Anybody noticed that there seems to be more power when the engine is cold?
It also feels more aggressive and more like it has a lumpy cam
After 5 mins its it normal again.
Its like the ECU is running with different timing or something when the MAF sensor is cold. Anybody else noticed this? Its normal?

I did read somewhere that apparently the engine does open the exhaust early or something so as to heat the Cats faster. You can hear this when you start the engine in idle and it sounds more "burberly" for a few minutes.

Not a car mechanic myself!
Something to do with the CAT needing to warm up.
Cold air=inc. air density=more o2 for fuel to burn
Need different MAP??
That's why some of us use high flow filter to allow more air into the combustion chamber


Compare with front engine car---midengine car aren't very good at getting rid of excessive heat in the engine bay! That's why our croc perform much better in the winter!

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Andy

When the engine is cold it is harder to get the gas to evaporate and spread out in the piston chamber. Less of it ignites and so it takes more gas to insure the minimum amount of power to keep the engine going.

When cold the engine compensates by putting more gas into the chamber at idle, and also to increase the idle speed so that in the event of a misfire, the engine has enough momentum that it does not stall.

As the engine warms it can lower the idle and also lower the gas needed.

Just my guess

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Wow thats cool, I did not know Porsche engines were this sophisticated. Is it a fact or an opinion? I'd like to read more about it.

thanks

If you think that's cool, there's also "VarioCam Plus" which continually adjusts valve timing with two-stage lift on the intake valves. Valve duration and lift are continuously managed accoring to conditions and engine load.

The engine has to be warm for VarioCam to be really effective, that's why you should keep things below 4,000 rpm or so until the oil has a few minutes to warm up.

There's also a two-stage intake manifold that opens things up quite a bit above 4000 rpm.

"There is no substitute".

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C.G.Mojo

My boss told me that our Porsche variable valve timing is among the most sophisticated-It can alter both the inlet and outlet valve. Just like a Honda VTEC system, it can alter the lift as well! This is probably why chipping company charge more for Porsche!

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Andy

Correct. The cooler air is more dense and contains more O2. The ECU has several temperature sensors so that it knows if it needs to richen the fuel mixture to compensate for cooler air.

Raising the idle for the first 20-30 seconds is a basic function of most electronic fuel injection cars. It's done to warm the catalytic converters up, because when they are cold they do nothing. This is likely what everyone is hearing/noticing.

Fact, and it's not limited to Porsches. Most all Fuel Injected cars will do this, again to warm the cats.

VarioCam Plus (VCP) is way more sophisticated than VTEC. Valves have four basic characteristics that will change the way an engine runs and how much power or efficiency it will produce:

1. Valve Timing - when the valve opens and closes relative to the position of the crankshaft. Open the valve earlier and you may be able to get more flow, close them later and you can also get more flow.
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2. Valve Lift - how far the valve is pushed into the combustion chamber. The further it goes, the more air it can move because the valve crown is causing less restriction.
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3. Valve Duration - how long the valve stays open for. Of course, if it's open longer, more air can enter or exit the combustion chamber.
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4. Valve overlap, when both the intake and exhaust valves are open at the same time.

VTEC essentially has two camshaft profiles. One with one set of timing, lift and duration. Another set of lobes with a second set of timing, lift and duration. The cars ECU switches between the two, and most driver can definitely feel when the more aggressive lobe is activated.

VarioCam Plus does more. Yes, it has two lobes kind of like VTEC, but it also has completely variable valve timing and overlap. The ECU can vary the valve timing and alter the overlap anywhere from 0-40 degrees relative to the crankshaft. This makes the system less ON/OFF and more transparent.



Mix VarioCam Plus with the Two Stage Resonant Intake Manifold and you have a very adaptive engine.



Air flows differently at different engine speeds. At some speeds it's better to have a smaller area in the intake manifold, at some speeds it's better to have a larger area in the intake manifold. The intake manifold in the Cayman is adaptive. It allows the air oscillation in the intake to be adapted to the respective engine speed. This aids the engine in making more torque at lower speeds without losing power at higher speeds. There are two flaps in the intake, a distribution flap and a resonance flap. The Distribution Flap opens from 3,500-4,900 rpm, and again from 5,200-7,300 rpm. The Resonance Flap opens from 4,700-7,300 rpm.

At low RPM, this intake system is really like having two 3 cylinder engines. This gives you better torque down low. At higher RPM, the flaps are open which is more like a 6 cylinder engine with a huge intake, which is helpful in producing maximum power at those high RPM. This feature was first introduced on the 1996 993 and at the time it resulted in an increase of 15 hp. Nice, huh?

So what's missing from the Cayman? Anyone? Beuller? I'll tell you, an adaptive exhaust system. If fine tuning air flow in the intake can result in a 15 hp increase, it only stands to reason that doing so in the exhaust will also yield a benefit. We all know that lower volume exhaust systems produce more power at low RPMs, higher volume exhaust systems produce more power at high RPMs. So why don't we have an exhaust system that is similar to the Two Stage Resonant Intake? I suspect that some day we will. Until then, I am excited to see Capristo's system, which is close to this.

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Gator Bite
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I'm not so sure I agree with you on this. First of all, all internal combustion engines will be stronger with cooler air, just because of air density and combustion efficiency. Turbo charged cars benefit even more because their basic design heats the intake air, and then they attempt to cool the air in the inter-cooler, and a cool atmosphere makes the inter-coolers more effective.

I do not agree that a mid engine car has a harder time getting rid of heat. I can see where your going with this, the engine is trapped under the car and it would appear that there is no where for the heat to go. But, have you popped the hood on any front engine car lately? Those engines are crammed in there and I don't see anywhere for their heat to escape.

Water cooled engines don't really need breathing room to get rid of heat. That's a function of their cooling system, which is supposed to take the heat away from the engine and dump it into the atmosphere via the radiator. On a front engine car, the radiator is usually within a foot of the engine and upstream in terms of air flow. So as the air takes the heat from the radiator it pushes it right back into the engine compartment. Consider the fact that on a front engine car that the intake plenum is usually somewhere in this area and you are likely to suck some heat. In the mid engine layout of the Cayman the heat is being moved far away from the engine before it is being transferred to the atmosphere and is not likely to get back to the engine comparment. Also, the intake is sucking cool air from outside the engine compartment far away from the radiators.

I would argue just the opposite, that the mid engine layout of the Cayman is better for heat scavenging. Now on an older 911, I would definitely agree. Those engines were air cooled and mid engine placement is definitely not good for that.

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Gator Bite
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What ^^ said.

Basic principles of an engine is combustion. More air, more fuel = more power.

The cooler air is more dense, so per every cubic inch you are getting X amount more of oxygen. The computers will compensate for fuel. So with more air and more fuel being squeezed into the same amount room (more pressure) you also get a bigger bang.

The principle is the same as to why cars get less power in high altitude locations.

My guess it that it's a combo....yes, the electronic FI/varocam system runs richer, but also something that's underestimated often is the value of cold air in general. We see track records fall a lot faster in the spring and fall than in the summer due to the much denser air. Nothing mysterious, the saying "heavy air" has been used for centuries on the water...20 knots of breeze when it's 30 degrees F out packs a lot more punch than 20 knots of breeze when it's 80 out. The thicker air generates a lot more lift AND lever action.

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A free flow air filter does nothing to increase air density. It may help if the paper filter system is restrictive, which is not the case with the Cayman.

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Dan