Porting the GT top case

Suzukidave · Post by **Suzukidave** » Thu Aug 27, 2009 2:13 pm

Where is it a good idea to port the top case

Post by **Suzsmokeyallan** » Thu Aug 27, 2009 2:32 pm

Dave this will draw all sorts of ideas but for reasons of logical "flow thinking" id alter the hard edge of the transfers ledge where it meets the bore section a smooth radiused curve instead.

Suzukidave · Post by **Suzukidave** » Thu Aug 27, 2009 2:39 pm

So Allan you think it would help to radius that sharp edge at the bore opening ? i wonder how much radius is OK as Suzuki didnt make any attempt to smooth that area .. in fact below that near the bearing web area there is another " step " in the aluminum casting .

ja-moo · Post by **ja-moo** » Thu Aug 27, 2009 2:45 pm

Airflow does not like sharp edges, it causes eddies or turbulance. The radi don't have to be huge.

Post by **Suzsmokeyallan** » Thu Aug 27, 2009 4:09 pm

Id be with Moo on this one, think of it in terms of flowing water and smoothing out the flow around any corners so you minimise the splashing effect of the said water.
More than likely, "smoothing and blending" of curves is what you want instead of abrupt edges so the fuel/air mixture transitions better in that area.
What ever you do you'll have to do it six times, and the same way too.

Suzukidave · Post by **Suzukidave** » Thu Aug 27, 2009 4:32 pm

OK ..yeah , X 6 ...... i would like for Teaser to post what he did with his as it was his email that even got me thinking about it .

tz375 · Post by **tz375** » Thu Aug 27, 2009 4:45 pm

There are a couple of problems with the GT crankcase and the first is those skewed ports. That means the porting is not symmetrical. It also means that the flow out of the cases is sub optimal.

The next thing to do is to fill those sharp edges with epoxy (after scoring and cleaning the metal) so it adheres.

Third change is to the shape of the floor of the transfer port. It's basically flat and the gas basically hits the side wall and has to change direction. That needs a change in shape so that the gas is directed upwards in a smooth change of direction.

But don't sweat the small stuff. Matching transfers to the cases doesn't make a huge difference even on a high HP motor.

Just try to make it all a little smoother and remove the worst of the steps.

On your reed motor the boost port will have a larger effect on power and economy than almost anything else I suspect.

Suzukidave · Post by **Suzukidave** » Sat Aug 29, 2009 8:26 pm

Well , good bad or just plain waste of time i tried my hand at case porting today .

Post by **Suzsmokeyallan** » Sat Aug 29, 2009 9:46 pm

I'd say you improved the flow and reduced turbulence on the edge by doing that smoothing modification Dave, it certainly wont make it worse, thats for sure.

Suzukidave · Post by **Suzukidave** » Sun Aug 30, 2009 4:57 am

Suzsmokeyallan wrote:I'd say you improved the flow and reduced turbulence on the edge by doing that smoothing modification Dave, it certainly wont make it worse, thats for sure.

I hope your right Allan , i guess if nothing else i made the top case a few grams lighter

rngdng · Post by **rngdng** » Sun Aug 30, 2009 1:46 pm

I agree! It won't be worse. It looks good to me.

Lane

ja-moo · Post by **ja-moo** » Sun Aug 30, 2009 2:21 pm

The crank cheek will probably cover the majority of the large radius, so you should be fine. You have to remember when you introduce an "angle" to the flow it will change it's direction.

If there wasn't a crank cheek in the way, you can see where there would be an up angular effect from the big radius.

Suzukidave · Post by **Suzukidave** » Sun Aug 30, 2009 3:39 pm

I should have thought about that John and dropped a old crank in there just to see what it looks like then .

ja-moo · Post by **ja-moo** » Sun Aug 30, 2009 4:43 pm

You should be fine.....

It's good to look at the "whole" assembly when doing mods.

Suzukidave · Post by **Suzukidave** » Sun Aug 30, 2009 4:49 pm