77 gs750 turbo set up help

[OldSoul67]

I'm looking at doing a turbo set up on my gs750. nothing to big just 5-7 psi. My two big questions is what size turbo would work best? and what's the best way to adjust timing? I'm still on the original points system. The top end has also been redone with a Weisco Big Bore kit making it an 850 with 10.25:1 compression roughly.  

[Gixer1460]

I'd talk to a Garrett, IHI or Mitsubishi turbo distributor and ask their advice as they should be able to calc the right core, housings and wheels to suit, otherwise its guesswork. But you are probably looking at something like a GT15 (that is just the family - many variants of that basic unit). Anticipate max. 120hp @ 7psi and peak power at 8,500 - 9,000rpm. You can keep the points although the whole system may be lacking under boost pressure. Slotting the backplate to allow movable timing is easiest way - better way is swapping out to a more 'modern' electronic system . . . . a Dyna 'S' may suit. The Wiseco pistons are good IF you can stay away from adding a 'bit more' boost, as at 10+ :1 CR, much more will induce detonation especially with std pump gas!

[Reinhoud]

I had a VF20 turbo on my GS1000 with 1245 big bore.

Turbo was on the small side for mine, but probably would be good on a 750, this is a ball bearing turbo.

 

[OldSoul67]

14 hours ago, Gixer1460 said:

I'd talk to a Garrett, IHI or Mitsubishi turbo distributor and ask their advice as they should be able to calc the right core, housings and wheels to suit, otherwise its guesswork. But you are probably looking at something like a GT15 (that is just the family - many variants of that basic unit). Anticipate max. 120hp @ 7psi and peak power at 8,500 - 9,000rpm. You can keep the points although the whole system may be lacking under boost pressure. Slotting the backplate to allow movable timing is easiest way - better way is swapping out to a more 'modern' electronic system . . . . a Dyna 'S' may suit. The Wiseco pistons are good IF you can stay away from adding a 'bit more' boost, as at 10+ :1 CR, much more will induce detonation especially with std pump gas!

I'll see if I can get in touch with those companies and see what they say. I already have my rings gapped pretty wide so i'm not too worried about that if i do go higher on the boost. Knowing me it'll be "a little more won't hurt" at some point, but ive got a gas station down the road that sells VP fuels and i don't take the bike out too often so I'm not against running race gas. I did see that dynatech made a digital points system but i wasn't sure if they had a spark control module to control timing as well or if it would be similar to setting up the points where its just the mechanical advance.

[OldSoul67]

13 hours ago, Reinhoud said:

I had a VF20 turbo on my GS1000 with 1245 big bore.

Turbo was on the small side for mine, but probably would be good on a 750, this is a ball bearing turbo.

 

I'll look up some numbers on that size and see what i can come up with, that might be a good option especially the fact that its ball bearing since the gs750 doesn't make a lot of oil pressure

Edited September 16, 2022 by OldSoul67

[Gixer1460]

The Dyna 'S' does rely on the mechanical ATC but has used this for ages - tried, tested and quite reliable!

Re : Oil pressure / GS's / Turbo's - if you can get the pressure up to about 30psi, its sufficient for plain and ball bearing units. Just because you may have a ball bearing cartridge doesn't mean low oil pressure is ok as most have a plastic bearing race that needs the oil flow in sufficient quantities to stop the plastic melting!

Wide ring gaps isn't necessarily a 'good' thing as blow-by into the crankcases brings its own problems! A ring gap set for NA with 2-3 thou extra is about right IMO

[OldSoul67]

11 hours ago, Gixer1460 said:

The Dyna 'S' does rely on the mechanical ATC but has used this for ages - tried, tested and quite reliable!

Re : Oil pressure / GS's / Turbo's - if you can get the pressure up to about 30psi, its sufficient for plain and ball bearing units. Just because you may have a ball bearing cartridge doesn't mean low oil pressure is ok as most have a plastic bearing race that needs the oil flow in sufficient quantities to stop the plastic melting!

Wide ring gaps isn't necessarily a 'good' thing as blow-by into the crankcases brings its own problems! A ring gap set for NA with 2-3 thou extra is about right IMO

I'm guessing the best way to get the pressure up would be testing out some oil restrictors to get it where I need. I had done some calculations for what the ring gap should have been for approx. 7psi however when i went and measured the rings they were already a little over that, but my piston to wall clearance was just about perfect. I don't remember off the top of my head what the measurements are but i've got them in a notepad for the bike. 

[Reinhoud]

On 9/16/2022 at 10:24 AM, OldSoul67 said:

I'll look up some numbers on that size and see what i can come up with, that might be a good option especially the fact that its ball bearing since the gs750 doesn't make a lot of oil pressure

You won't find any info of that turbo..