Boost ports?

Craig380 · Post by **Craig380** » Tue Jan 26, 2010 7:37 am

Has anyone experimented with using boost ports in the twins or triples?

Obviously it's a fair bit of grinding work, drilling & milling pistons, etc, I wondered if any possible gains are outweighed by the work in doing it?

I was recently reading the book "Stealing Speed" by Matt Oxley, about the MZ engineer Walter Kaaden.

In it, Kaaden's rediscovery of the boost port enabled his 125cc racing engine to run cooler (by not trapping & heating mixture under the piston) and gave 10% more power because of the increased efficiency.

tz375 · Post by **tz375** » Tue Jan 26, 2010 9:15 am

Craig,

A G Bell explains that well in his book on 2 strokes.

In fact Suzuki used a boost port above the intake on the TR500MK3 water cooled.

The same trick is not possible on a 750 because of the twisted port layout. It may be possible on a 380, but you can probably get a better bang for the buck from conventional porting.

Craig380 · Post by **Craig380** » Tue Jan 26, 2010 10:56 am

thanks, I guess it may be worthwhile if the motor is already highly tuned and stressed ... as the 380 motor is neither of these there are probably other mods that should be done first

H2RICK · Post by **H2RICK** » Wed Feb 03, 2010 5:38 pm

Craig, I believe it was you that I sent a writeup by jmendoza from the old board about how he had modded his 380 back in the day. If you have lost that writeup just let me know and I'll shoot it your way again. PM me on this so that it doesn't slip under my creaky old radar.....

tz375 · Post by **tz375** » Wed Feb 03, 2010 9:49 pm

Any chance of posting that so we could read it?

Suzukidave · Post by **Suzukidave** » Wed Feb 03, 2010 10:12 pm

The chrome bore GT550's also had boost ports

tz375 · Post by **tz375** » Thu Feb 04, 2010 9:10 am

Dave,

are those the secondary transfers around teh back there, like a GT250 that Tom Garcia is working on?

It looks like they added the second pair of transfers to the rear face. That's interesting.

Post by **oldjapanesebikes** » Thu Feb 04, 2010 9:36 am

Suzukidave wrote:The chrome bore GT550's also had boost ports

They made chrome bore cylinders ? When ?

Suzukidave · Post by **Suzukidave** » Thu Feb 04, 2010 9:43 am

I am pretty sure the 550s also came with a chrome bore that had the different porting stock .

Suzukidave · Post by **Suzukidave** » Thu Feb 04, 2010 9:49 am

http://en.wikipedia.org/wiki/Suzuki_GT_series " However, for the 1976 MY, the 550 received a very forward thinking design change that featured cast iron rings running in chrome-plated cylinder bores. This change MAY have had something to do with Suzuki's recent venture into the snow machine market in North America starting in the 1973 MY. For whatever reason, the only market to receive this innovation was continental Europe i.e. France, Germany, Italy."

Suzukidave · Post by **Suzukidave** » Thu Feb 04, 2010 9:56 am

The cylinders are completly different from the standard 550 . even the intakes are shorter

Post by **oldjapanesebikes** » Thu Feb 04, 2010 10:08 am

Learn something every day ! Cool !

Suzukidave · Post by **Suzukidave** » Thu Feb 04, 2010 10:17 am

Besides the 2 piece head that didnt do anything with HP .. its too bad they didnt do something like this with the GT750 .. well they did play with a few things on the MAB's to add in a few HP .

diamondj · Post by **diamondj** » Thu Feb 04, 2010 10:43 am

tz375 wrote:Any chance of posting that so we could read it?

As requested:

GT380 Porting for power
Wed, 20Sep00

Craig and H2Rick were talking about GT380 power and how the engine was so conservative. Well I had 5 of these beasts and thought the same !
The 380 has true pure Schnuerle porting with no auxiliaries or boosters and the ports are quite small in height and width. I got a great idea from examining my GT250 which basically had the same porting but with one major difference: the exhaust port had 2 small ports on either side near the top to effectively widen it without the risk of losing ring support. I know how to take a hint and drilled two 1/4 inch holes on either side of the 380's exhaust port, the tops of the holes being equal (in line, ed.) with the top of the exhaust port. Next, I used my Dremel and a carbide bit to drop the bottom of the new holes 3/4 of the way down towards the bottom of the (stock, ed.) exhaust port and slightly ovalled out the tops of the (new, ed.) holes.
Next, I drilled two 3/8" holes in the piston skirt on the intake side, just on either side of the intake port, but so as not to fall in the ring gap area.
Then using the Dremel I cut two troughs, or grooves if you will, in the cylinder walls that were even with the tops of the transfer(s) (ports, ed.) and the bottom of the grooves were even with the holes in the (piston, ed.) skirt at BDC. Basically I added 2 booster ports, angled right at the plug and widened the exhaust with webbed holes to support the ring(s). Next, I had the head milled to set the squish at .040" and went up 2 jet sizes on the main(s) (jets, ed.), used Uni-Filter foam on the stock filter cages and repacked the silencers. Talk about a difference....It would do roll on wheelies in first...just snap the throttle open and enjoy the view of the sky ! The (stock, ed.) 380 would crap out at about 7K (rpm, ed.), but this one would pull hard all the way to redline...and you didn't need to take it that far to get all the thrills you wanted. I got the booster idea, and drilling the holes in the skirt, from Aermacchis and RDs that I had seen back then. I never told anyone until now, as it was my big speed secret....and later I forgot about it all together. Now that I don't have the bike, I might as well tell everyone what I did.

jmendoza

diamondj · Post by **diamondj** » Thu Feb 04, 2010 10:59 am

Suzukidave wrote:Besides the 2 piece head that didnt do anything with HP .. its too bad they didnt do something like this with the GT750 .. well they did play with a few things on the MAB's to add in a few HP .

After also reading STEALING SPEED that's what I wonder about as well. Suzuki went to the trouble of helping Ernst Degner and his family defect from East Germany, paid him £10,000 which is about $115M today to steal Kaaden's tuning secrets and then didn't use them in any sort of large scale on anything they produced for street bikes. Imagine the T500 if they had used disc valve induction and boost ports. And didn't offset the transfer ports like they did. Would an extra 10mm of engine width really have been so bad? They used these tricks on the racing engines and had disc valves on a few of the dirt bikes (the TS80 and 100 spring to mind). I wonder if they were concerned about the other Japanese mfgs copying them?

I also wonder why STEALING SPEED was difficult to buy? I had an order in with Amazon back in September of 2009 before it was published in November and they finally let me know in early January that they weren't able to get the book in. I wound up ordering it directly from Haynes in the UK:

http://www.haynes.co.uk/webapp/wcs/stor ... g+speed%22

Even if you have no interest in where modern 2 stroke tuning theories came from, this book is worth reading for Oxley's description of Degner's 50cc win at the Isle of Man GP in 1962.

Jim