Exactly what I was looking for, thanks.
I'll need a bit to go through it all and digest the necessary work, but I didn't foresee CNCing pistons...
On a similar note, perhaps I should consider sourcing a neglected 500 engine and going for a rebuilt and drop it into the frame. I'll start looking into if that fits at all, unless you guys have some insight.
I have both the gs500 and the tscc 400, They are both pretty even. In terms of performance. Even though the 400 is heavier with a backrest, windshield and crash bar.
One thing that I would do though is get a set of slingshot carbs from a 500 with k&n Filter and a Mac Exhaust. It would wake up the engine quite a bit.
The 400 already puts out enough power I find.
But if you want to go that route,
Use your base with 500 cylinders, pistons, cam's and a 450 head (for the side exiting exhaust ports). Then fit the head with the 500 valves and port it for them.
*** There are a few people here that have done the 450-500 swap already just like this.***
Carbs, filters, jet kit for the 500 carbs, 2-1 Exhaust, All should be your first things to get and they will compliment the engine mod's where as the original stuff will restrict it.
If you can afford it, FCR 37's are the recommended carbs to go with.
One thing that makes the original carbs open up a bit quicker is reducing the length of the slide springs by half an inch.
It makes the engine feel like its trying a little harder where it would normally feel like its under full load.
I know with mine, that it would only pull so much. Even at wide open throttle the carbs would only allow so much flow until the RPM's increased.
If you want to keep the 8 valve head, and get the 500 cylinder block you can easily get some pistons made for it, It would be about $3-400 for pistons alone but its cheaper than what I did.
I bought gs1100 pistons and then machined the valve reliefs in closer to the center because of my head design.
Rapidray could get the pistons made for you from CP pistons. They just have to be the same as a 16 valve GS750 pistons in every way except with a larger diameter. That way the valve reliefs are in the same place and will work with your stock cam's. You could go up to 75mm with that block and have 3mm left which would be safe. That would make it a 500cc.
But the compression ratio would jump from 10.5:1 to 12.7 which is too much for that head. (they have a tendency to crack between the plug and exhaust valves)
So your going to have to open up the combustion chamber by 5cc's each to bring it back down to 10.5. Or if you want to leave the head alone you could raise change the piston to head clearance but that would effect your squish clearance and you'd loose power that way.
There is allot to it if you want to take the time to do it. It takes a good plan to start off with.
So for parts around the engine:
Carbs from 89-2004 gs500
lunchbox filter from k&N
Donojet kit (just for the needles really but the whole kit is useful)
Exhaust, Only one I know of is the the MAC on ebay.
GS500 ignition system, is a nice solid state upgrade.
Inside the engine:
8 valve way assuming your keeping the original cam's and original red line (so you don't have to change the springs) and stock head.
Get the pistons made the same as your's ( gs750 are identical) to what ever size you need.
Get the gs500 block.
Measure how tall the gs500 block is and how tall yours is. ( there is a difference)
Choose your gaskets. ( the gs500 and gs400 head and base gaskets are identical except the 400's are thick paper/fiber and the 500's are 0.010" thick and are metal)
Selecting the right gasket raises or lowers the head so that the squish clearance is the same as it used to be whith the original pistons.
You need to set the block so that the top of the piston is level with the top of the head and then select the right head gasket thickness.
Then call up COMETIC gaskets and have them make you one the right thickness. (order 2 just in case) They have the template for a gs450, Use that one.
Now assemble the engine and check the piston to valve clearances.
Put some clay in the valve releifs and turn the engine over several times.
Check your clearances and you should have the same as the original pistons had.
Now the issue with the combustion chamber being too small for larger pistons can be fixed by opening up the chamber a bit. From 3-5cc's. Stock is 17cc's total. You need 22cc's for a 75mm bore. Mine was 27cc's when I was done.
Re-assemble the engine and check your cam timing. 104 degrees intake 107 degrees exhaust is stock I believe and would work just fine. I'd go even lower though. Around 100 100 for more mid range punch. Higher gives you more top end but you won't need it since you won't be in that rpm band.
4 valve way
Get the gs450 head and cam's.
Get the 500 base and get the 500 pistons.
Choose the best gaskets to get the piston height just right.
Compression will be higher than normal but not enough to be a problem.
Check the piston to valve clearance.
Check the cam timing when your done.
The 450 head has a lower head volume than the 500's head and it has a combustion chamber shape that lets you use what ever big bore pistons you want to use from one of the other bigger bikes. ( the 500's head is a weird shape) You can use 500 pistons with a 450 head but not the other way around.
The 500's pistons are not as tall as the 450's so that lowers the compression ratio and using the 450 head doesn't change the compression ratio enough to worry about.
Get the 500's cam's, They are slightly taller than the 450's cam's. (if you want to. But the 450's are good enough)
One more thing, try and get the pistons made close to the same weight as your original ones so it doesn't vibrate more than it did stock. A little heavier is ok.
Yours vibrates allot at 5000rpm and smooths out at 7000. With mine I went with heavier pistons and that made 5000 rpm smooth but slightly buzzier at 7000 that I don't mind. I'm finding that the lower RPMs are nicer to ride in.
