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PostPosted: Wed Oct 05, 2011 3:49 pm 
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Moto GP
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Joined: Fri Oct 24, 2008 5:55 pm
Posts: 3972
Location: Lancaster Pa.
Country: US
Bikes owned: GT750 x2 97 -1200 Bandit 86 GSXR1100
tz375 wrote:

Dave,
Did you notice the extra area that ebos are trying for on the rear of the transfers?
Yes .. i saw that too .. RK that made the squish insert head had a similar step in his supplied port changes .. something else i maybe should have also added .

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PostPosted: Fri May 25, 2012 6:01 pm 
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Still in the Driveway

Joined: Wed Jul 07, 2010 9:53 pm
Posts: 5
Location: San Diego, CA USA
HI,
I have a 1mm OS TR750 motor hybred (real TR barrell) with a CR 5-speed GT box and a BiMotion designed modern squish head - 118 RWHP @8,200 rpm (w/rev limiter). I use this in a small 360 Kg sports racer.
Ignition - Lucas RIT LR105
Pistons: stock 1mm OS, but micro blaster (WRC process) and quality Swain ceramic top coated
Rods: stock, but cryo treated and WPC blasted
Crank: stock, rebuilt, straightened, and rod pins tack welded
Tranny: Custom 1st & 5th gears from Moore Engineering (UK) 1st=2.267 (34/15T); 2nd=1.778; 3rd=1.381; 4th=1.125; 5th=1.000 (20/20T)

I would be glad to post the dyno sheet if I knew how to do that, lol.

John


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PostPosted: Fri May 25, 2012 6:13 pm 
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Still in the Driveway

Joined: Wed Jul 07, 2010 9:53 pm
Posts: 5
Location: San Diego, CA USA
Here is a link to my GT/TR race car pics
http://groups.yahoo.com/group/GT750/pho ... 20&dir=asc

118 RWHP = 130 @ the crank ±

John


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PostPosted: Sun Jul 08, 2012 5:25 am 
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Around the block

Joined: Tue Jun 12, 2012 3:15 am
Posts: 85
Location: Chattanooga, TN
Country: USA
Bikes owned: '75 GT750 x2, '76 RD400, Guzzi
water cooled wrote:
If you are serious....this would give you a reasonable idea on cost to get there.
If you want 100 bhp (crank HP not RWHP):

JEMCo 3-3 Exhaust $575
(3) 36mm Mikuni $300-400
Cometics Spacer (under the block) $50-75
Cometics Copper head gasket $50
Squish head conversion $350-450
Port Block $500-600
Deck the Block $125
Motion Pro Throttle Cables $75
Jets $50-60

Misc: To get 100+ BHP you will move up considerably on the rpms so you also need to consider the following:
Crank Rebuild $450-650
New Seals
Balance rods
Balance pistons

This would give you a very exciting street bike that will still pull hard down low, retain the mid and give a strong top end. There may be other ways to achieve...this is just one suggestion. This can be done is phases over time but unless you are ready to drop $3k plus....

Providing the names of people that are very good and know what they are doing is the easy part....you just need to decide how much you want to commit


I'm new to Suzuki 2-strokes after decades of Yamahas, so I don't have a list of resources yet, such as reliable parts suppliers and machine shops so please pardon the newbie questions.
I have a couple questions about this. I have recently purchased a '75 GT750 and am going to build a strong street motor for it. Since I will end up with 34/36 VM Mikunis, which year barrel is better to work with, considering porting, carb mounts, cylinder spacer, etc?
Who supplies Cometics spacers and gaskets?
Also, for a separate project, who can build a race ready pre-mix only crank, and who does the squish head conversion?

Thanks for the help,
Mark

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PostPosted: Sun Jul 08, 2012 9:37 am 
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Moto GP
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Joined: Mon Nov 03, 2008 10:47 am
Posts: 5941
Location: Illinois
Welcome Mark,

Cometic will sell you gaskets direct, but I actually prefer their "normal" head gasket. Copper is harder to seal.

Barrels are easy - they are all much the same as a starting point. Sure, later barrels have taller exhaust ports and some castings have more meat than others, but if you are porting it, it doesn't much matter. We have a motor here running higher compression, stock carbs and JEMCO pipes and it make almost 80 RWHP before it was jetted correctly, so there's a little more to come.

There's really no point in going with pre-mix and it's a lot of work. Bill Bune can make the changes to the crank when he rebuilds your crank with new seals, but crankcases also need to be modified and there's not much point. Keep the pump.

Squish heads are a bit harder. The guy that supplied them stopped doing so after a couple of motors melted down and his heads were blamed unfairly for the problem. You can weld up a head and have it machined, or send it to RK-Tec and have them fit a set of inserts, but they need your barrels to match bore spacing. The biggest cause of failures on high HP GT750 appear to be bores not aligned to heads, oversized OEM head gaskets and poor carburation in the midrange.

Barrels need to be ported and bigger carbs need to be tilted up slightly to clear the clutch cover. And you need a decent ignition system.

JEMCO pipes can make up to 100HP but a motor making 100 RWHP on JEMCOs can make 120 on decent custom pipes. Above a certain power level, they are no longer optimal. For a hot street bike they are not bad. You could try Swarbrick TR750 pipes or get more modern pipes designed and built.


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PostPosted: Tue Jul 10, 2012 7:14 am 
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Still in the Driveway

Joined: Sun May 06, 2012 5:40 am
Posts: 6
Country: australia
Bikes owned: t250
Image
this gt from australia has done 232 mph.
interesting engine
regards
Ben


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PostPosted: Tue Jul 10, 2012 8:08 am 
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Moto GP
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Joined: Mon Nov 03, 2008 10:47 am
Posts: 5941
Location: Illinois
G'day Ben and welcome.

Yep, Brett deStoop has achieved the "impossible" on that one. 6 reed cages, his own cast block, his own squish heads etc etc and over 200HP. Pretty amazing really.


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PostPosted: Mon Jul 30, 2012 1:33 am 
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Yeah Man, the Interstate

Joined: Wed Apr 01, 2009 11:47 pm
Posts: 554
Location: NM USA
3 years and no dyno sheets....... my prediction may come true.....LOL :wink:
Seriously, anything new happening? :up:

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PostPosted: Thu Oct 04, 2012 2:49 am 
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Still in the Driveway

Joined: Thu Oct 04, 2012 1:39 am
Posts: 8
Country: uk
Bikes owned: Gt750 TR750 TR750 Sidecar
here you go, I have always wondered the same lots of bs, but no dyno sheets, can't be that hard to make a jpg?


Attachments:
File comment: Dyno sheet TR750 nothing special.
TR750 Dyno.jpg
TR750 Dyno.jpg [ 174.08 KiB | Viewed 3668 times ]
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PostPosted: Thu Oct 04, 2012 1:28 pm 
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Moto GP
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Joined: Mon Nov 03, 2008 10:47 am
Posts: 5941
Location: Illinois
Thanks James.
That's a healthy motor and enormous speed. :D

What can you tell us about the motor. Was that a "stock" YTR750 with factory pipes etc or a road motor that you and your team modified with special pipes or swarbricks etc?

BTW do you find much advantage with carbs larger than 34mm? I know of a motor making around 12-130hp with very large carbs, but our (MOTA) numbers seem to suggest that the engine is transfer area restricted and that in turns restricts the intake it can effectively use. MOTA suggests that there's a small amount of HP to be gained at peak revs and beyond but losses below the peak. Does the real world support that by any chance?


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PostPosted: Thu Oct 04, 2012 1:30 pm 
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Yeah Man, the Interstate
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Joined: Thu Oct 23, 2008 3:23 pm
Posts: 695
Location: Medina OH
Country: USA
Bikes owned: 1974 Suzuki GT750
Hi James,
Great to see you on the Forum. We talked last month about the TR left hand engine cover and taper shaft. You really make some excellent parts for the GT/TR motor. You should pop-up a link to your website. I think there are a few guys here that read this thread that would be interested to see your stuff.

Hopefully, your dyno chart will keep Ja Moo satisfied for a bit. Im glad you posted.

Regards,
Kevin Hutchinson


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PostPosted: Fri Oct 05, 2012 6:39 am 
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Still in the Driveway

Joined: Thu Oct 04, 2012 1:39 am
Posts: 8
Country: uk
Bikes owned: Gt750 TR750 TR750 Sidecar
Road Motor, with 36mm Mik's TR's 130deg, Ex 196 deg, In 194 deg. Trs are 40mm wide though and opened out significantly from the btm of the cylinder. CR6.2:1 sq 1.5mm, 4.5mm wide. Everything else is normal stuff, Inlets tipped up etc. Pipes are a copy of the TR Spec' and using Zeeltronic programmable Ig sys, with our pickups and back plate. This is what we run in the sidecar so has to be tractable. Also this is driving onto the dyno through a 14" slick, which will reduct the output compared to a motorcycle tyre significantly. Guessing 8/10 bhp down using low pressure tyres on the dyno as a guide.
The transfers limit everything, my initial calcs for this when we started was peak at 7400 rpm, initial runs showed this to be fairly on the money, but only if yr pipes are tuned for the same. If you have pipes carbs etc for 10k rpm, it aint gonna happen, too often the case. We have a single cylinder GT750 motor that we are developing to have 2 or 3 transfers either side and a boost at the back above the inlet but no reeds. Definately better with reeds, but not really in the spirit although it was done in the day. The reed blocks are gonna have to be vast to make it worth it.

Max Torque was 75 ftlbs @ 7250rpm!!!
http://www.bdkraceeng.co.uk/TR750s.html

James


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PostPosted: Fri Oct 05, 2012 8:16 am 
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Moto GP
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Joined: Mon Nov 03, 2008 10:47 am
Posts: 5941
Location: Illinois
Thanks James,

That all makes sense. We found through dozens of runs on MOTA simulation software that big transfers really make a difference, once the intake and exhaust are large enough. The latest set of runs we did had twin transfers which were physically larger than could ever be fitted with twisted ports and that lifted the torque and power curves more or less across the board.

Do you use inserts in that head or welded and machined to a squish shape - or is it a stock quiescent chamber shape like the original TRs?


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PostPosted: Fri Oct 05, 2012 9:54 am 
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Still in the Driveway

Joined: Thu Oct 04, 2012 1:39 am
Posts: 8
Country: uk
Bikes owned: Gt750 TR750 TR750 Sidecar
Welded and machined with O rings, squish head, 1.5mm sq, 4.5mm wide.


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PostPosted: Fri Oct 05, 2012 12:09 pm 
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Moto GP
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Joined: Mon Nov 03, 2008 10:47 am
Posts: 5941
Location: Illinois
Thanks James. That all makes sense. I missed the squish dimensions the first time I read your last response. I'm not sure which TR exhaust dimensions I have on file here but when I plugged your ports into MOTA, the output was impressive but at slightly higher revs, so I may need to look again for the real TR pipe dimensions.

It came up with a BMEP peak of 10.7 Atm. @8000 with the pipe dimensions I used.

The first reed conversion I saw for a GT had the reed petals inside the intake ports. They looked almost stock but fatter and deeper, but not different enough to attract much attention. My preference is Polaris triple snowmobile. MOTA suggests they will work slightly better than the neater, smaller Arctic Cat reeds but I think I need new liners to make it work.


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