The road to over 100hp- easy enough with a GT 750?

Getting your blazingly fast Suzuki powerplant to perform even better!

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cruisingram
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The road to over 100hp- easy enough with a GT 750?

Post by cruisingram »

How hard and expensive is it to get over 100hp from a GT 750, and where do you begin to collect parts to do a build up like this? What mods are the best bang for the buck? At what point does it become problematic and not very cost efficient to build over X HP/

I mean, what HP could a pretty decent mechanic with some mail ordering skills get out of a GT 750?

Where would you start?
jaybob
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Post by jaybob »

Here is a good place to start reading...

http://smokeriders.com/Technical/Suzuki ... ocket.html
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tz375
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Post by tz375 »

100 rear wheel HP? It's not impossible but that wouldn't be a trivial task either.

TR750s made that sort of HP but they weren't exactly street bikes. There are several ways to approach that number depending upon your skill and the depth of your pockets.

For an outrageous street racer, follow the TR750 route. It will be barely streetable and hard to keep in the powerband, but a rush if you could. You do that by raising the barrel with a spacer, porting the motor , fitting 40mm carbs on modified intakes (more downdraft), higher compression, Swarbrick pipes, close ratio box, dry clutch etc. It will tend to rev rather high so budget for rod replacements at frequent intervals too.

Or you could follow the old big bore route. That requires a little more ingenuity to design new liners and port them the way you want them.

Of course both ways round, you still run out of exhaust port area and transfer area, but with new liners you can bridge the exhaust port and when you are welding up the block, and moving studs, anything is possible.

So the best way to get there IMHO is to build a reed valve motor with additional boost ports. Of course that really needs pistons with ring pegs in a different place, but that's not too hard. The reed conversion gives you scope to change the transfer porting and add intake port area without the bad effect of too much intake timing. You really want to add a modern squish head to that package and the exhaust ports will end up very wide, so the shape is important and so are the rings you choose to use. Add in custom designed pipes and another $1000 or so to change to Fuel Injection and you should have a nice package.

On a realistic budget, I'd get a set of JEMCO pipes, 34mm flatslide carbs, get Eric on this board or Scott Clough, or Bill Tripp to port the barrel. Raise the CR and if you are very talented or lucky you will be getting close to 80Hp in a fun package.

Lane, What are your thoughts? Blueboy is one of the more powerful GT's around

Shannon has been involved with some high HP motors in Australia and as I understand it, there are years of experience buried in those projects.
rngdng
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Post by rngdng »

Mine dyno'd 80 rwhp, and it's still very streetable. Getting twenty more would require going all the way to TR specs, and I don't think it would be very user-friendly. However, if the cylinders were reeded, you could go to TR specs and be much more usable.

Dave may well break the 100 hp barrier with the radical porting in his current project, but look at the amount of effort he's putting into it.


Lane
If you stroke it more than twice; you're playing with it.

Too many bikes, too much time, ENOUGH SPACE, FINALLY! Never enough money.........
cruisingram
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Post by cruisingram »

rngdng wrote:Mine dyno'd 80 rwhp, and it's still very streetable. Getting twenty more would require going all the way to TR specs, and I don't think it would be very user-friendly. However, if the cylinders were reeded, you could go to TR specs and be much more usable.

Dave may well break the 100 hp barrier with the radical porting in his current project, but look at the amount of effort he's putting into it.


Lane
How much does the GT 750 lump weigh? I could live with 80hp.
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tz375
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Post by tz375 »

Lane, did you get that 80hp with VM34s or with the stock BS40's?
rngdng
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Post by rngdng »

tz375 wrote:Lane, did you get that 80hp with VM34s or with the stock BS40's?

VM34s. The bike still weighs right at 500 pounds, but several H2 riders have ridden it and liked it. It's not quite as fast as many H2s, but it does quite well.



Lane
If you stroke it more than twice; you're playing with it.

Too many bikes, too much time, ENOUGH SPACE, FINALLY! Never enough money.........
Kris Bernstein
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80 RWHP is okay but....

Post by Kris Bernstein »

If you are not a purest, put the bike on a diet!
Magnesium rims, aluminum swing arm, aluminum tank, fiberglass seat.
Add lots of titainium fasteners, magnesium shocks, triple clamps, CRM Crome Moly Frame...

Ha! What's your budget. I'm doing one up now and will set aside about 15 thousand dollars. You could buy a ragged RG or TZ750 for that but the wet triple is just fun to play on. Call me crazy but I just got a set of Ohlins forks for the project. Very light and modern radial stoppers!!!

PS: A lightened crank and strait cut primary gears (Nova Racing), will also shave four pounds of reciprocating weight and allow a 10,000 RPM redline,
but plan on rebuilding cranks "more often"....
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tz375
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Post by tz375 »

Kris,

With that sort of battle plan, I would hope for a little more than 100HP. For a little more you could add a reed conversion, maybe even go to 1000cc, 6 speed CR box etc

What is that saying? Go big or go home. :twisted:
cruisingram
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Re: 80 RWHP is okay but....

Post by cruisingram »

Kris Bernstein wrote:If you are not a purest, put the bike on a diet!
Magnesium rims, aluminum swing arm, aluminum tank, fiberglass seat.
Add lots of titainium fasteners, magnesium shocks, triple clamps, CRM Crome Moly Frame...

Ha! What's your budget. I'm doing one up now and will set aside about 15 thousand dollars. You could buy a ragged RG or TZ750 for that but the wet triple is just fun to play on. Call me crazy but I just got a set of Ohlins forks for the project. Very light and modern radial stoppers!!!

PS: A lightened crank and strait cut primary gears (Nova Racing), will also shave four pounds of reciprocating weight and allow a 10,000 RPM redline,
but plan on rebuilding cranks "more often"....
I build chrome moly frames- so that does have some part in my plan. I moslty want the "best bang for the buck" to get the max HP without breaking the bank.

Anyone know how much the lump itself wieghs?
Last edited by cruisingram on Sat Apr 18, 2009 12:15 am, edited 1 time in total.
Kris Bernstein
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Go Big if necessary...

Post by Kris Bernstein »

Never been a fan of HP numbers but the plan for the current GT project is to run it with the AHRMA open two stroke guys at Barber, Mid Oho, etc.

I agree the first order of business is reed conversion as it some what solves the lack of transfer area, in the GT design and better controls intake.
A 300cc cylinder was a proven design and should help if pistons can be sourced
that don't weigh a ton.
Six speed gear boxes are not likely any time soon. Graham Dyson at NOVA recently took loan from Paul Smart, one of the original TR six speed gear boxes for evaluation. Graham dismissed the item as a less than good design and most likely sent it back to OZ. We've never had a problem with the five speed box but everything's a compromise with this motor.
But still we go on....

Kris
Kris Bernstein
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Oh it does get sicker!!!

Post by Kris Bernstein »

The magnesium triple clamps arrived today for the current GT project.
Truly the Italians have a way with casting the sacred metals of the gods...
Will post pictures as soon as time allows but wanted to get the suspension goodies prior to ordering the frame from CMR.
A period monoshock design is planned with Ohlins damping front and rear.

Kris
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tz375
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Post by tz375 »

Kris,

You can get a lot more transfer area than at first appears and still have good flow, but it looks like it hits a wall at about 100 (ish) on my computer at least. You can steal a little at the bottom to maintain the right duct shape.

After that you need extra ports and reeds are the "easy" way to get that, but then the ring pegs start to get in the way and all the ports are still at odd angles.

After that exhausts start to become problematic unless it's bridged and/or you have thin flexible rings than can stand the abuse.

When you manage to get enough exhaust area, the exhaust outlet is then too small for good flow and so it goes on.

When you machined the flywheels to drop weight did you measure the primary CR by any chance. I have been avoiding that messy job and need to know the bottom end volume. Fortunately those long rods, keep it down a little.
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tz375
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Post by tz375 »

From teh pictures I've seen of Ocelot motors, it looks like they had the pistons made by Wiseco and finished machining them in house.

With the handed pistons, that needs to two sets of dies, and Ocelot cut their costs by making On piston blank and used a steel "mask" to do the transfer port cutouts.

Unfortunately that makes for a heavier piston and on those thin rods, that's not a good idea. A set of XCR800 Polaris rods would work with new big end pins but the flywheels would need a lot of metal off to drop the primary CR.

We looked at Mercury V6 pistons but they are pretty huge and some of the Wiseco V6 boat pistons might work with a new set of liners. But why not rotate the ports to normal position and cast a new block with smaller water passageways, etc.

Now it comes to me. get the guys who cast Cheetah blocks to cast up a new modern block. CNC machine a billet set of cases to take a GSXR100 gearset (which happens to be very similar to a stock GT set by the way) and watch teh TZ750s disappear the the proverbial rear view mirror.

Next time you speak to Graham Dyson, ask him about designing a gear change to allow a GSXR cluster to work in a set of GT cases. It's not quite that simple or esle we'd all be doing it, but Graham is smarter with that stuff than most of us.

Now where's that old lottery ticket?
Kris Bernstein
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So correct!

Post by Kris Bernstein »

You are so correct, my friend. It was bantered about that Sheene used an 850 motor on occation, back in the pre-silencer era and I'm certain that was to good effect.
Did primary compression ratio on our old T500 racers but that's sorta apples and oranges with this motor. No doubt we will loose some primary compression with the lightened crank but the numbers will have to wait.
Osolot and Jeff Bratton used cork and epoxy stuffers in their Swiss Cheesed
crank wheels to get back what they took away. But how to explain the H2 crank
with webbed wheels and their working just fine?

Kris
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