Ports - GT750

[tz375]

Are the barrels the same height? Yes - both will be decked to give zero deck height. On one that means almost 4mm off the top

Spacers: two stock gaskets, one above and one below the spacer.

Head gasket: Later gaskets are thinner, but almost all replacement gaskets are 75-76mm bore which fail at higher compression. The head gasket must be teh right size and must not either overlap the bore or have large gap for mixture to detonate in. So there are only 2 possibilities, Suzukidave copper with slight tweaking or the one I plan on using where I had to decide on bore size and thickness and construction etc. Hope like heck it works. If not I'll O ring with copper wire or Wills rings. Old school technology that still works.

I really should get head inserts like the pros use - Suzukidave and Watercooled hatchet use inserted heads. They know what they are doing, I'm just playing in the the sandpit trying to learn.

[water cooled]

Richard...

There is one other option... Flannery just redesigned the GT750 copper gasket and had Cometics make some back in early September. These have a 71 mm bore and are the same thickness as the gaskets Dave had made.

I dont have the P/N but could get it. Call Cometics...

Bob Prior just ordered one from Flannery last week too.

[ja-moo]

Are the barrels the same height? Yes - both will be decked to give zero deck height. On one that means almost 4mm off the top

Spacers: two stock gaskets, one above and one below the spacer.

To save you a lot of grief, drill small holes in the spacer and or drill small indents in the top case and the bottom of the cylinders in the mating surface. As the combo of spacer and double gaskets tend to make the gasket want to squish out. The holes and indents lock in the gaskets.

[tz375]

Thanks JA for that tip, and thanks Kevin, that's where the composite gasket came from. I bought a pile of GT and TZ gaskets recently. Good guys to work with.

[two-stroke-brit]

tezer will these mods make the motor run any hotter?
thanks mark

[tz375]

Heat is created by the combustion process. If that process is more efficient and burns more of the fuel in a shorter time, the motor will run cooler. If it has a higher compression, then that will increase combustion temperature leading to an increase in motor temperature.

More transfer time increases the amount of exhaust gas going down into the crankcase and that obviously makes the motor hotter. A more efficient exhaust could work either way - tp raise or lower engine temps.

If we cram more fuel and air in and burn it in the same time, more heat will be released into the motor.

So yes and no. We have to back off ignition timing because it burns faster and that's good, but it will probably run a little hotter, but until we run the beast we have no way of knowing by how much and which way.

As a point of reference, my TZ making about 70 HP ran cooler than my RZ making 56HP with the same radiators, so there's no easy rule to follow.

[tz375]

I just measured another 2 sets of barrels and it looks like the average deck height is more or less 0.7mm +/-0.2mm below the top deck and individual ports tend to vary a little more but within a +/- 0.5mm band. For street motors that's more than close enough. In fact it's hard enough to measure to that level of accuracy when a port actually opens or closes.

There are a lot of mismatches between the liner and the aluminum muff, but the worst appears to be the floor of the intakes. There is typically a 2mm ledge for teh gas to trip over that either needs to be filled with Devcon F or ground out. I prefer to shorten the intake timing to J/K/L levels so for me that means using a spacer or filling the gap.

A better way as I realize was set out by "Dr Q" some years ago is to slightly widen the intake ports and raise the roof but leave the floor. Longer MAB intake timing hurts low to mid rpm performance more that any other change, so for a torquer, keep it short and thick.

And that brings me to issue #2, intake width. If you go too wide, it's easy to end up with little or no piston skirt sealing - ask me how I know.... Pistons also have tolerances, so it may be possible to select an oversized piston that seals, but one set of ports here has less than 0.3mm of sealing between the edge of the piston and the side of the port. That one may end up with very large pistons to get it to seal or may have to get a reed valve conversion.

[two-stroke-brit]

tezer two questions .
1 what is the web in the intake track of the block for.
2 what is the title of Ray Battersby's book that you and ian talk of.
cheers mark

[ja-moo]

tezer two questions .
1 what is the web in the intake track of the block for.

Two smaller intake tunnels is supposed to increase intake velocity. As the GT 750 had very long intake ports.....

[tz375]

Interesting question about the port divider. JA is right that smaller ports create higher gas velocity, but splitting the one port into two has half as much flow in each half, so velocity stays more or less the same. I say more or less because teh divider has volume and decreases teh port size slightly.

I'd speculate that the divider is there to try to direct flow into the crankcase in a straight flow pattern because the intake port is offset at a different angle to the bore that the transfers or exhaust port. That creates a flow pattern that is neither straight into the crankcase, nor balanced between the transfers. The divider may help to reduce flow straight into one transfer port and not the other. I have not flow tested a GT750 barrel and crankcase, so it's just speculation on my part.

The book is TEAM SUZUKI and is available direct from the author or Amazon.

http://2stroker.createforumhosting.com/ ... tml#p15339" onclick="window.open(this.href);return false;

[sfront]

Who's got a link to good head gaskets, (that's read small bore)?
The one that came in the kit is WAY too big!
Are the stock Suzuki ones any better?

[water cooled]

If your looking for a high performance head gasket, we just created one in September for a GT750 cylinder head at Cometics Gasket. You can Google Cometics Gasket for their phone number and call them. It's made of copper and based upon 71 mm bore. I'm just not sure if thats what youre looking for.

[sfront]

Actually that was a better answer than I was hoping for!
Called, got to pick bore size, thickness, and material! .032 copper w/M71 bore.
(Just in case there CL numbers are a hair different than mine )
Ships Friday, I should have it by Wednesday.
Thanks!

[water cooled]

These gaskets are already soft enough so no need to anneal. Just check the fit and use some type of copper coat like Permatex Copper Spray Hi-Temp Adhesive/Sealant or similar. http://shop.advanceautoparts.com/webapp ... ku=7160111

Good luck!

[two-stroke-brit]

Actually that was a better answer than I was hoping for!
Called, got to pick bore size, thickness, and material! .032 copper w/M71 bore.
(Just in case there CL numbers are a hair different than mine )
Ships Friday, I should have it by Wednesday.
Thanks!

how much are they ,
thanks mark