boring cases 650

I realize you must have experience, but have quite a bit too, with high comp and boosted car engines mainly. I'm just looking for a little input, I don't mean to be an ass.

call me crazy but im thinking its gonna take some doing to get 90 plus out of an 810,im sure its doable but the ridability of its whats got me wondering!:laugh: i dont pay much attention to the factory hp numbers, thats just used to get ya on the hookB)

Oh yeah? The numbers aren't very reliable are they?

I'm just thinking on a 10.25:1 comp and the GPz cams it should be able to do 90 at the crank. I mean a carbed CBR600 in 1992 made over 100 at around that CR, and that was very rideable. I'm gonna tune it for a bit higher rev limit, I've got APE valve springs and a new cam chain, should be able to rev to 10G's reliably, and not overheat with the GPz750 oil cooler. If I'm wrong tell me, I'm just throwing ideas out based on my car experience, I dont have much experiance tuning bikes.

I'm half thinking just to go 700 and see where that gets me, it'll save me over $300, but on the other side, when I'm spending almost 3g's on the bike, what's $300.

the 600cc sportbikes have at least 4 valve heads and some of them have 5 valve heads.
you are working with a two valve motor,so it's not really fair to compare and expect the same.
i would try to build the strongest most reliable engine i could and then see where you are at compared to what you want,and go from there.that way you aren't setting yourself up for disappointment looking for high hp #'s.i have spent a lot of time and money to walk away from the dyno disappointed because i set myself up.
that's my .02 anyways.

leon holmes

I got ya Leon. But the main question is should I do the 810 or the 700? I can't see either being less reliable than the other. I'm still going to go with a stock KZ head with APE springs and seals and a new lap-in and GPz750 cams. The pistons will be the only difference in either setup, so if the 810 is only gonna gain me a couple hp, I think I'll just go with the 700, and save $300.

I hope you guys understand, done of us are putting you down or trying to discourage you. We are only trying to share some of what we have learned. We could just sit back and laugh but we don't. I have seen alot of people fail at engine building or give up and sell the bike. They didn't have forums when I started, it would of made life alot easier, and increased my learning curve. Our best wisdom has been (take your time, think, choose smaller sizes, seek help from others, know what you are going to use the bike for, etc.) If anyone just wants a parts list, we can do that too. I always wish everyone well, with their projects.

I'm sorry if I misunderstood.

So its your opinion to go small? I know the parts required, in fact I already have my GPz cams, oil pan and oil cooler, as well as my BS34's. I'll machine my 650 cases myself on a mill if I go 810. But based on your comments it seems like you think the 700cc option will be more reliable and make only a little less power. Am I reading you right? I'm kind of wary of the 700 at this point because I think the BS34's will be overkill for that small an engine. Am I out to lunch?

Im no pro but i would build the engine and then get carbs to match the engine, not build an engine based on the carbs i have at hand.

I have the cyls, 810 pistons , and a complete kz750 head. no turning back. I figured this would be a reliable setup for the 810, im not looking for tons of hp. The reason i chose 810 over 700 is because i figured my 650 head/valves werent optimal for the 700 ( I would need a 750 head) and if i was going to bore cyls i mind as well bore the 750s. good choice or bad, thats where i am now....

My goal is for the 810 to be as reliable and long lasting as possable. any suggestions as to weather the stock 750 head and cams will get me close to this goal? also, i found a set of bs34 carbs on a gpz750 at the bone yard, should i get them or is there better options? will they mount right up or does anyone know if i will have to do all kinds of work to fit them?

T_Dub wrote:

I'm sorry if I misunderstood.

So its your opinion to go small? I know the parts required, in fact I already have my GPz cams, oil pan and oil cooler, as well as my BS34's. I'll machine my 650 cases myself on a mill if I go 810. But based on your comments it seems like you think the 700cc option will be more reliable and make only a little less power. Am I reading you right? I'm kind of wary of the 700 at this point because I think the BS34's will be overkill for that small an engine. Am I out to lunch?

Even 29 smooth bores are alot on a 717cc motor. The 34's are big carbs. I would ask if the stroke on a GPZ750 is the same as the 650? If the stroke is the same, you would be closer to the ball park. If the stroke is longer, that could be a different issue. Bigger ports and carbs require higher rpm's to run at there peak. This is fine if your going to be running at high rpm's all the time. If you are going to be street riding and hot rodding once in awhile, I'll take the small ports.
A long time ago I built a 717cc with a ported head, 300*/.417" cams for a guy. When I rode it, it was alot for me to handle. It was way beyond his ability and poor thinking on my part. He finally took out the cams so it was streetable for him. It still runs good, he doesn't ride it much these days(painted, chromed & polished, from one end to the other) I built it over 20 years ago. I saw him at the store a couple of months ago, he said it runs better then ever. He said that he still has the cams wrapped up and put away.(I would love to own that bike) Where I live there is a guy named Ike, he has a 717cc with big cams and 29's. He runs a slick and wheelie bar on his bike. That bike can kick the crap out of most built kz1000's. I think we all get hung-up on numbers. Some of these small motors can run a 10 second quarter mile. That is real dam fast on a small bike. I would tell you, when you can go that fast, then move up. Give yourself time to gain experience as a rider and mechanic.
Megacycle cams says the kz650 cam (appx. .308"@220*/.040") and the GPZ750 (appx. .354"@250*/.040") this is a good increase, and should be streetable, in my opinion.

Here is a previous thread regarding the pursuit of power from a 650/750.

100 hp KZ650

Racing:
Ultimate KZ650/KZ750 road race bike

And the GPz750 Modification FAQ

Lot of info there, looks like I have some things to mull over. Thanks!

Okay lets look at what Kawasaki did:

My example is a 1977 kz650 & a 1977 kz750.
NOTE: both motors have the same stroke.

1977 kz650

---

62.0mm x 54.0mm (Bore & stroke)

9.5:1 compression

62 hp @ 8,000 rpm's

254* intake duration (22*/52*)
105* lobe center

260* exhaust duration (60*/20*)
110* lobe center

107.5* LSA

42* overlap

24mm carbs

Then they went to:
1977 kz750

---

66.0mm x 54.00mm (bore & stroke)

9.0:1 compression

74 hp @ 9,000 rpm's

270* intake duration (30*/60*)
105* l/c

270* exhaust duration (60*/30*)
105* l/c

105* LSA

60* overlap

34mm Carbs

All of these specs are as per KZR: So this is what Kawasaki increased, from 650cc to 750cc.
+ 4mm o/s bore (.157") over a 1/8"

- .5 compression

+ 16* intake duration

+ 10* exhaust duration

+ 18* overlap

???? oversize valves

+ 10mm bigger carbs

For a total gain of 12 hp and 1,000 rpm's
If all of that gained 12 hp, How much more do you need, to get to 90 hp?

Yes GPZ's sometimes have bigger ports & sometimes bigger valves and some times bigger combustion chambers & sometimes bigger carbs. Are these differances, worth 18 hp to reach your 90 hp?

If you only get 12 hp, there are easier ways, to do it. This is only one guys opinion.............

PS- I don't know if the kz750 has bigger valves or not? If so, it makes the picture look worse, for 12 hp.