944 turbo's do not use extra injectors.
an air compressor may be pumping more psi but it is pushing alot less cfm.

thats what im asking about there, whihc cars have additional injectors upstream??

thats probably a good idea, because like i said dudes, sugar don't mix good in cold tea. sugar being the fuel, tea being the air.
THe absolute best set up would be to mix the air and fuel in a HOT location, and then COOL the premixed air/fuel. SO that you don't lose any of the good properties heat has for MIXing things.

but the air compressor is forcing air into an enclosed area whereas a car with a turbo on it is refreshing and refreshing air over and over, Maybe turbines have so much surface area and spin so fast, that they are actually very ineffeciant?

Most performance turbos use additional injectectors, usually in the intake runners or near the mass sensor because their turbos are capable of compressing the air to the point that more fuel can be added. If a turbo doesn't have additional injectors, the normal injectors themselves are capable of providing more fuel than a NA. The outside temperature doesn't really get low enough to cause any combustion problems. Once the intake valve closes, the piston will compress that fixed volume of gas and the temperature will rise, no matter how cold it is outside, and it will explode when the spark ignites it.

Additional injectors are usually found on aftermarket setups when the main injectors are insufficient but larger injectors could cause part throttle drivability problems. It's also a cheap way to get enough fuel on home-brewed turbo setups.

Having a cooler charge is much more important than having a better mixed charge (it's not like they aren't mixing at all with cooler air..). There are tradeoffs in everything, just like accepting pressure loss for lower temps with an IC - the good outweighs the bad.

Turbochargers are fairly efficient compressors but they have a LOT of work to do compared to an air compressor.

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'86 951 Graphite Metallic/Tan

turbochargers spin upwards of 100,000 rpm.

yes so they are wacking the molecules at 100 000RPM, compressors don't, i thought maybe compressors worked the same way, ive never taken one apart, just have one that works good, no wonder there is heat in a turbo, that answers my question http://www.pelicanparts.com/ultimate/smile.gif

What cars...hmmm...only cars that come with additional upstream injectors I know about are all fuel injected rx-7's (n/a's, turbos, and 3rd gens)...they have a set of primary injectors and a set of secondary injectors that come on around 3200 RPMs, and when the secondaries come on, there is a sudden pause in acceleration that lasts a millisecond or two but is noticable...it gets worse with the age of the car, but my guess is that it runs rich when those injectors squirt at first.

About the off topic at hand...of the three turbocharged cars I have owned (rx-7 turbo, 951 and all-trac celica) I can comfortably say that there is a notable difference between dog hot and ice cold when talking about horsepower, throttle response, etc. My 951 feels like it has the biggest difference (probably 15 or 20 HP difference between 30 degrees and 90 degrees, seat of the pants, and the whole power band is boosted the same percentage), but the other cars all felt noticably faster in the cold as well.

That said, there are other things going on with cold air, too, like poorer mixing of gasoline and air (the gasoline vapor is what burns, not the liquid, and the hotter the air is, the more and quicker the gasoline "boils" and becomes the gasoline vapor being mixed with the air, and the air/fuel vapor then ignites better and more completely...good atomization of the gasoline is very important for the speed at which the gasoline "boils" at as well). The cold air will not stop the gasoline from burning completely but may make it so it isn't boiled into the air in the combustion chamber before the spark ignites, so the whole mixture doesn't explode all at once hence lower efficency/maximum power.

The disadvantage of poorer mixing is outweighed by the fact that more molecules of oxygen have made their way into your combustion chamber(denser air), letting you run more fuel into your motor making a significant improvement in horsepower. You can also run leaner or lower octane fuel in the winter because your car will (probably) not be approaching the flashpoint of the lower octane/less fuel because the air charge is cooler meaning that the combustion chamber is cooler meaning that detonation wouldn't occur nearly as easily.

What else...if you could somehow cool the temperature of the charge air in either a naturally aspirated or forced induction motor to below ambient temperature (meaning dead winter cold, like 20 deg. F, through phase cooled intercooler, peltiers, etc.) you would not only get the added bonus of a few extra horsepower(from denser air), you would also get the same effect of raising the octane rating of the fuel you are using (because the colder air reduces the chances of pinging/detonation), so if you were to build a motor with one of these active intercoolers in mind, you could do a few cool things...like:

run insane compression ratios on pump gas on an n/a motor, like 12:1 or 13:1

run gastly amounts of boost on a turbocharged car

run the same amount of boost on a turbo motor and up the compression ratio to something with a little more low end balls

run the motor very lean for much better fuel economy

a few other things

At least thats how I see it, all though I am no expert...I learned most of what I know about cars from reading car forums, web pages, and magazines. Anybody think I am wrong or talking out my ass?

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ribs, 86' 951

I think the reason you don't see any intercoolers for NA engines is that it's just not practical or needed. Most likely it would end up restricting the intake flow and defeat itself. Air/fuel burns just fine from temps of -30F to 120F. You never heard of anyone not getting to work because their fuel wasn't aspirating in their engine. The battery might have frozen, or other fluids may have thickened... but gasoline is fine at those temperatures. I think the point is... all a normally aspirated engine needs is a free unrestricted intake of FRESH air. If you add a simple cone in place of your factory box filter and no longer have the air channelled directly to the filter, you are sucking air that has the engine and exhaust manifold driving out oxygen, the radiator has already transfered heat to that air in addition to your air conditioner if you use it. If your going to go to a free breathing filter, find one that is located in the nose with custom tubing to tie into the intake, or stay with the factory box with a K&N and make sure plenty of air gets into the fender where the intake is. Now if rednek gets his custom air collectors made for his brake project, maybe I'll get one and modify it for a ram air for the front spoiler.

I have the formula for figuring it out, but even being the more accurate equation it is, bigger engines react worse to cold air than smaller engines. Bigger engines are way more sensitive because amount of air and fuel you are mixing is much greater. In short, the bigger the engine, (we are talkin NA here, since turbos run hotter and are different in many ways), the more the cold air will f!ck other things up in the process, especially with carbs because of the fuel getting balled up on the intake tubes. With smaller engines it is more beneficial. Likewise, with smaller engines, spark plugs and ignitions will not improve HP NEARLy as much as on a big engine.

Here is the formula, and we use degrees celsius or kalvin, not ferenheight, for you american *****weeds that are stuck in old times and sometimes get mixed up.

Getting on to the formula....

The square root of (Existing temp VS proposed temp) times current HP.

which is: square root of (ET over PT) times your current HP.

Bottom line is, smaller engines, colder air rules.

Now the 944s IMO have big engines for the amount of cylinders they have...were not talking about the overall engine size actually, its the amount each clinder is displacing that is important...on a v-12 ferrari they have small cyls, on a 2 litre 944 its fairly big. think about it, each cyl in a 944 2.5 litre is the same as a mustang 5 litre.

So on a 3 litre v-12 ferrari...compared to a 944 3 litre 4 cyl...well you get the idea, the ferrari is going to benefit more.

Race cars with bigger engines actaully heated up the air and fuel and manifolds to get better use of power FYI.


[This message has been edited by AMCPorsche924Powerhaus! (edited 08-13-2001).]

What are you basing that formula on? I don't think you can use HP since it is fairly unrelated to displacement (i.e., a 5.7L early chevy smallblock may make 200hp or less compared to 240hp from a 2L Honda S2000 motor).

Spark plugs and ignitions (et all) "help" all engines where the existing systems are not sufficient, however on high powered engines the percentage gains will be more measurable. Gains on previously modified motors will be more significant since the OEM systems you're replacing were probably insufficient.

I don't think the downsides of colder air are significant enough to even consider.. You'd have to be driving on the dark side of the moon before you started to have problems on a fuel injected motor. In the real world, colder air is always better, all else being equal.

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'86 951 Graphite Metallic/Tan

[This message has been edited by Macabre (edited 08-13-2001).]

the only thing I've heard about this from anyone is that colder fuel and colder air = more hp. why do people insulate their fuel lines? whats the point of header wrap? do race car drivers do this for no reason? I think not

Smaller engines have a much easier time blowing up a mixture than a bigger engine.
For example, ever hear of smaller engines getting better fuel economy? everything is happenning in a smaller combustion area, more effecient, LESS sensative to modification.

To take it to extreme, how hard would it be to combust the whole atmosphere? Very hard, it's a huge body of air, you'de need one strong spark plug to do that.

Turbulence and mixture in bigger cylinder cars come into effect a lot more than small cars.


Ever wonder why people with porsche 924s have an extremely hard time getting any power? whereas the buddy accross the street with his 12.9 litre v-8 camaro just put in plugs, MSD ignition, and a header, and got GREAT improvement? And how about k and Ns, and those swirl gimmick things from Performance products. I garuntee you will see a much bigger difference on a larger engine with big cylinders.

As for turbulence, in a big engine, its much harder to mix that huge amount of air and fuel in the cylinder than it is for that minuture japanese car's cylinder, and the spark will not be as powerful since it has a greater volume to explode, and once the fuel catches on fire after the spark popped, the fuel will take longer to saturate all the other fuel in the cyl compared to a small cylinder.

High compression smaller engines are harder to suck performance out of than a big gas guzzler, cold air is better for your small car than the big vette, and you will see more of a performance gain on a small engine turbo or small engine NA car with cold air.

It's pretty much everywhere that you see corvette owners bolting on performance mods, and this is why.

i think they insulate them to prevent vapor lock, and to keep them cooler. THere's always a too hot is too bad.
Header wraps are so you get more complete combustion in the exhaust system, and on turbo cars heat is what turns the turbine, not the movement of exhaust, but turbos are a whole different story.

....how about we throw more items into the equation.....I am enjoying these phylosophical discussions.........how about water injection for my 944......!!!! Lets lower my compression a notch.....and use this instead....

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http://www.alta.net/944/alexs944na.jpg

86' 944
79' 924 (R.I.P)

How about SUPER COOLING the Airbox?!

Craig...read...enjoy http://www.pelicanparts.com/ultimate/biggrin.gif



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ribs, 86' 951

Smaller engines get better fuel economy because they have less displacement. http://www.pelicanparts.com/ultimate/smile.gif It is not necessarily more efficient. Generally you can get more HP from smaller cylinders because the inertia of all the smaller parts is so much lower, which is why you've got V10 1.5L F1 engines.. etc. It isn't because smaller cylinders are more efficient, it's because they can turn higher RPMs.

Not really.. if you replaced the atmosphere with a fuel/air mixture it would combust quite easily. Remember that the spark plug does not ignite the entire mixture, it only ignites the air/fuel right around it, which in turn ignites the mixture around it, etc. It's a chain reaction, which would be just as easy to start in the atmosphere as it is in your engine. It would take a while, though, so you couldn't run very high RPMs in your atmosphere burner..

Turbulence is caused by all sorts of things. You could make a cylinder with the bore of few millimeters but a very long stroke that would have very little displacement but mix the mixture very well because of the long (but weak) suction from the intake stroke. It's not a simple function of displacement by any means.

Maybe it's because the V8 was poorly tuned to start with but the 924 engine wasn't? What did his car come stock with, ~200hp from 5.7L? Of course he can get more power easily. In addition to that, as I said earlier, percentage gains show up much more prominently on powerful HP engines than on weak ones. Obviously if the same mod gives both cars 5%, the 100hp car is not going to have as much of a measurable difference as the 400hp car..

Of course they're harder to get performance out of.. they're already closer to their potential! You start with a big motor that is tuned horribly and you can modify it significantly. The other way is much tougher. Just try to get a few HP more out of a Ferrari 360 Modena engine. It's big, so using your logic it should be easy to get additional power. Try it on a 550 too. Or how about a BMW M5 or McLaren F1 (6 liters, should be a dream to modify http://www.pelicanparts.com/ultimate/wink.gif)

Nope.. that's not why, it's because Chevrolet didn't do their homework on the older cars.

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'86 951 Graphite Metallic/Tan

[This message has been edited by Macabre (edited 08-13-2001).]

Ribs, you're really smart =D...

http://www.pelicanparts.com/support/smileys/clap.gif

Other factors that might contribute to your misconception on V8s is that most are older carburated ones? at very low temperatures they are more difficult, but that's because older systems didn't have a computer to handle those things. Carburated engines are capable of running at -30F.. even colder, fuel still aspirates enuf to burn, they have to be maintained alot in the winter is all. They also have so much torque anyway, that it's harder to notice the changes when it's colder, but it's running better, not worse.