Turbochargers & Superchargers: Theory and Application

robertmcdonald

Is there a clear "better" way of boosting your car (in the pressure sense of the term)? Are the losses of "turbo-lag" sufficent enough to justify going supercharger over turbocharger? Does it depend entirely on the car?

Lastly, if you think superchargers are better than turbochargers, why do so many sports cars (i.e., the 911 Turbo) use turbos instead of superchargers?

Thanks for your opinions!

8u6hfd

Jag & Benz use superchargers.

I believe there's no superior way. Both do its job, differently, with different characteristics of each.

jeprox

i could be wrong but from what i hear/know...
- supercharges are more expensive but you get less lag time. s/c is supposed to be much stronger too.
- turbo's are cheaper but takes a bit longer to get you going. older turbo's are more expensive to fix and break down easily.

8u6hfd

Superchargers are crank driven, by belts. They don't really exhibit "turbo lag". A roots-type or positive displacement (Eaton)SC will exhibit a very linear powerband. Eaton SC is used by GM, Toyota (TRD), Benz, etc.

Centrifugal SC shows more of a peakier powerband. THey also require a geartrain to spin it faster to be effective.

Turbos are exhuast driven centrifugal compressors. With proper design, lag can be minimized.

hpulley4

...you suffer large fuel penalties and other problems with a jumpy car due to very high idle speeds. Racecars use turbos with no lag by always using enough throttle to keep the turbine up to full boost speed, even if you are in neutral. Most street car drivers don't want to idle at several thousand RPMs all the time. Dumping all that into the clutch on every start is bad for it, as is putting that many revs on an unloaded engine all the time. This is why those racing engines don't always last the whole race and why they need a lot of work between races if they do survive.

Remember that neither system is a free lunch. You'll always get a more fuel efficient system with a naturally aspirated version. A SC that you can freewheel until needed is pretty much inert until you use it but while in use, much of the engine's power goes to the compressor instead of the wheels. You get more air through the system which yields more power in the end but the hp/gallon always goes down. The TC tries to be a free lunch by using the exhaust gases but it ends up being an exhaust restriction which hurts its efficiency. You get more power out of it but only at the expense of more fuel again.

8u6hfd

The WRX gets horrible fuel economy, for a 4 banger (something like 20/24 city/highway).

The VW 1.8T & 2.0L on the otherhand, get identical gas mileage (24/30 city/highway).

hpulley4

3 (yes, three) MPG according to an article on the racing team. 300hp out of 2.0L with lagless turbo won't get you an EPA award.

The 1.8T gets the same mileage as the bigger 2.0L when you would expect it to get slightly better mileage in the same car if it were NA. They are not just turbo and non-turbo versions of each other either (1.8T is 5 valve/cyl for a start). The 1.8T isn't nearly as high-pressured as the Subaru 2.0 so it isn't as obvious.

The turbo charger looks like a perpetual motion machine (using the engine to speed up the engine) until you see that it uses more fuel in the process.

rrossman

The biggest differences are pretty much already stated. But to run thru them again.. a supercharger is run directly by the engine, usually by a belt. Superchargers spin at lower speeds (in direct relation to the engine's rpms, and at much lower rpms than turbos spin) and provide pretty linear power. Turbo's spin off the exhaust, and are geared to spin in upwards of 60,000 rpm's. The higher spin allows them to move more air (but also causes higher temperatures, giving rise to the benefits of an intercooler). Turbo's usually provide alot better high end than superchargers, but superchargers tend to have better low end. This can be compensiated for on a turbo by lowering the spooling RPM.. and using a wastegate to vent the excess pressure made at the higher RPMs. (Without the wastegate, trying to make up for the spooling speed would cause too much boost in the higher rpms). Also, you can use a NOS Turbo kit, which feeds nitrous at the lower rpms to get the engine up to spooling speed quicker.

armtdm

A GM 3.8L SC V6 with 240 hp and a Mitsubishi 3000GT 3.0L 320 HP V6 twin turbo

No comparison. Sure the SC is smooth but oh so boring. There is nothing like those twin turbos kicking in and putting you back in your seat. The SC just doesn't seem able to do that, too tame and constant

8u6hfd

It's not really fair to compare the GM 3800 Series II supercharged to the Mitsu 3000GT VR6 either. They are tuned to perform in different markets (and the GM is also an automatic one)...

armtdm

It is really a difference of constant or smooth acceleration versus the kick of a turbop at 2500 RPM.

Turbos subject to cking if not idled down properly so it is more of a hassle to drive then a SC, especially if a daily driver, shopping multiple stopts etc. But, most peopel do not idle down for a minute either

8u6hfd

For turbos, though a lot people for the aftermarket are more concerned about huge power gains (huge turbos which take a while to spool up), a properly sized turbo can have minimal turbo lag.

For example the VW 1.8T has a very flat torque band, which (let's assume a 2001 1.8T in the Golf/GTI/Jetta/Beetle application) its torque peaks at 155 lb-ft at 1900 rpm. It stays in the near 155 lb-ft vicinity all the way to about 5000 rpms.

Let's take another small car example: the WRX. Below 3000 rpm, the turbo is not generating enough pressure for that "kick". After 3000 rpm, you'll feel a huge kick in performance. This is a case of a more serious turbo lag.

Twin turbo setups can have the same characteristics of either mentioned above.

Twin sequential, can have characteristics of both mentioned earlier.

For coking of the turbos, for most people, the idle down is not necessary. For customers of Volvo, VW, Saab, etc, where the vast majority will use it as regular transportation, the idle won't be critical (as long the oil is regularly changed).

If you're racing constantly from stoplight to stoplight, or keep the engine constantly revved closer to redline, then the issue of coking is more problematic (and oil quality), and hence you'll need to idle down for a few minutes, if not try to install a turbo timer.

So the real questions should be, which is better, turbo or supercharging for the following driving styles: light driving (point A to point , moderate (some racing of engine is necessary), & balls to the wall?
Right now we're trying to argue all aspects, but ultimately we won't get anywhere.

rezo00

First there are superchargers, which provide a linier increase in presure based on rpm (because of a real constant conection with the engine) engine spins faster so belt turns super faster.

Next you can have 2 little turbo's or one big one...2 little ones always offer less lag for a set boost because of less rotational inertia then the 1 big turbine...so they spin up much quicker...also engine rpm dosent have to be as high to get them moving...As for fule economy they can be made the same as a super or even better...
Intake air is hotter on a turbo because the exaust gasses heat the exaust section of the turbine and it is pulled through the metel rod (metel conducts) which connects the exaust and intake turbines. This is why new ones may be made of ceramic to reduce exaust/intake heat exchange...

fedlawman

I've heard that turbos only last about 50,000 miles because of the high RPM they operate at.

If this is true, wouldn't a SC be a better choice for increasing overall performance without sacrificing durability?

armtdm

Perhaps earlier Volvos etc had turbos go at 50,000 but now they seem to be as durable as the rest of the components. Of course in a Volvo that is usually 50,000 miles

8u6hfd

It just depends on high hard you use your turbo. It's mentioned earlier, to increase its longevity, allow the turbo to adequately cool by leaving the engine at idle for a few minutes (depending on how hard you flogged the turbo).

Centrifugal S/C has power characteristics similar to a turbo. In fact they are the same, except being belt driven.

mikemajesty

i dont know why you think volovo's crap out at 50 k miles. my girlfriends parents have a 760 turbo wagon with 180 k miles and everything is still original, even the turbo. h

scotian

http://www.gtiworld.fsnet.co.uk/Turbo.htm

armtdm

My opinion of Volvos has decreased significantly in recent years. What used to be a well built state of the art safe car is now a run on the mill luxury sedan built by individuals that take the entire summer off of for holiday. (try and get parts in August???) I know, that should have no bearing on the car.

Just based upon bad experience with Volvos and IMHO there is more scheduled maintanance on these cars then Amercvian or Japanese.

Overpriced purchase price, overpriced maintenance and overpriced parts.

swinga7

you could be one of those crazy guys that use a supercharger and turbocharger. the supercharger runs up to 4k rpm then shuts off and lets the turbo take over.

gives better low end response of the sc and the better high end of a turbo without the turbo lag.

saw an mr2 with that setup.. it was damn fast

badtoy

is that you can engineer one for ANY car. Much more difficult with a supercharger. There are many turbo manufacturers out there, and there are many shops with a lot of experience in turbocharging. Just don't go nuts with it, and you'll be fine.

andys120

I put over 100,000 miles on a SAAB 9000 Turbo and experienced no turbo-related or engine problems. Most of it was highway driving but with a lot of commuter traffic.
This was an early ('87) 9000 with no intercooler.

SPYDER98

I killed my first turbo at 70k.
I used mobil one during most of that period and always warmed and cooled the car for a few minutes.

On the downside, I beat on the car and ran higher than factory boost.

So...I can't complain

drmperalta

Super charger

Pros:
Consistently good torque at all rev range
No lag
Relatively simple

Cons:
Sucks usable engine power causing poor fuel economy.

Turbo charger:

Pros:
Highest power capability per unit displacement
higher torque curve over usable engine speed
improved fuel consumption compared to non-turbo of same power
better emission

Cons:
Needs enpensive heat resistant ceramic material
needs intercooler for optimum performance
low torque at idle and near-idle speed
turbo lag

stupendousman

Do the Veedubs (GTI, GOlf, Jetta, New Beetle) have intercoolers? If so, where?

isaacl

I got a friend who just got a used 98 Mustang GT with the 4.6 (as do they all) Anyway, he started asking me about turbo and supercharging and all that. (A little too much Gran Turismo....thinks a turbo will put him up 120hp or so...)I told him to research it good and think about common NA V8 upgrades. Cams, rods, air intake-and exhaust and all will make a 4.6 perform better. I don't understand how people want this "easy" bolt-on turbo w/out understanding the extra stress on a factory NA motor. Like you can just push all that extra air through and not damage parts that were made for only a specific degree of performance........Am I wrong????

armtdm

The car I have came in two version one with a twin turbo. I noted that the compression ratio for the turbo is much lower then for the non turbo version.Apparently the higher compression with a tubo could cause severe damage, at least in my model.

andys120

lower compression than their non-turbo cousins.

pantherburn

Check out www.miata.net

Guys are getting astounding amounts of hp out of turbos, but lots of fiddling with computer/fuel curves, etc... - $$$

SC - simpler, but much less power.

Again, this is with reference to the Miata. Lots of pertinent info on the above mentioned site. Check it out. I would love to turbo my Miata, but it's still lots of fun stock - Zoom Zoom !

8u6hfd

Yes, they have intercoolers. They are located on the sides, if you look at the passenger side intake grille, you'll see the intercooler (remove the grille for better visibility).

THe Audi TT, has them on both sides.

The Turbo Diesels have the intercooler in the same location as the GTI, Jetta, & New Beetle

stever

Do all cars with superchargers or turbochargers require high octane fuel to prevent engine damage or premature death? Or is this just a way to bump up performance another 5+ percent to appeal to the person who knows they want a turbo or SC engine?

Is there any difference in the designs that would require higher octane in a SC and not a turbo, or vice versa?

Steve, Host

carlisimo

And is there a difference between how a supercharger and turbocharger will reduce the life of an economy car's engine?

(I'm not saying I'm going to be doing that or anything... of course not...)

qbrozen

I don't know for sure whether ALL supercharged or turbocharged engines "require" higher-than-regular octane fuel. My guess is no, I'm sure someone has produced or does produce a car that doesn't "require" it. HOWEVER, the reasoning behind using high-octane would seem to me to be because of the higher pressures developed in the combustion chamber of a forced induction vehicle. Higher octane is needed the higher the pressure is in a cylinder. that's why vehicles that have higher compression ratios require it. So if you add forced induction to a car, you are increasing the pressure in the same manor, therefore you need high octane to avoid knocking.

carlisimo - of course, there is the standard strain of added pressure (see above) on an engine when forcing induction. In that respect, both are the same. It is my understanding, on the other hand, that a turbo results in much higher operating temperatures in and around the engine, so I would think that could negatively affect an engine that wasn't designed for it.

chris65amg

I guess I should tell you why...

 

Last Summer I was taking a trip in New Jersey. I was also in the market for a new car. I was vying for a new Solara coupe, or maybe a Lexus ES.

 

Well, the dealership was toyota-lexus, so the salesman had to go across the parking lot of the toyotas to get to the lexus-s. Anyway, I stopped him in the middle and asked him what that pretty black car was. (Yes, I like the way the '04 'rollas look better than the '05s. I think they look like lexus's.)

 

"That's a Toyota Corolla. It is a little smaller than what I expect you would want."

 

Then he tried to get me to buy the '05 XRS. >.< I got a fully loaded LE Corolla, and I've installed the navi. system, tinted the windows. My dilemna now is the engine. I'll tell you, I have absolutely NO experience with turbo's or SCs or whatever. I just want to turn my Corolla into a little luxury cruiser, and the engine is the last step. Any help you could give would be great Thanks By the way.... what's the plural form of lexus?

qbrozen

lexi?

 

highender

suburban (whipple supercharger) requires 91 octane or better. The increased pressure in the cylinder could cause premature detonation, thus the need for higher octane fuel...or else you run the chance of ruining your engine...

 

does the same apply to turbochargers ? don't know...but I heard that the lower octane do make the turbo cars turn out less horsepower....

bigfur

Every turbocharged car i have ever seen running a gas engine has always used the top level gasoline.

qbrozen

its not required on my volvo, AFAIK. I used to run premium in it just because I wanted to, but then gas prices went up and i switched to regular. I've noticed no difference.

highender

Previa 1994, which was factory installed....used only 87 octane....but the boost was very light//.....so maybe that was why higher octane was not needed.

calderon

TURBO IS A DRAG REALLY IT HAS A LOW POWER IN THE LOWER GEARS BUT AS YOU GET UP TO SPEED IN THE MID SECOND TO THIRD IT KICKS. WITH A HIGH END SUPER CHARGER NOT SOME 800 BUCK CHEAPY.GET A PAXTON WITH INTAKE COMBO YOU ARE GETTING FASTER GEAR CLIMB AND BETTER QUARTER MILE TIMES BUT TO TELL YOU THE TRUTH I DONT LIKE 4 BANGER OR A SIX. 8 ON UP IS MY MOTTO AND WITH GOOD SUPER CHARGER YOU CAN GET UP TO 140 EXTRA HORSES EVEN 160. AND A LOT OF THE GUYS ON THE STREET HAVE NOTHING JUST AN EXHUAST TIP THAT SOUNDS LIKE A BEE HIVE AND TO TELL YOU THE TRUTH CIVICS BLOW IF YOU AINT GOT OVR 350HP YOU ARENT CUTTIN IT SOME GUYS ARE PAYIN 40 GS FOR A 4 WHEN YOU CAN GET A 6.0 GTO 400HP 400 FT/POUNDS AND THE WEIGHT IS CLOSE TO A EVO 8 AND HAS NO SC

tidester

That would be easier to read if you turned off your CAPS LOCK.

tidester, host

calderon

miatas havent any good stock miata is a miata is a miata and will never cut it . people are spending alot of money on crap engines like that

panda_trueno

i'm new to all of these forum chats and such but i've noticed that there is not clear answer to what i would like to know. with a small car ( Elantra, Lancer, Corolla, Focus, Civic) you know that class, if i want to be quick around corners, tight or otherwise, what would generally be best a T/C or S/C? Is it even safe, or worth the performance, to TC or SC a 4 cyl?

I hope that didnt sound to mean, its just that i am frustrated with not being able to get a straight answer and find the info i want.

I appreciate any advice

Mr_Shiftright

Sure, it's always worth adding a turbo, since it is sort of "free power" but it has to be a well-engineered product. Less expensive as a rule than a S/C too, even though there's more plumbing and "messiness" under the hood than a S/C.

The REAL question though when we are talking about cars like Elantra, Lancer, Corolla, etc is the question of cost of modifying vs. cost to just upgrade to a faster car. In other words, maybe if you want a faster car you should just go buy a faster car. If you put a turbo on a 3-4 year old inexpensive car, you are never EVER going to sell it for the money you have in it. You may finding selling it AT ALL to be very difficult. So you are going to lose money on this type of modification on this type of car I think.

Supercharging is my preferred way to get more power since I like the driving characteristics of S/C vs. Turbo, at least in the "bolt-on" world. You can run a low boost, maybe 6 lbs with a S/C and get power right down low on the rev band. With a turbo, generally not much going on until 2500 rpm and then you get a big rush.

So I guess what I'm saying is that for that "class" of car, as you call it, I'd reallly hesitate to invest in a turbo or s/c---I think I'd upgrade first. You can buy a brand new or slightly used EVO and get a car that you couldn't really build up from a Civic or Lancer without great expense and effort.

john500

I think Mr. Shiftright's advice is right on. A supercharger is technically "parasitic" (meaning that you are attaching a belt off the crank to get the power and hence causing losses) but it is instantaneous and not subject to lag like a turbo. As long as the boost is under 6 psi, you will still probably get 150,000 miles trouble-free out of a Honda or Toyota. The real question comes to is it worth it. If you are looking for pure speed on a reasonably priced street car, I would go with a Mustang GT. Speed is mostly about the power to weight ratio. A current Mustang GT has about 300 hp stock and weighs around 3200-3400 lbs. The strongest Civic has at most 160 hp and weighs about 2700 lbs (new car data). To get the power to weight ratio of a stock Mustang GT, you would need to swap the Civic engine for the RSX-S engine and THEN supercharge it with full exhaust modifications to get the same power/weight ratio as a STOCK Mustang GT. From a cost perspective, it is easier and cheaper to just buy the stock GT. The GT owner still has a whole host of aftermarket parts to add on if he wants to pull ahead of the Honda owner again. Obviously, it gets more complex when you want other things out of your car such as reliability (which Ford's have a little more trouble with).

panda_trueno

I guess neither a S/C nor a T/C is the right choice for me. Because well you see i'm workin with a pretty limited wallet when it comes to buyin myself a vehicle. I have no other choice than to go with Used and i would love to find a used Lan Evo for the $ i've got (& believe me i would, the EVO and STi are my dream cars right now).

I dont mean to get too far off the topic of this Forum, but would you guys or anyone else have any suggestions of how i could increase the power (of any of the cars i mentioned in my first forum entry) and for a relatively inexpensive cost.

Once again thanks guys for helping me get some of my thoughts straightend out.

john500

Can't help you on the Elantra or Lancer. The Toyota dealerships have a bolt-on turbo for the 1.8 L Corolla that would probably net about 30-40 hp with an outlay of $3,000-4000. The Civic or Focus would be the most popular for moderate hp gains and some of the items mentioned can be obtained from www.eautoworks.com. Reported gains from a cold air intake (try to avoid the simple intake system as warm air displaces more volume than cold air and won't give as much of a power increase) vary from 3-10 hp and that would cost about $200-300 (www.aempower.com). A throttle body fits in between the intake system and the intake manifold. A larger diameter throttle body plate allows more air into the engine and can bump the hp up a reported 5-10 hp (about $300). A header pipe (replacement of your exhaust maifold) reduces engine backpressure and can give you 2-4 hp (usually with a slight reduction in torque). Finally, the largest source of exhaust backpressure is the terminal muffler. A free-flow muffler might add 1 or 2 hp. Almost all moderate methods of power increase involve simply getting more air into the engine (S/C, T/C, intake system, throttle body) and allowing more air to come out of the system (headers, muffler). More elaborate methods of power increase might involve replacement of the intake manifold (route of air into the engine after the intake system), changing the camshaft (timing of the intake and exhaust valve opening), boring out the cylinder diameter (requires expensive machine tools and is very invasive to the engine). Unless you are a backyard mechanic, I'd stay away from anything beyond intake, throttle body, headers and muffler. You might net about 10-20 hp for about $1,000. Making your car lighter with aluminum rims might add a little power also. Finally, if you need to replace a clutch, consider changing to a lighter flywheel so that you can get the rpm up quicker. It can get real expensive, real aggravating and real time-consuming in addition to having your car sit idle while you have to work or make a living somehow.

panda_trueno

Thank you [john500] for taking the time to explain all of these things for me it is really helpful and saves me from making some mistakes i would have regretted.

Mr_Shiftright

Great post, John, and "real numbers" too regarding HP and $$$. Obviously you've done your homework!

Have you done much research with chips, either substitutes or re-flash? I am finding some pretty extravagant claims (40 RW HP from a chip?!!!) and also some testing that suggests some of these things work pretty well and some don't and some do but are kind of risky because they raise boost on turbos.

Any comments on that? I think the chips relate to this discussion as some do affecdt turbo output.

john500

More like I've wasted my money in the past, but it is a fun hobby. No experience with computer chips, however, I have heard the same thing about them. The author of Civic Duty (a book written Alan Paradise outlining various car modifications to the entitled Honda Civic) claims that chip swapping on Honda's is somewhat risky business and best left to specialists, although I vaguely recall that he listed some impressive power gains. The guy on "Trucks" (Spike TV on cable) claimed to have increased the horsepower of a diesel truck by over 100 with a simple chip swap, no hardware. I also recall a rumor that in the late 80's and early 90's that Buick dealers were swapping the computer chips on Buick Grand Nationals because certain chips produced far more turbo output on the V6 3.8L..

P.S. Toyota actually uses a bolt-on supercharger, not a turbo as I had erroneously mentioned.

Mr_Shiftright

I could see a 100HP chip with a huge turbo boost but not otherwise. Sounds reckless to me. And that's flywheel HP I mean. RW HP would be pretty hard to believe.