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Heavy duty parts for short stroke 750?


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Hi all.

I am asking for some info for some beefier parts for my bike as I am in the middle of building my GSX 750 F -94 engine to better suitable for bigger boost (about 1.0 bar).

My main questions is, are there any HD aftermarket or oem parts like HD studs, conrods or pistons (more of these later on, I want to know your opinion on my idea) that fit the short stroke engine with no or little mods. I don't want to throw thousands and thousands of euros to engine workshops for minor effects on this project.

I know the 1127 or B12 conrods don't fit because of the difference with big and small end holes (btw. short block 750 wristpin is 19mm, not 20mm) and because of the stroke is different also.

I know the engine is not the best platform to start with as 1127 and B12 are bigger cc engines and better suited for boosting as the aftermarket parts are easily available, but this is what I have and this is how I plan to roll to with my faired sleeperbuild.

I have already rode the bike for about 5000 km as boosted with mild pressure (max of 0,65bar and 174hp at the crank) as I don't have an intercooler (I am in the middle of installing my diy water methanol kit though). Now I have disassembled the top end of my engine as I am planning to install a diy spacer under the cylinder block and in the process I noticed small cracks on two of my pistons. On #1 I have a crack between my top and bottom ring on the intake side. This crack goes all the way to the bottom of the ring crooves and contiues hidden there as part of the piston between rings can move a little up and down and I can feel a small high spot on the crack with my nail. On #3 I have a small crack on the top of the top ring and intake valve crevis, which at the moment is only at the surface as the crack cannot be seen at the ring groove. On top of the pistons I can't see any marks of detonation, so this might just be failure of the material?

So my initial plan was to just get two replacement oem pistons, but o boy they are a bugger to find "cheaply" and have always wondered if there would be any better and stronger ones out there.

As I digged around the Eblag and partzilla part numbers I came across DR250/Burgman 250 pistons. They are 73mm bore and 19mm wrist pins and the different heights of this piston is identical to the 750 short stroke oem piston. Only difference that I can see from the pics is that the DR uses flat top pistons and the 750 have crown on them, so the CR would be significally lower and squish would go to hell. The amount how much lower the CR would be ks unknown at the moment. But  have ordered one of these DR pistons

edit: fleabay link removed

to measure if it would be suitable to be run in my engine. Ad states that these are forced pistons (chinese pistons so you can never say for sure) so they should be stronger, right? As far as I have googled the valves are about the same size in both engines but the angle is also unknown, so there might be issues with piston to valve clearance. I know that the CR would drop significally with these pistons but my question is how low I could drop the CR to still have a rideable streetbike? Also the squish would suffer greatly.

As stock this 750 engine have 10.9:1 CR (after 7k rpm though because of valve timing) and on the bigger oilboilers people seem to run as low as 8.5:1 CR when build for boost. These engines are a lot bigger cc though, so the off-boost torque don't suffer that much than it would on a 750 engine. As the engine was unopened on my bike last summer, the bike would start to boost around 4k rpm and at around 6k it would already have near the max boost and a wonderfull screamer soundtrack. (Fyi, turbo is from a 2.0 cdi diesel mercedes, non-vnt). So if I can keep the low rpm turbo spool on my engine that shouldn't effect the rideability too much in my opinion, but that might be wishfull thinking.

 

Ps. Sorry for long post, so here is a link to my bike on youtube making tsu tsu sounds ;)

edit: youtube video link removed

 

 

Edited by IhmeJanneFIN
rules forbid these kind of links
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Other than you having already had the engine - why use the short stroke engine when a long stroke is better suited for forced induction - and easier / cheaper to get hold of!

Regarding the problems, please don't piss around using std cast pistons with boost - they all fail eventually! Forged pistons cost but bring reliability especially with increasing boost.

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6 hours ago, Gixer1460 said:

Other than you having already had the engine - why use the short stroke engine when a long stroke is better suited for forced induction - and easier / cheaper to get hold of!

Regarding the problems, please don't piss around using std cast pistons with boost - they all fail eventually! Forged pistons cost but bring reliability especially with increasing boost.

Thanks, but as stated, this is the engine I have and plan to use for this project for reasons of my own (stupid? maybe? crazy? definately.) so any info for this is still needed if any is to be found at all... I can live with that info also that nothing is to be found. At the moment I only would want to break the 200hp barrier at the crank (my engine dynoed 174hp at the crank last summer), so no need to go further with this build. Maybe my next project after a few other projects in few years will be a B12 turbo or some GSXR with a charger with better aftermarket support.

I know the engine is not the best canditate for more power as stated in my first post. But there are still a lot of people around the world running these short stroke 750 engines (mostly NA i would presume) for some crazy reasons of their own, so can we please, try to gather info of this specific short stroke engine here or show a thread where this info is, rather that tell of the bats "get a bigger engine"?

As far as I know there are this engine specific forced 73mm pistons to be found, but they seem to be higher CR versions only.

So far haven't found any beefier rods that use the same size bearings as stock crank.

1052 crank would fit the cases, but would require much more extra bits and work also.

Cams from few different engines fit. More of those in Frankenstain guide.

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High CR pistons aren't totally off the board - I used 12.5:1 Wiseco's in a 1186 T2'd with 10psi of boost and 35-40 deg of timing whilst using a 2mm decomp plate that took CR down to around 8.5:1 - so thats an option. Using a 1052 crank would be a good option due to the stroke increase - the short stroke 750 is and was designed to be a revvy little bastard with little torque - complete opposite of what a turbo wants to be, they are torque monsters so stroking helps. 

Remember with a will and enough machine tools ANYthing can be made to fit - odd size wrist pins - bore pistons & rods to 20mm or sleeve to 18mm - allows alternatives? Weld and offset grind a SS 750 crank to increase stroke? Stay with base stock cams unless you can afford fresh billet ground turbo cams - short duration better than long with increased lift! 

Not knowing the whole installation, you could may be achieve the target @ 10psi boost up from 7 ? Could be as simple as reducing intake temps with a decent intercooler BTW i'm not a fan of water injection - cure the detonation problem, don't use water to suppress it ! The old TurboBike magazine had a 750 F project with same goal as you but the mag died before the results were published but specs weren't a lot different to yours! They also featured a GPZ750 T making in excess of 200hp so it can be done although that used 72mm pistons and air 2 air intercooling but EFI. So looking for stock solutions to a very un-stock build, whilst economical now aren't necessarily the cheapest long term. Have fun regardless!

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10 hours ago, IhmeJanneFIN said:

 so can we please, try to gather info of this specific short stroke engine here or show a thread where this info is, rather that tell of the bats "get a bigger engine"?

 

Ask not what OSS can do for you but what you can do for OSS.

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Posted (edited)
7 hours ago, Gixer1460 said:

High CR pistons aren't totally off the board - I used 12.5:1 Wiseco's in a 1186 T2'd with 10psi of boost and 35-40 deg of timing whilst using a 2mm decomp plate that took CR down to around 8.5:1 - so thats an option. Using a 1052 crank would be a good option due to the stroke increase - the short stroke 750 is and was designed to be a revvy little bastard with little torque - complete opposite of what a turbo wants to be, they are torque monsters so stroking helps. 

Remember with a will and enough machine tools ANYthing can be made to fit - odd size wrist pins - bore pistons & rods to 20mm or sleeve to 18mm - allows alternatives? Weld and offset grind a SS 750 crank to increase stroke? Stay with base stock cams unless you can afford fresh billet ground turbo cams - short duration better than long with increased lift! 

Not knowing the whole installation, you could may be achieve the target @ 10psi boost up from 7 ? Could be as simple as reducing intake temps with a decent intercooler BTW i'm not a fan of water injection - cure the detonation problem, don't use water to suppress it ! The old TurboBike magazine had a 750 F project with same goal as you but the mag died before the results were published but specs weren't a lot different to yours! They also featured a GPZ750 T making in excess of 200hp so it can be done although that used 72mm pistons and air 2 air intercooling but EFI. So looking for stock solutions to a very un-stock build, whilst economical now aren't necessarily the cheapest long term. Have fun regardless!

Thanks. Fun is the exact thing I plan to do with this project.

Good thinking about the pistons.

I would have wanted to run an intercooler as it would so much easiers than to fill up with "boost juice" time to time, but the space at front of F is very limited. And I don't have equipment or skills to do alu welding for an intercooler. Even my turbo is at about an 45 degree from transverse to allow clearance for front wheel and my air cleaner is poking a little bit past my righthand front fairing. Looking at pictures of B12 turbos I would say i have about half the space between engine and front wheel, as my exhaust runners are basically nonexistance as I run a log style manifold.

Basically what this bike is, it's a learning platform. It's my first ever turbo build so my plan is to do things "cheap" and somewhat differently at some things and check what works and what doesn't. Take notes and try to replicate the good ideas and toss away the bad ideas for the next boostproject in a few years.

Btw, about my setup. The turbo I am using is a GT20 from a 2.2 liter CDI diesel merc (3 bolt pattern). At the merc it is cabable to do a little above 200hp, so my hope is it would do the same on my build. As this GT20 is from a diesel engine, it has a bit smaller exhaust housing as it's petrol variant, it likes to start building boost at quite low rpm. Also because of that I haven't found a specsheet for this turbo. This turbo is a non-VNT variant. Would like to try out a VNT for the kicks of it at some point. The turbo cost me 50€ so what the hell, I just slapped it in there as a try to find out if would even boost before redline. I was quite pleased to find out it boosted quite early actually and still revs to redline quite easily.

Because I didn't have any intercooling last summer, the torque started to die at higher rpm quite quickly, so my high intake temps might have been the cause. On my katriders site the dyno sheet can be seen and other bits of my mods.

https://katriders.com/forum/service-department/exhaust-mod-shop/2120086-yet-another-turbo-build-but-bike-is-actually-running-already

I am also still running stock ignition with +4 degree timing by turning the base plate of my ignition (yeah i know, crazy) but it still works even at redline with JR9B plug gapped smaller. With original gap it started to misfire near redline. Some point I wish to update to atleast dyna coils or even to full programmable ignition (Speeduino maybe, Dyna 2000 is quite expensive for my taste).

Fueling is still done by original 36mm carbs with a bit smaller main and pilot jets actually. Malpassi 1:1 fuel regulator with about 2-3 psi base fuel pressure. I also have factory pro needles at the moment on, cause it works best with those on off-boost situations. If I floor it before boost it goes too rich at around AFR 9, but once it starts boosting the AFR goes to around 11,5-12 and stays near that to redline. With oem needles it was jerky on off-boost situations and I rarely floor it so the AFR stays quite nicely around 12 at low throttle openings at off boost situations. Might try some stiffer springs at the carbs to slow down the slides with the factory pro needles as I think they rise too fast which then causes richness (or I am thinking this wrong)?

Cams and timing are original, but plan is to make adjustable gears and try the 110/110 timing.

Exhaust what I had last summer was a single Viper can on the right side. Now I have updated to 2 cans purely just for the looks. Exhaust was and still is 2,5" from turbo to can(s). Can outlets are around 55mm. Boost was originally controlled with the internal wastegate but that proved to be insufficient so moved to turbosmart style external wastegate with screamerpipe.

Maybe I should make a new thread of my build, and try to keep this topic focused to the actual engine (addes some pics of my bike) :D

 

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Edited by IhmeJanneFIN
writing errors
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Posted (edited)
1 hour ago, Hanma-shin said:

It’s not a katana, RTFR 

Uuuuhmn, I haven't said that word on this site, have I? O.o I myself know it only as GSX 750 F, as that is what reads on the fairings and I have spoken about this bike as an F, right?  And I put that "name which should never be pronounced here in this site"  in parentheses to the youtube video name only as clickbait for my the fellow bikerfriends on the other side of the big pond also known as Atlantic ocean :D okay, maybe i should't have posted the video and fleabay link in the first place as for the sacred rules, so why I decided to remove the links so you wouldn't loose your good night sleep because of me :P

Edited by IhmeJanneFIN
typo
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7 hours ago, mikeyd said:

Very clean build, I like the turbo placement and keeping it within the fairings. 

It has been one of my stupid goals with this to keep the oem looks, so bike looks as ugly as it is with them, expect the back end is swapped from a 600 purely for "better" looks.

 

6 hours ago, Hanma-shin said:

Sleeper for sure

Then I would consider the looks a success. Thanks.

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  • 4 weeks later...

Been thinking the pistons for my project as I found signs of starting failures on my oe cast pistons. I noticed that k1 k2 gsxr 1000 has 73mm and from looking at pictures they seem to be forged pistons, but 16mm wrist pins. So my thought was next: can i bush the oem conrods 19mm small ends to 16mm using properly sized bushes (obviosly at engine shop)? I have no idea if the pistons height and any other dimensions would work for the short block engine to make decent compression for turbo and not hit the valves. Anybody has any info on this?

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  • 2 months later...

@IhmeJanneFIN

glad to see another 750 turbo project on the go! There aren’t as many out there as the other bigger bikes. I’ll be following ya on this one. I’ve done a 750 turbo myself, but I used a 750L as my mule. I don’t know much about the short stroke 750’s, but there seems to be a lot out on the road still! In Canada at least..
 

I’ll be starting my second turbo bike project shortly- my platform will be a GSXf600. Target HP will be around 200. After discovering all the similarities the 600’s have with the long stroke 750’s, I can’t wait to see how the end result will work out! I have several longstroke 750 motors , and recently picked up 2 mostly complete gsx600F’s. I just need a place to work on them now 

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On 7/18/2021 at 8:11 PM, Jmckechnie said:

@IhmeJanneFIN

glad to see another 750 turbo project on the go! There aren’t as many out there as the other bigger bikes. I’ll be following ya on this one. I’ve done a 750 turbo myself, but I used a 750L as my mule. I don’t know much about the short stroke 750’s, but there seems to be a lot out on the road still! In Canada at least..
 

I’ll be starting my second turbo bike project shortly- my platform will be a GSXf600. Target HP will be around 200. After discovering all the similarities the 600’s have with the long stroke 750’s, I can’t wait to see how the end result will work out! I have several longstroke 750 motors , and recently picked up 2 mostly complete gsx600F’s. I just need a place to work on them now 

Glad to hear that someone else is also mad enough to build these smaller engines.

At the moment my engine is in parts as I try to build a "stroker" engine with different crank and rods, but use the original lower end and block & bore with k2 gsxr 1000 forged pistons. So I need quite a big spacer to lift the block. And I am trying to limit the spacer height, so I ended up trying shorter conrods.

Everything on this engine build is still unsure and very experimental, so I have no idea if it would even work. Will try to post results if I get it done.

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