Multicylinder 2 stroke into one expansion chamber?

[motu]

I had a GT750 with a 3 into 1 too - three header pipes jammed into a 3in tube with a muffler stuck on the end. The GT750 wasn't about top end anyway, it was a grunt machine. Certainly a cheaper option than the 4 huge mufflers it had stock.

[gplracing]

Originally Posted by scrambler73

Cool Glyn...and I do agree that with 180 phasing, if the 2 into 1 is designed well enough (and it sounds like you are definately on the right track!), you will not have nearly the "problems" with soundwave turbulence that one would have with a 3 cylinder.

How was low end grunt compared to the 2 into 2? Thats actually quite impressive that it was only 4hp and 300 revs down on peak.

The pipe that was tested flollowed the 2-2 set up with in 2hp, + at times and - in places. The test wasn't done very well to be honest. It was just bolted on with out any fueling or ignition changes and run.

The pipe in the pic is a different design and designed in the sim differently than the pipe tested. IMO the other pipe was designed with an unrealistic wall temp. Time will tell lol.

Glyn

[Duck_Pilot]

Originally Posted by scrambler73

2 strokes will always make the most horsepower with ONE individual expansion chamber per cylinder.
As soon as you add 1 or 2 more cylinders to the mix, the soundwaves (for lack of a better explaination) begin to collide in a way that disrupts the whole purpose of an expansion chamber.... Cramming unburnt mixture back into the cylinder before the port closes.

BINGO!! If you want the best out of a 2T engine, you need separate chambers. Next best would be a single-chambered 'twingle', where the pistons are in sync with each other..... there may be a pressure loss, but at least the sonics won't fight each other.

The shape of a 2T expansion chamber works kiss-'n-cousins to a supercharger, with no mechanical moving parts. The placement and shape of the forward cone generates vaccuum to help drag out the old, spent charge - and help pull the fresh charge up from the cases while the transfer and exhaust ports are all open (scavenging). Then the rear cone reverses that wave, to force-feed a portion of fresh fuel charge - that had been pulled into the headpipe - back on top of the piston, before the exhaust port closes. The powerband of a 2T engine is greatly influenced by the placement and shape of both cones.

If you need light weight and cornering clearance more than power, then the 3-1 chamber may be fine for you. I faced several Kawi 750's and GT-750's with those pipes on local racetracks, and my under-carbureted GT-550 outran 'em all easily. 200CC's lighter displacement, and still no contest.

[Deuce]

This was my first street bike. I was 18 at the time ('76). Has a custom made 2 into 1. Bike ran great especially on the 'pipe'. I had to repack that thing every 2 weeks if I wanted to be semi-quiet with it. Did a lot of miles with that bike travelling between Kingston, Ontario and Montreal on the weekends.

[vernon dent]

had a 72 h2 kawasaki back in the mid to late 70's. when i bought the bike it came with a three into one expansion chamber. bought a new set of chrome plated dencos for it($279.00 in 1977) and they made a world of difference on the 750. the three into one was binned shortly after.

[hugemoth]

My Rotax 582 ultralight engine uses a 2 into one pipe. It's 65 hp, rotary valve, very wide power band. I think the 100 hp snowmobile and watercraft versions use 2 into one also.