Dave, I'm not planning on doing any of this stuff guy ;D.
I'm trying to keep most my car stock cuz it's an '83 and is special http://www.pelicanparts.com/ultimate/wink.gif.
I might by another 944 sometime and do some of these projects, it'd be fun and interesting. I just like to hear other peoples points and stuff. I appreciate EVERYONE's posts on this thread, thanks.

Well, again, cold air and cold fuel are not going to mix as thoroughly...ever try to mix honey in cold tea? doesn't work...
Hot molecules bounce off each other more, causing things to mix easy...IMO carberators would work much better with cold air than CIS...carbs allow a longer period of time for the fuel and air to go into the engine, they have to travel through the manifold. Probably why K and Ns work better on carb cars too.

[This message has been edited by AMCPorsche924Powerhaus! (edited 08-12-2001).]

Hey i just thought of something, how the hell is your fuel system going to know that you need more fuel, with cold air!

It goes by volume, it won't detect temperature, at least on the CIS system, there is no temperature sensor anywhere.
Yer just gonna run leaner.

I'm prolly gonna get jumped all over for saying this, cause i'm not an expert at it and would have a hard time backing it up with real hard data, but the way I understand it, lower air temps have a higher concentration of oxygen per volume than at higher temperatures. Hot engines will drive out the available oxygen, it's a chemical property of gases, it's going to happen. Oxygen is what is needed to have proper combustion. The more oxygen you have, the more complete the reaction process for each single reaction in each cylinder on every revolution. Using nitrous oxide is not really burning nitrous, the nitrous breaks down and provides more available oxygen to be used in combustion, and that is where the power is coming from. (that is also where i feel uncomfortable because i have a very strong chemical background and i don't know the actual chemical reaction taking place) Most engines have less than perfect combustion and if you could optimise all the factors required for complete combustion, you'd have incredible power. That is what Ferrari has attained in the 360 modena, 3.6L and nearly 400 hp with nearly imperceptible levels of emmissions from a normally aspirated engine. There is no way to get your engines to burn as perfectly as the ferrari engines do, but you can make the air coming into it be at least outside temperature and not ambient air from inside the engine compartment that is much hotter at any given time than the outside air. Most of the cheaper K&N cones have no routing of outside air and just suck air form the inside the engine compartment. I think that the greater flow rate attained by the filter will be cancelled out by the lesser amount of oxygen present in the air, because the engine heat has already driven it out. Turbo's not only jam more air into the combustion chamber, there are also additional injectors upstream that have already added more fuel to the equation. Cooling of that charge is a priority, that's why all the turbo cars that are worth anything have intercoolers that are really radiators for the air going into the engine. But intercoolers won't really work on normally aspirated engines because the air going in hasn't been pressured to the point that it's temperature has gotten too hot. All you can do is make sure you are breathing plenty of fresh air with as little restriction as possible. http://www.pelicanparts.com/support/...amingdevil.gif

but what about my previous 2 posts, ....cold honey in cold tea?

The reason an intercooler wouldn't be worth spit on a na car is that, by design, it is set up to operate as a pressurized intake. The intake on a na is, by design, working on vacuum. That is what your "mpg" meters really read. The more "vacuum" that the sensor reads, the higher it thinks the gas mileage is. All an intercooler would do on a na car is to lengthen the intake runners, totally screwing up the throttle response because of the mass of air that will have to be moved to get into the cylinders. Intake velocity does matter since the mixture has to be moved between two discreet points and it has a mass that will be accelerated.

NOS helps in two ways- 1) by cooling the intake charge, making it more dense (more O2, Boyles Gas Law again, NOS is under pressure and by releasing the pressure the temp drops) entailing richening the mixture for the denser charge and 2) providing more Oxygen during the combustion process, again making it imperative to richen the mixture. That is why you have to richen the mixture to avoid detonation. The net result is mucho hp, possibly at the cost of reliability if not done correctly or too close to the ragged edge. Atmospheric pressure and humidity can affect whether on any given day an "edgy" NOS setup will grenade your engine.

In the pursuit for more power, the 951 is still among the most overall economical way to do it. Next would be to make a Porolet or was that Chevrsche. When planning this type of project, it pays to start with a platform that offers a lot of potential to start with. In my mind, that rules out all 944na models. Not that they aren't good cars, just that making hp with the existing engine will require mucho more bucks than would a 951 or a Chevy conversion. Find a 951 or a 944S with a toasted motor, get it for about $1k, put in the 350 Chevy for about $5k more, then fix all of the stuff that's not up to the hp for another $3 to $5k and you've got a death rocket. Somewhat less expensive "initially" than a tricked out 951, but no longer a Porsche (if you would care, some get really bent over this conversion). The downside of any conversion like this is that it breaks things in unanticipated ways, just remember to budget double your original estimate for fixem ups. Now we're more expensive than a 951 again.

If I had a 944na, I'd put good tires and sway bars on it and just drive. It was never designed to be a stoplight racer. It does shine on an open, twisty road where it is a pleasure to drive.

Dave951M

the reason an intercooler wouldn't work on an NA car doesn't require too much thinking, water is at room temperature, intake air is at room temperature. no point.
With a turbo the air is hot from compression.

NOw can someone tell me why air compressors that we use in are garages that pump up to 120PSI don't make air the air hot? I don't get that, when a turbine in a turbocharged car is only pumping up to 10-20psi on a normal car, the air gets hot through the process of compression. WHen an air compressor in the garage is pumping air up to 120PSI, the air stays the same temperature. No its not colder it just feels colder bcause its denser, but why isn't it hot???

because there is a fan on the back side of the compressor pumping ROOM TEMPERATURE AIR. on a turbo, you are getting heated exhaust air.

SHAUN

apples and oranges... we're talkin molecular level reactions that will happen if the conditions are correct. your computer is sending the amount of fuel it thinks is necessary for the instant of the spark, that plus the air that it knows just went in (either explosive cool air with alot of oxygen or hotter air with less), when compressed and a spark added.... will explode or combust, how much of the gas gets processed depends on the amount of oxygen available to completely 'oxygenate' the carbon from the gasoline molecules to co2 and other gases. If you have enough oxygen, all the gasoline will be converted to other gases which add to the total volume of gases coming out of your exhaust which makes your piston fly away faster after the spark starts the reaction. If it didn't burn, then that gasoline didn't get converted to gases which would result in less total gases for that one piston stroke, and that means less power. On a molecular level, in the kind of air temperatures ranges we're talking about inside the combustion chamber, the gasoline is still vaporizing into the available air vacuum created by the piston traveling down whether it's 100 or freezing. The only difference is how much oxygen is available to burn.

shaun, turbo's intake is fresh air, the exhaust is on the other side of the turbine that's used to spin the intake side. the higher temp comes from gas laws, higher pressure is higher temp..

ON my CIS fuel system cars, this is not the way it works, the car does not detect oxygen...it detects volume.
Cold air will not have any affect on the fuel system, my car will have more oxygen, but no more fuel, so it will run lean with cold air.

Now with AFM? do they have oxygen sensors on the intake side? LOL?

Yes, the exhaust temp will only affect it slightly...now why do air compressors not produce hot air.

If you don't believe me, just take a regular bicycle pump and have at it on a bike tire for about a minute. Feel the bottom of the pump cylinder and it WILL be warm. An air compressor has a much larger pipe going into the resevoir and will not build up too much heat (at least the modern ones don't) but they do get warm. The laws of physics still hold, if maybe not au Canada, eh? The intake charge on a turbo car is heated, not only by compression, but also by the compressor itself. The turbo is driven off of exhaust gasses, and is most efficient when those gasses are at the maximum possible temperature from the exhaust manifold. There is bound to be some heat transfer, and the heat from the engine compartment is a factor as well since all of the plumbing for the system soaks up some of the heat and will unavoidably transfer it to the intake charge. To cool some of the plumbing, there is a system out that will cool the intercooler by spraying the exterior of the intercooler with a fine water mist. I have wondered if the same concept could be applied to an intake manifold of a naturally aspirated car. Has anyone tried that yet?

Dave951M

PS Are you only checking the temp at the resevior outlet? Then again, Boyle's Law, drop the pressure and the temp will go down.

[This message has been edited by Dave951M (edited 08-12-2001).]

see... that's the whole point, it doesn't need any more fuel... it will burn more completely with the higher concentration of oxygen from the cooler air and have more power because of it.

of course it needs more fuel, with oxygen, you need to add more fuel...turbocharged cars don't use the same fuel system as NA cars..come on now

If u don't beleive me, look at your cold start system. when the engine is cold it requires more fuel. car won't run nice without cold start stuff on it.

[This message has been edited by AMCPorsche924Powerhaus! (edited 08-12-2001).]

DaveM, it's not that I don't believe you, it's a fact that compressing air creates heat, one reason being because because the molecules are ramming against each other, but anyway i was just curious as to why my air compressor which is 24 gallonns never gets a hot tank...tank is always freezing cold and its 90 ferenheight out right now where i live.

turbo's have extra injectors to add fuel to the extra air being provided by compressing the air with the turbo. so it's burning more air AND fuel... it's a different thing, but the power is still regulated by how much oxygen is in there too. as far as cooler temps go... it's cooler air, from a given volume of air, that has more oxygen dissolved in it than areas that are hotter in that same volume, add them all up and you get our atmosphere. when you cut off the atmosophere or suck air into something... it has the oxygen that came into it, you can't make any more, cooling that air is going to have very little influence. you would have to cool the entire area in front of your car and allow for the oxygen in the warmer areas surrounding to diffuse into the area in front of your car ... hmmmm obviously not practical. And my air compressor hose gets hot as hell.

At my former employers, we had a twin cylinder with a 100gal tank. The tank would always feel cool to the touch. If you touched the cylinders while they were running, there might be some human meat sizzling. We have a screw type where I am now, and it doesn't generate heat like the other one. As for the tank being cooler, my guess is that it is a lower pressure than the compression cylinders, therefore a lower temperature. It would seem that in order for the compressor to charge the tank, it would have to have a higher psi than the tank, ie a pressure differential and in the act of flowing to a lower pressure, drops the temp. That's my guess at the moment, I'll ask an engineer type tomorrow, interesting question.

Dave951M

[This message has been edited by Dave951M (edited 08-12-2001).]

Some notes- the reason that your car maintains the correct mixture of fuel and air whatever the intake temperature is not because the INTAKE can detect the O2 level but the O2 sensor in the exhaust does. By sniffing the exhaust going by it knows how much fuel it can add to the engine ( by way of injector pulse time) until it detects the least amount of O2 going by- indicating that the mixture has reached its most efficient (stociometric ratio, 14.7/1 ) The system is reactive, not active, meaning it looks at the last few cylinder cycles and adjusts the upcoming ones to be as efficient as possible. With gas engines, efficient burn= most power. It is a continual cycle, the O2 sensor "reads" about 10 times a second, sends the signal to the DME, and the DME adjusts the mixture accordingly by shortening or lengthening the injector duty cycle.

As far as compressing air, it does get much hotter when you compress it. Think of your A/C system- it works on exactly this principal. The compressor compresses the refrigerant, and it gets hot- this is why there is an additional "radiator" for the A/C. When the refrigerant is allowed to drop in pressure, it cools rapidly, which is what gives you the nice cold air inside the car.

The same thing happens with turbocharged cars. The intake air is compressed( it heats) and is then run through the intercooler to cool it. The air is more dense, both from the compression and cooling (although it is still much hotter than the ambient air) and to maintain the best mixture, more fule is added in relation to an NA car. That is why more boost=more power. The key is to remember that cars run on air, not gasoline. That is why all the power adding devices (turbo, supercharger, K&N, big exhaust, etc).. are all about moving more air, not more gas.

Brian
PS most air compressors have tanks so big that the air mass is so large it is hard to heat up, and only a small amount of air is actually being compressed at any one time. Air is only heated in the act of being compressed, and that heat is lost to the rest of the air in the tank, and to the body of the compressor, so the tank (especially on big shop type compressors) does not get hot

yes but for us gurus we don't use o2 sensors in canada, we take them off as soon as we buy are cars http://www.pelicanparts.com/ultimate/smile.gif

We don't have emmisions where i live, so basically what you gotta do is richen the mixture up on an old CIS system, if you don['t run an o2 sensor, but without an 02 sensor, all us canadians will DIE of lack of power.

THats interesting about the air compressor...but if the air compressor is trapping the air in the tank, whats the difference? shouldn't it get hot at first then?

ANd about the turbo injector system bob mentioned they used extra injectors or somethign, is that on the 951??? not on the 931, we have 4 injectors and a cold start on the 931, thats it.


[This message has been edited by AMCPorsche924Powerhaus! (edited 08-12-2001).]