Potential Group Purchase - Wiseco GS650 741cc pistons

[Ace07]

Hey guys,

Glad you are looking back into this project. I have been iching to get back after it as well, but I have been traveling for work alot, so the only thing that I have done so far is taking the bike apart completely and organizing the parts I have. Hopefully in the next couple days I will order some parts from bike bandit, and find a good place that does powder coating.
On the carb side of things, I am very new to tuning any carbs. I currently have my stock CV carbs. I was hoping that I could you those with different jetting. Is that an option? Is it a good option?

[boris.h]

Hey!
Unfortunately, you can not count me as interested anymore, I finished assembling the engine with standard gs 650 pistons and rings... It was too long for me. Maybe later, I would be interested. We are now buying a house with my wife so that's not a priority anymore for the instant

With my configuration:
full ported head
62.00mm gs 650 pistons
gs 550 camshafts
"big" exhaust (ported the head to be able to fit a bandit one or similar as kawasaki Z900 / 1000....
I will start with gs 850 carbs, BS32ss, which have the good venturi diameter for the engine... I put mikuni 112.5 main jets, which correspond to 1.25mm diameter. That was the diameter I calculated, so I think it would be ok for me, to start

[tkent02]

As I am just getting my head back to this project I have been looking the the valve seats in the 650 head. The stock seats have allot of room to go bigger, like 4 or 5mm more intake which would help immensely with the major increase in displacement we will have. The 650 head has generous material to carry the larger throat size all the way up to the carb face. It would not surprise me if 33s might not be wrong. I am quite sure I will run the 29s I have but newer carbs are an option as well for me especially if I have larger valves made.

550 and 650 valves are the same, I was thinking 750/850 valves or maybe 1000 valves might be a bit bigger diameter, I think the valve stems are the same diameter but they might be longer. No need to have expensive valves made if some off the shelf stuff will work just as well. This is a Suzuki after all. I'm not able to measure for a while, anyone know the diameter of the 750 or 1000 valves? How about the length? Still need to find a 650 head to do another engine.

Carburetion, I want to stay with some form of CV due to the large range in elevation I need it to work well in, using GS 650 BS32s now. I think some of the ones from 90s and 2000s year model bikes probably work a lot better. Haven't even started to figure out which ones yet. Can figure that all out later.

Anyway I'm still in, I can slap these big pistons and a freshly bored cylinder on my existing 550/675, don't need to wait until I build a whole new engine. Can do that later and switch the cylinders around again. Whenever the deal goes I'm in.

[boris.h]

Not need to go with bigger valves. Valves diameter is ok until 10500 / 11000 rpm... do you plan to go up than this limit? You will also find other issues above 11000... I kept the oem valves. I found aftermarket valves that are thinner than suzuki valves, above the angles where they seat.
Moreover, even if there is a lot of room on the seats, you have to know that the temperature is well driven by the seat if this one keeps a lot of volume (if you go to bigger valves, the seat will be thinner and won't keep the same physical caracteristics).

-> if you reduce the volume of the seat more that 20% (this is not so big), the seat will loose its properties (regarding the temperature of the valve)

so, for me this is a waste of money, time regarding the potential gain...

What I did (and this is free of money), I have 2 complete sets of valves, springs, everything. I measured each spring length and I measured the weight of every part moving then the engine is running. I found a lot of differences, as the spring length, and the weight of the parts (you'll need a precision instrument). I choosed the parts I found similar to make one full balanced set....

[Old Colt]

The 750 valves are a few mm larger than will fit on the 650 seats, they are also around 10mm longer than than our engines valves. I have not pulled the 750 valves from the head to get accurate numbers. I have not looked at other bikes to see what might be simple to fit.
For me, I will be installing larger valves. I have no issues with cutting the seats as needed. The 650 valves are undersized for me.
My 550 has always been run with a 12,500 rev limit and on some tracks in the past such as riding Daytona, the engine was at 12,500 all the way around the banking every lap. That was 9 sessions a day, 3 race groups. Always nervous of when it would fail but it never did. Other clubs I could run 4 race groups a day plus we rode an endurance race which my bike shined in.
For me now, this will be a trackday bike and not strung out to the limits as when the bike and I were young.

[tkent02]

Never rode it at 12,500 all day long, but certainly above 11,000 up long grades and such, ran the **** out of it all the time, very high RPM occasionally, the 550 just keeps making power as the RPM climbs. Never had a problem in many many thousands of miles, took my first 550 apart after 120,000 miles of this to fix a myriad of oil leaks, all of the metal parts looked fine and went back in. 550s are hella stout overbuilt engines.
Trying to make the bike easier to ride here at high elevations, using 8,000+ RPM just to start out from a stop gets old. The 650's top end and cam gives it some decent mid range torque, bigger valves probably won't help that but may help those looking for more top end power.

I don't really know what size valves would be the best, but if it makes a better engine it's worth trying. Couldn't a good machinist shorten a set of 750 valves and cut the slot for the keepers farther down??

[Old Colt]

I do not think the big valves would be right a high altitude. You need higher port velocitys for that thin air.

Yes the 750 valves can be shortened. But I am not a believer of reducing diameter and shortening. Manley sells valve blanks for builders. These would give the valve head for the desired use and then the stem is cut and grooved as needed.
But there might be a Honda or Kawi or some other valve that is right to work with.

[boris.h]

I calculated the valves diameter, and the results were, for max rpm 11500, were the OEM diameters. But I could understand that you want to put bigger valves... I just said that regarding what you are going to get (good power between 11000rpm and 12500rpm), it's for me a waste of money. Buying bigger valves, machining the seats, maybe cut the stem and reproducing the end of the stem....even if i'm a believer in exotic modifications, I won't use my bike everyday between 11000 and 12500 rpm, I prefer working on increasing the air flow on the carbs, and in the head... So you agree that, about increasing the valves diameter, it depends of the final use of the bike... if the bike is destinated to make races, where everything "more" counts, ok... but for a "daily / Weekend rides" bike.... that's, for me a waste of money. There are other places on the bike where to spend money better

[tkent02]

I do not think the big valves would be right a high altitude. You need higher port velocitys for that thin air.

Is this correct?

[Old Colt]

For midrange power I think so. You do need a good amount of compression, that will bring your power up.
Larger ports will make the engine lazy at low revs since the air column is lighter due to your altitude. A higher velocity port flow will pack more air in the chamber than a slow moving light load of air.

[Old Colt]

I calculated the valves diameter, and the results were, for max rpm 11500, were the OEM diameters.

I hate to be harsh here but I make my living in racing, I work with real engines not hypothetical software numbers.
For a 740cc engine with stock 550 valve sizes your max power will be well below 11K.

I will get as close to what the 750 came with in my motor.

[tkent02]

Should be far beyond what a 750 came with, the stock 650 has more power than an eight valve 750.

Colt, do you think I would benefit by making the ports smaller for my high elevation purposes?

[Old Colt]

Should be far beyond what a 750 came with, the stock 650 has more power than an eight valve 750.

Colt, do you think I would benefit by making the ports smaller for my high elevation purposes?

No, I expect that would strangle the top end power. It would be allot of work to shape down into the valve pocket to get a stronger low rev flow. The real consideration is maintaining power right to the original 9500 rev limit which is logical for road use and the stock ports are sufficient there.
I have not spent much time thinking about cam grinds for higher altitude use. Might be that a good talk with Delta cams might offer a decent approach to give your motor a fat torque band. More lift but short duration like the 650 cam. Possibly in simple terms a 650 intake cam with longer like 550 exhaust to relieve the pressure better.
I will be working with Delta once I have a clue what my valves and ports will be.

My bike has always had the Kaz Yoshima exhaust on it which has 1 3/8 head tubes but I think I will build the headers with 1¼" tubes with a much better merge collector. This will still flow well beyond what the crankshaft should be spinning but should liven up the midrange power a bunch.

[Ace07]

So who is getting close to wanting to order these pistons?

[Old Colt]

I am, I am