Turbo versus super charging

[tk064]

I was looking at a conversion for an old truck and couldn't fit the turbo in without significant mods.



I started thinking and I had plenty of room for a supercharger and I was wondering what the main differences are.



Thanks for any help

 

[lil red cummins]

wow, are you gonna get lots of answers on this.



1. turbos have lag when you floor it, blowers dont.

2. turbos only use waste gas pressure to run, blowers always require mechanical drive power even at idle.

3. blower compressed air tends to be a little cooler than turbo compressed air, however both increase air temp with pressure.

4. blowers do not require cool down time - turbos do.

5. a blower is considerably larger than a turbo, based on equal amounts of volume and pressure.

6. blowers become disproportionately expensive as their boost pressure capablities goes up. most don't go beyond 15 lbs.

6a. turbos go to 40 lbs or better in one stage.

7. i have never seen a wastegate on a blower. blower speed must be closely matched to engine displacement and desired max boost.

8. finally and most important:



turbos have a cool sound - blowers just make noise.





jim

 

[bmoeller]

Blowers also take some power to run. Turbos don't.



You can get superchargers with a turbo compressor housing instead of a regular blower (like a Detroit uses. )

 

[britannic]

Approximately 33% of an engine's power leaves via the exhaust, another 33% is turned into heat and exchanged through the cooling system, the rest is sent to the flywheel. A turbo salvages some of that 33% waste exhaust energy.



A supercharger uses some of the 33% that would have gone to the flywheel, but also generates more power to compensate. As already stated, superchargers are more responsive and generally give more low rpm boost, but a properly set up turbo is reclaiming waste energy, so at WOT, you can potentially get more power.



A turbo supercharger combination would be nice too...



Note: all %s are approximate and the proportions may vary on any given engine.

 

[lil red cummins]

thank you for reminding me bmoeller about the "paxton" style supercharger. these were made famous back on the old studebakers in the 60's. i believe they used them also on WW2 aircraft, but not 100% sure about that. they are still available with i believe the paxton name on them. andy granatelli (sp?) owned the company at one time. not sure who owns it now. they are called "regenerative" blowers.

jim

 

[bmoeller]

Originally posted by lil red cummins

the "paxton" style supercharger.

Thanks, I was drawing a blank on the name.

 

[tk064]

I knew the exhaust vs belt drive power differnce and I was thinking that the lack of a waste gate could be a problem. I think most of the superchargers I have seen are in the 7-10 psi range. I know that is lower boost than most people are using.



I know the paxton style chargers are advertised in summit racing. I don't know if they differ in boost capabilities from the roots type.



And I like lots of opinions, keeps us from doing everything the same old way.



Thanks for any (or more) points of view.

 

[Forrest Nearing]

how could you not have room for a turbo but still have room for a centrifugal blower? power-to-power a centrifugal blower is larger than a turbo. just mount the turbo wherever you have room and run the exhaust and oil to and from it...



Forrest

 

[1stgen4evr]

blowers and turbochargers

There is another consideration for selection of one over the other. To get the max out of a supercharger you need a different cam shaft with complimenting valve overlap. The exhaust needs to open a bit sooner and the intake needs to remain open a bit longer. The cylinder pressure needs to drop as much as possible before the intake opens for max intake. These engines sound like they are operating retarded with a guttsy blatt sound in the exhaust.



I am sure that someone can regrind a cam for best performance of the supercharger. Allis Chalmers used the superchargers with very good success on their equipment in the 50s. As suggested, there are more ways to do this job than with the turbo. However, from my perspective, the turbo is the all-round better choice.



With the turbo, the valve operation is the same as normally aspirated engines. I don't know what you are putting this in but look good for the space to shoe horn the turbo in there. Chances are that it will go. All the superchargers are pretty big as well.



Still, it IS fun to experiment. Pick one or all and go for it. Turboed, supercharged, intercooled, bad A** truck. Do it nice with lots of chrome and leave the hood off.



1stgen4evr

James

 

[y-knot]

Whats this stuff about blower not sounding cool??? Blowers are awesome, but what makes them sound so nice is really the 2 or 3 inch, belt that drives them. I'm referring to a REAL blower (6-71) with a Gilmore belt drive, not the small Paxton or like unit. Any how, the unique drive traps air as the pulley rotates and make for a wonderful sound.

Yes blowers take power, on a top fueler they require about 800-850 hp to turn them as they go down the track, but they also make 8000 hp in the process. Have you ever wondered how much fuel it takes for them to run 330+ mph? Next time you are in the shower, take a good look at the shower head and how much water is flowing out. Now try and visualize ten (10) more shower heads all flowing that same amount, that is how much fuel they are using at the high end of there run. Make's your diesel look like it's sipping tea or something.

The blower has the advantage of instant boost, it rollers are always turning and real boost is gust a touch away. They also are limited by high wear rates and belt wear. I have seen several diesels that were both blown and turbocharged. This would seem to be the best of both worlds, the instant low rpm help of a blower, and the higher end kick of a turbocharger (turbo's are feed from the blowers).

 

[1stgen4evr]

lots of answers

Litttle Red was right on with that even if he doesn't think too much of the sound of a blower. The Allis Chalmers engines I had used a v belt drive on the blower and did a good job. The blowers I mean. I haven't been close enough to a fueler to hear the Gilmer belts. The 6-71 blower does look cool with chrome and all. Go for it. The turbos have a high whistle that I have been around too long. I hear the whistle even with the engine off. But if you are going to drive this thing around regularly, stick with the turbo.



My two cents.



1stgen4evr

James

 

[britannic]

How's this for a twin turbo 9. 27sec terminal 142 1/4 miles diesel, he may have blowers as well, but it's hard to tell: #ad




#ad




#ad

 

[1stgen4evr]

Super. I have got to go to the track more often. Its been years and there is another whole different bunch of racers out there now.

 

[Mechaneck]

I was discussing this exact same thing with a co-worker recently and we found this web page. Although it's aimed at gassers the theories apply.



www.turbochargedpower.com/Turbo vs Blowers.htm





Keith

 

[GWDiesel]

Turbo vs supercharging

No matter which way you go, just remember to inter cool if at all possible,your motor will live a lot longer if you tow or carry heavy

loads,just my. 02 worth. GWD

 

[britannic]

YMMV, if boost is over 14psi, an intercooler becomes practically mandatory in the high ambient temps. to ensure there's enough oxygen and not just high pressure hot thin air...

Originally posted by GWDiesel

No matter which way you go, just remember to inter cool if at all possible,your motor will live a lot longer if you tow or carry heavy

loads,just my. 02 worth. GWD

 

[WestTN]

difference..

A turbo provides variable boost according to load, whereas a blower provides relatiely constant boost according to RPM's. On a gas engine, the air is regulated, so a blower works pretty well. Since the air is NOT regulated on a diesel, the blower will provide too much boost and waste power unless it is sized to provide inadequate boost for high power levels.

 

[nickleinonen]

Originally posted by britannic

How's this for a twin turbo 9. 27sec terminal 142 1/4 miles diesel, he may have blowers as well, but it's hard to tell:

i believe that engine there is an aluminum block 6v92 detroit.



on the 2 cycle diesel engines, they all have blowers [most mechanically driven, some electrically driven on marine ship engines] on them to provide the scavanging air, but they are considered naturally asperated. the blower doesn't provide boost, just air volume. at idle, there is just a few inches of water pressure in the intake below the blower. under load, there is a little more [but i believe it is still under 1 psig]



2 cycle diesel engine power cycle:

#ad

 

[bubba_zanetti]

The intercooler has another important job... it is part of the air cycle machine, and the cooling effect also increases the density of the air... at the cost of a few psi drop in boost.



It is that dense air that really helps the engine produce power.



As the turbo compresses the air, the air heats up.