Top end rebuild performance help

[Bruce p]

Hi all

as the summer starts to end I am looking into a top end strip down of my gs 550 katana 1982
What I would like to do it try to increase the performance of this engine but on a budget . I have heard of removing the air filter lid and increasing the jets but what about skimming the head or polishing the inlet or exhaust port ?
I want to keep the look original so I don't want to change the excuse or remove the air filter .

Any ideas guys

thanks in advance

bruce

 

[Wraith]

You can fit the GS650 top end to the GS550 which will give you more power, and/or polish the head and do some work on the ports (clean it all and regrind the valves at least!), but if you want more power the easiest way is to dump the air box and stock exhaust and put pod fillters on and a hi flow exhaust. If you don't want to do these then there's no point in trying to tune the engine becuase these are the very first things that you ever do in starting to try and get more power! First rule of thumb - more air in, and more quickly, more fumes out and more quickly. Standard air filter/box and exhaust tend to be restrictive. Timing and ignition (black box type) issues all come into play also, but are a waste of money really until it breathes in and out properly.
You wouldn't want to touch the carb jets unless you change the exhaust (and then not always) or air filter(s).
If you want more 'ooopmph' off the line, try changing the sprocket sizes and hence gearing ratios (nb power = torque x revs...)

 

[Chuck78]

You can fit the GS650 top end to the GS550 which will give you more power, and/or polish the head and do some work on the ports (clean it all and regrind the valves at least!), but if you want more power the easiest way is to dump the air box and stock exhaust and put pod fillters on and a hi flow exhaust. If you don't want to do these then there's no point in trying to tune the engine becuase these are the very first things that you ever do in starting to try and get more power! First rule of thumb - more air in, and more quickly, more fumes out and more quickly. Standard air filter/box and exhaust tend to be restrictive. Timing and ignition (black box type) issues all come into play also, but are a waste of money really until it breathes in and out properly.
You wouldn't want to touch the carb jets unless you change the exhaust (and then not always) or air filter(s).
If you want more 'ooopmph' off the line, try changing the sprocket sizes and hence gearing ratios (nb power = torque x revs...)

What he said...

Also, megacycle grinds performance cams for our bikes if you're looking to move the powerband up higher to gain hp at high revs at expense of low end street torque.

The 650 head/pistons &:cylinders give you 673cc's & 9.3:1 or 9.4:1 vs the 550's 8.8:1. The 550 case needs clearanced a lot to fit the bigger sleeves in there. AND very important - if using the 650 cams, you cannot use the 650 cam sprockets - must use the 550's cam sprockets. The 650 cams will give more mid range torque for street riding, the 550 cams have a bit longer & more aggressive valve timing that will give you more high rpm hp and a more aggressive exhaust sound with proper performance exhaust. I believe Mac still makes a gs650 4:1 exhaust. Their stock baffles sound like a louder version of an oem muffler. Their race/perforamance baffle is like a v&h or typical perforated straight through baffle - aggressive bark to it.

Also a dyna-s ignition and green coils will help with reliability and tuning. AND if doing the 650 top, grab the mechanical timing advancer setup from the 650 as well, the spring loaded arms looking piece that bolts to the crank, & maybe the sheetmetal timing mark reference plate as well. The 650 has more total timing advance than the 550, which is made possible by the very advanced for 1981 Suzuki TDCC/TSCC twin dome/swirl combustion chambers and pistons. Less detonation risk and thus capable of more total timing. The 83 650 may have switched to electronic advance and may not have the mechanical advancer, but the 81 definitely does.

If replacing piston rings with new, make sure to have a machine shop measure & hone the 650 cylinders to give a good grit to break in the new piston rings. Then properly follow the break in procedure for new rings/hone - get bike roughly tuned as best as possible before ever running engine (estimated jets, needle shimming, set timing with 12v test light), tune asap & go out at rev up the engine under good acceleration load in gear accelerating from 3500-6500 and then closed throttle engine braking decelerating back down and repeat this at least 10 times, then do the same but 4000~iah-7500+rpm's ten times or so accel/engine baking decel. This process forces the rings to expand to press against the cylinder walls and wear their imperfections down until they are a lerfect smooth match to the fresh honed bores. The honing pattern creates sort of like a microscopic file to chstom fit the piston rings to each bore, but after 20-40 miles on the engine, the sharp peaks of the criss cross hone pattern's cross hatching will be worn down too smooth to effectively break in the rings any further. So it's very important to get jetting & timing set close asap & go out and bream in the rings. Ride it in a similar style for 60-100 miles & change the oil. Break in with a cheaper motor oil (non-resource/energy conserving mark on API service rating logo on jug), then switch to shell rotella t diesel oil or the synthetic version. If you dont follow that break in procedure, it will take your rings potentially a few years to reach near the tight compression seal that this procedure gives you. The old rings are fine to re-use still if the ring gaps while sittiing freein the cylinder bores measure to spec. A very light hone isnt a bad idea even then to further break in the rings. Also, a good valve lapping at minimum is a great idea, if not a fresh 2 angle valve job or performance radiused cut inner angle (650 heads have a more direct flowing port and only take a 2 angle valve job).

From my 750 experience, going big bore (748->920cc) with original carbs means the jet needles & needle jets will need to be swapped to the spec of the bigger bike's carbs when both bikes use the same size carb venturi & basic model. Otherwise the mid-slide position will always be too rich of air fuel ratio. Having a wideband o2 sensor & AEM UEGO air fuel ratio gauge has been an incredible tool for tuning performance upgrades...

 

[Chuck78]

I'd also advocate k&n filter for the stock airbox with the lid removed or the inlet enlarged. If going pods, do not ever go with the cheap ones like EMGO, only K&N oiled gauze style, or UNI foam pods, etc. A pair of K&N universal dual inlet oval filters is better than pods if you can measure your mounting o.d. & #1-#2/#3-#4 cylinder carb centers, then match up to their fitment chart.

Bigger main jets will be a must. 3-4 sizes (in 2.5 incriments) larger than stock for the 550 or 650's jet specs will be necessary when upgrading air filters and exhaust.

There is a gsxr exhaust gasket also that let's you more easily bolt the gs550 exhaust to the larger 650 head, search here for the part # or maybe ask Suzuki Don or others who have done the 550-673 swap. I have a set in a box here somewhere if you need me to dig for the oem p/n.

And about the needle jets/jet needles, cheaper to buy the carbs off the 650 engine than to ebay those parts - if you want to get the midrange tuned better. I couldnt get a higher AFR than 11.2:1 with the stkck 750 carb parts in the mid throttle areas, shluld have been high 12's to 13.2.

 

[Guest]

Modern type performance valve job does wonders on those old motors.