Yoshimura GS750 8V exhaust?

[Chuck78]

Does anyone know specifically if Yoshimura ever made exhausts specifically for the GS750 8V aside from pipes made specifically for their first team Yoshimura race bikes that were 944cc 1977 GS750's?

My buddy is looking to possibly buy a GS750 with an early Yoshi exhaust, which I want to get from him badly (swap a different 4:1 onto it for him), but I am skeptical of whether or not it was specifically a GS750 pipe, or if it was a taller GS1000 pipe bolted to a 750. I have no photos of the pipe yet, but the bike was in pieces so he could not tell if there was a lot of clearance between the collector and the oil pan (i.e. hanging lower because it was a GS1000 pipe for the longer stroke taller engine)

[Chuck78]

A google image search only yielded a couple of results. These from Japan:










This awesome vintage race bike for sale (does not say specifically if it is a Yoshi exhaust, but looks quite possible:

http://www.michaelsmotorcycles.com/1978SuzukiGS750712.html

[Chuck78]

And this bike that was modified when it was nearly brand new off the showroom floor to near it's current state Tracy one piece bodywork and all, just freshened up, bars and fairing added http://www.sportwheel.com/listing/19...i-gs750-tracy/ (it specifically says this is a Yoshimura pipe):

[Chuck78]

Alternate to Kerker/MAC present pipe and Yoshi if GS1000 model

My buddy who is quite the vintage motorcycle expert said it is definitely an early Yoshi pipe, but has a non-yoshi baffle in it. Says it has a TIG welded on Yoshi name tag on it even, definitely the real deal. some minor dents and needs stripped and refinished, but this is the kind of thing I dream of acquiring for this build IF it is meant for a 750 specifically, for ground clearance reasons I am worried that it would maybe be a GS1000 pipe (that WOULD bolt directly to a 750 but hang lower)


I'll be putting it on a Rickman CR900 frame that I got with GS1100E engine mounts, but I am converting the lower mounts to GS750 position and getting some custom JE 894cc pistons. I have a MAC header and Kerker System K aluminum muffler but I have to fab a custom mid pipe from some v-twin pipe that should work out fairly well. The Yoshi exhaust would be far cooler. I am hoping it is tight fitting to the oil pan and frame and not a GS1000 pipe, as the Rickmans run a very low front end and very short forks, so ground clearance is imperative. If this doesn't work out I may save for a Marving flat collector upswept 4:1 to gain extra ground clearance.

Marving:



Suzuki GS850G with Marving 4-1 Race S/32/BC

[Chuck78]

He texted me a picture of one he said was the same style, THIS:





He did tell me Yoshi series 1. I found this on kzrider:
"my original series 1 had yoshimura racing engraved on about a 2 mm plate that was welded onto the muffler."

you can see the welded on name tag he mentioned on this GS1000 pipe:

[steve murdoch]

I think the MotoGPWerks early systems were supposed to be Yosh replicas.
They did make some for the GS750.

https://www.google.ca/search?q=motogp+werks+exhaust&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjx5uGI_5jMAhUquoMKHXVZBS8QsAQILg&biw=1280&bih=871#imgrc=_

[limeex2]

The turquoise bike and the bike with the tracy body have close to the same pipe. I had one on my Gs750. I will look in my old pictures and see what I can find.

[Chuck78]

Please do!


I have been thinking that I might just get the exhaust regardless, and if I don't like the ground clearance, the local vintage Japanese salvage shop has a GS1000 engine on the shelf, and a GS1100G that just came in with a good donor top end! The 894cc GS750 with good cams would be plenty adequate however, but an original Yoshi exhaust may warrant swapping engine plans....

I don't think I would gain any weight on the bike overall by swapping a kick-start only gs750 for an electric start only GS1000 with its lighter crankshaft to offset the added starter and battery weight... that is a lot of power on a lightweight bike though, more than adequate to say the least.
These Yoshimura Isle of Man cams would do much better on a large displacement bike in terms of idle quality and low end performance on the street, than what they would do on a gs750 big bore, although I could degree them with less valve overlap and for more low end, and get them to work quite well on the 894cc. .354" lift would be a lot more forgiving in terms of longevity than .380" or .395" that the Web and Megacycle options would give me. The higher duration will make the exhaust note quite throaty, and give substantially more high end power without compromising durability, only idle quality.

so I've pretty much convinced myself to get the exhaust if that's possible, regardless of which engine it fits, but if it appears to be gs1000... then I very likely will be changing my engine plans... have to look into the weight difference of the engines seriously. Gs750 with starter motor but without carbs was around 175 lbs I believe.

[Chuck78]

1135cc 10.25:1 +1100G head/cylinders + VM33 smoothbores + Yoshi Isle of Man cams means a really monstrous engine that would need the crank sent to John Pearson for indexing and welding, APE clutch basket, bracing added to this custom cromoly swingarm that came with the Rickman in addition to the original Rickman arm (too short according to Craig Vetter - his bike Don Rickman built a 1" longer swinger for).

$700 for one-off JE 894cc pistons sounded expensive! But... it is a Rickman. It's basically the ultimate twin shock 1970's classic styled superbike & frame until the BiMoTa SB2 monoshock model came along and blew everything else away in 1977.

[Chuck78]

Wife beat me to it, wasn't able to get the Rickman bodywork from Australia that I was begging for as a birthday gift, but she followed through on this pretty well!




Fairly snug tucked fit into frame, looks like the Rickman hanger and Yoshi hanger are both at or very near in agreement with each other. I need to get an engine in there to mock up chainline / gearing to see how steep of swingarm angle I can get away with. Then I will see if the Yoshi pipe really lines up perfect as it ls looking to do. Would have preferred the more radically upswept version but this thing is very cool, has awesome history, fits in great with the primarily vintage speed parts nature of the build, and fits in VERY WELL with the performance nature of every aspect of this build - this pipe is SUBSTANTIALLY LIGHTER than the Kerker System K setup I have as the alternate, and much more racing cred/lineage.








Uh oh, is this pipe going to work on my 894cc or 920cc GS750 engine? It was for a GS100!?!?!?!!!


I didn't think twice about fitting this thing on what would likely end up as a GS750/850 hybrid big bore, after comparing the difference in crankshaft stroke between that and a GS1000. 8.4mm longer stroke on the GS1000, so the engine likely is only 8.4mm taller, hence the exhaust hanging down less than a centimeter lower... I will definitely run with that if I choose a 750 big bore!




Looks like I will probably be getting some high end one off custom JE Pistons for the Rickman in 72mm, same as the MTC set I have in my GS750 workhorse. These will be 10.35:1 approximately as opposed to 10:1 on the MTC. That will allow me to put GS450 71mm bore sleeves into the GS425 (stock 67mm bore) block and achieve 489cc and around 10.85:1 and still have decent cylinder wall thickness as long as I am not boring all the way through the aluminum between the fins to fit these substantially oversized sleeves. I was leaning toward the 475cc 425 / 894cc GS750 Rickman for wall thickness and cooling reasons, but after getting the 920cc 750 in tune very well with stock cams and carbs this season and being able to spin the big 150 Avon RoadRider substantially, and also being able to lift the front end off the ground without any rider input other than rolling the throttle open a fair amount and somewhat rapidly... well the big cc's of the modded 750/850 on stock (but advanced slightly) cams was quite addictive. Lifting that big heavy 175lb 4 cylinder engine'd bike's front end off the ground substantially even with a 1.125" longer than stock swingarm is quite a feat, so that power was quite addictive.

On the little featherweight twin monster racer build, maxing out the potential of it is paramount, as I want it to be quite the little ripper as to not be sitting idle because I would rather ride the bigger bikes. jumping from 475cc to 489cc is one more thing to add up on that thing to make it a beast. .380" lift megacycle cams and possibly bigger valves and some minor porting work by Rapid Ray or Rockdale Cycles plus a japanese imported 2 into 1 exhaust and either custom twin cylinder racked VM29 smoothbore carbs or custom racked 2 cylinder RS34 carbs, I think this thing may be the best bet for the RS34's of all of my builds (largest displacement per cylinder of any of my bikes), and my buddies have a spare 4 cylinder set with one broken slide that is no longer available, and will make me a deal on them. Accelerator pump setup smoothbore flatslides that take the same main jets that all the VM carbs use. Less parts for me to stock is good. the 29's would allow me to stock even less as the rebuild parts are mostly similar to the vm26's etc oem carbs.

I think I can take the GS425E's claimed 40hp and easily push 57hp @ the crank if not 60hp. Some minor head porting and larger valves may be necessary to squeeze the most high rpm potential out of this. Maybe stock GS1000 size aftermarket valves may do the trick. I don't think the heads will need much porting as they are already designed for 34mm CV carbs (just recalled this when looking up hp/tq specs, RS34 it is!), so the head for 34 cv's has BIG intake ports. I don't want to increase the volume of the port much at all as I don't want to kill all low end response (bigger ports take longer to fill with air/fuel charge, so they make it a less fun street engine and only improve the fun factor at police-attracting exhaust decibels at high rpm operation)
So I'd have a 2 cylinder bike that weighs 330lbs or so (60% of a GS1000) and has half as many cylinders as a GS1000 but almost identical displacement per cylinder, and more horsepower per cylinder by a longshot over a "STOCK" GS1000. I think this combo equates to a screaming little twin that would be nearly as fast as a stock GS1000 up to 75 or 80mph until the aerodynamic drag pushed too hard on the lower torque output twin cylinder racer. This should be one of the fastest bikes to ride in the twisty roads for sure.

I am still slightly considering the other option - 80-87 GS450 engine, GS500 sleeves bored and pressed in, GR650 Tempter TDCC head and pistons. For $800 I can get the best pistons possibly ever made for this type of setup, 10.5:1 CP pistons made by Carillo. This would give 527cc's. It has been done with stock GR650 pistons before. the thread on GSR is deleted but the youtube video "GS527 Beast" exists still as evidence of this monstrous twin combination. This would lose my kickstart only and roller bearing crank bottom end, but would give me more readily available plain bearings and other more readily available engine parts (some 750 bottom and a few 400/425 bottom end parts are no longer available now). I like the press pin roller bearing crankshaft though, virtually indestructable. no worries of throwing a rod when the the rod does not have a bolt-together seam! If I get bored in the next year or two, I might attempt a GS450/527cc clone of my 489cc build and use stock GR650 cams (bigger lift than any factory GS cams ), and have a fun racer bike for the wife to tear around on. More budget oriented than mine with stock cams and GS500 forks and caliper with a single 310mm rotor, but very similar.

[Buffalo Bill]

Are you going AHRMA racing with this bike?

[Chuck78]

Will start out with track days and excursions in the twisties at first, but vintage racing may be in the future. I may have to swap to early 1989 GSXR1000 41mm cartridge forks depending on racing rules. These Bandit style (RF900R) forks, Hayabusa calipers, and CBR900RR rotors would likely not fit into the rules for most vintage racing classes.

[Buffalo Bill]

Yeah, racing rules are strict. I just looked at the AHRMA rule book for Vintage Superbike. Seems my 82 1100G does not qualify, the cc limit is 1025cc.
They're having a race event 1st weekend in June near me, I'll have to get up there and spectate.
Hope to have my bike ready for track days by then too.

[Chuck78]

& if I were serious about racing, I'd be running a GS1000 8v engine. The 920cc is an absolute blast, a monster even just with retimed stock cams, but it'd get whooped on by the gs1000 and kz1000 competition in vintage superbike . And a GS1000 would possibly get me in more trouble on the street! Already hard for me on the heavier GS build to keep the back wheel not spinning and/or front wheel on the ground. The Rickman 920 will have lighter higher compression JE Pistons, maybe a ported head, Yoshimura cams, and VM29 smoothbore carbs! And will be 25-30 lbs lighter!
Some sanctions/classes allow 1075cc and 1085cc gs1000's. But apparently not AHRMA.

It will look like one of these by next year, but a GS engine. Black & gold. Either naked or the Rickman quater fairing on the red bike. The full fairings Rickman made are excessive and unattractive looking in my opinion:


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[Buffalo Bill]

The red bike looks real good, and like it's got a short swingarm.
The black bike, don't like chrome or polished frames… street cruiser, show bike bling/bling.