How do you hot up a GT380?

[sportston]

How do you hot up a 2-stroke engine? I know that a set of performance pipes help, but I am talking about the actual motor itself. I seem to remember reading about it a long time ago and it involved enlarging the port length but I can't remember much about it.

[Zunspec4]

In simple terms it involves raising/widening the height of the exhaust port and lowering the transfer ports. The tricky bit is knowing how much and matching the expansion pipes/carburettor/ignition timing to suit. That's the bit that costs money either in professional help or much home experimentation.

Barton Engineering, way back, produced a very fast bike built from the bones of the 380 engine. Go for it

Cheers Geoff

[sportston]

Ah I see thanks. So no-one on hear has done it themselves then?

[Zunspec4]

Ah I see thanks. So no-one on hear has done it themselves then?

I'm sure several have tuned their 380's, you'll have to hope they will post. If you were asking about a T500 I could be more definite. Any tuning for more horse power will inevitably result in an engine with a peakier power curve, you pays yer money and makes yer choice.

Cheers Geoff

[Craig380]

It really depends how much more power you want, and where you want that power.

The best (and easiest) modification is to fit expansion chambers, which you're doing anyway. The factory exhaust system is designed for looks and easy rideability, and it's also very heavy. Chambers help the bike breathe better (especially above 5,000rpm), giving a useful boost at the top end without sacrificing low- and mid-range rideability too much, especially if you keep the standard airbox / filter.

Chambers also save a useful amount of weight and make the bike feel slimmer. With chambers alone, a properly set-up 380 will put 95/100 on the speedo any time you want to, without having to flatten yourself on the tank.

After this, you can get a bit more pep at the top end by raising the roof of the exhaust port by about a millimeter (keeping the same shape), and skimming the cylinder heads by 20 thou / 0.5mm.

That's about the limit of what most people can do for themselves. After that, you're into messing with the transfer ports, which most people (me included) don't have the skills or experience to do, so you're into professional tuning.

Remember that the 380 weighs as much as a Yamaha R1, 95 / 100 feels PLENTY fast enough given the weedy single front disc, skinny forks and 70s frame. I put a Bandit master cylinder and abrasive Brembo pads on mine to improve the brake, and it did improve it ... but you can't cheat physics. 550+ pounds of bike and rider travelling at 70+mph is a LOT of energy for one disc and a single-leading shoe drum to get rid of!

At the end of the day, it's your bike and your money. My 10p worth is, chambers transform a 380 and give it an edge that the standard bike lacks, without significant trade-offs or expensive work.

[Vintageman]

Have not heard of anyone who was happy hotting a GT380 via messing with port timing (there is a video of a guy racing one with a 3 into 1 and he gives his details of port mods.

http://www.youtube.com/watch?v=5Ik52cXFecg" onclick="window.open(this.href);return false;

Are you trying to make a racer or something for the street?

I think my bike has plenty of top end for street and afraid if it had much more and I used it a lot due to loss in bottom end trade off. it would just result in crank failure.

2 mods I may try.

Raise compression to increase bottom/mid power. This bike has squish type heads so may be OK to go up near a point more on compression (say around 0.020" off head)

Run GT550 carbs. Read somewhere this works. I would imagine gives even more top end.

Or try following these guys aproach (lol)->

http://www.youtube.com/watch?v=e_3nP7pdAPk" onclick="window.open(this.href);return false;
http://www.youtube.com/watch?v=R6opJ6_lCTc" onclick="window.open(this.href);return false;

[sportston]

Very useful info thanks.
I am merely curious at the moment. I won't be racing it, it is going to be cafe racer style street bike. I was wondering whether it might be a bit slow for my tastes without a bit of modification because my last stroker was a RD350 YPVS, which is supposed to have a lot more oomph. But I will wait until I have had it on the road before I make the decision to do anything other than racing pipes. I've never ridden a GT380 before. My dad had a KH250 that I used to maintain for him, which was a little slow in comparison to an LC. I'm guessing the GT380 should have a bit more poke, but at the end of the day it is not likely to be anywhere near the output of anything liquid cooled in standard form, I guess.

[sportston]

OMG Just looked at the videos! The blokes in the last two vids... I'm wondering if shooting is too good for them. I've never seen such awful pukeworthy bikes! How could they violate something as lovely as the gt380 in that way? Ewww, it makes me feel so dirty just to think about it...I think I need to go have a shower and lie down for a while.

[Craig380]

There's quite a lot of difference between a YPVS and a 380 For one thing, the YPVS handles and stops, is lighter, and has an extra 15 - 20bhp There's a decade between the two bikes, the 380 was never really developed from its launch in '72, Suzi just changed the cosmetics and added a disc brake.

However, the 380 triples have a unique feel, they're torquey and a set of expansions really does set them free. Also, the unique triple wail when you give it some beans at 5,000 rpm.

In a perverse way, 75 / 85 mph on a GT triple FEELS a lot faster than the same speed on a more modern bike, because of the wobbles, weaves and crap brakes

[Vintageman]

Whatever power the bike has you will use it. There is point it becomes scary versus fun. The GT380 when it runs right is so much fun. And power enough to cruise and interstate as well as back roads
Once I was riding through a town near me and a fellow on a Yamaha R1 saw me and set to hunt me down to prove his point (Modern four strokes are faster than old 2 strokes).

When we exit the city limits the road changed from 30 mph top 50 mph as it went around a bend. I dropped down a gear and gave it about ½ throttle. Then the guy on the R1 did the same, but a little more aggressively and passed me. I never heard an R1 hit the rev limiter it a horrible damaging sound.
However, I was so proud he felt to ensure he would succeed, had to push his engine to the max before shifting. I can ensure you he did not, but there is something about the sound of a 2 stroke on pipes that speaks of legends. Or maybe it was just the unspent fuel fumes choking him out and if he did not pass he would have simply passed out !

[sportston]

Lol. The fumes for sure! Thats what I love about strokers the noise and that gorgeous smell.

[Alan H]

I think it was Bartons that did a water cooled 500 conversion for the 380 'back in the day'.
Saw one racing but it wasn't competetive and never saw another.
380s/550s and 750s were GT models - Grand Tourers.
Cafe racer style doesn't make a racer - the handling will still be 'interesting'!!
Just enjoy the bike for what it is or you'll end up spending lots and being disappointed.
The 350/400 yams had reed valves and power valves depending on model.
They were also lighter than the 380. If you want to frighten yourself with a stroker, I'd suggest going for one of those.

[sportston]

I think it was Bartons that did a water cooled 500 conversion for the 380 'back in the day'.
Saw one racing but it wasn't competetive and never saw another.
380s/550s and 750s were GT models - Grand Tourers.
Cafe racer style doesn't make a racer - the handling will still be 'interesting'!!
Just enjoy the bike for what it is or you'll end up spending lots and being disappointed.
The 350/400 yams had reed valves and power valves depending on model.
They were also lighter than the 380. If you want to frighten yourself with a stroker, I'd suggest going for one of those.

Well I've got my Gt380 and it cost about half what a rd350 would have been. I would love to get another RD350LC but they all go for silly money these days. I've always wanted a GT380 ever since I was a teenager. What I like about them is that they are a simple 2-stroke. No water jackets to worry about, no powervalves to go sticky, no radiators to get clogged etcetera and although I loved my YPVS it didn't sound as good as a triple! It sure put a grin on my face...until the crankshaft bearings went. But that was all quite a few years ago now. I've been pining for another stroker since. So when a GT380 came up at a good price I jumped at it. I know It won't be a decision I'll regret, but I do like a bit of speed (don't we all?) so if after a while I get a bit bored or feel the need for more BHP then maybe I will sell my GT and get something a bit more powerful. I'd love a gt750 but that is way out of my price range unless I get a lottery win. For the moment I will enjoy restoring and then riding the 380. When it is done it will be a cafe racer in style but not necessarily a genuine race ready bike.
THe Barton liquid cooled model sounds very interesting. I wonder if any still survive?

[ja-moo]

Come on guys, a stocker is just a blank canvas. You may not get performance of other brands of the same size, but you can make more HP than a stocker and not ruin a motor. It's all power to weight, so get everything off that is not absolutely necessary, and replace the heavy stuff with lighter stuff. You can take a ton of weight off by just putting on chambers. And port correctly to get a good boost in hp. A much funner bike for sure.

[sportston]

You can take a ton of weight off by just putting on chambers. And port correctly to get a good boost in hp. A much funner bike for sure.

Do you have any specifics on porting correctly? This is something I would be interested in.