All about Pipes

Header
The header's length has a significant impact on performance. The rule of thumb is that a longer header is better for bottom-end power, while a shorter header makes your engine scream on the top end. The longer it is, and it resonates at a lower pitch. The shorter it is, and it resonates at a higher pitch. The idea is to adjust the length until the engine and exhaust system are in sync and “singing” in harmony. You can’t go too far in either direction, so don't be reckless; you'll do more harm than good. The ideal header would also expand outward (conical shape). This subtle expansion, when combined with those of the tuned pipe, helps scavenge, or suck, the exhaust from the engine. The header length is the number you play with when tuning your pipe. A heavier car demands a broader power curve, so a longer header is best. A light car, on the other hand, can be tuned for peak power on a narrow power curve with a shorter header.

Divergent cone
·A sharper angle of the divergent cone makes scavenging more efficient but limits it to a more narrow rpm range.
·A more gradual divergent cone reduces the intensity of the negative wave, but it lasts much longer, so this increases the rpm range.

It's a balancing act of sorts: more performance over a limited rpm range or less performance over a broader rpm range.

Belly
Parallel portion of the pipe, that connects the divergent to the convergent cone. It's length determines the relation between the negative and positive waves.
·A short section is best for developing maximum power at high rpm ranges, but narrower power curve.
·A longer section implies in a broader power curve with less peak horsepower. Its more suited for developing low-rpm power.

Convergent cone
·A sharper angle of the convergent cone limits engine to a more narrow rpm range.
·A more gradual convergent cone increases the rpm range.

Stinger
The convergent cone ends at the stinger ( the pipe portion opened to atmosphere ) which expels the burned gases way out. It works as a pressure bleed valve and controls back-pressure, enhancing the port plugging efforts. If it is too small or too long, you may have engine overheating problems. Too small a stinger causes excessive back pressure into the pipe and raises the pipe and engine temperature.
The ideal stinger diameter should be .58 to .62 times the header diameter, and its length should be 2.86 to 3 times its own diameter.

Stinger diameter affects the top and bottom end.
·Bigger = top end at the sacrifice of low end torque.
·Smaller= low end at the sacrifice of high end revs.
Stinger length affects the top and bottom end.
·Shorter = top end at the sacrifice of low end torque.
·Longer = low end at the sacrifice of high end revs.

The stinger's ideal diameter and length are important to performance, but are limited and governed by most racing sanctioning bodies.

Tuned Pipes Design Examples
Small volume - narrow operating range (peaky)
High volume - lower power (if too big) - broad range
Steep angles - 'peaky' - high power
Shallow angles - broad range - moderate power
Shorter or larger diameter stinger - lower or higher pressures and heat.

How to Pick a Tuned Pipe·Torque biased. Sharp cone on each end long flat band center, single chamber.
·Low-mid biased. Aggressive divergent cone.
·Mid biased. Moderate divergent cone.
·Mid top end biased. Moderate divergent cone aggressive convergent cone.
·If the engine is a short rod rever you need a torquier pipe to enhance the bottom end as engine will be biased and take over on the top.
·If the engine is a long rod engine you need a rev pipe to help the engine unload on the top.

Pipe length
The way you intend to use your car in combination with your engine, will dictate the optimal length for the pipe.
The shorter the pipe, the higher the peak horsepower and torque, but the range of the horsepower and torque gets narrower and drops off faster. Also, the shorter the pipe the more fussy your engine will be.
·Shorter=top end at the sacrifice of low end torque.
·Longer=low end at the sacrifice of high end revs.

For optimum performance, the following guide may prove useful.

A) Overheating / Hot Weather
·Increase combustion chamber volume or head clearance.
·Increase stinger diameter or decrease stinger length (to reduce pipe pressure).
·Decrease nitro content of the fuel.

B) Cool Running / Cold Weather
·Decrease combustion chamber volume or head clearance.
·Decrease stinger diameter or increase stinger length.
·Increase nitro content of the fuel (if the competition rules allow).

C) Pipe Length Too Short
·Frequent blowing of glow plugs
·Sand blasted head
·Over heating engine
·Difficult to get 'on the pipe', sensitive needle
·Excessive carbonizing of the head
·Engine sags under load
·'Harsh' running

D) Pipe Length Too Long
·Very easy on the needles
·Smooth, quiet running
·Prone to burbling, rich running
·No power
·None of above, try shorter and see what happens.

AFM