Rd400 barrels on gt550

[Vintageman]

Tz375,

Thanks. I just want a little more hit top whilst still keeping some of it nice broad power.

Again not much out there on this bike
Here is one person I think some have seen but did not saw how much he raise Ex on his GT550.

http://www.youtube.com/watch?v=sxxS2CR1Lxc" onclick="window.open(this.href);return false;
"... get's on pipe has no problem picking up front end""

Update. He did reply to me (Jeff Kushner. he went 1.6mm up on exhaust and 0.8mm each side.... he wish he went 2.5mm up). 0.020" off head. He put a lot of effort opening and blending intake passage. The intake does look restrictive say versus T350/305. That bloody divider. He went 2.4mm off skirt and did some case to cylinder transfer blending).

I don't think 28mm carbs are a problem for GT550 for my expectations.

I do agree the intake aluminum casting divider looks a bit much and may be a good idea to push it back some.

Dang brass oil feed tube is in the way. And, port looks too narrow to push it through to get out... need to check again... hate to ruin it?

[ja-moo]

The Kawi's just have a hole at the bottom of the intake port, there is no oiling problem. I see no problem just cutting the oil tube flush with the port wall.

[tz375]

JA is right. Just cut it off or push it out. Refer to the port map thread for some more 550 specifics.

[Vintageman]

Search locks up :

For example Search Key Words-> "Port Map GT550" get 105 finds, see first page OK, but, move to next get message -> Sorry but you cannot use search at this time. Please try again in a few minutes. Been that way for a while. I use IE.

Yes, I forget we have talked about this option on other topics. Suz must have felt it added value so why they changed to this, But even later T500 did not change . I don't think Yam RDs for example don't use a tube either and they push oil way back at carbs and not in cyl wall below intake port. I agree.

But, I think it would be better to cut than remove (or shorten to remove if one wants some of it)
When I prime oil pumps on the GT/T250-350 by removing clutch cover and spinning pump shaft thhe oil actually sprays a fair distance above the tube each time pump plunger cycles. So I think it would be better to cut tube than remove for if hole too large it may not spray up and thus may not get sucked in as efficiently. Just need to run a proper size drill to ensure opening not blocked with a burr from cutting.

Thanks

[oldjapanesebikes]

Search locks up : For example Search Key Words-> "Port Map GT550" get 105 finds, see first page OK, but, move to next get message -> Sorry but you cannot use search at this time. Please try again in a few minutes. Been that way for a while. I use IE.

I get that all the time - but if you use the back arrow (or previous page button - depends on the browser), wait a moment and then re-try, it usually works fine. It seems to be some sort of timing issue and I get it on Chrome and Firefox also.

[Vintageman]

With IE can't go back... kind a locks up.

FireFox can go back to search screen, but can't change page regardless. Don't have Chrome

I don't think it was like this a while ago (was using XP of few months ago now Windows 7)

Oh well.

If you just search web in general (google, Bing...) and put in "GT550 Port Map" I think it would point here if it is here. If done this on other topics and seen our posts show up at times. Not sure how that works but cool it does (at times).

[tz375]

Sorry, I didn't mean to send off to Google purgatory. I meant that some of the same stuff and GT550 specifics were posted in the Street Bikes section in a thread about port mapping. The thread wasn't specifically about 550s but I included some numbers there.

this one:
viewtopic.php?f=2&t=9856" onclick="window.open(this.href);return false;

[Vintageman]

Yes, read it. Good stuff. Yes both exhaust and transfers real mild. Not sure how much value just raising exhaust ( I think you predicated a few more ponies) and see why you suggest raising barrel as an option to change both.

Oh well too late now.

With that said, maybe I will focus putting some tapering of the inlets into transfers looking at bottom side of jug.

If that truly added some more flow to transfer it might help scavenge a bit more.

You see this done on some bikes and not others. For example the GT250 does, but the GT380 does not.

GT380:
http://www.ebay.com/itm/1974-SUZUKI-GT- ... cc&vxp=mtr" onclick="window.open(this.href);return false;
Early T/GT250:
http://www.ebay.com/itm/1973-Suzuki-GT2 ... 0a&vxp=mtr" onclick="window.open(this.href);return false;
Wow Check out the porting on these early GT/T250s
http://www.ebay.com/itm/GT250-SUZUKI-19 ... 62&vxp=mtr" onclick="window.open(this.href);return false;

http://www.ebay.com/itm/GT250-SUZUKI-19 ... 55&vxp=mtr" onclick="window.open(this.href);return false;

And CC for CC the GT250 is putting more power than GT380

This takes the factory one extra step to add I think and was omitted for cost?

I wonder if that really helps or trivial or only for higher RPMs (for example Yam Tz cylinders and blended so beautifully)

Also if one adds this chamfering. I suppose if both side don't match it could make things worse, similar to havening transfer ports one higher than the other.

Experience on this topic anyone?

[tz375]

Raising the exhaust port slightly will make a slight improvement at the top end. My point about spacers is to look at the whole motor and avoid fixation on one port or one dimension. If you like the change, you could think about a thinner spacer - say 2-4mm and shave a matching amount off the top of the cylinders. That would raise power at the mid to top and lose some lower down but would probably work quite well. Any change to exhaust duration will tend to raise peak RPM a little.

A 6mm spacer on a street bikes sounds ridiculous until you start to analyze stock ports and look at different spacer dimensions to see what that might do. We could never do any of that sort of modeling back in the day. No software, algorithms were not well understood and neither were wave and flow dynamics., ad of course no PCs to do the number crunching.

Today we have all that knowledge available to guys like us that are not working in a secret room in Japan or East Germany or wherever. That doesn't make us experts but makes a huge body of work available.

On the floor of the transfers a chamfer won't hurt but it wouldn't make a lot of difference. Try to make them even on all ports.

[Vintageman]

Tz375.

Thanks. I do hear you when you mention using good tools and science to determine best outcome and respect the seriousness you and others use. It is ad hoc to change only one of the ports given how well this bike seems to have the Intake, trans and Ex matched so well for a ~ +6000 RPM peak

Raising the exhaust port slightly will make a slight improvement at the top end.

I'll start here and see if I notice any difference. I said I only wanted little more top end (funny how one can get carried away with this stuff... need more GT550s)

Speak of going all the way. did you guys see my previous reply link to those finely ported GT250 cyls. Fine work

Back To GT550 transfers

Check this out->

http://i266.photobucket.com/albums/ii25 ... us/058.jpg" onclick="window.open(this.href);return false;
http://i266.photobucket.com/albums/ii25 ... us/057.jpg" onclick="window.open(this.href);return false;
Piston cut out so much smaller than cyl cut out into transfers.

This is like other performance engine vs mild engines . Not sure how much a diff this makes in power or power band shape...

Even the T305 has a much larger piston cut out than T350.
T305
http://www.ebay.com/itm/SUZUKI-TC305-T3 ... 79&vxp=mtr" onclick="window.open(this.href);return false;
T350
http://www.ebay.com/itm/SUZUKI-NOS-PIST ... 8c&vxp=mtr" onclick="window.open(this.href);return false;

I wonder if it is worth taking some material off Ex side of piston cut out? But, looks like one can't go too much for that piston seems reinforced in that sport and that would be removed. I think I saw some where it is remove angled versus staying same shape.

What follows next I am not too serious about but, worth some discussion maybe with respect to tranfer port flow

Need a better GT550 piston.

Start with P.Millers Wiseco and shape it (not sure if it could handle it better tha the OEM)

Or, PE175 piston for Gt550? Heard this was an option for T350 if you raised jug a lot... not sure if it would fit GT550. either early or late PE175 piston ) One guy one eBay selling early PE 175 piston says it fits GT550 and he did it.
http://www.ebay.com/itm/Piston-Kit-447P ... 20&vxp=mtr" onclick="window.open(this.href);return false;

Later PE175 piston maybe even more cut out
http://www.ebay.com/itm/1982-1983-1984- ... 07&vxp=mtr" onclick="window.open(this.href);return false;

What GT550 Ex looks raised 2mm
http://i266.photobucket.com/albums/ii25 ... us/060.jpg" onclick="window.open(this.href);return false;

[tz375]

That T250 barrel was really interesting with the extra boost ports.

You are correct that it's easy to get carried away and end up with a rev monster that's hard to live with. Stock motor didn't make 40hp at the rear wheel, so if we want 60 or more HP we can be sure that the bike will have changed its nature

For a mild street bike to ride on sunny Sundays, a 6mm port hike is probably not what you are looking for. Start with your 2mm and perhaps a little more compression and keep and eye on ignition timing and CHT and you should be able to wake it up a little without changing its nature.

If you want an 80hp motor that peaks north pf 8,000 then that's a different package.

[ja-moo]

Does anyone have the stock 550 port timing? Or, did I miss it.......

[Vintageman]

ja-moo.

It is not compiled in one place I know of unfortunately, it is spread out between several posts and and informal measurements. For example

1) The one Tz adds a link into this post for has Trans and Ex.

2) arneg puts his link into this post for his measurements with degree wheel (controversial, but if you look at degree spread for each port opening and not absolute angle values data is reasonable).

Using 1 and 2 and Bell's suggestion about the three port timings it seems to reflect a 6000-6500 tuned engine... what is is too. Non of this is certified. I will also measure once I get acess to my bike with a degree wheel and confuse it even more. I will take paper trace of ports as well, piston specs and deck height.

I don't have rod data for GT550? does anyone know it center to center length

3) Also, port height is being compared to RD400 (what kicked off this post)

[Vintageman]

Still wonder if Cut out size in piston makes much of a difference, My guess is not much ... I'll look at some modern engines to see what they do

[tz375]

Modifying pistons is a poor man's porting tool that is really useful when barrels are unobtainable and pistons are cheap. There are rarely any good reasons to shorten the skirt on the intake side unless the intake port is really weak and prone to cracking.

The time it can be useful is if the bottom of the skirt hangs down below the roof of the inlet port if the port timing also needs to be extended. There is never a good reason to cut the exhaust side of a piston except when experimenting with port timings and the piston is basically used as a testing device to determine how much to take off the port roof in the barrel.

Well, OK "never" may be a little harsh, but it's not the best way to do things.