Engine Tech

Breaking in a new Engine

There are a few schools of thought for braking in a new engine, baby it for a 1000 miles change the oil and drive normally. Or Drive it hard sooner than later. The primary task your trying to cover when breaking in a new engine is to get the new piston rings to seat. On a road race engine, set a limit of 4500 rpms on the first session, a limit of 5500 rpms on the second session, and 6500 rpms on the third session. After three sessions, the engines can raced as normal.

With a street engine, keep the rpms to a maximum of 4500 rpms for the first 500 miles, and after that the engine parts should be fully mated to each other.

CIS Modifications

Building a Adjustable WUR

An engine equipped with a Bosch CIS (K-Jetronic) fuel injection system depends on the accuracy of the control pressure for 
starting and drive ability performance.  The WUR can be modified to provide for external adjustments by the addition of a pull-out
screw and nut which permits very accurate movement of the plug. 
DIY Link

Intake Tuning

Power output of the engine is directly proportional to the amount of air and fuel that it can ingest, the goal is to pack as much mixture as possible into the engine during the intake cycle. Good article on the importance of proper flowing intake system and what affects air flow. The Intake Cycle Part One
Great article that discusses the many factors that affect total intake airflow, and horsepower output. Including intake pressure wave tuning.
The Intake Cycle Part Two

Exhaust systems

Exhaust tuning theory

As the exhaust valve opens a few degrees before BDC(or at BDC for that matter), the exhaust gases exiting the combustion camber create a pressure wave. This pressure wave of exhaust gases also form a sonic pressure wave. A sonic wave travels the speed of sound. The speed of the exhaust gases travels slower and is based on the diameter or the tube and other restrictions. When the pressure high pressure sonic wave reaches a large area change, such as a collector, muffler, or end of pipe, the wave reflects backwards and changes pressure(from positive to negative).

So the high pressure wave exiting the head, entering the header, reaches the first pipe merge reflects back toward the head as a negative wave. Sucking additional gases from the chamber. If the valve timing(during overlap period) and wave timing is the same, then the (sucking) wave pulls air in from the intake system at several times the force than the piston does. Before the piston even has started to pull air in. When this happens the combustion chamber is filled with fresh charge, and the intake process is off to a quick start with high velocity intake charge. this has been called the 5th cycle on racing motors.

Here are some basic calculations I did to see how long the runners on the headers needed to be to give the boost of intake charge.

Sonic wave travels about 1130 ft/sec in hot air
Basic cam timing is 1/2 crank rotation.(keep things simple)
Equation ((1/2 crank rotation/rpm) x wave speed = total distance /2 = runner length
<math>((30/rpm) x 1130)/2</math>

rpm vs. runner length
1000 16.95 ft
2000 8.48 ft
3000 5.65 ft
4000 4.24 ft
5000 3.39 ft
6000 2.83 ft
6500 2.61 ft

It seems that tuning for 6000 to 6500 rpm is reasonable. That would mean that the first collector(point where two pipes merge ie area change) would need to be about 2' long. Since the port length on the 8v motor from valve to gasket surface is about 5 inches.

Links for reference
Exhaust Cycle Part One

Picking the Right Muffler

"The trend is that as flow is added to an initially flow-restricted engine, power increases rapidly at first then gains tail off. Once the available flow exceeds about 2.2 cfm per hp, the gains possible by increasing muffler capacity drop to less than 1 percent."
"Knowing that 2.2 cfm per open-pipe hp means zero loss from back pressure allows us to determine how much muffler flow your engine needs."
For instance, a VW 90 horsepower on open exhaust will require 90x 2.2 = 198CFM

Exhaust Science Demystified

Compression

The stock JH 8 valve motor found in the Rabbit GTI and some Scirocco's has a static compression of 8.5:1. There are various techniques to up the compression to up the horsepower and torque. Replacing the pistons with flat top pistons or decking the head. The pistons found in the JH motor have dished pistons.

Compression Ratio = (CD + PV + HV + HGV)/(PV +HV +HGV)

Where:
CD = Cylinder Displacement
PV = Piston Volume
HV = Head Volume
HGV = Head Gasket Volume

Cylinder Displacement = (bore x bore x stroke x .0031416) /4
Plugging in JH values in mm:
445.22 CC = (81 X 81 x 86.40 x .0031416 ) /4

Values for stock JH motor:
PV = 21 cc
HV = 28 cc (this varies between heads, and combustion chamber on the same head 28 cc -30 cc )
HGV = 9 cc

Compression Ratio plugging in JH values
(445.22 + 21 + 28 + 9)/21 + 28 + 9)
(503.22)/58 = 8.67  
Expressed as 8.67:1

Increasing Compression

Decking the head - removing material from the surface to decrease the volume of the combustion chamber. Removing 0.040" of an inch reduced the volume to about 26 cc.

Rerun calculation with revised HV values
(445.22 + 21 + 26 + 9)/21 + 26 + 9)
(501.22)/56 = 8.95  
Expressed as 8.95:1

Now that you see the math behind the calculations, there is a very nice online calculator to do this for you.
Online calculator: link

Rebuild

CC check March 25/2007 New Piston Volume = 10cc

Wheel Horsepower WHP & Crank/Block Horsepower BHP

WHP is the amount of power available at the wheels - including the drive train losses.
BHP is the amount of power available at the end of the crankshaft.
Obviously BHP numbers appear higher since they don't include the amount of power loss through the transmission etc..
Here is how to estimate BHP from WHP Assuming a conservative 15% or 18% drive train loss:
WHP + (WHP x .15) = BHP
or WHP + (WHP x .18) = BHP
FYI If you Dyno results show 100 WHP than you can estimate that the BHP is 115.
NOTE: Not all Dyno's are created equally, and produce varying results. Dynapack and Mustang Dyno's seem to give favorable results for the A1 platform. Dynojet results seem to be a bit low. Your mileage may vary. When comparing dyno results keep the dyno brand and correction factors in mind.

Porting

Increasing air flow into and out of the engine is how it makes horsepower. The majority of the improvement potential is in the head.

There are various techniques to increase the air flow. Here you'll find links to the best resources to describe these porting techniques and technologies.
Whats Extrude hone?

How to port and polish your cylinder head. With careful attention to port shape and smooth-ness you can port your own Mk1/ Rabbit/ Caddy/ Cabby and Scirocco 8v VW head
Porting article

How to port and polish your intake manifold.
Porting a 8V intake, got tips?

Tests results for various VW mk1 intake manifolds. Provides the best performance on the VW 8v motor?
A1 Intake Manifold Testing

Glossary

List of terms and their meaning.
CC - Cubic Centimeters, a measure of volume
bore - diameter usable portion of a cylinder chamber
stroke - length usable portion of a cylinder chamber
static compression - compression not taking into effect cam timing, just compressing volume x into smaller portion of x
CE2 - second generation of central electronics,VW standardized wiring system based on the same fuse block and harness connectors from 1990.52 - 1992