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Hi all, here is a question, or two, or three, that has bothered me since I started trying to figure out how to get more air into each cylinder w/o going the forced air route or winding the guts out of the engine. I know there are a lot of smart people on this board and I am hoping to get a few ideas so here we go............ Would it be better to bore out the cylinders to the 810 kit and leave the stock valve sizes, leave the bore size as is and increase the valve area per cylinder OR, just flow the stock head and call it done? Not looking to turn it into a rocket, just bump it up a bit. The machine would be used as intended, an everyday rider with 50% in the city and the other 50% on the open highway. Whaddaya think?
 

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i'd go for porting and polishing the heads along with a jet kit and k&n filter. remove the white resrtictor at the air cleaner snorkel and if you don't mind the extra noise go for an aftermarket can.

my reasoning is that valve work and bore kits are both big ticket items that can increase horsepower greatly but may reduce daily rideability and also reliability. you would also need to do all the above modifications anyway. the things i listed are reletively inexpensive and shouldn't greatly alter the good manners the bike has, just give ti a bit more push. since you're looking to keep it a daily driver i think less is more.

scott :)
 

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Another way to go without touching the top end is try lighter weight wheels and add 3 teeth to the rear sprocket . It will get you off the line quicker, but you'll lose some top end. It may be easier to drop some weight and add more power with some easy add ons than to go through the top end and keep packing 450 lbs around. Change some of the steel items to a lighter weight alternative.
 

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Hi guys,

Just my opinion on this.

Flowing the head is great but don't expect your bike to keep the driveability it has now. You'll get more power but most of it will move higher in the rev range.

A big bore job can work wonders if done properly. Properly means adjusting the squish band to get optimal burn rate. Adjusting compression ratio for better efficiency. As you may know a part of the power gain when boring is made up by the increased volume of your cylinder, while another part is free with the boring as the compression ratio will increase even if you just use larger diameter pistons of the same kind as the originals.
The results of the big bore will be more power throughout the rev range!

Why don't you go all the way and get the head flowed as well as puuting in the big bore kit and also lower the head a little to get 10,5/1 comp ratio.
With these mods and by lowering the gearing the ZR should be able to reach at least 160 mph! :eek:

Aris
 

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Discussion Starter #6
Thanks for all the replies. I found an 810 kit which would be a simple sleeve bore job and the pistons would bump the CR to 10.25 to 1 but am trying to find the most bang for the buck. The engine should easily take this mod w/o any problems as it's been around for quite a while. Another thought is to eliminate as much friction in the moving parts as possible, IE: coat the piston skirts,
polish the crank, etc. Still thinking. Thanks again.
 

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about power and speed

Gettin a bit chilly here in Finland.
Yesterday i had to use ice-scraper to mirrors and seat... During night it was 4celcius below zero(about 25 fahrenheit), semi dry anyway so no ice on the roads, not too much anyway.

Anyway, i've tried to learn about zr-7 engine and now mine is pretty ok. Last month i did 1-mile acceleration and i got 209 km/h or 130mph.
I did that with 17/38 sprockets.
According to gearingcommander my theoretical topspeed would be little over 150mph. But to be able to get that on gps i should go to Germany and give it a try on free speed autobahn... Maybe next summer.
Dyno showed that i should have 79hp on rear wheel on 10400 rpm.
It was a little lean so i put .1175 main jet before that mile run...
Havent tested in dyno since so i dont know if that was any good..

Have fun driving in the warm countries..

Please correct if i wrote something strange.
 

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How much weight can realistically be saved with lighter wheels? Tire weight makes a decent difference since it's what's furthest out on the wheel. Anyone know the weight of the stock wheel vs an alloy one for instance? Reducing rotational mass is a great way to make anything faster.

You could also decrease rotational mass of the engine, but balancing the entire rotating assembly to some really tight tolerances would be mighty important if doing so. Same with bearing clearances, end play, etc. Sometimes you get luckier than others. Increase bore/piston size and run some custom pistons for a higher compression ratio. I'm not sure what's available. You could probably go bigger than 810 if you get the block re-sleeved. I think someone does regrind our cams. I've never seen the head but I'd assume some porting here could go a long way depending on how you want your power to hit, same with larger/flat faced valves, etc. Regardless a lot of calculations would be needed to figure out your compression ratio. At this rate you'll need to run 93 and definitely want to get it on a dyno and spend a bunch of time messing with jetting and timing.

If the engine has a lot of miles I would rebuild with a big bore kit, focus on machine work, getting those clearances perfect, and do as little else as possible.

If you want a power increase without touching the bottom end, mess with the head but realize that you're gonna make more power up top and less down low.

Personally I wouldn't dig into the bottom or top end of this bike. In the end I suppose it's all about how much you want to spend. I would of course also avoid boost of any sort if you like the twisties.

I suppose a reasonable answer would be, shave as much weight as possible, mess with timing/jetting, exhaust. If you had some time I suppose you could yank the head and not really open anything up, but instead smooth things out. I have no idea how these things are setup, but if the carbs are attached directly to the intake ports, I would consider roughing up the area at the carbs' outlet/head's inlet and graduating that into a quick smooth transition to help with mixing up the fuel.
 

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Don't waste the money. Put those $$$ toward a used liter-bike to gain horsepower. I get the feeling that you may not be satisfied with the outcome, after shoveling in the money. Part of the mystique of the ZR / GPz engine is that it is air cooled and a little rough around the edges.

Also, with those mods, are they really practical for the money, for an air-cooled engine, since their tolerances have to be greater, for expansion and contraction?? It is kind of like someone who once asked me if he could get his Ford Explorer to go 150mph. I said sure you could...but WHY would you want to?? That would be like putting a lift kit on a 'Vette for the deer-hunt.

IMHO, for those mods, you'd be better served with a liquid-cooled engine to modify.

Maybe running a thinner racing oil would be a cheap way to increase HP. The 15w40 I use is pretty thick, as oil goes. The cheapest fixes for increased HP, is to clear out the airway with a K&N and an after-market can, adjusting the pilot screws to compensate and shimming the jets. Then, if still not satisfied, you can fiddle with jet sizing and so on.

Just think though, if you wreck the bike after all of that machining that you are thinking of; then all of that time and effort will be for naught.
 

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Speed

My view is dont waste time on top end performance that just looses your licence fast. Accleration is the fun part. Sitting at traffic lights & leaving a 911 turbo worth 60K for dust, thats sweet:)
 

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Personally I'm not doing any performance mods to my bike. I think it comes down to how long you're gonna keep the bike and what your level of skill is in this area. Also remember that modding = downtime = less riding.
 

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Ditto

I have to put in my 2 cents. I agree with the previous three. If you want more power, get a Ninja. I modified one of my ZR-7s with a full Muzzy and an Ivan's jet kit with airbox mod. It also has the original 16T sprocket. It was lots of fun at first, but I regret it for one main reason. My wife rides this bike and the fuel economy she used to get (50 mpg) is gone. It's now down to low 40's. This means that when we toured together four times this summer, the convenience of the long range I get with the Concours is nullified by the more frequent gas stops she has to make. As has been said so many times on this forum, the ZR-7 is what it is and does a superb job of being a very reliable standard motorcycle.
My 7 is pure stock (except for a 17T sprocket) with over 50,000 miles and I prefer it totally to the one my wife rides. I get 55mpg while enjoying my ride to work.

From my point of view, of you want a race bike for the street there are many better choices. So much for an eight year old thread.


Jack
 

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Gettin a bit chilly here in Finland.
Yesterday i had to use ice-scraper to mirrors and seat... During night it was 4celcius below zero(about 25 fahrenheit), semi dry anyway so no ice on the roads, not too much anyway.

Anyway, i've tried to learn about zr-7 engine and now mine is pretty ok. Last month i did 1-mile acceleration and i got 209 km/h or 130mph.
I did that with 17/38 sprockets.
According to gearingcommander my theoretical topspeed would be little over 150mph. But to be able to get that on gps i should go to Germany and give it a try on free speed autobahn... Maybe next summer.
Dyno showed that i should have 79hp on rear wheel on 10400 rpm.
It was a little lean so i put .1175 main jet before that mile run...
Havent tested in dyno since so i dont know if that was any good..

Have fun driving in the warm countries..

Please correct if i wrote something strange.
DAMN YOU I didn't even notice! I blame that guy (age of thread).

BTW darkember are you mixing up top end/acceleration with your powerband (where in the rpm range you make the most power)? Just about any mod will increase both, with the exception of gearing and sprockets, etc. I hope I am not jumping to conclusions but it seems a lot of people have been misguided to believe torque = acceleration and hp = top speed.
 

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I like it!

I always enjoy it when an old thread surfaces to the top again! See some names that have not been around for a while.....
 
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