Real NA Performance

[Lordalfa]

We will touch in NA. How to get the most out of your NA engine.

 

4 stroke Otto Cycle.

The 4 stroke engine is literally a pump.

 

1. Induction. Intake valve opens. The air fuel mixture is sucked into the cylinder with a downward motion of the piston.

 

2. Compression. Both valves closed. The mixture is compressed as the piston moves upwards.

 

3. Power. The spark plug is energized and releases a flame to combust the mixture causing the piston to move downwards.

 

4. Exhaust. Exhaust valve opens. Wasted gases are expelled as the piston moves upwards.

 

Repeat. This is 1 cycle or 1 rev. Imagine your F1 engine screaming at 19,000 of these 4 cycles a minute. Something closer, you Honda CBR600RR motorcycle can perform this kind of rev magic too. Sounds very good too.

 

The key thing to a more efficient engine is to pack as many oxygen molecules into the induction as posible. How?

 

1. Cooler air. Concepts of CAI is in here. Over beaten topic that I will not touch.

 

2. Compressing the air. I will touch on turbocharging and supercharging concepts in another thread.

 

3. More oxygen. Oxygen is not stable. Pure oxygen will readily cling to any agent. So we need a slightly more stable gas that is easily breakable. Enter Nitrous Oxide. Another thread hopefully.

 

4. For purely NA, improving volumetric efficiency. In simple terms making the cylinder suck in as much mixture as possible. At the induction stroke, due to the nature of gases, they do not rush in to fill up all 400cc of mixture in the induction stroke before the valve closes. The idea in volumetric efficiency is to overfill this induction.

 

Most 16v cars are have VE of 90%. On race cars, it is possible to get 110%.

 

How to improve VE? This is the most expensive way to mod a car comparing to FI or NOS. BHP/$$ is the highest.

 

Pity that the 4 stroke engine is a variable condition engine. It is a lot difficult to tune to variables of the road than say a generator which operates at constant speed.

 

Before there was 2v per cylinder. These engines have 1 intake and 1 exhaust valve. This means that the cylinder head was not fully utilised to for the induction. The flow depended on the size of the intake valve. Pie x Radius x Radius is the opening that the cylinder has. Flows are not efficient either because of the size of the valve, bigger diameter also means that air flows more lethargically. VE of 2v engine are typically 75%.

 

4v per cylinder engine have the head almost as a whole opening. The total area is larger than the 2v engine by quite a substantial area. The valves are smaller and thus making the flows at higher speeds. VE of 4v engines are in the area of 90%.

 

you can improve VE by changing to smaller stem valves. Smaller stems can encourage more flow by less obstruction.

 

OK. Most engines are 4v now. How to increase the VE?

 

VE is not contant throughout the engine range. Most road cars are made with a VE operating maximum at say 3000 to 4000 rpm. Mid range. This due to the engine speed and camshafts. The opening of the intake valve is controlled by the camshaft. Race cars will have special camshafts that shift the VE to the high range where the want the maximum devlivery of induction. So variable valve timing takes care of this. That is why VTEC is so successful. 3 camshafts in 1 car depending on the condition of the engine is a wonderful idea.

 

Other methods is to increase air velocity. Longer intake manifold at low engine speeds aids in collecting the air to a substantial speed before entering the chamber. But at high engine speeds, a long intake tract will cause the VE to drop because a long intake tract cannot supply air fast enough. So a short intake tract is needed for high enging range. This is solved by a technology call Variable Intake Geometry. Long intake for low range, short for high range. An electronically operated valve will switch between the tracts depending on engine speed detected by the ECU. Example of cars with VIG, Toyota Levin, Alfa 156 and Chevy Aveo.

 

Increasing air velocity can make use of a port and polish. Porting is a method which the ports of the cylinder head is a process in which by hand we remove the blemishes made by the metal casting process. You can slightly enlarge the ports to the gastket shapes to ensure a smooth flow. Polishing is mostly done at the exhaust port to facilitate the quick escape of exhaust gases. Polishing the exhaust ports is particularly good for turbocharged engines. The manufacturing process is so good today that porting is generally not needed. A good polish if the ports is however quite sufficient.

 

You can port and polish with a flow measurement. Meaning that you can port to a point can all cylinder flow the same amount of air. This equates for equal mixture for all cylinders.

 

So for NA cars, the goal is to improve VE.

 

1. Most cars are now 4v per cylinder. Nothing much can be done here except changing the valves.

 

2. Intake geometry. Good if you car has it. Want power? A short cone filter is all you need. Want torque, get a long tract.

 

3. VVT. I think this is a given. The champion here is iVTEC and VVTiL. Excellent engineering. Change the camshafts will only improve is shifting your power band upwards. I suggest Stage 1 for driveability.

 

4. Port and Polish. A good finishing touch to more perfection.

 

I'll touch on fueling next.

[DarkLord]

 

Both of you brothers really are "car-know-it-all" sia!

[Jiayong]

Ah...the Lord Alfa himself. Rem me? Hee hee...i met you before once at Bishan and another time at PG.

[Maded]

Just a question dude...

 

Aren't the 4 strokes (Induction, Compression, Combustion, Exhaust) accomplished in 2 revolutions of the crankshaft?

 

Means that in the F1 car @ 19K RPM, the crankshaft rotates 19,000 times per minute, but the 4 strokes happened 9,500 times in that minute... right?

[Lordalfa]

Yes. You are sharp. 2 revs make 1 cycle. On a 2-stroke it is 1 rev make 1 cycle.

[Lordalfa]

The AE86?

[Jhoo]

This port and polish is done only at the cylinder head, exhaust ports? A friend did it on the throttle body?

 

Seems like the in-thing now!

 

Please enligthen further, besides the performance plugs, CAI, higher flow filter, semiflow muffler and V-Power, nothing else is of much use on my ride . Need to optimise my setup further before heading for the piggy chip. Does a PBV/Fuel pressure regulator helps? My stock is alreday at 3 (psi?)

 

As mines an auto, I would enjoy lots of low and mid end enhancement for my ride.

Edited March 1, 2005 by Jhoo

[Normal_aspirated]

Both of you brothers really are "car-know-it-all" sia!

u mean Genie47?

[Jiayong]

good memory!!!!

[Maded]

Is intake manifold the same as throttle body? Would it be sufficient to say upgrade the throttle body and fit huge cai piping to ensure that the engine always has enuf air to breathe?

 

ChevvyAveo, Black, No mods, No roof rails

No Guages

Stock stock stock stock stock

 

no offense to your sig!!!

[DarkLord]

So obvious harz?

[Lordalfa]

Actually porting the throttle is minimal. I do not recommend a larger throttle unless you are using for all out flat foot driving like racing. You can port and polish the throttle but it is minimal. If you want to change the throttle, change to a slide throttle. Most throttles in cars are butterfly throttles.

 

Slide throttles are instant response. It is like slush gate like those at Kranji Dam. Once open, a flood comes in.

 

You port and polish both exhaust and intake ports but more polish on the exhaust. The intake needs to be ported but not to a mirror finish because you need some turbulence in the intake ports for fuel mixing.

 

It is a myth, spark plugs do not improve performance. Done there tried that, all hallaboo. Unless you boost the car above 1.5bar, you do not need to change to colder plugs. Stick to your manufacturers recommended. Spark plugs only do 1 things, ignite the mixture. Whether Iridium or Gold, all do the same thing.

 

An AFR(adjustable fuel pressure regulator) increases is needed if your injectors are maxed out at full throttle. Inlikely if you have a stock car. On low loads, ie cruising, the AFR is not into effect because your ECU will compensate the injector firing using a closed loop with the O2 sensor. Most stock FPR are tuned to 3 bar pressure line.

 

But using AFR can increase power but it must be tuned with a wide band O2 sensor. Most cars for safety are tuned rich to protect the engine at high loads. At WOT, the ECU goes on open loop and ignores the O2 sensor. But too high in my opinion. Lambda of 12+ for full throttle. For NA, I try for Lambda at 13.0 to 13.5. For FI, about 12.5 to 13.0.

 

Plug in the WB O2 Sensor before any cats, warm it up, get a good stretch, floor it in 3rd gear, remember the lambda reading, screw anti-clockwise on the AFR 1/16 of a turn, try again. Repeat until you get 13.0 to 13.5 lambda.

 

Don't worry about idle and cruising that the engine is lean, your ECU will compensate.

 

Try cruising with the WB O2, confirm that the lambda is around 14.0 to 15.0.

 

These methods confirm to save fuel and increase power but tedious to tune as this is a mechanical device. A certain risk especially you are impatient and turn the screw a whole 1/4 turn. Engine goes too lean and piang.

 

I post again on how to read lambda sensor.

[Lordalfa]

Bigger pipe loses air velocity. Compare a big water hose and a small one. The manufacturers have tuned the pipe diameter.

[Lordalfa]

I have recently seen a 4AGZE at AD.

[Jhoo]

Thanks for reply,

 

I guess the most practical mod for best yield is still port and polish both exhaust and intake ports.

 

Kindly PM me if you have a reliable source for the job, thanks.

 

I'll kiv the AFR and piggy, unless I can get on a used set to trial (just for the modding interest)

[Jiayong]

At AD? where is that? hee hee...but i have always preferred NA..

[Ferrariz]

jiayong, we are organising another track at pg..wanna join...late april thou.

[Porker]

A few questions for you bro...

 

1) Do unburnt fuel and air get ejected throught the exhaust valves on variable valve timing systems?

 

2) I think the stoichiometric ratio for complete combustion is 14.7 parts of air to 1 part of fuel right? If so, does that condition exist constantly in the cylinders or is it always alternating between lean burn and rich condition?