Forced Air? TURBO? Options

[bob91403]

Could someone tell me why a scoop can't increase air pressure, as you go faster, and create the same kind of HP "boost" you get from turbo or superchargers? Excuse me for being ignorant. But, isn't it just a matter of increasing air pressure to the intake, and pumping in the right amount of gas for mixture? What about a pressurized tank of air, or both air and propane tanks? Couldn't you use a small compressor for boost, or as a source to refill a "boost" tank? I really don't understand this obcession with tubocharging. Nitrous systems have been around for a long time, and are much simpler. I was told, by my top rated Porsche mechanic, that, "Yeah, higher compression heads, turbocharging, supercharging, nitrous oxide, will all increase horsepower. But, anything you do to increase the horsepower will seriously lower the longevity of the engine." He doesn't even recomend european compression heads for a rebuild. I do understand, tubocharging a smaller engine gives you increased horsepower, plus the weight advantage of not having to put in a 3.2L six. But, if you have to rebuild it every 50K, instead of 150K miles, doesn't conversion cost less? Curious to hear your replies.

[redshift]

A rebuilt 2.0 cost $6,000.00, a rebuilt 3.2 cost more than twice that. To convert a 2.0 to a turbo, you need a turbo, a shoestring, and some PVC.

To use nice parts, it's going to cost you more than a 2.0 rebuild to modify the car for a 3.2

You can't use a scoop to 'turbo' your car, because you'd have to be going about 300 miles per hour, and have a very odd tube that is shaped like a trumpet, with a 5' mouth, and 18' long on top of your car to collect the air.

Nitrous is for somebody else, we aren't drag racers.

(IMG:style_emoticons/default/smile.gif)

Superchargers are rare around here, when you find one, let me know.


M

[bob91403]

A rebuilt 2.0 cost $6,000.00, a rebuilt 3.2 cost more than twice that. To convert a 2.0 to a turbo, you need a turbo, a shoestring, and some PVC.

To use nice parts, it's going to cost you more than a 2.0 rebuild to modify the car for a 3.2

You can't use a scoop to 'turbo' your car, because you'd have to be going about 300 miles per hour, and have a very odd tube that is shaped like a trumpet, with a 5' mouth, and 18' long on top of your car to collect the air.

Nitrous is for somebody else, we aren't drag racers.

(IMG:style_emoticons/default/smile.gif)

Superchargers are rare around here, when you find one, let me know.


M

$6000? Check Ebay $1500 or less. Not rebuilt. Remanufactured.

[bob91403]

A rebuilt 2.0 cost $6,000.00, a rebuilt 3.2 cost more than twice that. To convert a 2.0 to a turbo, you need a turbo, a shoestring, and some PVC.

To use nice parts, it's going to cost you more than a 2.0 rebuild to modify the car for a 3.2

You can't use a scoop to 'turbo' your car, because you'd have to be going about 300 miles per hour, and have a very odd tube that is shaped like a trumpet, with a 5' mouth, and 18' long on top of your car to collect the air.

Nitrous is for somebody else, we aren't drag racers.

(IMG:style_emoticons/default/smile.gif)

Superchargers are rare around here, when you find one, let me know.


M

All these "boost" references are in pounds. I know NA is 1 atm. How many atms does a turbo achieve? And, wouldn't it need an equal amount of fuel for the mix? i.e 2atm = twice as much gas?

[SLITS]

NAP is 14.7 lbs (sea level). A turbo, in theory, could produce unlimited boost - like Formula One engines, they ran at 80+ lbs of boost - it has to do with the compressor blade and the turbine blade design + the housing.

That said, a "normal" turbo on most production engines is limited at 7-10 lbs of boost by use of a popoff or bypass valve (exhaust gasses bypass the turbine blades). They usually have a stock CR of 7 - 7.5:1

Without a popoff/wastegate, the turbo will continue to build pressure till it blows the head off the engine or blows the crank out the bottom (IMG:style_emoticons/default/ohmy.gif)

In theory if you double the AP, meaning run 14.7 lbs of boost, you double the HP of the engine.

A scoop is great for getting cold (realtive) to the engine, but not much else.

And I forgot - superchargers take HP to produce boost (5 - 7 HP wasted) - turbochargers just run off the flow of exhaust gasses.

[airsix]

Could someone tell me why a scoop can't increase air pressure, as you go faster, and create the same kind of HP "boost" you get from turbo or superchargers?

You can't compress air against a surface (scoop) unless the velocity is supersonic (your car would have to go about 700mph). Below supersonic speeds the air just moves out of the way without being compressed.

What about a pressurized tank of air, or both air and propane tanks?

Ok, there is about .07 cubic feet in 2 litres. I have an 80 cubic ft scuba tank (big heavy tank, 3,000psi). If you only provided air to a 2.0 engine at atmospheric pressure that's good for 80x.07x4cycles-per-revolution = 4,571 revolutions of the engine. If you're averaging 4,571 rpm then you're good for exactly 60 seconds. That aint much, and you were'nt even using "boost", just suppying air at atmospheric pressure.

Couldn't you use a small compressor for boost

This comes back to the "electric supercharger thread. How are you going to power the compressor? It takes serveral horsepower to power a pump with enough capacity to provide forced induction. It doesn't matter if that pump is powered by exhaust gas, direct drive, or an electric motor. All of those methods require the same power INPUT give or take, and you can't supply several horse power with your alternator. Even if you could it would be much more efficient to use direct-drive. Any time you convert one form of energy to another you loose a bunch of energy. So going from mechanical engergy (belt drive) to electrical engergy (alternator) and back to mechanical engergy (pump) your losses are huge.
Look at how race cars make power. Cubic inches, high rpm, and forced induction via turbo or supercharger. If electric fans or compressed air tanks worked they'd be using them.

-Ben M.

[soloracer]

For increased power you need to increase both the oxygen and fuel that are going into an engine. Getting more fuel in is easy - just upsize your fuel system. Getting more oxygen in is more difficult.

One atmosphere is 14.7 psi. Turbo's can generate over 100 psi if you want them too. However, most stay between the 10 psi to 30 psi range. Turbo's have an efficiency range where they work best that you can determine by looking at their compressor maps. If they are forced to work outside their efficiency range they tend to heat the air which can lead to detonation. Turbo sizing is very important when matching a turbo to the motor and the desired performance characteristics.

Like Redshift said the "Ram Air" style of getting more air into an engine will only give you a slight increase in airflow to the motor and be no where near the same as the turbo is capable of doing. Nitrous systems or systems that use a compressed gas also get more oxygen into the engine. However, the supply of oxygen is limited by the volume in the bottle. You run out of gas in the bottle and you have to go buy more. Works great for short distances but you would run out of gas in about 5 miles if you were on it steady.

The nice thing about a turbo is that once installed the extra power is there all the time and IS basically free. It's also easily adjustable. Want more power? Just turn up the boost. Or if you find the turbo you have is not giving you the power you were looking for you just bolt on a new turbo and change your mixtures. No pulling the engine, no cracking open the block to change the internals. An additional advantage is turbocharged applications also make good torque gains. Plus for many of us the feel of a turbo car is more of a rush. I rode in a Viper that has more power than my 944 turbo and it did not feel as quick. I know the Viper is faster but because the power is so linear it doesn't have the same "power rush" that I get with my 944 turbo.

P.S. I would like to know where you are getting a rebuilt engine for only $1500. I spent over $7000 rebuilding my 944 turbo engine and know a Porsche 6 costs more to do. I can't even buy a core engine for $1500.

[lapuwali]

A properly placed and ducted scoop would raise the inlet pressure some, but not by a lot, and very high speeds are required to gain much. Kawasaki fitted such a system to a very fast bike 10 years or so ago, and the system was only effective above 75mph or so, and even then it was pretty marginal (less than 1psi of boost).

1 atmosphere = 14.7psi = 1.02 bar = 102 kPa, which are all of the commonly used measures of air pressure. A typical turbocharger will provide between 7 and 15psi of boost, or 0.5 to 1 atmosphere, more or less. Ideally, 1 atm of boost will double the power. In practice, it usually ends up adding about 75-90%. And a turbo will do this at 10mph, not just above 100mph.

Nitrous is useful for short spurts, but it's basically just a drag racing thing, good for a few 1/4 mile runs or the odd spotlight drag.

Compressing the air to provide even 6psi of boost takes a lot of power. A Rootes-type supercharger of roughly 70% efficiency takes about 4hp to do this. That's 3kW, or enough to power 2-3 averaged size houses with all of the appliances turned on. The "small" compressor can't be very small and still provide a useful amount of boost.

The primary benefit of a turbocharger is it's using exhaust heat that's otherwise wasted (roughly 70% of the energy in the gasoline you pour into the tank is lost out the exhaust stream, only 15% of it makes it to the drive wheels) to drive a turbine to provide the pressure, so you're substantially increasing the efficiency of the engine by capturing "lost" energy to do useful work.

[airsix]

1 atmosphere = 14.7psi = 1.02 bar = 102 kPa, which are all of the commonly used measures of air pressure.

Almost all of them. My dad is an engineer and flight instructor. I can't get him to talk in bars or psi. He always want's to use "inches of mercury" <_<

-Ben M.

[SLITS]

They all mean the same thing, so what's the problem?

[lapuwali]

No problem from me. Some people get rather, um, annoyed by units. Years ago, some (European) guy went off on a rant on a newsgroup about the use of non-metric units and how stupid esp. we Americans were for using such an outdated, archaic system of units. So, a few of the other people colluded and began to discuss things only in wonderful units like furlongs per fortnight for speed, or rod/slugs for torque, etc.

On older Unix systems (Linux, alas, doesn't normally come with this), there was a great program called "units", which would convert between a huge array of units. It actually had furlongs, fortnights, slugs, cubits, etc. Alas, it only did units where there was a linear conversion, so one of the most common conversions (C to F), wasn't available.

[airsix]

They all mean the same thing, so what's the problem?

Trying to convert in my head durring conversations.

[phantom914]

1 atmosphere = 14.7psi = 1.02 bar = 102 kPa, which are all of the commonly used measures of air pressure.

Almost all of them. My dad is an engineer and flight instructor. I can't get him to talk in bars or psi. He always want's to use "inches of mercury" (IMG:style_emoticons/default/dry.gif)

-Ben M.

1 atmosphere = 29.9" of Mercury (IMG:style_emoticons/default/wink.gif)


Andrew

[SpecialK]

I prefer a less restrictive method of measurement...such as "shitload", "C***hair", or for even smaller tolerances refer to Mike Z's "Red C*** Hair". C***hairs aren't particularly good for setting your valve adjustment, since C***hairs can vary a shitload depending on the person.

Okay, back to the forced air/Turbo topic.....

[redshift]

So, a few of the other people colluded and began to discuss things only in wonderful units like furlongs per fortnight for speed, or rod/slugs for torque, etc.

(IMG:style_emoticons/default/monkeydance.gif)

Oh, I missed the 6 when I typed before, Ben is right!

[bob91403]

P.S. I would like to know where you are getting a rebuilt engine for only $1500. I spent over $7000 rebuilding my 944 turbo engine and know a Porsche 6 costs more to do. I can't even buy a core engine for $1500.

I was reffering to a 2.0L four, not a six. Importmotors.com offers three different engines. A 2000cc for $1235, a 2165cc longblock for $1799, and a 2165cc Performance for $1875. They give $150 for a core 1.7 or 1.8, $300 for a 2.0. It seems they use a 2.0 case only for their "performance" engine. Anybody familiar with their products? Just go to ebay and search for 914 engine, then sort the list by highest price first.

[redshift]

Uhhuhh..

A GOOD 2.0 cost 6k up.



M

[Red-Beard]

You can't compress air against a surface (scoop) unless the velocity is supersonic (your car would have to go about 700mph). Below supersonic speeds the air just moves out of the way without being compressed.

The German, in WWII, created a subsonic RAM jet cruise missle, AKA the V-1.

The US also used a scoop on the P51, along with a jetted duct from the exhaust from the engines to increase top speed.

However, you need significant speed to produce any boost.

Turbochargers _do_ increase back pressure and rob some HP, but they way more than make up for it.

As far as 2 ATM boost is concerned, most of our engines operate under some vaccuum. If you had a guage and it shhowed 14.7 PSIG in the manifold, you would be closer to 2.5-3 times output. 7-10 psig is about 2x output.

[mike_the_man]

I can't remember for sure, but I think there has been some bad things said about them. That seems waaaay cheap to me. There's gotta be someting up.

[Red-Beard]

6K for a 3.2 6cyl, purchase plus a no BS rebuild. Yes. It can be done.