GT550A top end woes

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Alan H
Moto GP
Posts: 2867
Joined: Thu Feb 16, 2012 11:50 am
Country: England
Suzuki 2-Strokes: 3 x GT550s - J, A, B.
Location: The Republic of South Yorkshire

Re: GT550A top end woes

Post by Alan H »

Ok, it'll be 'some time' though.
Think of how stupid the average person is, then realise that half of them are more stupid than that.
To the on ramp
Posts: 264
Joined: Sun Mar 07, 2021 2:32 pm
Country: United Kingdom
Suzuki 2-Strokes: GT550A 1976

Re: GT550A top end woes

Post by vulcanman »

Time not a problem as i cant ride at mo due to my hopefully temp double nxteye scan this Sat ,hoping for some better meantime im slowly working on 650 Honda single ive aquired.all up n running but needs fork seals ,tyres & some cosmetic tlc.ima long way from you but happy to make the drive in East Sussex & only 7miles from coast.just let me know and i be up.thank you Alan
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Suzuki 2-Strokes: Suz, Yam, Honda, Kaw.
Location: New Hampshire

Re: GT550A top end woes

Post by Vintageman »

I see people recently discussing GT550 Pipes. Always great topic

I believe Jemco 's 3 into 1 is where Omar asked them to copy Strader's 3 into 1 design ->

I have Strader on mine now. Strong mid and still can over rev into redline, where it is I who choses to back off vs it running out of breath. I think the chamber section makes a difference vs straight like Higgs 3 into 1. Also, the Strader's tuned length is on shorter side vs even some 3 into 3s, So maybe why it doesn't ruin top end and I'd say it is equal to stock at least (Haven't tried my stock exhaust for a while though, so honesty don't recall what I was getting, but don't remember being disappointed that it would not get touch redline)

I also have 3 into 3 Bassani's (so I have be told), Well made, can keep center stand, and have a longer tune length. Very strong low end and good midrange boost, better low end than Strader. It did take away from top end a bit as getting into redline was not a natural affair.

I have 3 into 3 Ocelots with short tuned length, not as much bottom/mid as the the others above. Strong mid is fun street riding for sure.

My GT550 is 1973. The last mod I did was to stock rubber intake boot. I took out the inner straight rubber tubes. They extend intake tuned length in theory and appeared to also limit my top end. They also extend very near to the back of boot, possibly so close limiting air flow. The 74-77 boot also has straight tubes, but not as long as 72-73 and/or at least not as close to back wall of boot. I did this mod while running Strader and that allowed me to get into redline notably further I am now curious to see how Ocelots work with this mod.

I just order studs vs exhaust bolts. The idea is that I can now switch between my Strader or Ocelots more easily and not worry about stripping aluminum exhaust threads in the barrels.

Other mods

My Ex ports are a 2-3 mm wider, and+1 mm raised vs stock, <1.5 mm off Piston skirt and running 0.020" head gaskets. Originally, the Bassanis' and intake boot may have been what was holding back top end as those mods. not radical by any means, did not give me the change I expected. Soon to find out.

Oh, with the pipes that give boost lower RPMs, where the GT550 tune from factory is already strong, would cause pinging when I backed off throttle. I had to back all the way off throttle, after a pull into upper RPMs for no pings to occur. Very annoying. I finally cured this by larger needle jet. Changing Pilot or raising needles was not the right spot to squelch the ping properly and caused to rich idle or poor cruising MPGs respectively.

Great bike! 3 into 1 and 3 into 3 each give unique sound and character.
Current Bikes
74 GT250 (T350 upgrade),
76 GT250 (T350 upgrade),
71 T350,
70 T350,
74 GT380,
75 T500,
73 GT550,
75 GT750,
72 Yamaha DS7 (R5 upgrade),
77 Yamaha RD400 (Daytona Cyls),
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