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**pete** · 03-05-2017, 04:01 PM

Ok, I'll be staying tuned!! Looking forward to this

**Chuck78** · 03-05-2017, 04:03 PM

I really loved the GS450S / GS450E '80-'82 tank, but so do all sorts of Cafe Racer Builders all across the world, and these tanks go for an exorbitant amount of money quite often. I really would like to have had one, but I already have a pristine stock tank. I also traded the original seat with a slight hump for a flat 77 seed in perfect condition.

Well... fast forward a little bit. I spotted a GS400 Italian aftermarket Giuliari seat on ebay in Germany for a modest price... knowing what I thought the ultimate look could be on this project, I searched for the highly sought after 450 sport tank and surprisingly found several I. The $100-300 range for a change! Last I looked there was a c substantially dented rusty one for $150 and pristine tanks for $400-600!

I ended up with two GS450 sport tanks like Rich Graver's racertain above, & a 6 week customs delay but eventually got a lost mint June 1978 manufacture date Giuliari GS400 seat! I was pretty thrilled about this as the bike will really look the business now as well... also mocked it up to see that the 450 sport tank fits a GS550 77-79 frame with some slight relocation of the front mounts!

I started finally organizing and unpacking the basement after a move 8 months or more ago, who which got me sidetracked into doing a mock-up of potential parts to build this by bike with from all of my spares:

Lots of go-fast goodies, & there are more options than just these as I am a serious GS Go-fast-parts hoarder...

I have a different 2-into-1 header & different aluminum muffler plus the stock MAC megaphone from this header, GS1100E aluminum swing arm (maybe slightly too lengthy of wheelbase for this bike but it WILL be a wild wheelie machine otherwise) as well as GS450 swing arms. I have some billet cnc aftermarket rearsets in addition, & several vintage high performance shock options in 3 different varieties of Fox's plus some Koni 76F alloy bodies...
I also have some killer RF900R 43mm cartridge forks that would go AWESOME on this, but Formula 500 race class rules limit forks to 38m, & these 37mm GS500 forks are a direct bolt on with GS wheels/speedo drive/82-83 GS1100E aluminum triples. I could do the RF900R forks (AWESOME FORKS basically Bandit 1200 forks but shorter stanchions), but in WERA, I'd get bumped into the lightweight Superbike class which would mean I wouldn't be competitive unless I went to the largest bore possible to get it to the 520-540cc range with huge cams and shim under bucket, & mandatory extensive head porting. That means welded crank as well, & more mods. It would be a peakey high rpm engine then that wouldnt be as enjoyable on public roadways...

**Chuck78** · 03-05-2017, 04:23 PM

Here's where I'm at so far...

*3.50x18 DID alloy rear rim & 140/70-18 Shinko SR741 (very sticky!) (F500 rules limit rim to 3" but I may be able to race anyway - but if I am beating everyone, they can protest and I forfeit the win/placing)

*Cool drilled GS rotor that I'm not sure of the exact model sourced from
(1st Gen GSXR underling opposed piston caliper in the mail - may or may not require a custom hanger for this diameter of rotor, or a custom rotor adapter to fit the gixxer 250mm(?) rotor. Hopefully it fits a GS hanger)

*Dresda style custom TIG welded comply box tubing swing arm with underling brake stay mount (needs narrowed slightly, considered GS500 or Ninja 250 swing arms as well as to not cut this desirable piece up)

*Nitrogen charged Fox Factory Shox - very awesome damping, very sought after is these were the best vintage high performance shocks leading up to the end pf the twin shock era

*GS1150 aluminum brake stay arm that I hope to be able to adapt

*Hayabusa rearsets with 3 bolt vibration isolator rubber mounting & folding footpegs with steel "pavement grinder" posts hanging off the ends!

*Red poly coated Core stainless steel brake line

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**Chuck78** · 03-05-2017, 04:32 PM

*GS500F late model 37mm forks
-runs GS's 15mm axle so speedo drive will be no issue)
-will add Racetech Gold Valves and Sonic Springs

*GS1100E 82-83 aluminum upper & lower triples - gives me correct offset and trail whereas the GS500 triples are tla totally incorrect offset for this build and the stem won't work in the older GS frames
(I think GS1000G's - NOT GL's - use this same lightweight aluminum lower triple for straight leg forks, & possibly 79 GS1000's with straight leg forks. In ebay photos you need to look at the bottom underside to see if the stem is welded in (steel triple) or pressed in (lightweight aluminum lower triple), & also if the lower triple is rusty, it is steel! Shiny silver bare metal = maybe aluminum. The steel teeming stops are different on the steel vs aluminum lowers - also a good way to spot the aluminum. The left side is much longer and arcing. Aluminum versions also look like they were cast with an extra boss on the rear to have a lower stem pinch bolt... strange)

*clubman bars

*Tokico master cylinder with fancy aftermarket adjustable reach levers on clutch and brake

*stainless braided front brake line

*1/2" billet aluminum cnc'd custom GS500 fork brace

*Tokico twinpot 2 piston sliding caliper

*CB1 310mm floating rotor (F500 rules will nix this as I'll need to make up some custom centers for 89-ish GSXR rotors as they have to be period correct style meaning no floating rotors)

*D.I.D. 2.50x18 alloy front rim - has 110/90-18 Shinko on it but that needs to get swapped for a 110/80-18 in a Pirelli Sport Demon

*VF750 fender - needs some heat gun and Dremel manipulation to fit the GS500 fork brace mount area

.

**Chuck78** · 03-05-2017, 04:40 PM

I'm really into riding tight twisty winding roads in the Appalachian hills of Southeast Ohio, Eastern Kentucky, & all of West Virginia... I've made my 77 GS750 as light as I reasonably can in reasonable street trim. I really wanted to do another GS project with emphasis on it being the lightest thing possible for a super fun backroads canyon carver, & with top notch suspension upgrades, first rate braking power, wider rubber, and improved geometry and chassis.

Taking a GS twin and making it handle exceptionally well on the back roads isn't too much of a task, but maximizing the engine's potential to make me not think twice about it vs a 920cc GS750 or an 1105cc GS1000 is a big challenge that I wanted to take on to make the lightweight GS400-425-450 chassis work on all levels for me, hence seeking out the 425's cylinder jug as it has 2mm larger sleeves than the 400... could go out to 475cc with custom pistons, or easily go 449cc 10.4:1 with off the shelf Wiseco GS750 pistons (APE sells sets of 2 with proper head gasket). It has hot cams stock, but a set of hollow core GR650 Tempter cams have higher lift and make a great street torque cam or excellent basis for a re-grind. I have such a set of GR hollow core higher lift cams here awaiting this project..

The 400 & 425 are 1st generation GS's of the era where EVERY GS came with a brute tough roller bearing crank. The 450 is of similar architecture, but uses a plain bearing crank, shorter stroke/bigger bore, & slightly altered cylinder stud spacing.

Being a HUGE 1st Gen GS / 70's Superbike fan, this was a no brainer to pick the 400-425. Longer stroke on a tougher crankshaft gives more potential, & off the shelf Wiseco k844 GS750 pistons drop right in to give you a lighter piston, higher compression, & bigger camshaft choices than the GS450. The 450 of course can take 1989-2010 gs500 cylinders & pistons with some deck height adjustments and (for aftermarket big cams) some piston valve pocket machining, but the 1st gen won in my book. No off the shelf aftermatket pistons are a drop-in for the 450's or 500's. Custom only.
The 450 frame does have a simple tubular brace behind the ignition coils that the 400-425 & 550 lack, however... easy to add to make it sail through high seed turns without noticeable chassis flex.

Then comes the bug to do track days and some less serious WERA Formula 500 and other vintage classes and possibly AHRMA...

**Steve** · 03-05-2017, 05:29 PM

What are your plans for carburetion?

That was the first year of the EPA clamping down on emissions, so stock jetting was nastily lean, mainly on the pilot and the needle.

With your proposed big-bore kit, re-jetting will be obvious, just letting you know that you are starting from a point that is considerably leaner than usual.

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**Chuck78** · 03-05-2017, 06:37 PM

Vintage road racing class rules require period correct style carbs (i.e. round slides, no flat slides), so basically Keihin CR smoothbores or making a custom rack of 2 cylinder VM29 smoothbores are the only real options. Excellent options though, ZERO complaints here!

The REAL/ULTIMATE ENGINE GOAL HERE is as follows:

Custom JE pistons in 72mm for 489cc or 72.5mm for 495cc. Lightened up a bit, shorter skirt in areas, 10.5:1 compression. This will require GS450 sleeves bored into the 425 block. A friend from down under designed some custom JE pistons a while back and is going to order some more for me with some valve pocket depth / bore size / dome cc's alterations from his original design. I am very thrilled about this prospect.

Then I'd want to send the GR650 Tempter hollow core cams to Web or MegaCycle for a performance regrind and run .354" lift minimum, maybe .380" lift intake and .354" lift exhaust, or if Web, .395" lift intake and .365" lift exhaust. I'm leaning towards the MegaCycle .380" option as I'd like to try and run shim over bucket, but might cave in on that idea upon recommendation and just do the .395" lift Web intake and .365" lift exhaust and shim under bucket. Only 4 valves not 8 to adjust so it'd go quicker than the kz650's shim under setups that I've dealt with before.

Going this preferred route, I'd be sending my head to rapid ray for a road race porting job and likely 1mm oversized valves. This is really the ultimate goal.

then the best plan of action on the carbs would be some Keihin CR31 smoothbores. The only ones I can find spec'd off the shelf for twins in 29 or 31 are for smaller CB twins & ninja 250's, but road racers tend to prefer CR29 or 31 often for this displacement per cylinder on tighter courses.

I can get Keihins already spec'd for GS500's which seems the easiest route, but they are CR33's. I don't think I'd regret going CR33, but some will say that I'd get better response on the midrange throttle opening areas with 29's or 31's.

I don't think a welded crank on a light bike such as this is necessary, but I'd I do the max performance potential on this thing, it may be a decent consideration.

**Chuck78** · 03-05-2017, 06:40 PM

I have 2 gs425 engines. I may end up building 2 similar bikes, or may ho the budget route at first and do the following engine as the first and more budget route.

If I do a second similar but more budget build 400/425, it'd have the stock mag wheel front in GS550 forks and a rear 2.15x18 disc brake mag wheel and GS750 swingarm. Run stock carbs and dynojet needles, Wiseco K844 pistons and GS400 big bore head gasket from APE/GSZone.biz, & choose between GR650 cams (higher lift street torque cams), early (with tach drive gear vs later electric tach) GS500 cams (medium lift medium duration), & 78-79 GS400/425 cams (biggest duration for high rpm power but modest lift for durability). Dyna-S and Serdi valve job.

**Chuck78** · 03-05-2017, 06:55 PM

From an old thread on here about a GS400 with Wiseco K844's for 449cc:

Originally posted by bogmonster View Post

got out for a few short shakedown rides, so far impressed with the power. I never rode the bike before the motor work so i cannot comapre to stock performance. I will say a buddy was on his xs 650 ,and he was having trouble keeping up even though i was being easy on it to break in the rings.

Plan on getting it on a dyno this winter for the final tune. More pics to come

^^^^ THAT IS the kind of result AT MINIMUM that I am shooting for. A lightweight agile superb handler that really surprises people with how quick it is.

there was another old post on here about a similar build where a member commented that this GS400 or 450 was so quick off the line that it had ejected unsuspecting test riders after lifting the front wheel very rapidly towards the sky! I want to say that the owner of that bike is no longer registered here but his name was (something)-orange

I can get a pair of two Wiseco K844 pistons for $213.50 shipped plus a custom head gasket, or possibly Big Jay still has sets with a proper 69mm GS400/425 head gasket. 40cc or 46cc additional may be well worth the hundreds of dollars that resleeving + much fancier custom JE pistons would cost, as this is something I am doing to push the limits of what vintage bikes of this original capacity can do. It's a fun challenge, & the budget can just be drawn out a little longer to afford the additional expenses.

**Chuck78** · 03-07-2018, 02:18 PM

I'm thinking pretty hard on several of my project bike builds, scouting for good deals on parts, contemplating pistons and camshaft profiles, etc...

I looked up specs on the GR650 Tempter cam grind again. They are .364" lift and 268 degrees duration @ 1mm/.040" valve lift. This would be a very good torquey midrange street cam for certain...
My engine choices are now between the budget build:
*Mildly ported head for more low lift flow, Serdi valve job
*GS450 71mm stock sleeves bored into GS450 block
*bore cylinders for my used early 80's MTC 72mm pistons for around 10.25:1 & 489cc (old school forged pistons, heavier)

OR:
*full street porting job, Serdi valve job
*send cams to Web, regrind to #218 profile? .418" lift 242 degrees duration @ .050" lift (very torquey street cam!)
--**OR** Web #109 profile - .418" lift 260 degrees duration @ .050 (more mid and upper rpm range big power boost)
((Both will require KZ650 style shim-under-bucket parts & hi-performacne valve springs))
*Custom JE or Carillo Pistons, 73mm for 502cc, 74mm for 516cc? Much lighter - will spin up faster, & rev higher

I'm guessing plan B will run me $1250 additional for the more extensive porting, the cam regrind, shim under bucket, and the custom pistons... BUT... the thing would be an absolute screamer, and be fierce competition for even older 500-650cc fours, and would very much smoke an XS650 or even a Triumph 750 old school twin...& weigh only 325-330lbs!

Plan A will surely be a pleasing and fast engine to run, especially in the lightened up chassis with the much more advanced suspension that I'll be running on it. BUT... Plan B will be building this thing to the hilt, & may leave me generally reaching for the "little twin" over the big Fours when I head out to the twisties or just cruise in the city... the 920cc GS750 made me a bad rider in the city... too much powerr, can't keep myself from twisting that throttle wide open ALL the time... It's addictive!

What it ultimately comes down to is how much money I will have to spare for this build when I get this thing worked over. I'm really thinking that I would like Plan B so much that I might want to build a second bike even, in which case the other pistons and the gr650 cams as stock would really work well. I could even see myself building up a couple of these to flip on craigslist with stuffing in just some stock 850 pistons for 449cc 9:1 and milling the head for more compression (9.75:1?)

Plan B would definitely only be something that I would do for personal satisfaction and merit, as I would not be able to get that money back out of the bike if flipping it in the future unless I really did it up cosmetically to look like some Los Angeles hipster Cafe Racer build... I'm guessing that due to the light weight and the power these will make, this bike will be a definite lobg term keeper for me, but you never know.

Announcement

'79 GS425 big bore lightweight canyon carver / track bike project

'79 GS425 big bore lightweight canyon carver / track bike project

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