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Thread: Gs750

  1. #1
    Join Date
    1st June 2014 - 21:23
    Bike
    Ducati 748R
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    nelson
    Posts
    159

    Gs750

    Hey guys,

    My current ride is a aprilia rsvr but I'm working on a new toy so i thought I might share my project it's a 1977 gs750 motor in a 1981 gsx 750 frame I was given a rolling chassis a motor and a whole heap of stuff in boxes. I've been sitting on this for awhile because I couldnt decide what to do with it or if it was actually worth putting time into but I aquired a turbo ..... that sparked some ideas so I hope to have a cheap rego bike that I can ride year round with a turbo!

    i wish i had taken pictures of the bike from the day i got it, imagine 18 years sitting in the top of an old shed... it was home to all kinds of fury critters.

    The motor is a total unknown it came from a TQ midget, all this is fabrication is a first for me so feel free to critique and share a better way to do anything.

    I'm chewing over ideas how to feed the turbo I'm thinking a seperate system fed by a scavenge pump, the motors oil pressure is far to low to feed a turbo because it's a roller bearing crank, well this is what I'm told anyway, I've managed to take the exhaust housing off the turbo so I can index it, what a pain in the ass that was.

    Anyways I'm fabing up an exhaust to feed the turbo at the moment, I just bent the headers because they where mangled now I'm just starting to make a 4 into one collector.

    20180522_204408
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    20180522_204145
    20180522_204122
    20180522_204322

    Sorry about poor quality pictures! must of had some dirty prints on the lens! ill upload better ones tomorrow.

    ive just raised the bars on the aprilia by 20mm with a spacer and in the process of geting new brake lines and grips and leavers, its a rsvr converted to tuono

    Ha, i just realised i put the swing arm upside down. i just needed to test fitment of exhaust piping.

  2. #2
    Join Date
    3rd February 2004 - 08:11
    Bike
    1982 Suzuki GS1100GK, 2008 KLR650
    Location
    Wallaceville, Upper hutt
    Posts
    4,251
    The GS IS a roller bearing crank so you are right about that. It's possible to twist the crank with big HP numbers (because rollers = seperate pieces pressed together) it was common for GS/GSX motors to have welded cranks when used for drag racing.
    Fueling with the turbo may be interesting - what is the plan? blow/suck or injection?
    it's not a bad thing till you throw a KLR into the mix.
    those cheap ass bitches can do anything with ductape.
    (PostalDave on ADVrider)

  3. #3
    Join Date
    1st June 2014 - 21:23
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    Ducati 748R
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    nelson
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    159
    Quote Originally Posted by pete376403 View Post
    The GS IS a roller bearing crank so you are right about that. It's possible to twist the crank with big HP numbers (because rollers = seperate pieces pressed together) it was common for GS/GSX motors to have welded cranks when used for drag racing.
    Fueling with the turbo may be interesting - what is the plan? blow/suck or injection?
    Yeah.. but I also read that gs750s and gsx 750s from 70s to 82 have larger oil pump gears . I don't know what to believe I think I just need to have a look and count the teeth.

    For fueling I'll need to plumb a fuel pump in with a pressure regulator to keep the fuel pressure higher then the boost, I only want to run ~7 pounds, nothing crazy. Aparently the best way to do it is rob parts from a common rail diesel.

    It's going to be a blow through system

  4. #4
    Join Date
    3rd February 2004 - 08:11
    Bike
    1982 Suzuki GS1100GK, 2008 KLR650
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    Wallaceville, Upper hutt
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    What carb(s) are you going to use? And what is the turbo? I have read of, but have no experience with, ball bearing turbos, would they work with the Suzuki oil system?
    I did a blow thru turbo 1440 mini for speedway years ago. IHI Rhb41 turbo, used a DCOE Weber with sealed ball bearings for the throttle butterfly shaft and Del'orto floats (plastic) because the brass Weber floats collapsed with boost pressure in the float chamber. I made a regulator to maintain fuel pressure at boost + a couple of PSI. Fuel pump was Triumph PI (this was in the days before you could buy everything you need off the shelf). Made a good reliable 130 at the wheels with no more than 10psi boost.
    it's not a bad thing till you throw a KLR into the mix.
    those cheap ass bitches can do anything with ductape.
    (PostalDave on ADVrider)

  5. #5
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    1st June 2014 - 21:23
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    Ducati 748R
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    nelson
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    yeah a ball bearing turbo would work but i got this turbo for a steal and its in very good shape.

    im going to use mikuni slide carbs but i have another set in a box that looks complete, the turbo is a mitsubishi turbo from a 1.8L diesel van unsure of what model it is.. i know its a journal bearing turbo with 35mm exhaust inlet and 35mm inlet for air, this will be a steep learning curve but im up for the challenge. as i said above im all ears for the "best" way to go about this project.

    heres a question, so beucase the exhaust housing has a 35mm inlet does that mean i want to run 35mm exhaust tube from the headers to the housing?

    i really want to go finish welding and beet it into shape, but i dont want to be that "neighbour"

  6. #6
    Join Date
    3rd February 2004 - 08:11
    Bike
    1982 Suzuki GS1100GK, 2008 KLR650
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    Wallaceville, Upper hutt
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    Look for this book by Hugh MacInness https://books.google.co.nz/books/abo...MC&redir_esc=y Its an old one but a goodie. MacInness patented the floating sleeve bearing used by Rajay - knows what he talks about.
    Goes into great detail about matching and sizing the turbine and compressor to the air flow the engine requires. While just about 'any" turbo can deliver boost, making useable power requires a little more precision.

    One of the problems with a used JDM turbo is that it has probably been designed for a specific engine, and that getting a compressor map (to work out the sizing) is near impossible.

    But beat of luck with your project. I love both GS Suzukis and turbos, so i'll be following. Keep updating.
    it's not a bad thing till you throw a KLR into the mix.
    those cheap ass bitches can do anything with ductape.
    (PostalDave on ADVrider)

  7. #7
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    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Lower Hutt
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    1,074
    Looks interesting, +1 on keep us updated. I haven't done any practical work with a turbo yet so can't help there sorry.

    Photos I can help with though - what are you shooting with?

  8. #8
    Join Date
    24th April 2016 - 19:07
    Bike
    2001 zx9
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    bop
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    26
    The book Pete refers to would be a good bible to have on hand for this project for sure... For the oil pressure issue on the kawasaki 1000s (roller crank also ) a 1/4" restricter was fitted adjacent to the flow/pressure switch (after the pump before the engine) which bumped up the pressure available for the turbo. the turbo oil take off of course was before the restricter. the volume of oil from the pump was enough to look after the engine and turbo no problem.
    Given power is closely related to mass airflow through an engine a rough guide would be to look at the power of the turbo's original engine (100 hp or so ?) and if that matches your expected power of your engine then you'll be in the ballpark - again roughly. I have seen a nicely matched turbo on a 1100cc bike (mid-range boost through to massive top end) that was sized for a 2.5 L car engine ...
    One school of thought on the headers is that you want to preserve energy in the exhaust stream so go for smallish headers into a tidy collector that would be matched to the turbo inlet - this should help it climb onto boost early(ish).
    If the crank is good and clocks up nice then welding the pins would be a good move as mentioned, as while your tuning it/setting the boost it would be easy to "over-do" it and wreck it...
    It wouldn't hurt to ease the compression a bit because detonation will be always waiting to dive in and wreck it too. Good luck with it.

  9. #9
    Join Date
    1st June 2014 - 21:23
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    Ducati 748R
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    nelson
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    alright guys thanks for the info, im trying to decide where to mount the turbo, originally i was going to mount it up behind the carbs but now maybe below the swingarm is a better idea due to pipe routing... if i come up though the side it will be right by my leg and i dont fancy cooking my leg.. i could make a heat shield but i would be coming out 2.5 inch from the frame if i mount it below the swing arm i dont have any exhaust routing issues but i have oil feed issues .

    dealing with intercooling pipe is easier then hot exhaust pipes, i did think about puting a hole in the swing arm and routing the pipes though that but i think ill end up with issues come cert time, theres not much beef to the standard swing arm as it is.

    i need to tweek the headers some to make em more inline, ill get onto that tonight and finish welding the collector.

    i was advised by a few local people that 2 inch exhaust to the turbo is a good idea with a 4 into one i would choke the motor if i went too small.

    the motor produces around 60 horse standard, if i can get 80-90 horse ill be happy, the standard compression is 8.7:1 a guy at turbo NZ said as long as i dont get silly about boost that should be fine, he knows someone with a gs1000 a running standard motor with 10PSI boost and its been reliable .

  10. #10
    Join Date
    24th April 2016 - 19:07
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    2001 zx9
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    bop
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    I think it'd be a good idea to get hold of Hugh Maciness' book and study that before you go too far - you need to have good info to base your planning on rather than unknown people on the internet and well meaning mates .

  11. #11
    Join Date
    3rd February 2004 - 08:11
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    1982 Suzuki GS1100GK, 2008 KLR650
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    Wallaceville, Upper hutt
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    The most successful of the Japanese turbo bikes was the GPZ750 (didn't hurt that all the others were 650s) - they had the turbo down the front. The thinking of the time was to keep the headers short, to preserve the heat energy. Make them out of bends of steam pipe (thicker than regular muffler moly). Expect them to crack regularly. Don't worry about the weight, if it works you'll have more power than you know what to do with anyway.
    it's not a bad thing till you throw a KLR into the mix.
    those cheap ass bitches can do anything with ductape.
    (PostalDave on ADVrider)

  12. #12
    Join Date
    3rd February 2004 - 08:11
    Bike
    1982 Suzuki GS1100GK, 2008 KLR650
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    Wallaceville, Upper hutt
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    Lots of very good information here - https://www.turbobygarrett.com/turbo...ompressor_maps

    (Found while perusing a GPZ750 website http://www.750turbo.com )
    it's not a bad thing till you throw a KLR into the mix.
    those cheap ass bitches can do anything with ductape.
    (PostalDave on ADVrider)

  13. #13
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    13th June 2010 - 17:47
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    Exercycle
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    Out in the cold
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    4,776
    Couple of points - the oil pump drive gears you want are those from the plain bearing GSX750 engine. They drop into all the roller bearing GS's and up the oil pressure significantly.
    750 from a TQ and found in Nelson....If it's got a ported head I probably did it. The roller 750's were not popular for TQ's - heavy - but I did one down here which promptly disappeared up to Nelson.
    Reason is a tool - remember where you left it..... The late, great, John Clarke

  14. #14
    Join Date
    1st June 2014 - 21:23
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    Ducati 748R
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    nelson
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    I got the collector finished off, and I found a Harley oiling system, it's a pump and scavenge in one so I may try graft that onto the motor.. I also have some demensions of a oil restrictor that some people have used and I've been talking to various people online who HAVE put a turbo on these bikes some are just running on the low pressure system with no problems some have fabricated full oil pumps

    I have no idea if the motor has had any work I haven't opened it up yet, but if it's been ported I'll let ya know!

    Slow progress as I ran out of argon trying to problem solve some welding problems so I had to finish the collector with the mig horrid Flux core wire, I'll definitely buy some 309 stainless rods sick of shite tig welds with the rods I have.

  15. #15
    Join Date
    1st June 2014 - 21:23
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    Ducati 748R
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    nelson
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    20180602 110208
    20180602 110252
    20180602 110547

    Excuse the welding Flux core is a total pig
    I'll look into the 750 GSX oil gears because that's much cleaner and less messing about

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