HP/Compression calculation?

Okay. The Big Bore kit will be here soon enough.

Here's the engine setup:

-79 KZ650
-784cc Big Bore
-Compression as is would be 12.5:1, but I would lower it. lol
-Good sized oil cooler
-GPZ750 cams
-Smoothbore 29's

Now, here's the question of the hour. What kind of power am I looking at, properly tuned, with that setup, and how do you come to this number when you figure it out? Seems everyone has different methods.

most estimates are semi educated guesses,strap it on a dyno than theres no doubt.goodluck,happy wrenching!:whistle: hows that tank coming?

wireman wrote:

most estimates are semi educated guesses,strap it on a dyno than theres no doubt.goodluck,happy wrenching!:whistle: hows that tank coming?

meh, waiting for some suspension parts for Goblin so I can go buy some 023 and weld those to the frame and finish the tank in the same day.

I plan to dyno the bike anyhow.... I just thought someone might have a rough idea.

i can make a fairly educated guess on 900-1000s but im not sure of baseline for smaller bikes.

wireman wrote:

i can make a fairly educated guess on 900-1000s but im not sure of baseline for smaller bikes.

Let's put it this way. I'd like to break 80hp. Possible?

stock 78 kz1000 is around 83 hp electronic ignition and 28s pushes it to about 93 header 95-97 1075 100-105 cleaned up head and drop in cams 110-115 these are just semi educated guesses again.if that 650 baselines at around 60hp i would think 80 should be doable.

wireman wrote:

stock 78 kz1000 is around 83 hp electronic ignition and 28s pushes it to about 93 header 95-97 1075 100-105 cleaned up head and drop in cams 110-115 these are just semi educated guesses again.if that 650 baselines at around 60hp i would think 80 should be doable.

I thought the base was closer to 68.

evenbetter!see your allready making horsepower !blaha:whistle:

there are some programs out for building engines, just not sure if they have any for bikes. I used one years ago at a speed shop, thing was pretty close, when we put them on a dyno we always got more out than the program stated

Stock 83-85 GPz750 is listed at 85 hp, and you have more displacement, more compression, more carb potential, but less airflow through the head. with a 750 head you would "probably" be somewhere near 95 hp, but with a stock 650 head you would maybe hit 85 hp. The bigger valves and ports of the 750 head would help out quite a bit.

You say that the compression ratio is 12.5:1, if that's with a 650 head then the GPz750 head would help to lower that a little.

If bigger valves and ports in the 750 head make that big of a difference I wonder why virtually everyone does a 810 kit on 650s? The majority of the time they keep the 650 valve head...

I can't actually remember seeing a 750 with an 810 kit, only 650s... wierd.

Some people use the 750 valves and enlarge the ports on the 650 head because it has a smaller combustion chamber and gives more compression, some people use the 650 head because it's cheaper to use what you have than buy another head, and some people do use the 750 head.
There are a bunch of GPz750's with the 810 kit, and quite a few KZ750's, but there are a whole lot more members with KZ650's than there are with KZ750's, so you see more 810 kitted 650's here than 750's

I'd like to do another 79 KZ650SR and this time use a KZ750 bottom end with a 810 kitted GPz top end instead of using a GPz750 motor like the last one.