GT550 casting holes in the crankcase?

[Allan k]

in each 'port' in the crankcase, above the main bearings.. what are these holes for? and would it be okay the weld these holes off to give the port more flow?

some of these holes is filled with kinda hard glue, but its like its come off in some of the holes..?

[tz375]

Filling those casting holes and carefully matching the barrels to the crankcases will make little or no difference. Don't spend a lot of time down there. Widen the intake and exhaust ports slightly. Raise the exhaust port roof by 3mm and get decent set of pipes.

Longer exhaust duration raises the rev band and so does longer intake duration and they both lose power at the bottom end. Good chambers are a "must have" item. Just the weight saving is worth the performance improvement. clean up the intake ports and raise the roof so that it's at the same height as the bottom of the piston skirt at TDC, but keep checking your work as you go. Ideally you don't want the piston ring visible in the intake port at BDC.

And raise the compression. Squish heads would be best if you can get them welded and machined.

[Allan k]

If there is a chance that i will add power to the engine, then i will do it.. I have plenty of time to do it, and i'm used to weld aluminum where I work.. just wanted to make shure they could be filled.

About the cylinders, I'm a little worried about porting them bigger in the ports, because the cylinders is the nikasil type. I have a theory about the chrome comming off if you grind in the ports. thinking that it will seriously shorten the life of the cylinder plating and the rings. But i'm not shure how it will end up? anyways, the intake will be made bigger at the start of the cylinder/carb area.

Can you pull out that little brass pipe in the intake? or do you just grind it down to the intake wall?

About Squish heads.... how much power is there really in that head? I have acces to the machines needed to make the original head to squish heads, but have clue about the shape of it..

[tz375]

Filling the holes will not add any power. On a Yamaha they are oil feeds to the big ends and main bearings but the Suzuki has oil pumped down there - at least on the 750 it does. Either way, it will not help power to fill them.

Yes, porting the barrels may cause the plating to lift, but not the way that hard chrome on the early TZ Yamahas did. Nicasil tends to have a much stronger bond, but normal practice would be to re-plate them after porting. Talk to the guys at EBOS about that.

Squish heads are better for power because the create a more turbulent mixture, but the other reason to use them is to reduce the chance of detonation. Squish heads should run a higher compression ratio without problems and that is really where the power comes from. Billy Alvaarson has a neat software package at Bimotion.se I use that software to set targets and initial shapes and port time areas and then fine tune alternatives in MOTA. He also has a piece of software just for head shapes that is very good.

We have done some analysis of the GT but not with a spacer plate. I'll try to do that over the next couple of days and see if it can stand more transfer time.

[Allan k]

Little update on my GT550 Tuning

Holes have been welded off and im getting to the cylinder/crankcase

[Allan k]

a little more

[Suzukidave]

It sure would have been nice if the GT750s were engineered with better intake ,transfer and exhaust ports . If it had been designed right off the board as a sport bike instead of a touring bike there's no telling the power they could have developed .

[Alan H]

I think there might have been issues with fuel consumption. Two strokes were never renowned for lots of miles per gallon, and the higher the tune, the less economical they tend to be as 'hooligan mode' tends to be used more.

[Allan k]

I'we finished the porting job. hope it works...