Supercharger questions

[Nick Kickass]

Why are intercoolers/water cooling used on superchargers? I would imagine hotter intake temps in the case of a turbo are because the turbo is on the headers and gets extremly hot but I can't imagine the supercharger getting that hot.

Does that make any sense? Basically, what I'm asking is, are intercoolers/water inj as important on a supercharger as on a turbo?

I've heard superchargers are easier to tune too wheras turbos are tricky - is a well tuned supercharger as reliable as a well tuned turbo?

Thanks
-Nick

 

[DrBoom]

air still heats when it is compressed weather its a turbo or supercharger, but still cooler air creates more power.



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[Uncle Bob]

as drboom suggest, compressing air causes heat. Its a byproduct of compression. The way the different forced induction systems are rated is by how efficiently they compressor air, which translates to X psi of compression = X degree's of intake temp increase. The more efficient mode of forced induction, increases the intake air temp the least per psi.

As a general rule, turbo's are THE most efficient compressor for forced induction systems for engines. IE, they heat up the air the least amount for a given psi. So your base assumption that SC's are better for this are false. The closest example of a SC that competes with turbo's in efficiency is a "procharger" which is basically a turbo that has a belt driving it....but they don't have the mid range power that a turbo has...not even close.

 

[Don Hardcastle]

Cooler air is more dense, therefore more O2 per cubic centimeter, more O2 = more combustion = more power.

A turbo is the most efficient because it doesn't take any power away from the engine to run it. Unlike a supercharger that is turned by a belt, shaft or gears depending on the set up.

 

[Uncle Bob]

no, a turbo eats power just like any forced induction system.

The advantage to the turbo over a SC is its uses SOME of the wasted energy from the motor, exhaust heat, to power the turbo. But there is still a power loss, more than you might suspect, from the turbo.

Turbo compressor maps never show the parasitic power loss (thats not the right phrase for it, but you know what I mean) in their efficiency maps, but SC usually do.

 

[Don Hardcastle]

no, a turbo eats power just like any forced induction system.  

The advantage to the turbo over a SC is its uses SOME of the wasted energy from the motor, exhaust heat, to power the turbo.  But there is still a power loss, more than you might suspect, from the turbo.

Turbo compressor maps never show the parasitic power loss (thats not the right phrase for it, but you know what I mean) in their efficiency maps, but SC usually do.

Hmmmmm,
I have to disagree. How can utilizing exhaust gases rob power from the engine? Unless, it is by the increased back pressure due to a restriction in the exhaust path.


Don

 

[Uncle Bob]

well, the next friend of yours that has a naturally aspirated bike that you would like to play a gag with, stick a potato up his exhaust can with a tiny hole drilled into the center of the potato, and then challenge him to a race.

Severe restriction of the exhaust costs power. A very free flowing (large) turbo will still have a 2:1 ratio of exhaust pressure vs intake pressure. In other words, if you have 15psi on the intake, you will have 30psi on the exhaust. This pressure reduces efficiency because the engine has to work harder to overcome the pressure in the exhaust, and of course, an SC'd engine will have no notable back pressure in the exhaust, assuming they built it half intelligently, so they will not have this issue.

A undersized turbo can be as high as 4:1 ratio.

 

[Sloto200]

 

[Gary Evans]

Obviously the high header pressure cost hp but a 2:1 situation would be a worse case example on a bike. I actually measured the header pressure on my last bike and although I don't reminber the exact value with 18 lbs in the exhaust side peak was something like 15psi. This was with a relatively small IHI turbo on a 1100cc engine.

 

[Uncle Bob]

its impossible to be that close to 1:1, are you sure you're not refering to the pressure after the turbo? Pressure differntial is how a turbo generates the intake pressure. Having a higher pressure in the intake vs the exhaust would be called perpetual motion.

edit: let me rephrase that: higher flow in the intake than the exhaust would be perpetual motion. Although PSI isn't a direct relationship to flow...its definitely related



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[suzuki4life]

its impossible to be that close to 1:1, are you sure you're not refering to the pressure after the turbo?  Pressure differntial is how a turbo generates the intake pressure.  Having a higher pressure in the intake vs the exhaust would be called perpetual motion.

edit: let me rephrase that:  higher flow in the intake than the exhaust would be perpetual motion.  Although PSI isn't a direct relationship to flow...its definitely related

I disagree.

intake pressure normally is higher than exhaust pressure because intake pressure is contained and exhaust pressure is vented. Now of course I am talking overall in the system and not focusing on one elbow or inch of the system.

Remember, the exhaust gases turn the turbine in much the same way the river turned the wheel at the old saw mills. To estimate or compare reasonably in these terms you would need to be a lot more specific because the engine requires a certain amount of backpressure to operate properly...however, it doesn't need anymore accessories to add drag.

now lets talk applications:

stock motor....no backpressure...runs like crap.
stock with turbo...no back pressure beyond turbo.....spools fastest but tends to backfire on decel.
stock motor with supercharger...no backpressure....really runs like crap.

 

[Nick Kickass]

So if reliability were the main criteria, would a supercharger be better than a turbo or worse or pretty much the same?

 

[Gary Evans]

Terminology of my example.

18lbs intake manifold pressure.
15psi turbine inlet pressure.

I don't have a lot of experience with this ratio having only tested my own but Corky Bell (Maximum Boost) suggests that a ratio over 2:1 indicates the turbo is too small and that race applications should be less than 1:1.

 

[Uncle Bob]

So if reliability were the main criteria, would a supercharger be better than a turbo or worse or pretty much the same?

there is nothing inherently better or worse, reliability wise, between a turbo and a SC.

 

[Uncle Bob]

intake pressure normally is higher than exhaust pressure because intake pressure is contained and exhaust pressure is vented. Now of course I am talking overall in the system and not focusing on one elbow or inch of the system.

I am not an engineer, nor have I tested back pressure on a system. But I do read a lot of turbo forums, and have read many accounts of people datalogging pressures....they are always higher in the exhaust. My understanding of physics says this only makes sense.

I would be curious if a turbo system builder would comment on this, if they have ever tested this on their systems. I have no doubt that the 600+ HP busa systems have very low pressure ratio....but I would still expect it to be over 1:1.

Corky Bell is a common referal to turbo systems, but incase it hasn't been pointed out, a lot of people disagree with a lot of his points....but that being said, I have a couple of his books, and I'd have to get one out to double check, but I believe he also said, 2:1 is normal for a well sized system.

 

[Uncle Bob]

here's just an example of one I found after a quick search. This cat has a drag race car with a very massaged 302 SBF with a GT88 turbo making 900 HP to the wheels. Yes, this is a completely different application compared to bikes, but this is a full on race car, definitely not an undersized turbo for the application.

RPM...INT....EXHAUST
3640 ...0.0 ...5.9
3750 ...1.7 ...7.8
3950 ...3.2 ..10.8
4200 ...5.5 ..12.7
4470 ...6.4 ..15.7
4740 ...7.8 ..19.1
4850 ...8.0 ..20.1
5120 ...8.9 ..21.1
5290 ...8.3 ..22.1
5390 ...9.0 ..22.5
5530 ...9.0 ..27.5
5630 ...8.7 ..24.5
5720 ...8.7 ..21.6
5820 ...8.9 ..23.0
6000 ...9.0 ..23.0
shift
4900 ..10.6 ..23.5
5070 ...9.9 ..22.1
5130 ..10.5 ..21.6
5180 ...9.7 ..21.1
5240 ..10.3 ..23.5
5320 ...9.2 ..23.5
5400 ...9.6 ..24.5
5500 ...9.9.. 25.5

 

[Gary Evans]

5.9lbs of turbine inlet pressure at 0 boost indicates a lot of restriction between the exhaust valves and turbine fan. The fan may either be set up extra tight for the purpose of driving the compressor at high boost pressure or its smaller than normal and being overdriven for the same reason. Hardly a typical application and not IMO relavant to bikes or the average automotive application.

 

[Uncle Bob]

no....it indicates a large turbo. The fact that he isn't hitting full boost until 5000 RPM's should be a good indication of how much inertia is required to get it spooled.

bikes are air pumps just like cars. I don't see how its not comparable....but I've said my piece. Until someone can actually post data remotely like this, I'll rest my case. We can talk about theory all day without data and go no where real fast....faster than a turbo'd busa

 

[suzuki4life]

5.9lbs of turbine inlet pressure at 0 boost indicates a lot of restriction between the exhaust valves and turbine fan. The fan may either be set up extra tight for the purpose of driving the compressor at high boost pressure or its smaller than normal and being overdriven for the same reason. Hardly a typical application and not IMO relavant to bikes or the average automotive application.

okay 5.9lbs of pressure...so what's a stock system produce at that same distance from the exhaust valve? I am using a stock base (ie: 100% OEM bike) to determine "excessive".

 

[suzuki4life]

here's just an example of one I found after a quick search.  This cat has a drag race car with a very massaged 302 SBF with a GT88 turbo making 900 HP to the wheels.  Yes, this is a completely different application compared to bikes, but this is a full on race car, definitely not an undersized turbo for the application.

RPM...INT....EXHAUST
3640 ...0.0 ...5.9
3750 ...1.7 ...7.8
3950 ...3.2 ..10.8
4200 ...5.5 ..12.7
4470 ...6.4 ..15.7
4740 ...7.8 ..19.1
4850 ...8.0 ..20.1
5120 ...8.9 ..21.1
5290 ...8.3 ..22.1
5390 ...9.0 ..22.5
5530 ...9.0 ..27.5
5630 ...8.7 ..24.5
5720 ...8.7 ..21.6
5820 ...8.9 ..23.0
6000 ...9.0 ..23.0
shift
4900 ..10.6 ..23.5
5070 ...9.9 ..22.1
5130 ..10.5 ..21.6
5180 ...9.7 ..21.1
5240 ..10.3 ..23.5
5320 ...9.2 ..23.5
5400 ...9.6 ..24.5
5500 ...9.9.. 25.5

this is also good info...but where was the reading taken? Closer to the head normally means smaller pipes and hotter gases thus more pressure. Like I said....overall. I mean you can't honestly believe you won't get a higher intake reading the closer you get to the turbo. As said...to compare evenly, you need more specified and controlled bases