TOPIC:

When I went from the 16T to the 17T, it really took all the space away from the sprocket guard (meaning it got paper thin close). Will moving up to the 18T cause me to lose the guard? it is down to mm of space right now? It is easier and less money than to swap out the rear sprocket to a 38T

Sounds sweet to me (looks too!) but true maybe a little too loud.....coming from a guy with a comp unpacked baffle ....... (I realize your talking a 550 while mine is a 650 but) with a 15 tooth front sprocket I'm right around 5 grand at 60 and I agree its just a little too much..... but I love the hole shots and snappy feel it gives........ the stock gearing gets me back to 4,500 or just over and makes a hell of a difference on the highway...... just don't go too far a 17T/41T front/rear gets me just over 4,100 if I remember right but it killed the acceleration and would never go back there........betting Loud will know how far you can go before the acceleration starts to suffer.

Smaller rear will lower the revs some but is does have a cost in take off. Chain adjustment will change too. With a 16 tooth front sprocket on mine, I can barely get the chain on. Stock 15, no problem. Not the same as yours but something to consider.
Steve

If you want performance, go the big bore kit, and some GPz cams.

I've got an extra cylinder block for my Gpz550, so if I ever have it rebuilt I will have all the machine work done, the gaskets ordered and on hand, and I'll make it a bolt-on weekend.

A GPz550 in good tune will turn 120mph on demand with the mirrors taken off, feet on the back pegs, etc, depending on the headwind.

In the fall of 1981 I pulled 10,300 rpm in top gear that way when I had a stout tailwind. Nothing like being young, when I was 10 ft tall and bulletproof

loudhvx wrote: 16-38 gives 122 mph
16-40 gives 115 mph
17-40 gives 123 mph

At 60 mph, I get:
16-38 gives 4679 rpm
16-40 gives 4925 rpm
17-40 gives 4636 rpm

Ok, Here is what I get with my tire (12/90-18 = 83.265 Circum.) and since the bike already rips through the gears, I am going to drop it from 40T to 38T. There are no issues with the acceleration and power but it just pops a little to much on decel so I am going to up the main jet(s). I know it has a lot to do with the free flowing exhaust also.

How did you get the circumference? The effective circumference should be measured by rolling the bike, and measuring how far it travels for a specific amount of wheel rotations. The resting circumference (wheel off bike) will be larger than what you see on the bike since the weight of the bike will squish the tire.

I just put the stem at the lowest point, and then roll for two or three turns, then use a tape to measure the distance. Divide that by the number of turns.

I would avoid the 18T. You can try a 38T in back, but the chain may get too long, so you may need a new chain with that, or it may be still be usable since the 17T is bigger than stock.

Kirkpatrick wrote: pops a little to much on decel so I am going to up the main jet(s). .

Did you remove/disable air injection system?

How did you get the circumference?
- Just used a tire calculator online.

I just put the stem at the lowest point, and then roll for two or three turns, then use a tape to measure the distance. Divide that by the number of turns.
- I will be away from the bike for the weekend so will let you know on Sunday night.

I would avoid the 18T. You can try a 38T in back, but the chain may get too long, so you may need a new chain with that, or it may be still be usable since the 17T is bigger than stock.
- I checked and have room to play with a smaller rear and like you said since I already bumped the front to 17T that should offset the smaller rear a little.

Irish-Kawi wrote: Really like that header and can combo, is that one of the Dime City Cycle stainless shorties? Very good looking!

Brett

Sorry for my delay in reply, thanks for the info and that pipe looks killer! Love the sound too very very nice and sounds mean, though I agree that is hella loud and would be a challenge to adjust to! Thanks for sharing man

Brett

Nay all the way. A tuneup and just enjoy for what it is. After all said and done you might be lucky with a 10% increase in torque- no hp yet, okay 12-13% if you have the time to cherry pick parts and service. Then, you'll need a cam, carbs, have to work the head and all while hoping everything else on the bike holds together long enough to enjoy it after the work is done and only with the help of an ambitious (keyword here ambitious) dyno go after that elusive 5 hp gain while keeping the bike streetable. Now your bike is no longer a joy to ride because it'll over heat unless you are willing to do steps x y z at the same time and to the correct degree.

I'd keep the bike stock, tune it up, enjoy it for what it is, use your time toward a rocket rider that you're after that'll give you more for the same amount as doing a big bore. Talk with other bikers, guys who have some biking in their dna, guys with lives they have committed to the industry, that won't sugarcoat facts or try to impress you with pointless theory about how to correctly set valves. The decision might actually be a lot easier than it is.

Kirkpatrick wrote: Anyone have success with the 615cc big bore kits? I have an 83 kz550a4 Sport which I love to death and just bumped the front sprocket to 17T for more top end. I am actually thinking about going to 18T but the clearance is super tight right now at the front sprocket guard. The bike is a screamer but at 6-01, 215 pounds (me), It is still quick as ever but I need more top end. Was wondering if the 615cc kit is worth the money down the road and/or if there are other mods that can be done. Already have the exhaust, pods, and jet kit done. I am not looking to get on the freeway and take long trips just to scream around town but if need be, hit the freeway. Hits 60 mph at about 5500 rpms and it does not help that I have an open Lossa Eng. pipe on it which screams.

Im a little confused by what you are looking for, you say you are just looking to ride this thing around town and not spend a lot of time on the freeway, so why are you worried about its RPM on the freeway? Like Tyler said, these motors are designed to rev and it will be absolutely fine at 7500 for thousands of miles. If you are actually interested in a city bike I would do mods to keep low and mid range grunt, that means a longer exhaust and airbox on a stock motor. My vote is to hot rod the motor though.

Olajoe the motor in my sig. gets street rode with 16-45 gearing and never over heat's.

Do the 615 kit a mild clean up of the port's and some GPz camsand it'll haul ass