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PostPosted: Sun Oct 31, 2010 6:11 pm 
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The voice of reason
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There really is a valve speed problem, much less time to accomplish the required breathing. Piston or rotor ported engines open and close their ports much faster then valves move. Four strokes also have much longer valve durations.

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PostPosted: Sun Oct 31, 2010 6:29 pm 
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My old neighbor Eric Buell built a 750cc 4 cyl 2 stroke race bike back in the mid 80s. It made so much power no chassis or rider could handle it. Well over 200 :shock: :shock: ! The AMA outlawed it :( . As far as the 500 GP bikes: they didn't have more than 200 hp because they couldn't use it back in the old days before traction control and fuel injection.


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PostPosted: Tue Nov 02, 2010 9:48 pm 
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vroom wrote:
My old neighbor Eric Buell built a 750cc 4 cyl 2 stroke race bike back in the mid 80s. It made so much power no chassis or rider could handle it. Well over 200 :shock: :shock: ! The AMA outlawed it :( . As far as the 500 GP bikes: they didn't have more than 200 hp because they couldn't use it back in the old days before traction control and fuel injection.


The Yamaha TZ 700 and later TZ 750 that you refer to got to about 130hp if I remember correctly.

The 500 GP as I said never went much over 200hp on track and that was maximum development. If I recall the best was the Factory Honda fuel injected 205hp and first time ever to reach 200mph bike of Okada's at Hockenheim, a track where traction was irrelevant. Doohan later went to the close fire "big bang" engine which was more ridable but even that ended up at around 190+hp.

Saying that a 2 stroke will make double the hp because it fires twice as often is a fallacy because it has big holes in it's cylinders that reduces burn time. It also creates a paradox, you need bigger holes to go faster but that also gives you less burn duration.

You also have the problem of size, the 2 strokes pressure wave supercharger is somewhat difficult to package and takes up more space itself than a whole 4 stroke engine.


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PostPosted: Tue Nov 02, 2010 10:53 pm 
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Actually Erich's engine was a rotary valve square 4 and was outlawed along with the TZ700 and 750, which Kenny Roberts used on a dirt tracker a truly awesome ride :shock:


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PostPosted: Wed Nov 03, 2010 7:40 am 
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The TZ700 and TZ750 made between 170 and 180HP right out of the box with the factory flat sided expansion chambers. Good pipes added another 10 to 20 HP with power starting as low as 8,000 RPM and going up to about 13,000 RPM. With a power band that wide it was relative easy to control on a road course like Pocono for a GP bike.
Dave W


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PostPosted: Wed Nov 03, 2010 9:07 am 
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There is so little understand of 2-strokes it's quite sad. I have a TZ500G and an Suzuki RG500. No TZ700/750 ever put out 180bhp, I don’t think the full factory bikes ever made that amount. I was a Barber Motorsport Park for the AHRMA event in early October. It was the 25 anniversary of the RG500 so there was quite a group of 2-stroke at the event. We had a genuine TZ750 in the group. 120bhp max if well tuned and setup.

Graham


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PostPosted: Wed Nov 03, 2010 11:31 am 
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TZ750 had more powerful engines available to them they could not use because of traction. Kenny Roberts would go to Daytona with several grade engines in boxes but was unable to use the most powerful ones. Perhaps there is some marketing there. The peakiest engine possible wold not be what you want. Tires became much larger after the big TZ was in it's day.

Kenny had expressed that it was just scary going 180 on a bike with the rear tire at it's limit. That's just not fooling around territory. :shock:

Dave, I was going to say the same thing but realized I was probably confusing their speed and power.

Quote:
With a power band that wide it was relative easy to control on a road course like Pocono for a GP bike.


Pocono has pretty shallow banked turns, not like your typical stock car tracks or Daytona. Not at all. High speed and big power to the back wheel would really have your attention - big time. So not so sure you can really say "relative ease", I know it's tempting - but it's a very challenging place. I didn't know they ran those bikes there actually. Even my Formula Ford with it's raging 106 ponies on 10 inch slicks is scary there. A member of my local club hit the wall at the exit of the oval and died...

FastG, thanks for the info - you have some nice stuff. Pardon our ignorance and thanks for your comments. I know it's really not our thing but would love to hear a little more and maybe a picture or two from the event you went to. We do have some racers here. Did you ride in the event?

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PostPosted: Wed Nov 03, 2010 2:53 pm 
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Here are a few pictures of the Barber event taken by Russ Hoffman

http://www.whiterose.net/~russ/Barber1/
http://www.whiterose.net/~russ/Barber2/
http://www.whiterose.net/~russ/Barber3/

Link to many more pictures

http://www.gammagathering.rg500delta.co ... hotos.html


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PostPosted: Thu Nov 04, 2010 9:26 am 
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In the late 70's and early 80's the tires where good enough to pull wheelie at 130+mph with a TZ750. I only rode one once but it was a good 20 MPH faster then my 500.

Here the spec for and older 700. The 750 was good for another 15 to 20 HP and even more with three under one over expansion chamber set up.
Dave W

Compare:
the 1974 TZ700 and the 2000 R7 Superbike
TZ700 R7
Wheelbase 56.28" 56"
Weight 345 lbs 356 lbs
Front Tire 3.25 x 18 3.5 x 17
Rear Tire 3.5 x 18 6 x 17
Horsepower 145 173


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PostPosted: Thu Nov 04, 2010 10:54 am 
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Wow, I'm surprised how many folks here have driven or owned these big two stroke bikes, especially the race ones. There can't be very many people in this country that have done so and to have several on this board is amazing!

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PostPosted: Thu Nov 04, 2010 11:41 am 
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It's surprising how many of the big old 2-stroked are still around, they have an ardent following and are still raced today. I have a TZ500G awaiting to be restore, but it will return to the race track maybe in 2012.

You can always build your own using modern parts. I just sold to raise money for my Locost.

http://cgi.ebay.com/ebaymotors/ws/eBayI ... 0532632200

There is nothing so intoxicating as the hit of a big 2-stroke. The engine gurgles as if clearing it's throat, then the horizon leaps towards you, and the noise of a 4 cylinder 2-stroke is amazing.

Graham


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PostPosted: Fri Nov 05, 2010 1:20 am 
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Considering I have 3 RD350's in my basement, I can imagine people hanging on the the big ones!

Quote:
There is nothing so intoxicating as the hit of a big 2-stroke.


I built one of mine for the track at Louden but noticed how many of these guys were limping or in casts so decided to go another way. I remember the power hit so hard on that bike that even as you were unwinding the throttle it was gaining power so fast it felt like it was jammed. It had a nice porting job and chambers.

So here's an advantage for two stroke BEC's. One of these bikes had a crappy electronic ignition, that had bad timing at idle because of the magnetic pickup mounted on the alternator. THis bike could flip from forward rotation to reverse rotation without stopping. In fact if you let the revs drop letting out the clutch in first gear, it would do this. The first time this happened I was at a stop light and nearly hit the car behind me. I was really shocked :shock: . Later I learned to do it on demand. So the thing is you don't need a reverse gear with a two stroke!

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PostPosted: Fri Nov 05, 2010 8:36 am 
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We are Slotus!
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Horizon said:
Quote:
This bike could flip from forward rotation to reverse rotation without stopping. In fact if you let the revs drop letting out the clutch in first gear, it would do this. The first time this happened I was at a stop light and nearly hit the car behind me. I was really shocked :shock: . Later I learned to do it on demand. So the thing is you don't need a reverse gear with a two stroke!


Get it spinnin' backwards, work your way thru the gears, and you could do 140 mph... :shock:
BACKWARDS!!!! :evil: It'd be like driving the Forklift from Hell!!! :evil:

:lol:
JDK

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PostPosted: Fri Nov 05, 2010 5:49 pm 
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I guess I am not surprised there are so many ex bike rr types here. Where else?
Regarding Erich's bike it had rotary valves which made more than the usual TZ of the day power and skinny tires and a very willowy tube frame.


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PostPosted: Tue Nov 09, 2010 2:09 am 
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davew wrote:
The TZ700 and TZ750 made between 170 and 180HP right out of the box with the factory flat sided expansion chambers. Good pipes added another 10 to 20 HP with power starting as low as 8,000 RPM and going up to about 13,000 RPM. With a power band that wide it was relative easy to control on a road course like Pocono for a GP bike.
Dave W


While I have never worked on a TZ700 or 750 I have however worked on (and ridden) a number of TZ350's in the day and the best I ever saw almost touched 70hp and for a 750 you could double this but then take into account larger engine parasitic losses, that compares with Yamaha's own claims of around 120hp for their production bikes oh the day.

This is a modern dyno run for a TZ750 with a few modern parts, Lectron carbies and modern thinking port specs ... probably as good as you will ever get a TZ750;

Image

Australia had the Swann Series motorcycle racing series in the late 70's to mid 80's which was a run anything you want big money series and in '85 Michael Dowson ran a highly modified and modernised OW31 against Wayne Gardener's factory Honda 500/4 GP, Wayne Campbell's Ex Freddie Spencer 500/3 GP and Rob McElnea's RG500 GP bikes as well as the best open superbikes of the time although they were rarely close to the 2 stroke GP bikes.

I can not get youtube but I believe the Surfers Paradise round is here ..

http://www.youtube.com/watch?v=ug8_EGpmcyQ


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