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Last Updated At: 5/10/2003 10:00:15 AM This article is provided "as is" without any representations or warranties, express or implied. Team-Integra makes no representations or warranties in relation to this website or the information and materials provided on this website. |
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Engine Building: Swapping Parts To Get A Better Engine Package
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Content
A. Introduction: What Do We Start With In A B18 Engine?
B. Swapping Out Parts For More Displacement
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A. Introduction: What Do We Start With In A B18 Engine?
Integras have low rod ratios (i.e. rod ratio = connecting rod length divided by stroke) and therefore, our engines :
1a) have Short Piston Dwell Time at TDC
1b) have High Piston Speeds Away from TDC
2. prefer Long Duration, Big Overlap Cams
3. need Static Compression Ratio Increases to compensate for big overlap cams
4. prefer Small Port Volumes but these still must be bigger than a B16A's port volume
5. cannot rev as high as the B16A due to a lower rod ratio which increases cylinder wall piston sideloading againt the cylinder wall and as a result, has more vibrations at higher rpms.
This is the engine package characteristics of a B18 engine from which we start with. You can max out on the B18 engine with extreme mods but if you keep the low rod ratio and 1.8L displacement, you can only go so far with this typical high performance N/A engine package with: small port volumes, big overlap cams, big compression, and big header/exhaust. Most people that know how to build 1.8L B18C's and tune them usually max. out at around 215-225 peak whp for a reliable daily-driver. This thread will cover what we can do to change the odds in our favor to get more than this by swapping out parts to get : a) more displacement, b) a better rod ratio, c) a better engine layout (called oversquare layout).
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Skip this section and go to Page 2 if you already understand what rod ratio is and how it affects engine cylinder filling, cam choice, and headporting port sizes.
The "features" of a 1.8L B18 N/A engine briefly are:
1. Piston Geometry: Honda B18 series engines have a low rod length to stroke ratio or "rod ratio". For the Honda Integras, the rod ratio is in the low range at 1.54-1.58. The rod ratio determines the way the piston behaves as it travels up and down the cylinder. This behaviour is called "piston geometry". The consequence of the B18's piston geometry are :
1.a) they spend a shorter time at Top Dead Center (TDC) [which is at the very top of the piston travel] compared to the B16A. This is called a Short Piston Dwell Time.
With short piston dwell time, there is less force compressing the air:fuel mix on the compression stroke and the piston quickly changes direction downward as the mix is being ignited. The air fuel mix, with less compression force and rapid change in piston direction downward, does not combust as completely.
Secondly, on the upward exhaust stroke, the piston quickly changes from pushing the burnt exhaust gases out of the combustion chamber to sucking in fresh air:fuel at the start of the intake stroke.
We have fast transitions from compression to power strokes and exhaust to intake strokes. The piston changes direction or flip flops at TDC quickly at each engine cycle or stroke (intake, compression, power, exhaust strokes).
1. b) the piston drops down very fast away from TDC during the intake stroke and power stroke. This is called high Piston Speed Away From TDC.
On the intake stroke, high piston speeds away from TDC generates high flow velocities through the intake port at low-midrange rpm because the piston has a higher sucking force to draw in more intake air:fuel mix into the combustion chamber at low-midrange rpms.
On the power stroke, high piston speeds away from TDC unfortunately means the piston can run away from the spark flame front travel causing incomplete burning of the air fuel mix.
High piston speed away from TDC also reduces cylinder pressures too rapidly, especially at high rpms. This lowered cylinder pressure reduces the force downward on top of the piston making less power.
1 c) More importantly, with a low rod ratio, the B18's cannot rev as high compared to the B16A, due to a larger angle created between the connecting rod and the crankshaft (called the "rod angle")as the piston travels. Higher rod angles increase wear damage and vibration due to increased piston sideloading on the cylinder walls. Rev too high and you can push a piston through a cylinder wall into the coolant jacket.
2. Camshaft Choice: With the piston geometry described in 1. , B18 engines like Long Duration, Big Overlap Cams because we need more scavenging and time to fill the chamber, especially at high rpms .
eg. of high overlap cams :
- for the B18A/B Crower 62403 or 62404.
- for B18C Toda Spec B, Jun Type 3, Skunk2 Stage 2, Crower 63403, Zex 57300.
The exception to this rule is when we add nitrous, a turbocharger, or a supercharger. Intermediate overlap, short duration cams are chosen to prevent the boost from shooting into the exhaust manifold with a long cam overlap.
eg. intermediate overlap short duration cams for forced induction:
for B18A/B - Crower 62402/62403, Crane 101-0014 turbo cams
for B18C - Toda Spec A, Jun Type 2, Crower 63402/63402A, Zex/Compcams 57100 or 57200, Crane roller 253-0510 cams with roller rockers.
However, with more intake cam duration there is a greater chance of cylinder pressure being lost out of the opening intake valve. We lose dynamic compression . Along with High Piston Speeds Away From TDC, big overlap cams will reduce cylinder pressures and prevent efficient burning or combustion of the air fuel mix.
3. Port Sizing: the B18's like small cross-sectional port area and longer port length on the cylinder head intake ports to maintain high flow velocity and flow quality. However, the B18's preferred port size is still bigger than the B16A intake ports.
So this is where we start from with our B18 engines. Are we stuck with 1.8L displacement, big overlap cams, lower redline, and a low rod ratios? Of course not! This is why we swap parts to change the engine package's piston geometry, displacement, and it's breathing ability. The next section deals with doing this.
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Posted 2/14/2002 7:35:22 PM
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