GS Twins Wiki.

[Rensdw]

Check out my topic to see what it takes to actually use the GR650 head, it's sounds like a good way to go but you actually lower the compression by a bunch, most likely losing power.
Without any experience I would recommend using the GS500 pistons and jugs to up the displacement a bit, and then start thinking about shaving off some material of the head and thus bringing the CR up.
Once you have done that start reading and watching vids about porting and polishing heads and exhaust and do that, you will make the bike a lot more fun with a properly designed intake and exhaust system.

All the above is still affordable, and the engine will still be reliable, once you start making more HP than the above you will lose money quick.....very quick, I suggest staying single for stuff like that.

[CrawlingForward]

Check out my topic to see what it takes to actually use the GR650 head, it's sounds like a good way to go but you actually lower the compression by a bunch, most likely losing power.
Without any experience I would recommend using the GS500 pistons and jugs to up the displacement a bit, and then start thinking about shaving off some material of the head and thus bringing the CR up.
Once you have done that start reading and watching vids about porting and polishing heads and exhaust and do that, you will make the bike a lot more fun with a properly designed intake and exhaust system.

All the above is still affordable, and the engine will still be reliable, once you start making more HP than the above you will lose money quick.....very quick, I suggest staying single for stuff like that.

I had started reading through your thread and thought you had solved the compression issue through custom pistons? Part of the appeal was learning the custom aspect of boring over cylinders, rather than just bolting on. Definitely excited about working on putting and polishing, though.

[Chuck78]

Yes, Rensdw got some custom CP (Carillo) pistons made at a healthy chunk of change , but now others could order these off his order #. Make sure he used the stock wrist pin size (18mm) as he did go with Carillo rods as well. Run GS500 cylinders gs450 bottom gr650 head& cams gs450 2:1 mac exhaust & early gs500 carbs with dyno jet kit... vroom vroom!
Serdi radiused seat valve job, minor porting, polish exhaust ports, possibly back cut the valves, good to go. If you plan on aftermarket cams in the future, talk to rapid ray about the best springs to use for an aftermarket streetable cam in the range of .365"-.395". Megacycle sells regrinds for the GS twins, and Web will also do custom one off grinds.
Slotted sprockets and then degree the cams in to 106-ish fir torque or 110-ish for power to be shifted to higher rpm high hp / less low end power.

Pay attention to deck height withe 500 cylinders, I think it is slightly different and requires thicker gaskets, or have ray put gs500 or gr650 sleeves into a gs450 block to keep things simpler (stock gasket thicknesses).

[Rensdw]

I had started reading through your thread and thought you had solved the compression issue through custom pistons? Part of the appeal was learning the custom aspect of boring over cylinders, rather than just bolting on. Definitely excited about working on putting and polishing, though.

Yes, I have solved the issue of low CR with custom pistons and rods.

Curious on Chucks thought about using the stock 500 pistons in the GR650 head, the CR will be extremely low, wouldn't a ported 450 or 500 head be better?
Why I chose the GR650 head with high CR pistons is because in the end, the GR650 uses a more modern combustion chamber design.

[Chuck78]

yes you absolutely want to use a piston that is designed for the head being used, unless you can find a similar shaped piston to the GR and modify it. This is highly unlikely though. save up your money and order a set of the pistons that rens had made.

there was formerly a set of pistons for a Kawasaki application that gs500 guys on the GS twins form had been using in GS 500 engine successfully. They were a Wiseco aftermarket big bore piston kit. Unfortunately Wiseco changed the design of the dome for that particular application and they no longer worked for a gs500 head, but it would be the only candidate that I could think of that could potentially be modded to work in a gr head that may bring up compression when using a 500 cylinder and GR650 head. I don't know the specifics of the piston shape however. For the amount of work going into it and potentially not a whole lot of payoffs or not working at all, it's more worth it to save up for a while and drop some big money on the custom Carrillo pistons. you can get an entire running gs450 for that price, but building an engine with those for a 527cc10.5:1 gs450, and putting in the .380" lift MegaCycle Cams, or better, the .380" intake cam combined with the .354" lift exhaust cams, would give you a gs450 that would give a pods&pipe gs550 a run for the money, and definitely with some suspension mods (sticky tires in a bt45 battleaxe or am26 roadrider, gs500e front caliper and forks w/Racetech gold valves & 98-99 310mm cbr900rr rotor, GS1100E triple clamps from the 82-83 non-leading axle model 1100E to mount the 500 forks, $200 hagon/progressive or $300-350 Hagon/YSS shocks 1" taller than stock) would beat it through the twisties or in a race on an incredibly tight race track.

if you are building up a hot rod engine and putting it in a nice restoration project, I strongly urge you to do all of those mods that I just mentioned. That alone will completely transform the bike. All of those chassis mods are more important than the bigger engine even. A bike with those mods would be worthy of a bigger engine transplant. the medium sized twins can be transformed into excellent handling bikes that will be much more agile in tight turns and very very light weight and flickable. also, with a Mac 2:1 exhaust with their optional race performance baffle installed, GS500 carbs, K&N air filter(s), and a d
GS500 Dynojet kit,the stock engine or the modified engine will sound incredibly awesome, a very good twin sound indeed. Nothing like the four cylinder Japanese bikes. And... you could probably outrun a Harley 883 with the fully modded out 527cc 10.5:1 gs450!

[Chuck78]

GS400/425 high performance canyon carver build plans!

So I am getting ready to send off a GS425 cylinder for machine work by Rapid Ray & associates for resleeving larger to fit an old set of MTC Engineering big bore GS750/850 72mm 920cc pistons. This is in preparation for getting started on a good summer 2019 project bike from the point of dreams & parts boxes of go-fast goodies, to the beginnings of the reality that the build will become.

As you may have read previously, I am trying to build up a lightweight highly upgraded GS twin chassis with all upgraded brakes/wheels/suspension, & trying to make a respectably fast engine out of the little 400/425 2 valve per cylinder roller bearing engines...

I'll be having the stock set of spare cylinders resleeved to GS850 sleeves or perhaps GS450 sleeves if I can get the tapered bottom of the sleeves turned down thinner for better crankcase clearance per Ray's recommendation (less grinding on the crankcase top half to fit, thin them externally to be similar to the o.d. of GS850 thickness below the bottom of the jugs).

Stock 400/425 sleeves are good for 449cc & around 10.4:1 using half of a 4cyl set of Wiseco K844 GS750 pistons (you can buy a half set of these 4cyl pistons for a 2cyl build from APE with a custom APE head gasket, or buy 2 individual pistons &order up your own altered spec Cometic gasket) & allow you to run big lift cams (deeper valve pockets) & also give you high compression, OR you can also use GS850 +1.0mm overbore (870cc on a 750/850 4cyl) pistons & stock-ish cams for 462cc & 9:1 compression, more compression ratio if milling the head's gasket surface and/or milling the cylinder block &/or running thinner head gasket to get the best most ideal squish band aka quench height of around .038"-.043" or roughly 1mm.
I think I determined that 71mm into a 400/425 sleeve may be pushing it for reliable street use as far as cylinder wall thickness, becausedespite my hopefulness that the 425 cylinders used thicker sleeves, I believe when measuring them oh, it did not appear that the sleeve thickness inside of the block was the typical 3.9 or 4 mm. this led me to believe that Suzuki just changed the 398cm³displacement number cast into the front of the cylinder for the 79 model 425's 423cm³, & bored the walls 1mm thinner (2mm overall bore increase - 1mm off each side). I'll have these cylinders in my hands in the near future to check again.

I have several exhaust options, including some interesting F1R dual aluminum mufflers with upswept modular inlet pieces, MAC 2-1 header & heavy chromed steel MAC muffler (won't be using this hefty MAC muffler can), Kerker "System K" aluminum muffler can and random mid pipes, and an older 2-1 header with a 45 degree bend in the #2 cyl head pipe to make it the same length to the collector as the #1 cylinder which travels from the left front side to the right rear side. I've seen these before but unsure of the manufacturer, they have not been made for a long time. Yoshimura Series 1 stovepipe style exhaust would potentially get fabricated out of stainless tubing if I use that header. + Yoshimura reproduction badging in tribute...

Here is an older mockup of all the parts I've been stockpiling for this epic little GS twin build:




Hoping to diet this bike down to a target of 325lbs, while drastically increasing the little twin's engine output, & substantially upgrading the suspension. GS1100E '82-'83 aluminum triples, GS500 forks and Tokico brakes on a 310mm 98-99 CBR900RR rotor, stainless brake hose, Fox Factory Shox, billet GS500 fork brace, narrowed GS1100E alloy swingarm (not pictured), rearsets, semi-custom exhaust, clip-on bars, etc... Taller rear stance, shorter slammed front end stance to steepen the rake 1.75 degrees or more (29 stock & the light aluminum 1100E 82+ triple has less offset than the heavy steel GS850/1000 37mm stanchion tube 185mm spaced triple)



Topping it off cosmetically with some great flare using a vintage aftermarket Italian Giuliari seat & GS450S knee dent tank to put it in serious racer looking trim, as well as GS400 badged side covers... Had to sneak a little of the "sleeper" element into the ol beauty to not totally give away the near 500cc size and high performance engine top end work!
Ray loves to tell about the 562cc(?) GS500 they built that would pull past 600cc 4 cylinder bikes in the looonnggg back straight at their home racetrack in Hawaii at the time... The bore limit (stud spacing) on the early roller bearing engines limits me to 502cc or 520cc with custom pistons, and I want cams that produce a more broad streetable power curve, so I won't be going THAT big, but I have some fairly lofty real-world performance goals targeted here with this thing.





For now a set of GS1000 hubs with probably a GS500 sprocket carrier(?) & offset front sprocket (?), 3.50x18 & 2.50x18 D.I.D.aluminum rims, 140/70-18 or 130/70-18 or 130/80-18 Shinko SR741 or Pirelli Sport Demon or BT45V Battlax tire, 100/90-18 or 100/80-18 front Shinko 230 or BT45V or Sport Demon. May seal up the spoke nipple areas with some small plastic domed pieces + some 3M marine sealant/adhesive & 3M Extreme Sealing Tape products and go with tubeless valve stems to save further rotating weight & to free up additional horsepower so that every bit of power that Ray & I can squeeze out of this smaller displacement engine's head porting, big bore/high compression, bigger cams, and carbs can be more effectively transmitted to the ground with less parasitic losses from rotational weight... Every bit helps...

If I race this in WERA's Formula 500 vintage class, there is a 3.00" rim width limit +as well as 18" minimum rim diameter to keep it fair & authentically vintage appropriate), & 12"/304.8mm brake rotor limit, and floating rotors are not allowed, so I would have to do a semi-custom rotor and caliper mounting configuration if I were actually becoming competitive in the class, as well as use a different set ofold NOS Akront TC rims that I already have handy waiting here for the occasion. that is a good thing, as I could run the street tires on the existing wheels or use those on a bigger bike, and run race rubber or track day rubber on the slightly skinnier setup. or I could run it as is for the first few races, because no one is really going to protest if I am not winning races and beating them! If I did, however, anyone that I placed ahead of can protest my setup and I would lose my ranking. Which doesn't really matter to me, I just wanna ride ride ride!

[pete]

Now that looks like a whole lot of fun Chuck! Do I recall correctly that they are 'Busa rearsets you're planning on using?

Once my Kat is done I'd like to give my little 450 a new lease on life as it's such a fun bike to ride, but probably nothing as extreme as this although some extra pep would sure be nice!

I'd actually like to get away from the 2 valve head in favour of a GSX400 4 valve and big bore it to be honest... I find shims incredibly tedious. Despite having 16 valves to adjust, I found setting the Kat right for the first time was such a pleasure not having to worry if I had a spare shim of the right size or not, especially after finding a lock nut type adjusting tool on eBay that made it very simple.

[LAB3]

Sounds like we've got some in-the-know guys on this thread so I'll ask a question or two. I've heard that it's relatively easy to put a GS500 engine into a GS450 frame, the only issue being that the exhaust ports on the GS500 would hit the frame so the GS450 (two valve) heads would need to be used. Would the GS450 heads need any machine work to fit onto the GS500 engine? Chances are I'll never actually do this but who knows!

[Chuck78]

No, but you can't go crazy on bigger lift camshafts, as if I recall correctly, the 450 vs 500 valve pockets are not in exactly the same places, so doing a clay mock-up for checking piston to valve clearances is critical. Machining the 500 pistons to shift the valve pockets over slightly is not terribly difficult however, & should be a breeze for any competent machinist with a basic milling machine and fly cutter bit. This is nice because then you can run GS500 cams that have bigger lift.
HOWEVER... Big lift is not the only thing that can cause piston to valve interference... Longer duration like the GS400C/GS425 cams along with altered camshaft timing (which can happen even just from milling the head and block gasket surfaces which shortens the timing chain's crank to cam distance & also alters the camshaft timing) can also cause clearance problems.
HOWEVER... many people have these pistons and heads living happily together from careful attention to cam timing and clearances, or just plain good luck. A head and block in great shape that dont need milled for a fresh head gasket surface will keep timing more in the safe zone and away from any dangers of an internal component collision.

If it were mine & I was NOT going to get some custom 450 pistons made in a 77mm bore..., then I'd be both milling the head a fair bit to bump up the compression ratio, AND machining shifted/slightly deeper valve pockets into GS500 oversized pistons bored in to a 500 block... Then slotting the cam sprockets and degreeing the cams in around 108-110 centers.

Also, I think the 500 block is shorter height??? So perhaps boring 500 pistons into a 460 block is better unless you want to do some custom base gasket spacing? I can't remember if it was a minimal or a large deck height difference, but maybe it was Stephens build, I can't remember, but someone made a thick aluminum base gasket spacer and ran to base gaskets, one on top one below.

This is all going from memory from a bike model and engine combination which I have never had my hands on the insides up or owned. Please correct me if I'm wrong, I will re-edit.

[Chuck78]

Now that looks like a whole lot of fun Chuck! Do I recall correctly that they are 'Busa rearsets you're planning on using?

I'd actually like to get away from the 2 valve head in favour of a GSX400 4 valve and big bore it to be honest...

Yes, you are correct, those are Hayabusa rear sets in the photo! I especially like those for the twin, because they have 3 rubber mounted vibration isolators for their frame mounting bolts... As well as the disposable grind away pegs to warn you when you are leaning over so far that you are scraping the ground before actually grinding the footpeg itself!

A set of custom pistons or custom machined 750 16v TSCC pistons would go nicely with the sought after Canadian 4-valve per cyl (8 valve twin) 400 head!

[pete]

Cool Chuck, good to know! I'll be watching particularly to see how you end up mounting those rearsets also.

[LAB3]

Thanks for clearing that up! Like I said, I probably won't do it anyhow but it's always kinda cool to know what COULD be done. The spec differences between a stock 450 and 500 are so close that there really isn't any reason to devote those kind of resources into doing it, sounds like lots of part swapping and machine work are in order to make a noticeable difference. Have fun with your project!

[Mekanix]

Thanks for clearing that up! Like I said, I probably won't do it anyhow but it's always kinda cool to know what COULD be done. The spec differences between a stock 450 and 500 are so close that there really isn't any reason to devote those kind of resources into doing it, sounds like lots of part swapping and machine work are in order to make a noticeable difference. Have fun with your project!

https://www.thegsresources.com/_forum/showthread.php?251658-Some-upgrade-parts-for-the-450&p=2473052&highlight=#post2473052

What I have there is two pistons that push the 450 to 500 cc and have the proper valve clearances. With brand new rings. This was for a mod but didn't get used.

OR


MODS: Parts needed:

• Gs500:
  cylinders
  Pistons
  head gasket and base gaskets
  camshafts for more lift
  tensioner ( need it as if only fits this cylinder block.)
  Slot cam sprocket (because they will be 2-3 degrees retarded from the whole head being 0.010 shorter than it was)
  GS 500 carbs are much better and a good dynojet kit with pod filters wake it up a bit more.

So far the following people have successfully created a gs450-500 swap

wera90ex
bwanna

Easiest way to go is: GS500: pistons, cylinder block, chain tensioner, head gasket and, gs450 base gasket, gs450 head.



With my build I had made a thick base gasket to raise the whole head. It was necessary because the pistons were too tall to begin with.
For the 450 to 500 swap its pretty easy if you use the right combination of parts.
Going for the 500 block and the 450 head with the 500's slightly taller cylinder block you need to use the 500's gaskets to keep the right deck height. But this is also going to increase the compression ratio just a bit since there is less head volume compared to the 500. Its not much but hey cc's count here. Then again the 500's pistons are not as tall as the 450's so that lowers the compression ratio which makes it just right again.

[GregT]

Just to clarify. 500 pistons in bored 450 barrels WITH STOCK CAMS on stock timing shouldn't need the valve pockets cutting.
Any more lift or duration, it's wise to measure valve to piston clearance.

Anyone thinking of using the 8V 400 head, should go into it with eyes wide open. They crack from the exhaust valve seats to the plug holes.


16V GSX750 pistons can be used as an oversize in the 8V 400. With an alloy base gasket of 1.2mm thickness. There's a thread of mine here somewhere where I did it for a race engine.

[sam000lee]

Just adding my 2c since I recently did the 450 > 500 swap on my GS450. Documented here: https://www.thegsresources.com/_foru...nd-Piston-Swap