GT550 transfer ports? Different year size design?

[mtaylor]

What is the deal with some years having the angled transfers and others having large squared off transfers? It looks like suzuki was going to make a 750 air cooled motor. My cases have the big transfers and I just matched my cylinders to the cases when I ported it. I'm having the crank rebuilt now and while it's apart I'm going to epoxy the transfers to make them flow better.

[tz375]

It's not that complicated. Early motors and all US motors AFAIK had singl;e transfer port each side so they had small transfer passages in the crankcases.

Later Euro models and some other export markets got chrome/nicasil plated bores and two transfer ports each side and they changed the crankcases to match the larger port opening at the base of the barrels. I believe that US imports continued with the same carryover barrels with iron liners and did not get matching plated alloy barrels, but you will need to check that to be sure.

[Allan k]

I have pictures of the nikasil cylinder from my gt 550 on my blog

http://Www.allansgarage.blogspot.com" onclick="window.open(this.href);return false; at 'piston change'

The Extra port next to the exhaust port on the nikasil model is called 'schnuerle' port. These port helps push out exhaust gasses better Than the 2-port model.

[Allan k]

Link that helps

http://en.m.wikipedia.org/wiki/Schnuerle_porting" onclick="window.open(this.href);return false;

By the Way, As you Can see on my blog, the base gasket is also bigger at the ports Than the 2-porter

[Vintageman]

Allan k

So your GT550 has the Nikasil with extra ports. The bike must not run out breadth after 6500-7000 RPM like the ones without. I have the late gt250 with these extra ports and that bike just wants to rev (go fast) versus the 74 Gt250 I had (single transfers). But in the GT250 case no bottom end (trade off).

Please do tell how your GT550 runs...

[Allan k]

Regarding the schnuerle port Thats not All correct, since they point in the opposite direction of the original schnuerle port...

Anyways, i have never tried this bike with anything Else Than the 3-1 exhaust.. And this pipe is known to kill top end power and High revs.. Top speed is 100mph with anything Else stock except bigger main jets. I Can pull All the revs i want But its power decreases after 7000rpm. Im looking for a tuning option though.. I want that High revving High power engine.

[Vintageman]

What I mean is if you look at the later GT250A/B Cylinder it has a very similar extra port design approach to your Nikasil GT550 looking at your pics.
Clearly this design was intended to do more efficient scavenging. Maybe not HP versus RPM profile change?

The later GT250 also changed exhaust port timing too so maybe why its power profile moved to higher RPM than earlier design. Having had both GT250 it is a huge difference in engine mannerism.

Maybe the Nikasil GT550 did not change Exhaust or Intake port timings when transfers were changed thus keeping same power profile?

It looks like towards the later 70s Suz tried to get more top end as you see changes with the GT750, your GT550, and The GT250.

I have the 73 GT550 with unknown to me brand 3 into 3s (retains center stand). It also looses peek HP after 7000 RPM too although it will over rev a bit beyond that if you wanted, but no gain in HP. Pipes did add a boost at 5000 - 6500 versus stock pipes.

Do you have a video of it running? I have been curious about the extra port GT550 performance.

As said non sold here in USA

[Allan k]

I have made a short on-board video showing rev and speed. 0-100mph. Will post somewhere on the net within some days...

Im looking for some tuning.. And im currently rebuilding another 'nikasil' engine wich im going to port a little bit and im thinking about raising the cylinders and milling off the same at the top of the cylinders +0,5 mm to raise compression. Finally im putting pod filters and maybe a set of jemco pipes..

Im just in doubt of how much i Can raise the cylinders and still maintain driveability.

Any ideas on power est?

[Vintageman]

Allan K,

I don't think you can port a plated cylinder? I think the port chamfers are done ahead of plating. If you raise a port you will have plating edge that will catch. if I am wrong some will say, but good thing to check

I bet that current porting design will respond great with 3 into 3s. Particularly, If Suzuki did raise the exhaust port along with new ports ( i bet they did for that is their MO with other bikes) . Can you measure the exhaust port height for a comparison?

Does that motor still use domed heads or squish? That will limit your compression if still domed heads for chamber boost will raise compression too

Someone USA has a video on youtube about what he did to has late model GT550 and Jemco's He was on this board at one time too I think

[tz375]

Schnuerle loop porting simply means that the ports are designed to promote flow to clear the cylinder. The classic design points ports towards the rear (inlet) side of the cylinder so that they flow back and up pushing old gasses out of the combustion chamber.

On a Nicasil 550 all ports are Schnuerle type as are the single transfers on an iron liner cylinder.

There are three advantages to the Plated design:
Better heat transfer
More port area
Better port shape - both ports can point in different direction providing a more complete clearing of old gases.

It's interesting that Suzuki chose to make that additional pair of ports more like a boost port in an RD Yamaha rather than as a regular secondary transfer port.

A plated cylinder can be ported but it's better practice to re-plate it after porting. Scott Clough ported a nicasil motor recently for a Cali racer and it reportedly makes 75hp at the rear wheel and that sounds reasonable and doable.

In terms of revs, there are several things holding back a 550. One is exhaust port dimensions which are restrictive and the motor needs more duration and more width. Intakes are also a little short of time-area. Jeff Kushner built an iron liner 550 with Jemcos and said that he thought that it was critical to improve intake flow and to leave the transfers alone, but no data to support his comments and no HP data either. Stock they made 38hp at the rear wheel and peaked at around 7,000 and power fell off sharply after that.

And let's not forget that it's a long stroke motor - same as an RD400 on stroke but smaller bore, no reeds and same sized carbs.

[tz375]

I decided to run a GT550 through the simulation software and immediately realized that I don't have a whole lot of data on either a stock motor or a later set of nicasil barrels. Does anyone have a decent port map or rubbing?

[Allan k]

I have posted a short video on Youtube. http://www.youtube.com/watch?v=7T1a_J4Y0dY" onclick="window.open(this.href);return false;

I am aware that I can't do much to the ports on the cylinders without destrying the nikasil plating... it wouldnt last for long if i did..

However, the left cylinder on my spare "Nikasil" engine had "Steel" liner fitted... i could see from the cylinder head that there were traces from a seizure or break down of the cylinder, and then the PO had a Steel barrel fitted and a new piston...

I believe that this would be the ultimate vs. cheapest way of making one hell of a bad ass set of cylinders for the GT 550... 4 ports and all the porting job you could wish for... and also the abbility to use oversize pistons... who said GT600

[Allan k]

The exhaust port on the nikasil cylinders meassures from top down to port begins 36mm and stops again at 63mm

dont know if this is useful for anyone..

The cylinders heads on my engine are still domed-type..

The GT550 was rated to 53bhp in the nikasil model.. and 50bhp with steel cylinders.. so power was increased, but if it is only duo to the extra ports or also caused by the removal of the balancing pipes at the exhausts pipes i dont know.

The GT 750 also had a power increase from 67bhp to 70bhp but i dont know what caused it.

[Vintageman]

Allan K

That steel liner, I assumed preserves the extra ports? But only on is lined.
You can replate the other of course too.

I am glad you measure the exhaust port. I hope someone else does too on two port design. I am curious. I don’t have a spare.

The later GT750 and GT250 as one power improvement raised exhaust port. I bet the Nikasil 550 was raised too.

There is one interesting point about the extra ports above intake. The GT250 when it did this, had to change locator pin on piston for the two rings versus older model, else it would catch on new ports. I wonder if the GT550 original piston had to change as well for Nikasil or was lucky.

Also, if you stayed Nikasil, then there may be a specific ring (non chromed for example.) maybe steel liner uses non chromed, but steel could use harder ring. If ring too hard it can scratch plating if I recall reason for this.

I had bad luck with plated cylinders on 2 stroke, particularly that vintage (Kawasaki, Fuji, Rotax, etc tried it too on air cooled engines). Supposedly better at heat transfer, but there is a limit and if surpassed ... what a mess and quickly (per my experience). Issues were about the exhaust port first since the heat was now a problem for the aluminum to handle, where before the steel held it first.I can see why a liner existed for your 4 port gt550, Nice!.

I also believe as you the 4 port design is the ultimate performance version/start point. I am still thinking it should have a top end boost over of 2 port straight from Suz.

Nice sound. Your tach limit running looks similar mine. I can get > 8K RPM easy too. I wonder if the exhaust is your limit as you said or even ignition too. I run Iridiums, but on my 550 I did not gain not top end like I did when placing these plugs in my GT380 or Yamaha R5. I still run stock timing with chambers on 550 and maybe I should retard if I felt like driving that way. It is well documented that the 2 port 550 is tuned for low/mid performance. My chambers seem to stay with that theme.

Not sure whose chambers are better for more top

[tz375]

Have you had a chance to run that bike on a dyno? I'd be very interested to see what the curve looks like. BTW, is that a Piper or ROCA or other three into 1 and do you have any pictures of it.

Conventional wisdom holds that a 3 into 1 will not rev and yet there you are at almost 8000 which is more than stock peak. That's why it piqued my interest.