Impulse Engines : How It Works : Exhaust Headers

High Velocity Tri-Y Headers

NEW header design combines 5 conventional pipe designs to substantially increase vacuum and produce a supercharging effect

Tri-Y Header
Small Pipe
Short Pipe
Stepped Pipe
Megaphone Collector

Negative Pressure Supercharging Tri-Y header works differently to other headers and does NOT work alone

The NPS Tri-Y header produces Compressed High Velocity Exhaust Gas by using small-short pipes and a megaphone collector. This produces a much higher vacuum than other headers and pulls a larger intake charge into the engine.

However, special valve timing is needed to trap the higher vacuum in the cylinder at the end of the exhaust stroke and move it to the intake stroke during the overlap period. Otherwise with conventional valve timing the higher vacuum produced by the NPS Tri-Y header pulls the intake charge into the exhaust system instead of into the cylinder.

Therefore, the NPS Tri-Y header works differently to other headers and does NOT work alone even though it uses a Tri-Y configuration.

Difference between NPS Tri-Y header and conventional headers

Negative Pressure Supercharging
Tri-Y Header...

Conventional
Tri-Y and 4-1 Headers...

Produces Compressed High Velocity Exhaust Gas (CHVEG) which produces a much higher vacuum and pulls a larger intake charge into the engine.

Produce a much lower vacuum that is able to only scavenge the exhaust gases from the cylinder.

Uses small header pipes that produce a much faster gas speed and a higher vacuum.

Use large header pipes that produce a much slower gas speed and a lower vacuum.

Uses CHVEG in the small header pipes to increase gas flow.

Use large header pipes to increase gas flow.

Uses short header pipes and a megaphone collector to prevent the CHVEG in the small header pipes from building up backpressure and restricting gas flow.

Use a large collector after the long header pipes to prevent the long header pipes from building up backpressure and restricting gas flow.

Gradually increases the pipe diameter along the length of the header and collector to maintain a high gas velocity and prevent a sudden drop in gas speed and vacuum.

Substantially increase the pipe diameters of the header and collector which cause a sudden drop in gas speed and vacuum.

Small-short header pipe and megaphone collector design prevents the CHVEG from flowing back into the engine during the intake stroke.

Large header pipe design allows the exhaust gases to flow back into the engine and dilute the intake charge.

Does NOT work with conventional valve timing that has...

•	Late closing intake and exhaust valves
•	Excessive overlap duration
•	High exhaust valve lift

Work with conventional valve timing.

MUST be used with Synchronised Valve Timing (SVT) in order to...

1)	TRAP the higher vacuum in the cylinder at the end of the exhaust stroke.
2)	MOVE the higher vacuum to the beginning of the intake stroke during the overlap period.
3)	TRAP the larger volume of air pulled into the cylinder by the higher vacuum during the intake stroke.
4)	PREVENT the higher vacuum from pulling the intake charge into the exhaust system during the overlap period.

DO NOT need to use special or synchronised valve timing in order to work.

NOTE
NPS Tri-Y header works ONLY with synchronised valve timing and special ignition timing.

NPS Tri-Y header compared to conventional headers

Negative Pressure Supercharging Tri-Y Header		Conventional Tri-Y and 4-1 Headers
Gas speed	600 ft/sec	300 ft/sec
Primary pipe diameter	1/2 the diameter	2 times larger
Header length	1/3 the length	3 times longer
Stepped pipes in 1/8" increments	Full length of header	No
Megaphone collector	Yes	No
Reduces cylinder pressure (increases vacuum)	Yes more details	No more details
Produces Compressed High Velocity Exhaust Gas	Yes more details	No
MUST be used with Synchronised Valve Timing	Yes more details	No
Compact header	Yes	No
Exhaust scavenger	No	Yes
Produces backpressure	No more details	Yes
Small primary pipes restrict gas flow	No more details	Yes
Uses pressure wave tuning to optimise pipe length	No	Yes
Allows gases to flow back into the cylinder	No	Yes

NPS Tri-Y header reduces cylinder pressure (increases vacuum) to pull a larger intake charge into the engine

	When the exhaust valve opens after combustion the high pressure gas forces itself through the small pipes of the NPS Tri-Y header. This compresses and doubles the speed of the gas in the small pipes of the header which produces Compressed High Velocity Exhaust Gas (CHVEG).
	The CHVEG produces a much lower pressure (higher vacuum) behind itself in the small pipes of the NPS Tri-Y header which reduces cylinder pressure (increases vacuum) during the exhaust stroke and pulls a larger intake charge into the engine.
The short pipes and megaphone collector of the NPS Tri-Y header allow the CHVEG to gradually expand into the larger section of the megaphone collector before the CHVEG builds up backpressure and restricts the gas flow in the small pipes of the header. This also allows a larger volume of gas to flow through the small pipes of the NPS Tri-Y header. However,

NPS Tri-Y header MUST be used with Synchronised Valve Timing

To get the higher vacuum produced by the NPS Tri-Y header to pull a larger intake charge into the engine, the higher vacuum needs to be trapped in the cylinder at the end of the exhaust stroke and moved to the intake stroke during the overlap period using Synchronised Valve Timing that uses...

•	Early closing intake and exhaust valves
•	Low overlap duration
•	Low exhaust valve lift

Conventional valve timing shown below does NOT allow the higher vacuum produced by the NPS Tri-Y header to pull a larger intake charge into the engine.

•	Late closing intake and exhaust valves
•	High overlap duration
•	High exhaust valve lift

For more details see Negative Supercharging Valve Timing

Small header pipes with a short length do NOT restrict gas flow

This is because the limited amount of high pressure gas that remains in the cylinder after combustion can be forced through a small pipe for only a short distance before it builds up backpressure and restricts the gas flow. Therefore, by making the small pipes of the NPS Tri-Y header short and connect to a megaphone collector it prevents the small header pipes from restricting gas flow.

Conventional Tri-Y and 4-1 headers are NOT able to reduce cylinder pressure because the...

•	Gas speed is too slow
•	Vacuum behind the slow gas flow is too weak
•	Diameter of pipe is too large
•	Length of pipe is too long
•	Pipes join together too far from the exhaust port
•	Exhaust gas flows back into the engine during the intake stroke

Lower pressure (higher vacuum) is produced behind all moving objects that travel at a high speed

Therefore, the faster the speed of a moving object, the lower the pressure (higher the vacuum) is behind the object. The same principle applies to the gas flow in the primary pipe of a typical header. The smaller the pipe, the faster the gas speed and therefore the lower the pressure (higher the vacuum) is behind the gas flow in the header. However, this only works if the small pipe is short and made shorter the smaller the pipe.

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Inventor of Negative Pressure Supercharging