Potential Big Bore Performance kit for GS550

[Neveragain55]

Hi Gang,

The bug has bitten me to start another project, so I'm finally going to build the café racer I've always wanted to build and the prefect platform (for me) is the GS550.

I considered the GS400 & GS450 parallel twins for their light weight, but they don't give/have that inline-four sound that I love.

Having said all of that, I've searched hi & low for a company that sells a big bore, high performance kit for the GS550 and it looks like Wiseco discontinued the one that they used to sell.

Yes, I've seen all the posts, write-ups, and chatter about grafting the 650 head on, but I really don't want to go through all of that.

I did find a couple of company's that sell slightly larger pistons for the GS550, but 0.56mm to 1.0mm more isn't much and isn't going to give much of a horsepower gain that you would really notice.

Is there, or is there not a big bore kit out there for the 550 that I can use to gain more horsepower, in addition to maybe a hotter cam, slightly larger carbs, and better exhaust system, without having to go the "grafting on a 650" route?

Any & all answers are welcome, thanks in advance.....

[salty_monk]

I wonder if you can fit the 83-85 700 / 750 Engine in that frame.... Sounds like you're going to be grinding on it anyway and using pods etc. Might be easier than all that engine work.

I think that engine is pretty small and having restored both a 83 750 and an 80 550 I can tell you the 750 has a decent amount more power.

[Neveragain55]

Yes, my daily ride for over 20 years has been a 79 GS750E slightly modified and she goes like lightning.

It would really help if I could find a definitive guide or chart that gives the specific weights of the various air cooled GS engines but I cant find one anywhere.

I wouldn't mind going with a larger engine, but only if I can manage to keep the weight down

After all, that's the entire point of building a cafe racer.

[Nessism]

Do the 650 conversion. That's the biggest bang for the buck you can do. There are several long threads here to guide you. The only hassle is that you should fully tear down the engine, so when the top case half is clearanced, for the bigger sleeves, all the chips won't go inside the bottom end. Building the engine is fun. Even if it's your first time, there are lots of guys here to help.

[rphillips]

May not work at all, but wondering if just transplanting a GS650 eng. be much easier and cheeep er?

[Neveragain55]

Do the 650 conversion. That's the biggest bang for the buck you can do. There are several long threads here to guide you. The only hassle is that you should fully tear down the engine, so when the top case half is clearanced, for the bigger sleeves, all the chips won't go inside the bottom end. Building the engine is fun. Even if it's your first time, there are lots of guys here to help.

I just may have to as a big bore kit for the 550 doesnt seem to exist.

Plus, I have a buddy that's a Suzuki legend in the area where I live and all this guy does is build Suzuki powerhouse engines.

If anybody would know how to do it, do it well, and get the most out of the engine, it would be him.

Thanks for the reply.....

[Neveragain55]

May not work at all, but wondering if just transplanting a GS650 eng. be much easier and cheeep er?

Yes but the GS650 is a shaft drive engine and the cost & work to convert it to chain drive would be insane.

I don't mind shaft driven bikes, but this project has to be conventional chain.

[KiwiAlfa156]

Yes but the GS650 is a shaft drive engine and the cost & work to convert it to chain drive would be insane.

I don't mind shaft driven bikes, but this project has to be conventional chain.

The 650E is chain drive and derived from the 550 (roller crank), while some parts are interchangeable, the 650G shaft engine (plain bearing crank) is a new (at the time) design.

[Neveragain55]

The 650E is chain drive and derived from the 550 (roller crank), while some parts are interchangeable, the 650G shaft engine (plain bearing crank) is a new (at the time) design.

My bad, and I stand corrected, you are correct sir, looks like my options are increasing.....

Do you now if that engine will bolt into a 1980 GS550 frame without having to fabricate completely new mounting tabs?

[Neveragain55]

This is what I envision the bike will look like, but with a thicker seat that won't fire up my sciatica after three miles of riding the way this "tissue-thin" seat would, and regular street tires, not the "bobber style" tires that this bike has.

#4.jpg

[oldGSfan]

My bad, and I stand corrected, you are correct sir, looks like my options are increasing.....

Do you now if that engine will bolt into a 1980 GS550 frame without having to fabricate completely new mounting tabs?

For '79 GS550E / '82 GS650E, the diagrams show the same crankcase part number and the 3 long mounting bolts are also the same number. For some reason there's no 1980 GS550E listed on Partzilla, but the 79/80 should be the same case and mounts etc. So it's promising. Personally I'd just look for a 650E as it has improvements (dual discs for example) but you must have reasons you like the platform better.

https://www.partzilla.com/catalog/suzuki/motorcycle/1979/gs550e/crankcase

https://www.partzilla.com/catalog/suzuki/motorcycle/1982/gs650e/crankcase

Some chatter on it here, says the frame is nearly identical on the E models:

https://oldskoolsuzuki.info/forums/topic/6883-gs-550650-frame/

[Neveragain55]

For '79 GS550E / '82 GS650E, the diagrams show the same crankcase part number and the 3 long mounting bolts are also the same number. For some reason there's no 1980 GS550E listed on Partzilla, but the 79/80 should be the same case and mounts etc. So it's promising. Personally I'd just look for a 650E as it has improvements (dual discs for example) but you must have reasons you like the platform better.

https://www.partzilla.com/catalog/suzuki/motorcycle/1979/gs550e/crankcase

https://www.partzilla.com/catalog/suzuki/motorcycle/1982/gs650e/crankcase

Some chatter on it here, says the frame is nearly identical on the E models:

https://oldskoolsuzuki.info/forums/t...-550650-frame/

When I used the word "platform", I was referring to a small, powerful, inline 4 engine over anybody's parallel twin.

Why you ask, purely the sound and nothing else.

I've seen countless video's (and heard in person) parallel twin café racers. (mostly the Yamaha XS650 that folks love to build)

It's an awesome bike but, (for me) all parallel twins make a weak, muted, lawnmower engine (without a muffler) sound that doesn't excite my soul the way an inline four does. A parallel twin makes that "put put" sound, where as an inline four literally roars to life when you're on the gas, or revving them.

I realize that a parallel twin engine would be the lightest in terms of engine weight, and that it would truly give that whole "British Café Racer" vibe a bit more, but I just can't seem to tear myself away from inline four motors.

Having said all of that, and after reading all of the replies, I think I've come down to doing one of three things:

1. Rebuilding a stock 550, using the 1.0mm larger size pistons that I found and having my Suzuki buddy massage as much power out of her as possible with modern carbs and a good exhaust system. This is the largest piston kit I could find for the GS550: https://www.cruzinimage.net/2017/08/...ns-set-57-00mm

2. Having my Suzuki buddy help me with the 650 head surgery, and go that route

3. Get my hands on a solid 650E engine and massage as much power out of her as possible with good carbs, and an exhaust that would work best with the modern carbs.
Wiseco doesn't make an overbore engine kit for the 650 either.

All of the replies have really helped, thanks gang......

[Nessism]

This is what I envision the bike will look like, but with a thicker seat that won't fire up my sciatica after three miles of riding the way this "tissue-thin" seat would, and regular street tires, not the "bobber style" tires that this bike has.

#4.jpg

No disrespect, but this is what I see...

- Tires way oversized for the rims. Low grade Coker tires. Real Cafe bikes are supposed to be functional, racing about, not focused on appearance.
- Low bars, and a plank for a seat. Only a kid, or a masochist could ride that bike for more than 30 minutes.
- Cheap junky china pods

If you decide to make a cafe, make sure it's rideable and functional. And nothing you do to a GS550, including spending $5000 on upgrades, will make it better than a cheap as dirt Jap 600 supersport. Don't throw good money away. Enjoy your GS for what it is!

[Neveragain55]

No disrespect, but this is what I see...

- Tires way oversized for the rims. Low grade Coker tires. Real Cafe bikes are supposed to be functional, racing about, not focused on appearance.
- Low bars, and a plank for a seat. Only a kid, or a masochist could ride that bike for more than 30 minutes.
- Cheap junky china pods

If you decide to make a cafe, make sure it's rideable and functional. And nothing you do to a GS550, including spending $5000 on upgrades, will make it better than a cheap as dirt Jap 600 supersport. Don't throw good money away. Enjoy your GS for what it is!

None taken, but, read what I wrote. Everything you pointed out is what I said I would not use.

I'll re-post it again here, and I'll highlight the points we're both making:

"This is what I envision the bike will look like, but with a thicker seat that won't fire up my sciatica after three miles of riding the way this "tissue-thin" seat would, and regular street tires, not the "bobber style" tires that this bike has."

I think I found the answer accidently by crawling through (of all places) YouTube.

There's a guy on there that built a GS550 café racer and used a Wiseco 615cc overbore piston kit made for the Kawasaki 550 of that same era.

It makes perfect sense if you think about it because Suzuki & Kawasaki copied off each other like hell back in those days and their engines are damn near identical.

Here's the kit that Wiseco makes and I'm almost positive it will work in a late 70's, early 80's GS550

https://www.svspowersports.com/products/wiseco-top-end-rebuild-kit-k615

[KiwiAlfa156]

Worth a read

https://magazine.cycleworld.com/article/1981/6/1/suzuki-gs65og