How do you hot up a GT380?

sportston · Post by **sportston** » Wed Jul 17, 2013 4:11 pm

ja-moo wrote:Gheesh, you can safely widen the EX 6.7mm...........

Wow thats a lot. How did you find that out?

tz375 · Post by **tz375** » Wed Jul 17, 2013 5:47 pm

Those are pretty much what you would expect with a 54mm stroke peaking at less that7,500 rpm. Compare that to say an RD250 peaking at say 9000 or a TZ peaking at 12,000 and there's room for a whole different set of numbers in there.

How wide are the transfer ports and the intake and is it bridged?

sportston · Post by **sportston** » Wed Jul 17, 2013 5:54 pm

tz375 wrote:How wide are the transfer ports and the intake and is it bridged?

I have no idea. I haven't stripped the engine yet. As far as I know it is a standard GT380M engine. But I am not familiar with the particular idiosynchrocies (yes I know that isn't spelt correctly. Sorry) of the suzuki triple 2-stroke engine. This is my first one and I have only owned it about a week.

tz375 · Post by **tz375** » Thu Jul 18, 2013 12:14 am

That big of an exhaust won't help much because the rest of the ports don't support it.

I'd need to get my hands on a 380 jug to see what can physically be done but I'd suggest as a plan:

Raise the exhaust port roof 2mm to 31mm down and widen it by 2-4mm
Leave the transfers alone.
Lower the intake port from 88 to 93mm. Past that point, you lose more bottom end than you gain at the top end.
Fit a set of GT550 carbs or similar aftermarket/RD carbs
Raise compression by skimming head/barrels to set squish first and adjust CR as required
Fit decent electronic ignition
Fit good set of pipes
Make sure tires, suspension and will are in order and enjoy having almost 60HP to play with at 8,500rpm. That's more than a stock GT750 or a stock RZ350 (YPVS). You will lose bottom end and will have to change gearing to match the freer revving nature of the new beast.

All the above assumes that there is enough metal in the castings to make those changes.

Enjoy

Craig380 · Post by **Craig380** » Thu Jul 18, 2013 12:57 am

Sorry, forgot to post the transfer port width - they are approx 26mm across, and of course it's just a single transfer port each side.

The intake port is bridged, and the bridge in the liner is pretty thick too, as is the casting in the inlet tunnel.

From memory, the bottom of the transfer ports (where they meet the base gasket) usually have some extra meat too, making them smaller than the base gasket cut-out. You could probably gain a couple of horses just by cleaning up and flowing the inlet & transfer tunnels without even touching the windows in the liner.

sportston · Post by **sportston** » Thu Jul 18, 2013 2:22 pm

tz375 wrote:Make sure tires, suspension and will are in order and enjoy having almost 60HP to play with at 8,500rpm. That's more than a stock GT750 or a stock RZ350 (YPVS). You will lose bottom end and will have to change gearing to match the freer revving nature of the new beast. Enjoy

Wow that would be quite a power hike from the standard 38HP. I'm tempted to do that now...60hp seems to be calling to me...
Electronic ignition is a must in my mind. There is no way I am going to be getting the thing on the road without it. I can set points and maintain them but, why bother when you don't have to?
I wasn't planning on taking the engine apart as it has compression and supposedly works ok (though I haven't even bothered trying to run it since there were petrol leaks and blockages in the fuel system) But maybe I should take the head and barrels off, just to inspect them, and while I am at it a little mild porting could be done, seeing as I'm already there.

ja-moo · Post by **ja-moo** » Fri Jul 19, 2013 12:27 am

Well, a safe EX width for the street is 68% of the bore (cordle width) and even with major port, head work, very good custom pipes and big carbs, I seriously doubt you would get anywhere near 60 hp, but I love to be proven wrong......

ja-moo · Post by **ja-moo** » Fri Jul 19, 2013 1:02 am

I looked this up, go to the dyno page, the numbers are pretty interesting........

http://kawtriple.com/mraxl/articles/kh4 ... tkh400.jpg" onclick="window.open(this.href);return false;

tz375 · Post by **tz375** » Fri Jul 19, 2013 6:52 am

JA, what sort of HP are people getting out of a well developed 400 Kawasaki?

That should give us some idea of what's possible with a similar motor. I haven't ported a 380 so I have no idea if there's enough metal to carve out to get decent port shapes, but if there is, it could be an interesting exercise.

Craig380 · Post by **Craig380** » Fri Jul 19, 2013 7:16 am

ja-moo wrote:I looked this up, go to the dyno page, the numbers are pretty interesting........

I've got a dyno plot from a UK test of the 380, pretty much the same at the back wheel as that KH400, about 32bhp plus some small change. The torque curve was flatter with the Suzi as I recall, I'll have to scan it.

I know when Cycle did that giant test of all the middleweight bikes, the 380 gave 31bhp on the dyno but they also noted that it had an 'oiling problem' in the test report. Whether this affected performance unduly isn't stated.

tz375 · Post by **tz375** » Fri Jul 19, 2013 9:01 am

Sounds about right Craig.

Who do we know that has a tuned KH400 or GT380 to see what a good one actually makes in the real world?

In Brand Y models an RD350 or 400 makes around the same amount stock and it's not too hard to get them to 60HP on a tuned motor.

Looked at another way, a GT250 which is more or less 2/3 of a GT380 makes around 40HP on a good tuned motor, so 60 should be possible if there's enough meat in the barrels with a really good set of pipes.

A mild tune and average street pipes should still be 45 - 50 if done properly.

ja-moo · Post by **ja-moo** » Fri Jul 19, 2013 1:33 pm

Took pretty hard porting, big carbs and good pipes. 62 RWHP

http://www.youtube.com/watch?v=b1r5ZB5_W7c" onclick="window.open(this.href);return false;

Allan k · Post by **Allan k** » Wed Jul 31, 2013 1:52 pm

i tuned my 550 a little more than just spannies... top speed is true 106mph.. (dont know if this is alot or a little compared to the tuning done, but it a little more than before..)

check my blog. http://www.allansgarage.blogspot.com" onclick="window.open(this.href);return false; alot of pictures...

i believe this is what can be done without being an expert..
i did the cylinders in the intake and exhaust.. and the crankcase ports. didnt touch the ports to the cylinder.

fitted jemco's and runs great.. i use #105 mains..

Craig380 · Post by **Craig380** » Thu Aug 01, 2013 12:58 am

@Allan, det er fedt, mand!

Looks great, and great detail on your work. One question - was the cylinder head already in 3 pieces when you bought the bike?

Also, I did not know the 550 pistons had little oil holes on the skirts.

sportston · Post by **sportston** » Fri Aug 02, 2013 4:24 pm

I too was curious about the oil holes in the piston skirts. Is that normal? And does it decrease wear? Also wondered about the three heads. Are they like that on 550s normally. I notice on 380s that it only has one head instead of 3 separate ones. Nice looking bike. I like what you've done with her.

How do you hot up a GT380?

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