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Zaddict wrote:

evil-ride wrote: himeji-gs.com/
This shop makes 710cc!! The price is about 7000 USD.
So I think use the wiseco kit is the best way.And then use gpz 400 cams is better.
Or,,,there were Yoshimura Stage 1 High-cams for 2 valve before.But now it is sold out.
I found the last 1 set at shop.If you need that, I send to you

710cc!! and $7000!! Both figures are shocking. I couldn't find any information on performance. How much power does a 550 engine put out when bored to 710cc? Does the engine last more than three seconds?

I'm curious about the Yoshimura Stage 1 High-cams. Please send more information. There is a shop here in California that grinds performance cams for KZs, GPZs, ZRs - Megacycle. There is a member on this forum (Corey - he posted earlier on this thread) who modified his GPZ 550 with a Wiseco 615, K&N pod filters, Megacycle Cams and Moriwaki race exhaust and now gets about 80 hp (at the crank, 65hp at the wheel).

I never measured the engine at the crank, so I don't know. 66/39 at the wheel. Same dyno, same operator.

From the stock 553cc to a 6mm (674cc) or 7mm (695cc) overbore on a 550 won't work, as others have tried. The head gasket kept blowing. Now 615cc 12:1 Pistons from Wiseco would make a reliable difference, and they can make you any bore size you want, for whatever engine.

I never measured the engine at the crank, so I don't know. 66/39 at the wheel. Same dyno, same operator.

From the stock 553cc to a 6mm (674cc) or 7mm (695cc) overbore on a 550 won't work, as others have tried. The head gasket kept blowing. Now 615cc 12:1 Pistons from Wiseco would make a reliable difference, and they can make you any bore size you want, for whatever engine.

Ah, OK, I just extrapolated from the 65hp at-the-wheel figure using a ~30% conversion. 80hp at the crank should be ballpark, yes?

Would 12:1 pistons require racing fuel?

Seems like the shop evilride recommended has the 650cc+ bores figured out. There's even a comment about durability -

"Is long life and durable than normal engine easy to ride the exhaust amount of this 710cc"

(use Google translate, some beautiful engine builds here):

himeji-gs.com/?p=2886

zaddict
Yes,710cc unbelievable I am concerned too. But the shop do not talk about horse power.
I think that they want to keep secret about it.They makes original piston and use GPZ cams.
I will inform you about Yoshimura cams Please give me a little time.
Mr.Corey's GPZ excellent! Megacycle cams and Wiseco pistons is best combination

Hi all, New to the forum here...
Came across this thread cause I have a zephyr 400 not kai but regular 1990 8 valve version. I picked up a condition unknown 550kz engine for around $80. Was thinking or hoping to take all internals, crank and rods and put them into a bored up head of the 550 into the 400 crankcase. In BC, Canada the insurance rates are a rip-off. So instead of forking out my money to "the man" I want to place the money "into my ride". I couldn't have said it any better than another forum member when comparing the bike to a flat chested woman... yes, I love her, but let's give her some boobs. Might as well, Already has Brembo on the front, ohlins in the rear, and gold valve emulators in the front forks. Managed to get decent settings on the stock carbs for the kerker 4 in 1 with pods and a factory pro stage 3 kit.
Would love to fit some fcr or cr carbs on her. But first, she needs some more power. Then, I'll worry about controlling it. Any advice or input would be great. Anyone know if the cranks are interchangable? How about the piston pitch?

Himawari if you use a 550 top on a 400 crank you'll get about 500cc : the stroke is shorter on the 400 motors. If you bore and stroke with a 550 crank you can get up to 615cc Wiseco forged pistons.

62mm and 2nd oversize GPz305 pistons gives 630cc but at the same 10:1 compression.
Yoshimura did a 596cc 12:1 3 ring cast high silicon alloy race piston race kit, unavailable now.

There have been attempts to go bigger than this but reliability is a problem: you can only bore out a liner so far...A big block or custom liners could be the answer...maybe the 7k 700cc is a big block conversion.

Not sure a 16 valve head would be such a big improvement, Both Corey and I have experimented with +2mm big valve conversions on these with no improvements, even Yoshimura only went +1mm O/S on the inlets.

Would 12:1 pistons need racing fuel? Yeasr ago I run mine on 4 star about 100 octane, but used an extra base gasket to reduce the CR a touch. I think longer duration cams would work well with high compression pistons to reduce pinking, which can be a problem on early 550 motors.

So I can use the crank and block from my kz550D engine in my 400 with no issues?

The 400 crank with 550 pistons will fit together, but the I'm not sure what you would need to do regarding the different stroke of the 400 and 550 motors. Maybe best to change crank and rods complete into the 400 motor...or just bolt the 550 motor in. You may have
to change the ignition if you keep the 550d motor in a later 400 frame.


That Jap website s really interesting, it seems he has gone from 400cc to 475cc using yoshimura pistons, getting 49 rw bhp. Then he uses the 550 crank and 1mm OS inlet valves with the 615 wiseco 10.25 pistons and gets to 60 rw bhp. (has he pressed a bigger liner into that zephyr block?) Finally he is 650cc using custom made pistons and getting 73 rwbhp.


From the jap website, translaton courtesy of google

Well, the power of 600cc in Yoshimura piston + Zephyr550 crank? !
Is amazing!
Is the power that you have never experience (laughs)
If you inadvertently open the accelerator in first gear, the front has to float it in the adoption of an inverted fork, despite the dimension of anteversion!

this bit bothers me...

But! But! !
World, so much sweet is ridiculous trouble without it 1000km also traveling that was not followed in the next ... (explosion)

Do we have any better jap translators here?

Tyrell Corp wrote: ..or just bolt the 550 motor in.

This would be easiest. Should be a direct bolt on.

Have you compared parts diagrams to see exactly which differ between the 400 and 550? They've been identical for the most part for everything I've looked up outside the engine.

Tyrell Corp wrote:
That Jap website is really interesting, it seems he has gone from 400cc to 475cc using yoshimura pistons, getting 49 rw bhp. Then he uses the 550 crank and 1mm OS inlet valves with the 615 wiseco 10.25 pistons and gets to 60 rw bhp. (has he pressed a bigger liner into that zephyr block?) Finally he is 650cc using custom made pistons and
getting 73 rwbhp.

Which website is this from? 73 rwbhp is about 90 at the crank. That would be an insane(ly awesome) amount of power for a light little 550. Though seems like Corey was able to get near that without such drastic modifications.

Evilride, our only resident Japanese forum member (as far as I can tell), might be able to give a better translation.

If I know the page it is coming from, perhaps I can take a look. I understand basic/intermediate Japanese since I lived there for a short time a past life ago... Unfortunate, my understanding of bike lingo and mechanics is less than that of my Japanese. Just because I like to tinker, doesn't mean I know what I'm doing. The reason why i don't do a direct swap of the 550 into the 400 frame is I don't want anyone to be able to tell I have done modifications on it. So, my plan would be to take the conrods and crankshaft of the 550 and use it with wiseco pistons in the 400 crankcase. That way the serial # is unchanged and it still would read 399cc on the jug. Otherwise, I'd just buy a zephyr 750 or gpz750turbo. In B.C. once you go 401cc-750cc the insurance doubles.

Thinking more about it i guess boring the 400 block needed liners, a 550 block would take a 615cc 61mm wiseco without needing replacement liners.

Building a motor for fast road iand a dyno graph is rather different than building a consitently reliable motor for race use, the liner thickness is the limiting factor on boring out.

It seems the ZR may have bigger and squarer cooling fins than the GPz and ZX variants. Maybe a 'big block' ZR block and oversize liners with HD studs might be the answer.

p.s. the joke is on goofy google translate, not the japanese.

Zaddict wrote:

Tyrell Corp wrote:
has he pressed a bigger liner into that zephyr block?

Yes, he uses 400 block,and 400 head with 550 crank.
Finally he enlarged crank case