gs 750 oversize valves

[gizzmo]

Hi can any one tell me if gs 1000 valves fit the 750 head or any other valves and is it worth doing,going wiseco 844 kit with a tunned motor many thanks paul

 

[hannibal]

I think I've read that 750 and 850 have the same valves. The 1000 are bigger.

 

[Chuck78]

I think I've read that 750 and 850 have the same valves. The 1000 are bigger.

^^^True. 750 77-79 & 79 850 are same head. 80+ 850 is CV carb big port head but still same chamber and valves.

+1mm oversized is recommended for a really worked over 844cc 750 (cams, wiseco, mild porting). Not sure what size 1000 valves are vs 750. Ray?

 

[TeamDar]

Stock 750/850 valves are 36mm intake and 30mm exhaust. Stock 1000 valves are 38mm intake and 32mm exhaust. GS1000 valves are shorter in length. When you put oversize valves in either head you must maintain .180" distance from intake to exhaust valve when seated to prevent intersecting when operating. You have to sink the valves deeper into the seats to maintain the clearance. Dar

 

[Chuck78]

Stock 750/850 valves are 36mm intake and 30mm exhaust. Stock 1000 valves are 38mm intake and 32mm exhaust. GS1000 valves are shorter in length. When you put oversize valves in either head you must maintain .180" distance from intake to exhaust valve when seated to prevent intersecting when operating. You have to sink the valves deeper into the seats to maintain the clearance. Dar

Very excellent info, Dar. Thank you.
So when going custom pistons and oversized valves, go with bigger domes, as the combustion chamber cc's will measure slightly more volume, hence more dome needed to keep compression up.

 

[TeamDar]

Very excellent info, Dar. Thank you.
So when going custom pistons and oversized valves, go with bigger domes, as the combustion chamber cc's will measure slightly more volume, hence more dome needed to keep compression up.

Actually you just mill the head. You have gained a lot of piston to valve clearance by sinking the valves. This is all common hot rod methods used on Kawasaki KZ 1000 engines. Dar

 

[Guest]

When you sink the valves, then you need to do an unshroud cut to help with low lift flow.

 

[Z32650S]

Good discussion and info here. Chuck, you mention a +1mm valve oversize as the recommended approach for a 2V GS750 with a 844cc Wiseco pistons, cams, mild porting. Where did you find those valves? Maybe Big Jay has some, but I didn't see +1mm listed on his website for the 2V 750 (most of the ones listed are for the larger GS bikes). Does anyone know where to find dyno graphs showing that setup and the resulting ballpark gains? Even graphs of a 844cc Wiseco on a stock 750 would be nice to see.

If not going with larger +1mm valves, would it significantly impede the performance of this package? Just trying to determine if a hot street (i.e. mild WebCam #118 with 844 wiseco pistons, and mild porting) would really necessitate larger valves. Going for a torque monster not 1/4 mile runs (I realize cam timing will be the biggest help).

All that to say, are +1mm larger valves the only way to make the most from a Wiseco 844cc piston and mild #118 Webcam setup?

 

[TeamDar]

Good discussion and info here. Chuck, you mention a +1mm valve oversize as the recommended approach for a 2V GS750 with a 844cc Wiseco pistons, cams, mild porting. Where did you find those valves? Maybe Big Jay has some, but I didn't see +1mm listed on his website for the 2V 750 (most of the ones listed are for the larger GS bikes). Does anyone know where to find dyno graphs showing that setup and the resulting ballpark gains? Even graphs of a 844cc Wiseco on a stock 750 would be nice to see.

If not going with larger +1mm valves, would it significantly impede the performance of this package? Just trying to determine if a hot street (i.e. mild WebCam #118 with 844 wiseco pistons, and mild porting) would really necessitate larger valves. Going for a torque monster not 1/4 mile runs (I realize cam timing will be the biggest help).

All that to say, are +1mm larger valves the only way to make the most from a Wiseco 844cc piston and mild #118 Webcam setup?

Just something to think about. Kawasaki KZ 900/1000 engines use the same size valves as a GS750. If they are big enough for a stock 1000cc motor then they should be fine for a 844cc mild build. Dar

 

[Z32650S]

Thanks Dar, that's some good perspective.

Also, I failed to mention, the carbs would be either the VM29SS off a Canadian GSXR or a rack of RS34. (unsure if the 34s might be a tad big on this setup)