GS Twins Wiki.

[Chuck78]

Can any other GS400/425 owners chime in if anyone has built a 449cc GS400/425 using GS850 or Wiseco pistons??? I'm very curious to how much improvement a properly jetted pods/pipe 449cc build would have as far as making it a decent accelerating bike. 502cc's in modded and properly tuned form would surely be a hugely noticeable change over stock, and the weight savings of 30-35lbs off stock would absolutely improve the engine's feel as well. Might be able to steepen the gearing a slight bit (+1 tooth up front?) to take advantage of extra torque added to the engine with the bigger bore, and make it more highway cruise-able aside from the lightweight bike getting tossed around in the wind.

I wonder if a small bullet style nose faring would change much in terms of highway abilities? Also, milling the head a fairly sizeablble amount and then slotting the cam sprockets to re-adjust the cam timing back to where it was before the decking, while running 850 pistons, if that would be worth the hassle to save the expense of buying Wiseco 10.25:1 pistons while running OEM re-purposed slugs and trying to get the dismal stock compression ratio of the GS850 bumped into the high 9's or near 10:1? WITHOUT having to check valve clearances or cut into the piston faces to add more valve clearance...

[Mekanix]

Stephen, I often get confused in references here on the compatibility between models. When you refer to the GS400, GS450, GS500 compatibility, I often wonder if you are referring to the 80+ GSX400's that Canada got that I believe are a smaller bore GS450 with the 4 valve per cylinder (8 valve) heads and plain bearing bottom ends. If you'd get a chance to edit posts and state which you were referring to (77-79 GS400/425 or 80+ Canadian GS(X)400 4 valve per cylinder 8 valves total), that might help clear my confusion. Correct me if I'm wrong on any of that info. Didn't you use the 4v/cyl head on your Frankenbuild?

Edited.

The GSX is a special model that Canada and Europe got with a smaller bore and a better designed 4 vale per cylinder head making the same power as the 450.
There is quite a difference in the head, pistons and cylinders which means that only the GSX is something that you can't swap any parts from one engine to another. But the base is the same. They are still all plain bearing after 1980.

Mine was the 4 valve per cylinder engine to start off with.

[Chuck78]

Is there any 2:1 exhaust available for the 77-79 GS400/425? If not, will the 80+ exhaust adapt fairly easily to the earlier models?

Any idea on the cylinder block height differences between the GS400/425 and the GSX400/GS450/GS500? With a totally different stroke, I wasn't sure if the block would still be something that could be adaptable with oil passage modifications or not. Re-sleeving a 77-79 block may be easier if going for bigger bore.

Any opinions on my brainstorming ideas for the big bore 1st gen GS twin vs just going for a GR650X Tempter?

Lastly, are the carb spacings the same between all generations? running something in a more modern lightweight cv flatslide would seem very appealing. Are there various models of GS500 carbs available throughout the years? I am going to guess that the 1989 through early 1990's is going to have a better quality carb with less plastic parts. The air jets, needle jets, and jet needles are going to be more closely sized for a 502cc engine than a carb spec'd for a 400 or 423cc engine, and it seems likely to be a very beneficial swap if going with bigger pistons.

[Big Rich]

I can't help you with much Chuck, but I can tell you the carb spacing between a 1980 GS450, 1983 GR650, and all GS500's are identical. I'd like to think the 400 / 425 is the same too but I can't confirm that.

From 1989 to 2012 there were basically 3 types of carbs for the GS500 (I say basically because there are some minor differences for California models). From 89-2000 was the first generation 2 jet carbs (main and pilot) , 01-02 carbs have 3 jets (main, mid main, and pilot) but have some oddball differences to the other years, and from 04 up have 3 jets. The last generation carbs are generally considered to be the best stock carbs for performance.

[Mekanix]

Is there any 2:1 exhaust available for the 77-79 GS400/425? If not, will the 80+ exhaust adapt fairly easily to the earlier models?

Any idea on the cylinder block height differences between the GS400/425 and the GSX400/GS450/GS500? With a totally different stroke, I wasn't sure if the block would still be something that could be adaptable with oil passage modifications or not. Re-sleeving a 77-79 block may be easier if going for bigger bore.

Any opinions on my brainstorming ideas for the big bore 1st gen GS twin vs just going for a GR650X Tempter?

Lastly, are the carb spacings the same between all generations? running something in a more modern lightweight cv flatslide would seem very appealing. Are there various models of GS500 carbs available throughout the years? I am going to guess that the 1989 through early 1990's is going to have a better quality carb with less plastic parts. The air jets, needle jets, and jet needles are going to be more closely sized for a 502cc engine than a carb spec'd for a 400 or 423cc engine, and it seems likely to be a very beneficial swap if going with bigger pistons.

Larger bore will mean you will have to balance the crank to the new piston weight.

500 carbs work good.

Resleeving is the only way with the 77-79 if you have the room.

http://www.ebay.ca/itm/MAC-2-1-Full-Exhaust-System-with-Megaphone-Muffler-Black-Chrome-For-Suzuki-GS450-/191198879813?pt=Motorcycles_Parts_Accessories&hash =item2c84576045&vxp=mtr

[Chuck78]

Big Bore pistons and balance shaft/crankshaft balancing? + Exhaust retrofits

Larger bore will mean you will have to balance the crank to the new piston weight.

http://www.ebay.ca/itm/MAC-2-1-Full-Exhaust-System-with-Megaphone-Muffler-Black-Chrome-For-Suzuki-GS450-/191198879813?pt=Motorcycles_Parts_Accessories&hash =item2c84576045&vxp=mtr

Is it the crank, or the balancer (counter balancer?) shaft that needs rebalanced if using larger pistons? The balancer shaft makes sense to me, but the crank has the pistons 180 degrees apart, right? So I am envisioning the balancer shaft as having weights that are 90 degrees apart from the rod journals on the crank, both being 180 apart from each other, to make it a smooth fluid revolution. Is my theory how they work in reality? Aftermarket pistons are substantially lighter than stock cast pistons, as I read a thread where someone upgraded from 67mm stock pistons to 70mm wiseco pistons, and they were like 25 grams lighter despite being much bigger. I am thinking you could potentially specify when having custom pistons made that the pistons and rings be weighed and the pistons balanced to within 10% max over the weight of the stock pistons, and then you would be fine without trying to find a machine shop locally that has any clue about rebalancing a balance shaft motorcycle engine.


That exhaust is for a 1980+ GS450. Any idea how adaptable those are to the 77-79?

EDIT: I have read that if bolting onto a 77-79 twin, the GS450 exhaust mounting flange plates sit quite far off the head, and apparently will need much longer bolts, or else will need the exhaust itself cut shorter where it meets the head.

[Chuck78]

GS527 with 450 bottom/500 cylinders/GR650 pistons and head!

I thought I would repost this before the only mention of it on these forums gets deleted as the original build thread did. Seems that aside from Mekanix's method of building a big bore modified GS twin into the mid 500 cc range, this is the other best way. The GSX400 8 valve twin head that Mekanix used is fairly rare, and his method requires a fair amount of custom machining (piston valve reliefs and base gasket spacer). This other method with the 1980+ plain bearing engine requires tracking down other rare parts - a GR650 Tempter head being the crucial part. Apparently this all just bolts up, but I am not sure if the deck height had to be modified any.
"GS527 Beast" by youtube user hemi500:

https://www.youtube.com/watch?v=tQEVHd1cSyw

youtube user comment from our beloved franken-twin pioneer Mekanix:

Steve Mekanix
2 years ago
This is a GS450 base, GS500 cylinder and head. GR650 pistons. Bore 77 Stroke 56.6 540cc is the max you can go on a stock 500cc block @78mm. After that you can use GR650 sleeves in the 500 block and push it to a max of 570cc's @80mm. The exhaust appears to be modified at the flanges to exit at an angle instead of straight. Very nice mod."

I'd like to add that JE and Wiseco both make custom pistons, best to go through someone like RapidRay who is a knowledgeable builder/dealer to get them ordered correctly and at better pricing than retail direct. with a head intended for 650cc's, I think you would get better/quicker throttle response from going with a larger than stock piston anyways, but 77mm is +3mm o.s. on the GS500 sleeves, so best to resleeve if going bigger than that. With a custom JE/Wiseco $$$ 77mm piston, you could get the weight down substantially over a stock cast GR piston, so very little balance shaft/crankshaft balancing would need to be done, AND you could run 10.25 or 10.5:1 compression for more performance! This is a pretty awesome combo if you can search the ebay sites from other countries that had plentiful amounts of GR650's for the entire 5 or 6 year run of the model, as opposed to the US which only got it for 2 years.

Oh, and RapidRay highly recommends the more expensive but absolute best CP Pistons (Carrilo, as in the popular Carillo connecting rods in many race bikes/cars). If money is no object, Megacycle offers several performance cam grinds for these twins as well.

[Chuck78]

77-79 GS400/425 roller bearing bottom end big bore options

So here's my brainstorm ideas for the 1st gen (77-79) GS400/425 big bore build.

449cc's:
*The GS850 pistons will bore right into either cylinder and give you 8.8:1 449cc's using a custom bore Cometic head gasket. This could be doctored up a little more by milling the head a fair amount to increase compression into the mid 9's, but then you would need to slot the cam sprockets and use a degree wheel to properly time the cams.
**Alternatively, you could buy the kit that I believe Jay from APE puts together with a pair of GS750 844cc Wiseco pistons for the twins that will give you 10.25:1 and 449cc's with lighter and higher compression pistons, and the head gasket that you need.

462c's:
*This would require the GS400/GS425 cylinders to bored to their practical limit of 70mm for GS850 +1.0mm oversized pistons.

489cc's:
*This will require resleeving with GS850 sleeves, and boring custom 72mm pistons into the 850 sleeves. This is what I am doing, however I have 7 old stock 920cc big bore MTC Engineering GS750/850 pistons 4 of which are going back into my GS750 with a ported performance head & Yoshimura cams just finished by RapiRay. So I'll have 2 left + a spare for the GS425 build

502cc's:
*This would require fitting the GS400/425 block with shortened GS1000 sleeves (70mm stock bore) bored out +3mm o.s. to 73mm, and a set of custom 73mm pistons in 10:1 to 10.5:1. This is quite an appealing size here. Again, some skilled head porting and at this point, some larger valves ( GS500 or GS1000 2V spec?) would make this combo produce a lot more horsepower, but even without, it would make a good amount more torque and make the little twin much more highway capable (and able to run a taller gearing to keep rev's down from stock). This will require some slight crankcase webbing clearancing to accept the larger sleeves.

520cc's?:
*This is questionable and would only work if using custom turndown GS450 sleeves so that the top flange is slightly smaller diameter by 1 mm or 1.5mm overall diameter, & if the portions of the sleeve protruding below the aluminum cylinder block add the outside diameter turned down substantially to be the same as a GS850 sleeve O.D.

*Edit - looking into gs450 (71mm stock bore) sleeves as best potential swap.



I was going to consult Rapid Ray on these possibilities, as those twins are basically half of a 2 valve gs750 but with longer stroke. he mostly does tscc 4 valve per cyl bikes, but is an invaluable wealth of performance engine build knowledge. Maybe he can do all the necessary machine work all well if I were to ship the engine to Cali.



Oh, also the crank & balance shaft need to be rebalanced after going big bore on these. A 425 to 69mm may be able to get away without it, maybe even the 475cc version,as the cast stock pistons are much heavier than several sizes larger overbore on the aftermarket cnc machined pistons. The larger pistons may be able to be made to be within 10% over the weight of the stock pistons, but if more than that, you would need to find someone who can rebalance the crankshaft and balance shaft, and this seems to me to require a specific machinist who really understands the balance shaft system, and one you can really trust to do it right.

[Chuck78]

People will definitely say "why bother dropping well over $1000 into a custom engine when you can just buy a bigger bike?" Well, to counter that, with a kickstart engine (which I am terribly fond of), you can delete the starter/starter gears/cut off the flywheel gear, use a large value capacitor (points ignition) or 16oz LiFePO4 Lithium Iron Phosphate 4 cell battery (electronic ignition), center stand delete, seat shaving, frame detabbing, GS500 slingshot carbs and K&N lunchbox filter, MAC 2:1 exhaust, custom aluminum battery box, GS1100E swingarm with drum brake stay attachment welded to bottom, lighter-than-disc-brake rear drum hub (plenty adequate), 3.00x17 lightweight aluminum rear rim and 130/70-17 tire, 1.95x18 alloy front rim or 2.15x18 with a 100/90-18 tire, GS500 fork legs and the popular twinpot caliper (GS500's and Ninja's) with a 310mm CBR900RR or CBR1100XX single brake rotor, chopped springs, fork brace, Cartridge Emulators, clip on bars, GSXR or similar rearsets, passenger footpeg delete, and a custom muffler baffle to look like the Yoshi GS550 road race pipe. With this bike build, I believe I could get the 380lb stock GS400/425 down to 325lbs. a 325lb bike with a 449cc/489cc high compression roller bearing engine with possibly some Megacycle Cams would be one heck of a combo for a lightweight corner carving beast of a little twin, and with a longer back end to help the power to weight ratio. Some OSS frame bracing would definitely be in order for this setup with such an awesome power to weight ratio.

[Chuck78]

I was google image searching & found some AWESOME Japanese aftermarket exhausts listed for GS twins. Google searches don't really like to show much in the way of search results from across the globe from the user's I.P. address, but I was able to dig up exactly what I wanted, as I despised the way the collector routing looked on the MAC 2-1 exhaust. Japan.WeBike.net has some awesome offerings:

$446 + free USA shipping (on orders above $428, AWESOME!)
ALL ALUMINUM "Mad*Star" 2:1!

http://japan.webike.net/products/21802929.html

http://mad-star.JP - use https://translate.google.com/m/translate set on Japanese to English/etc.




$230 + $64 shipping to US
MadMax upswept chrome 2:1:

http://japan.webike.net/products/21423657.html

$335 + $83 shipping to USA
KSY Racing Project upswept Yoshi race style chrome 2:1:

http://japan.webike.net/products/3236958.html

I love all three of those, especially the KSY upswept race pipe. the aluminum intrigues me, & goes with the build theme of weight savings, but I think it's more likely to rash the side of the muffler on extreme aggressive cornering like where I like to ride in Hocking Hills State Forest here in Southeast Ohio:

KSY GS400 etc exhausts:

http://japan.webike.net/SUZUKI/GS400/Exhaust/613/1001/mc/p.b=905/

More from webike:

http://japan.webike.net/SUZUKI/GS400/Complete+exhaust+systems/613/1002/mc/

With the free shipping on orders over $428, it'd be quite tempting to order the Aluminum 2-1 & the KSY upswept racing pipe just to compare, & then resell to someone in the USA whichever one was lesser favored, as they are both amazing looking, & I'm sure would sell quickly here once imported.

If getting just the KSY, one could add some of those cool BEET brand finned ignition covers & can end cap covers etc to get them for just a few dollars more total than just the exhaust + shipping... The exchange rate must be highly in our favor, those prices on those products are GREAT.

[Chuck78]

Several more Aluminum & Steel 2:1 exhausts from Mad*Star:

http://mad-star.jp/?mode=cate&cbid=1308833&csid=2

May also need to use translate.google.com to read that in languages other than Japanese. Several attractive exhausts there, and more in Aluminum, but the three I posted photos of are still my favorites. Very awesome. Makes me wonder what other parts are available primarily from Japan for the GS Twins. The GS400 is a hugely popular model to this day over there, as in major cult classic as Z1's, CB750's, &smaller CB's are here in the USA. So many more aftermarket parts available over there for them.

[Chuck78]

More on 520 conversion sprockets

I dug up all this info and figured it's a good idea to have it here. Pretty easy to sort through all this on JT Sprockets website too.

Here are the stock GS450 sprockets (I'm just guessing the GSX400 and other vintage twins are similar if not the same):

http://www.jtsprockets.com/catalogue/model/5704

The old GS300 rear sprocket has the same dimensions, but uses a 520 chain instead of 530:

http://www.jtsprockets.com/catalogue/model/5688

But the front sprocket is completely different. Luckily, Suzuki decided to use a similar sprocket on their GS500 with a 520 chain:

http://www.jtsprockets.com/catalogue/model/5718

Be aware though: the front sprocket from any year GS500 will fit a GS450, but the early GS500 models did not come with a spacer behind the sprocket (the late model GS500F sprocket listed above does have the spacer built in).

Hope this helps somebody trying to cut weight / improve performance a little bit.

Wow, you can get those JT sprockets in steel or aluminum for under $30!
Another tip for 520 conversions - there are 520 conversions available for the 98-02 Bandit 1200, which uses the same 6 bolt pattern as the old GS rear wheels. Not sure if the front sprocket is the same, but you could cross reference a gs550 countershaft sprocket (530) in an aftermarket offering with the bandit, or a Bandit 520 conversion cross referenced with a GS500F.

Also, SuperSprox makes awesome "Stealth" sprockets with steel outer teeth ring & aluminum centers for the 98-02 bandit (I have a 530 on my GS750, very nice piece, $89), and for $109 they will custom machine them any way you want, any bolt pattern, any inlay design, and chain width or pitch.


SuperSprox also makes front countershaft sprockets for the gs500f & bandit that look similar to the awesome Vortex fronts (drilled with holes to save weight), but with self cleaning notches machined in as well as holes for lightening.


Vortex makes some flashy looking 520 conversions listed for some gs models also. 1979 only showed gs425 & gs550 (could be due to the bigger bikes being 630?), but most gs models are compatible for conversions to 530 or 520. 1000cc+ GS's I believe need an additional spacer behind the sprocket.

[Chuck78]

This is the actual Suzuki 1200 Bandit version that shares the same 6-bolt pattern with old GS's, and is a 530 (can be special ordered in a 520)

[Rensdw]

Don't know if this is still relevant but here is some specs that you can add to the list


GR650 combustion chamber volume is 47CC.
GR650 Piston dome volume is 9.43CC
GR650 Piston pin to deck height is aprx. 18mm
GR650 Piston Wrist Pin is 18mm

[CrawlingForward]

I thought I would repost this before the only mention of it on these forums gets deleted as the original build thread did. Seems that aside from Mekanix's method of building a big bore modified GS twin into the mid 500 cc range, this is the other best way. The GSX400 8 valve twin head that Mekanix used is fairly rare, and his method requires a fair amount of custom machining (piston valve reliefs and base gasket spacer). This other method with the 1980+ plain bearing engine requires tracking down other rare parts - a GR650 Tempter head being the crucial part. Apparently this all just bolts up, but I am not sure if the deck height had to be modified any.
"GS527 Beast" by youtube user hemi500:

https://www.youtube.com/watch?v=tQEVHd1cSyw

youtube user comment from our beloved franken-twin pioneer Mekanix:


I'd like to add that JE and Wiseco both make custom pistons, best to go through someone like RapidRay who is a knowledgeable builder/dealer to get them ordered correctly and at better pricing than retail direct. with a head intended for 650cc's, I think you would get better/quicker throttle response from going with a larger than stock piston anyways, but 77mm is +3mm o.s. on the GS500 sleeves, so best to resleeve if going bigger than that. With a custom JE/Wiseco $$$ 77mm piston, you could get the weight down substantially over a stock cast GR piston, so very little balance shaft/crankshaft balancing would need to be done, AND you could run 10.25 or 10.5:1 compression for more performance! This is a pretty awesome combo if you can search the ebay sites from other countries that had plentiful amounts of GR650's for the entire 5 or 6 year run of the model, as opposed to the US which only got it for 2 years.

Oh, and RapidRay highly recommends the more expensive but absolute best CP Pistons (Carrilo, as in the popular Carillo connecting rods in many race bikes/cars). If money is no object, Megacycle offers several performance cam grinds for these twins as well.

This whole thread is amazing, but specifically very excited about this portion.

I'm a bit ahead of myself, as I'm still in the early stages of building my scrambler 450, (using a GS850 front end for dual disc brakes and taller seat height along with a ninja 250 swingarm and shock from a ninja Zx6. I bought the bike completely disassembled and in multiple boxes, so I don't feel too guilty.) but I've got a spare 450 engine in the donor bike that I was hoping to build up as a project to learn engine building, which is a huge blind-spot in my mechanical experience thus-far.

I found a GR650 head on ebay for $75 that I was originally just going to use for the cams, but now I'm debating punching up the displacement as well. Been reading through the documentation by Mechanix, but I'm definitely still processing all the information. Same as he, the point won't necessarily be a bigger engine, but more to learn about the whole process, and all this and the rest of the education on here is a huge help!