Ports - GT750

[water cooled]

They were about $30 each on the first set of 3. Check with them just in case.

[tz375]

FYI, sealing copper head gaskets is not always easy and on such a long head with such an odd distribution of bolts. An easier alternative for the street is from the same supplier but in a laminated material with fire ring. That steel ring (like stock gaskets) created more clamping load around the bores than a gasket of uniform thickness.

The one I got a few months ago is hands down the best fitting gasket I have seen for a GT750. I have J, L, A, Athena and other head gaskets and not one is close to being as perfect as the COMETIC - on my set of barrels.

Bores can be in different places on different barrels and heads are often way off too. So it pays to loosely bolt teh head, gasket and barrels together and turn it all upside down to see how well/badly they fit. We found significant variations form one to another. It really helps to have a selection of heads to choose from (or a Dremmel).

[sfront]

So after measuring all these cylinders, do you have a diagram of what average, stock ports measure and time at?
Been reading up on current pipe design lately...

[Suzukidave]

Depending on what yr GT you have i believe there are 3 different port layouts . early J with the bolt on intakes then J,K,L and then M,A,B

[sfront]

I'm interested in the numbers related to my B but I'm sure
the overall knowledge would be appreciated by the general masses!
You can find all sorts of info out there on what people think
the best modified port configuration is but I haven't found
anyone who's documented what the ports "should" have been from the factory.
I'd really like to find an article with the factory drawings so
I could see which way the tolerance stackups went!

[water cooled]

Not sure if this is what you are looking for but the MAB barrel should have the porting dims found on Chapter 7 page 1 on this link:
http://www.3cyl.com/bulletins/service_bulletins.html

This is the factory porting change for the later model barrels. I know its not complete without the other stock dims but maybe it helps. I cant comment on tolerances or how far out one block might be from another. I think Richard might be the best to comment on that as he has compared several barrels and found differences from what they were supposed to be.

[sfront]

Yeah, I've been to 3cyl before.
I guess I've been looking for info more in the lines of this.





These are tech inspection charts for the Piston Port class for Kart racing.
The first column is the specs for the Yamaha pictured.

[tz375]

Spec classes have that well documented to avoid cheaters. We had similar rules in the FUSA Aprila Cup classes and it didn't stop people from creatively modifying parts so they still looked stock.

Some tuners obviously were more creative with their interpretations. We found the selective assembly and clean up where it was either allowed or not policed increased power from around 59 to above the class limit. That way others improved their were to add compression to increase punch out of corners and then creatively cap top end HP to avoid being DQ'd.

I'd use that bulletin as a fair indication of stock timing and how it changed, but we all interpreted that to mean that pistons were at the top at TDC and failed to realize that wasn't accurate. It's basically where the ports are +/- 1mm or so.

That doesn't help much with pipe design though. You need all the relevant angles plus the taper angle of the port and you will want to look at duct shapes and tapers as well as their radial and vertical angles to model any motor.

We compared pipes from several software designs all supposedly based on the work of Gordon Blair and the simulation software seems to think that they are not all created equal. Some of those piggies are more equal than others. You may also see interesting effects of changing taper angles and the relevant sizes of the first and second cones.

Then you need to try them on a dyno to get the full effect. But for a simple change, any of the software will generate a lighter pipe than stock and that's worth HP. What was the old rule - 7 pounds = 1hp in power to weight.

[sfront]

I learned a long time ago.......if you're not delving into the grey areas........you ain't winning!
That bulletin only calls out port location from the deck.
Nothing about port widths, roof angles, radii, etc.
There's nothing I've found so far that dimensions the entire cylinder.
I guess I'm looking for just the factory specs of what Suzuki designed.
They obviously had a blueprint and all the variations are production tolerances.
I'm not looking to reinvent the wheel.
Eventually I'm gonna build a set of pipes for my bike and document what I build them to.

[Suzukidave]

For a stock ported motor i bet a set of chambers close to Jemco specs with added tapered head pipe would be close to a good all round design

[tz375]

I don't think anyone has a copy of the original production plans. That would be interesting to see.

Dave,

Those Jemcos seem to be pretty good pipes. Lane has a set of Blueboy and Kevin used them until this year when he outgrew them and needed full on race pipes.

[Suzukidave]

I think this is more what you are looking for but this is for the GT550

[tz375]

Dave,

I remember that chart and all the incorrect timing numbers on it. Port dimensions were measured by on owner and drawn up by another who unfortunately didn't convert mm to degrees correctly IIRC. Nice chart though and much tidier than my chicken scratch sketches.

[Suzukidave]

Dave,

I remember that chart and all the incorrect timing numbers on it. Port dimensions were measured by on owner and drawn up by another who unfortunately didn't convert mm to degrees correctly IIRC. Nice chart though and much tidier than my chicken scratch sketches.

Oh dang .. if its not correct i better delete it

[sfront]

I took the degrees pictured to be radial dimensions of the ports and not timing numbers.
A diagram like this for a 750B would be great.....anyone have one!
Even an untidy version would be fine!