My Custom GT750's

[tz375]

Yep .. that's the plan it would be cool if the squish came out right

Have faith and as they used to say, Measure twice and cut once. I can't remember the dimensions of that block or what the deck height was, but I don't think much has to come off the block. With that head and the copper gasket, I'd expect it to be in the region of 30 thou. You'll know as soon as the solder comes out

[Suzukidave]

Its very nice now that http://www.cometic.com/" onclick="window.open(this.href);return false; is making copper head gaskets in different thicknesses

[Suzukidave]

[tz375]

Dave,

You have a couple of brass tubes sticking into the transfer ports - shouldn't they be removed to improve transfer flow???

I do realize that they are SRIS tubes. I just modded a J block and pushed the brass tubes out and used 8mm grub screws in the front of the block and crankcases.

[Suzukidave]

Its a old picture .. the tubes are now gone , it was just to show what you were posting about making sure the head is aligned with the bore

[tz375]

Dave,

I was stumbling about in places I have no good reason to be, and found out that there's a whole slew of guys reprogramming their GSXR and 'Busa ECUs using all manner of Backdoor and other methods to read, modify and write tables.

It's enough to make you head spin. I even downloaded some of the raw map files and there are so many lines of code that it's amazing. It would be neat if we could take say a K9 GSXR1000 ECU and modify the error codes to get around all the failsafe conditions and then use it to drive 6 injectors (upper and lower sets of 3).

Edit:
Last night I downloaded the binary and xml versions of aa GSXR map and opened them with RomRaider software. The basic tables are complex enough but there are dozens of additional 2D maps that I have no idea where they are used or what the logic is that invoke one versus another.

Actually need to see the decision tree in the software to make any sense of that - if that's even possible.

[Suzukidave]

Interesting .. the code sorting still has my hopes on the very easy to reprogram Microsquirt system but its good to know that guys are probing into reprogramming the stock GSXR control box.

[two-stroke-brit]

good greif you two are getting all "matrix trilogy" on us.
but thats soo cool if you can rewrite the code to suit.

[Suzukidave]

I need to get some fatter solder to check my top end squish .. i may need to try another method as the clearance could be over 2mm right now ... maybe a clay ?

[tz375]

Stock GT750 has a lot of clearance.

Piston below deck 0.5mm on average
Head gasket 1.2 depends on model and material
Combustion chamber depth 1.3 at the edge on average
Total clearance 3.0mm or so. That isn't a squish clearance, but it is a problem.


Oops. Forgot, you are using an RK squish head with inserts. That should measure up at less than 2mm unless you added a spacer plate and didn't take enough off the top of the block. What height is the barrel plus spacer plus gasket between barrel and spacer?

All up, we are looking for around 129.5mm IIRC

[Suzukidave]

Yeah Richard , i am going the full Monty and putting in the spacer plate with the 2 base gaskets as thats really the way we set the porting up so theres a large gap at TDC between the piston and head of maybe 3.5mm . I suppose i could break it back down and measure the spacer and gaskets separately and then i should be able to use the solder i have to measure the squish and then add them together .

[Suzukidave]

Kevin , what did you end up running the squish on your race engine at ? Instructions that came with my modded GT head say .032~.045" so i was shooting for .040" . http://www.youtube.com/watch?v=nirUG-jY ... re=related" onclick="window.open(this.href);return false;

[tz375]

Dave,
.040" is a little tight. I should check my notes, but IIRC it should be 1.2mm (.047"). How thick is the head gasket you plan to use?

Do you have a long dial test indicator? If you make a simple Deck height tool, you can work it out.
It looks like this:
[img]http://www.rscycles.com/images/tools/de ... t2.jpg[img]

You set the DTI to zero on a flat surface and then place the tool over the edges of the bore so it straddles the bore and read the piston height at TDC. That assumes you know what the OEM piston height is, but that can be measured.

Those Cometic base gaskets do compress slightly so talk to them first because if you measure it all loose and then torque it all down after machining, clearances may get a little tight, so allow for that.

[Suzukidave]

Hummmm , .047" is wider than RK suggested and the is after we opened up the chamber volume some . I was able to get 1 more stock base gasket from Suzuki and i am useing one of the copper head gaskets i had and the base plate i purchased from RK that is 1.5mm so i think all the base stuff was to add up to 2mm.

[water cooled]

Dave,

For my application, the squish was set to .057". There are different thoughts and opinions about having the squish set that high but DF feels that on these older 2-strokes (as compared to modern 2-stroke snow mobile motors) if the squish is too tight, it actually hurts top end performance. Its hard to argue that with a couple of 130+mph passes under our belt. I checked around last year, and although every setup is slightly different, there were several racers running squish in the .050-.055" range.

My squish setting was only our first attempt at setting this motor combination up but we seemed to have good results and generate pretty good HP to the RW.