options for new exhausts / expansion chambers

[Alan H]

I can accept opinions that are thought out and sensible. If you think this is aggressive you need to get a life, bearing in mind I've been working on 2 Suzuki 2 strokes since 1967, and Suzuki GT550s/GT750s/T200splus other manufactures (Ariels, BSAs, Fanny Bs, Yamaha V4s, Wartburg 3s etc.) since 1972 plus having rebuilt Suzy several triples in the last 15 years or so.

[jabcb]

My gray 75 GT750 had been rebuilt & modified by the PO. Had early-model individual carbs, pod filters, Newtronics ignition & 3-into-3 expansion chambers.
The PO’s notes included performance mod instructions but I don’t know what, if any, porting mods he did. The bike had very little power below 4k rpm & was a peaky screamer above that.

I switched to Jemco 3-into-1s to get some bottom end. Now the power starts at around 2.5k rpm. From 2.5k to 5k rpm its way more peppy than my red 75 GT750, which is stock & also rebuilt.

3-into-1s supposedly act as a rev limiter in that they run out of power at some point — somewhere over 5k rpm on the GT750. I don’t generally run GT750s over 5k, so I can’t comment on how true that is.

The GT750s are geared for around 112mph. If I accept the 90 mph limit claim, then that works out to a 3-into-1 power rev limit of:
90/112 * 7k rpm = 5,625 rpm
A 3-into-1 power rev limit of 5,625 rpm is credible.

Perhaps Piper did something to raise the power rev limit to the 7k rpm limit in exchange for less bottom end.

If you have some interest in going over 90 mph on a GT750, then this might be an issue for you. I don’t ride anywhere where it would be reasonable to do that.

Other than that, the 3-into-1s make for a sweet fun-to-ride GT750. Plus you can get this look:
GT750-1975_0583 by jabcb, on Flickr

[jabcb]

Video of the Higgspeed GT750 3-into-1. Per the description they are available for the GT380 & GT550. Perhaps they are in the works.
There is not much of a big-fat-middle expansion section, so I wonder how they perform.

https://www.youtube.com/watch?v=BVKPjrg5mpo

https://higgspeed.com/product/expansion ... i-gt750jk/

[jabcb]

Zenshin has a much improved website.
https://www.zenshinpipe.com
translated: https://www-zenshinpipe-com.translate.g ... r_pto=wapp

Lots more configuration options than I had realized. Price list shows a wide range: around 500 to 1,700 US$ depending on the configuration.
The 1-2 cross chamber looks interesting but is 1,500 US$. Plus shipping and TBD other costs. Ouch!
https://www.zenshinpipe.com/部品/チャンバー/1-2クロスチャンバー/

[Alan H]

Video of the Higgspeed GT750 3-into-1. Per the description they are available for the GT380 & GT550. Perhaps they are in the works.
There is not much of a big-fat-middle expansion section, so I wonder how they perform.

https://www.youtube.com/watch?v=BVKPjrg5mpo

https://higgspeed.com/product/expansion ... i-gt750jk/

Only the 'bent around a brick downpipes' chambers for the 550, unless my eyes are painted on!
Video of a 750J (import) with twin discs too.....how original

[jabcb]

Higgspeed website now lists GT550/GT380 3-into-1s
https://higgspeed.com/product/expansion ... ring-copy/

[jabcb]

Anyone have feedback on how the Higgspeed GT550 3-into-1s perform?

I just contacted Jemco about the GT550 3-into-1s -- they make the 3-into-3s but not the 3-into-1s. Quadruple double rats!

[jabcb]

Lots of pics & comments on the Higgspeed Facebook page: https://www.facebook.com/pg/higgspeedpe ... cts/posts/
Page has these two comments for a GT750 3-into-1 video:
“Sid Bamboo Sounds great, mate had one on his KH250 in 1979, have you had it on the dyno?”
“Higgspeed Performance Products Stew Naylor no we know they don't really work but sound awesome”