Rd400 barrels on gt550

[tz375]

Dave is exactly right. Frankenstein ideas are the last step for those moments when a whole lot more is still not quite enough and sure as heck is not the place to start.

Good pipes help and the right ports help and as Dave said, the right head shape will allow the motor to build more internal pressure without blowing a fuse. Stock head shapes are nothing short of terrible and caused all manner of issues with the TR5750 and severely limited power output.

For a street motor 10-15% is easy to gain. Stock porting is extremely mild compared to other more sporty bikes of the time. Thaqt's what makes it so soft and mellow to ride.

[Vintageman]

Since this is an Rd400 barrels on GT550 post. Can some one measure the exhaust port height on a GT550 ... if they have a set handy? The non Daytona RD400, that is 76-78, the height 35mm and width is 37mm.

Lets see how mild this GT550 is !

Arneg, what are you looking to do with the bike? street rider? Track bike?

+15%. Make the GT550 near that of the stock H1. 49 hp upped to 57 hp. increase peek hp by +500 rpm
So right off we can take the pipes out of the equation. Looking for that one right mod (or two) to get here

To me changing head shape is not on easy for I could not do the machining. Any suggestion as to who could. Would you recommend for volume same, more or less? If that would alone add the 6, 7, or 8 % power worth cost. I mean just pop off head and 30 minutes later you are good to go.

Remember that factory bulletin about increasing power on T500 (more than my 15% goal)? They did not change head shape but lowered compression. They Just raised exhaust port 5mm and lowered intake same (too much for my taste I am sure). They shaved head but no way restored what was lost with 5mm raised exhaust. I am thinking that recipe is not want I want for a street machine.

I am thinking the exhaust port must be raised on that GT550 for this goal. I don’t know the exhaust timing now but it must be real soft.

1) Does anyone know the engine specs so I can run port timing. I want to see how much timing would change and what it is stock.
2) For those who have raised exhaust ports just a little how much compression would you restore by shaving head for example. All, none, or some? The reason one would lower it I think is if the engine is to be run at high rpms sustained. Not sure

I have not found much for tried mods published for the GT550. Guess it was never used in that manner much. With My Bassani pipes longer intake timing helped, put have not gained 15% -20% yet me thinks. This bike has mass of midrange power, just runs out of breadth I think a little too soon. Fun stuff

[tz375]

Work the data backwards.

62mm stroke is safe to what revs? Insert your own MPS number in to solve equation for RPM.

Then look at what Bell has to say about exhaust duration for a given peak RPM. Compare that to stock exhaust timing and I think you will find it to be 3-5mm less than might be expected. Stock exhaust is around 22mm high compared to an RD400 which is 27 tall (35mm down from TDC)

You could think about a 3mm spacer under the barrels and raise the roof by another couple of mm.

Forget everything you read about so called "corrected compression" it's a another misunderstanding of how engines work. When did you last read a 4 stroke specification as CR from the point that the valves closed?

Why is that? Because it's dynamic CR that's important and that's a function of a lot of variables including RPM, intake, transfer and exhaust waves just for start. It's just a number and it tends to suggest things rather than being a hard fact.

[Vintageman]

5 mm less would be significant. The RD400 is actually kind of mellow too. This is like the low power India RD350 vs USA rd350. I would like to know the exact exhaust timing and use Bell suggestion for the RPM wanted.


Anything "Dynamic" is always complex. But, the problem is simpler if you changed just one of the variables involved, Exhaust port height,

The question I struggle with is and looking for advice. If you raise the exhaust port, would you restore compression lost: why or why not. To narrow down variables let say 2mm raise of exhaust port.

So if I have 130 PSI when I kick it over before 2mm mod. What should I have after. I am thinking get it most all back 125-130 psi for this street goal

Approximate also the fact one only wants another 500-750 rpm shift in up peek power, if dynamic is a function of rpm I think it can be ignored. The question may be heat if one does runs at this new rpm sustained. I think the GT550 may be OK shedding a little more heat it not running too long with it.

For example. You see the GT250 change the exhaust port from 32 mm to 29.5. originally they held the same corrected compression, They also retarded timing but, later backed off compression due to customers running sustain high rpms melting down engine. The r5 vs rd350 they lowered compression . Maybe felt reed valve made up the difference is street riding ability.

I think one of the reason I have dislike exhaust port mods for street, it kills the power everywhere but top end.
I think I did not restored the compression back enough. Again most mods you see are road or drag race, compression much less, but rpm running much higher and for longer. Am I correct given what the goal is to be. I just don't know how best to manage restoring compression once I raise exhaust a couple mm.

[D&D CHASSIS]

if you set it at 155 psi, that'll put you to using premium fuel, but better mid range torque and power.....
try widening the exhaust instead of just raising it, broader power is the result. Transfer work would consist of measuring all the cyls, and setting the heights to the highest transfer, thus "blue printing" that part of the motor.
I cant stress enough how poor the factory designed heads are, ship them to me and I can weld them up for you, then ship them to Richard to be cut?

[tz375]

David is exactly right. Stock tolerances are all over the map and 125PSi is an indication of how low the power is. My street bike runs 165PSI but that's probably higher than ideal for regular gas. With a 3 into 1 it never gets much higher as revs go up, so it's not as bad as it sounds. With reasonable pipes, cylinder pressures get much higher and decent gas is useful insurance.

It's not about changing the exhaust 2mm and how much will the head need to be changed for that to work. A 5mm taller exhaust with no change to the head but a much better exhaust may increase actual dynamic cylinder pressure under load so that it's actually much higher than stock.

The whole thing is a system. Decide what exhaust height and time area you need as a target and then work out the width and height you want to use to meet that time area target. Raising the exhaust port raises RPM at which it peaks and the exhaust can be modified to force that up or down but if the exhaust port timing and exhaust system design match, you get a whole lot more of everything.

So:
Set a HP and RPM target
Calculate the time area to support those targets
calculate the width and height to meet that time area

Decide on a static CR and then run the data through a simulation software package and check not just for power but also for port and box filling and emptying efficiencies and pressure changes. Check the pipe temps and cylinder pressures.

Then start to tweak those variables to add more meat where you need it under the curve or to fill holes.

[Vintageman]

I have the exhaust I have so need take exhaust out of equation. There a few examples of factory doing such a changes with GTs, Rds, and Ss. Like them, don't want to widen ports for ring life. Gain area by height only. Don't be too greedy and try to save as much bottom as one can knowing what this mod does. Not looking for too much more RPM. Like factory 500 rpm shift would be nice.

I think if it was me, I would try 2mm off Ex. Stay with stock corrected compression of 6.8 to 1. The only thing is I doubt that will give 15%, maybe 8%, but with pipes too may be close and not loose it's sweet manners.

Not much out there on GT550 mods even the kind I want nor monsters. No factory stuff about mods or period articles I could find. Can't experiment much either for parts are getting rare, cranks, pistons etc.

If someone ever comes up with the port timing for this thing or other bikes let's make a sticky.

Didn't man to hijack post

I guess long ago I heard rumors of cylinder kits (GT380 at least) analogous to bolt in RD400s.
If you could put RD400s on you would have unique bike for sure.

[ja-moo]

don't want to widen ports for ring life. Gain area by height only.

Unless you are looking of 30,000 ring life, you are really hampering power production by not widening your exhaust ports. Stock ports are very small, and to produce power, it is all in the time/area, bigger ports flow more. It's all in doing the port roof and chamfer on the port correctly.

[Vintageman]

Vintageman wrote:

don't want to widen ports for ring life. Gain area by height only.


Unless you are looking of 30,000 ring life, you are really hampering power production by not widening your exhaust ports. Stock ports are very small, and to produce power, it is all in the time/area, bigger ports flow more. It's all in doing the port roof and chamfer on the port correctly.

Was thinking the GT550 was wide for street, just don't see that change from factory as they modified a specific bike model up or down. Warranty ends at 12K not 30K. As rings chip so goes the cylinder walls etc. Yes need very good chamfering for ring is going to ride in it.

But you guys are right! There must be some room for increase as long as one is not too greedy maybe 2mm here as well. And, don't need to worry about restoring compression either! Are we at that 15% goal yet! Man would like to compare GT550 width to H1 for example maybe even a T350

[tz375]

I wonder if anyone here has an H1 port map

[Vintageman]

kawtriple.com/mraxl/portmaph1stk.pdf

use IE and search on "Kawasaki H1 port map" first hit

[arneg]

So I actually recently measured the ports on the GT550 and came up with the same that was posted here: viewtopic.php?f=2&t=5351&start=60:

Bottom line:
Exhaust Port Timing: Opens @ 97° ->to-> 260° (open for 163°)
Intake Port Timing: Opens @ 285° ->to-> 72°AfterTDC (open for 147°)
Transfer Port Timing: Opens @ 120° ->to-> 240° (open for 120°)

I do it all in degrees and percentages not mm to keep it comparable to other strokes and bores. The exhaust can be raised 2mm and widened 1mm and you're still in pretty safe width (anything below 70%, I am not scientific but mine endet up at 67%). I ended up at 175 degrees exhaust. Waiting for the crank to return from Bill Bune, once it's all assembled I'll post a video of how it runs.

Looking at it though the RD's much larger transfer area, boost port, and intake would improve what simply can't be done on a GT barrel. I doubt that a stock cyl can get more than 60HP (rear wheel). Unless you go with massive pipes - but that gives a whole new set of problems (like the total lack of power before power band that is ridiculous).

[Vintageman]

arneg,

Nice! Can you summarize what you did for mods to your ports if any?

That timing data-> intake, exhaust, transfers are all just as Bell says for a bike <6500 rpm. No doubt it is as such

So that's why when I changed just one, intake, no gain in top end for other two are very low rpm holding back

I think now i would raise jug 2mm to up transfer and exhaust equally, shave skirt 3-4mm given exhaust still covered, ( bet it will be)

Easy for me to make a plate, shave head, thinner gasket (or shave top of jugs), and piston skirt shave.

Since I learned how to add pics here is my GT550 given how cool arneg's is

http://i266.photobucket.com/albums/ii25 ... /014-3.jpg" onclick="window.open(this.href);return false;

[arneg]

nice bike! love the pipes. I forgot to take pictures of the exhaust port... maybe just embarrassed. Here is one of the work being done:



So I raised the exhaust 2mm and widened 1mm to each side. If you only did the intake I wouldn't expect much change, maybe even a bit worse performance low down and more blow back. The exhaust is very small and the limiting factor. Especially with expansion chambers.

[Alan H]

Since I learned how to add pics here is my GT550 given how cool arneg's is

http://i266.photobucket.com/albums/ii25 ... /014-3.jpg" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

Nice K. Hopefully my similar model will be running and back on the road very soon.