But if you've ever driven a higher end production turbo cars(like the audi TT or a porsche turbo), they all have pretty noticeable lag if you try to gun it while cruising at 2000rpm(My father's TT will barely move if you do this..). But after driving the car for 15 minutes, you'll know exactly where the turbo works and where it doesn't, and shift accordingly. I must say, with the high ratio gearing and incredible handling of that car, its a blast to drive like a demon, as long as its under 65mph. After that the car's power to weight ratio gets pretty evident, but the gearing in the first three gears gets the car up to speed pretty fast.

[Hypsi87]

t-3's on a 302. Kinda small for the setup I would think