450 twin upgrade/modification possibilities???

[Guest]

Howdy,
I've had, what I've just discovered, is a GS450 twin frame and engine (originally was told it was a 400, possibly gsx) sitting in amongst my other projects for a while now.

I've been asked to get a bike ready for some clubman racing in the next year or so and seeing as these bits (alongside a complete gsx250) owe me bugger all I figured I'd see if I could get something happening.

Now I've been doing a lil researching (always a bad sign) and the wee part of my brain that is always try to cause trouble for the rest of me, has given me the idea that I might be able to either/and/or take this thing out to a 500 as well as slap the 8 valve head (with the necessarily upsized valves) from the 250 on top of it. There was a small part of me that thought/hoped this might've been a gsx400, but the odd hint, plus a proper look at the engine and VIN has given me the news that I have a 2 valve per jug 450 rather than the hoped for 4 valve per jug gsx400.

Soooooo, am I being totally silly wanting to swap this head over??? Should I also stop thinking about upping the cubes to 500?? Aaaand on a sorta, but not really unrelated note, can I possibly use the pipes off the 250 on this thing without totally strangling it??

Oh yeah and while I'm at it, I seem to remember that the gsx400 shared inlet and exhaust valves with one of the larger displacement GS(X)s, could someone enlighten me as to what that might be as I haven't had any luck looking (although I do have a dim dark memory that I may have actually purchased the necessary items a while ago but have forgotten the details)

I already have a set of wire wheels for this thing that I picked up last year so that's a start eh???

Any and all help, muchly appreciated.

Oh and I'm located in occasionally sunny Melbourne, Australia so if there are any fellow GS wrench spinners local to me I'd love to hear from you...

Cheers Raff

[pete]

Well, not quite local... couple thousand km's north

I don't believe the 8 valve head will work, but you can certainly stick some barrels and pistons from a GS500 on there for a nice capacity increase. Haven't done it myself but I believe it's fairly straight forward with maybe some stuffing around with the head gasket. Others here have done the swap so I'll let them chime in on that.

GS500 carbs and camshafts drop straight in also, although you may need to fiddle with the shims on the camshafts to get them seated nicely with no slop. I run both from a 2001 model and they have definitely made her breathe a little easier, and the 500 cams seem to move the power a bit lower down in the rev range so she has a bit more midrange. If you're looking for top end, might be better sticking with the stock cams... depends where you're racing I guess!

Ignition is potentially a big issue if you don't have the ignitor etc. with the motor. In theory you could also retrofit a GS500 signal generator and ignitor on it and use the electronic advance built in, but I believe they hit full advance a little later in the rev range. Can't quite remember now...

If you go the GS500 carb path, beware getting velocity stacks is a little tricky as they're a huge 60mm inlet. I'm pretty sure these are the ones I bought:

http://www.jntperformance.com.au/index_i6515601.html?catId=269035

They have no mounting method so I cut 4 slots at the front to allow some stainless steel hose clamps to clamp them on to the carb inlets. I also had to trim some off the front to make them a bit shorter to clear the frame rails. The left stack still touches the fuel tap but it's worn a groove in it now so it's no longer an issue...

Exhaust wise, I'm not sure on the 250 heads, but I know 500's are out of the question as the 500 head's exhaust ports point straight at the frame rails on the 450 frame.

I do find in the twisties in the hills I can *almost* keep up with my mates on their big Katanas providing the road isn't too open, so I don't see a 450 engine being anything other than fun myself

If this motor starts getting tired I'll be thinking of some 500 barrels myself...

[Raffspeed]

Well that's a pain in the arse... I was hoping that the 250 head was the same basic casting as the 8 valve 400 (which I thought this was when I bought it...)

Thank Christ for the rebirth of the humble 500 though, heaps of parts around for them at reasonable prices...

[pete]

Hopefully someone can confirm on the head side... haven't looked into it too much myself... pretty sure some of the oil galleries don't quite line up or something along those lines.

And yep, plenty of 500 stuff around the place and prices aren't too shabby at all!

[GregT]

Well that's a pain in the arse... I was hoping that the 250 head was the same basic casting as the 8 valve 400 (which I thought this was when I bought it...)

Thank Christ for the rebirth of the humble 500 though, heaps of parts around for them at reasonable prices...

Just bore it to suit 500 pistons. That's quite cheap and well worth doing. If you search, somewhere on here is a pic of a 500 piston with valve pockets cut to match 450 ones. There's some discussion on that thread as to whether it's necessary for a road motor. That application was a race motor with quite big cams.

The 250 is a physically smaller motor. If you overlaid 400/450 head gaskets over a 250 head gasket it's quite obvious the 250 has very different stud centers - and bore spacing.

[Chuck78]

Great base bike to start a racer/fun in the backroads bike out of!

You don't want the 4 valve head, they aren't that great as they don't offer much performance gain over the 2V, are prone to cracks, & many parts are obsolete for them. Custom piston work only as well.

What you do want to do is upgrade to GS500 cylinders and pistons, but double check your compression ratio quite well with deck height/piston depth into hole, piston dome, head gasket compressed thickness, & measured chamber volume with a 450 head after a fresh valve job. Deck the head accordingly if you are too low. The bores are much bigger do smaller piston domes are necessary, but the GS500 piston domes are much smaller. The valves are in a slightly different location as well, do a clay mockup if you can.

Another trick I read of is that GS1100G pistons can be bored into the 450 block or BIG GS1000 big bore pistons bored into a GS500 block. The combo I recall yielded 470cc & higher compression (?) maybe with the stock or .5mm over gs1100g pistons. Of course dome height and valve clearance to domes need checked. The compression height of this setup is lower, so it may be necessary to substantially deck the cylinder jugs top and bottom to make this work

The 500 setup and minor valve clearance is easier. There were some 78mm GPZ1100 Wiseco pistons that fit the GS500 but you'll have to research that on gstwins.com. I think it was the 79mm V&H big bores made by Wiseco that also worked way back when... one or the other changed the dome design and no longer worked with the smaller-diameter-than-gs450-chamber gs500 heads. May still work for a gs450 with 500 cylinders.


The 1978 GS400C / 400EC cams offer the most duration and high rpm hp (& best exhaust snarl), the early gs500 cams (with mechanical tach drive gear) are the best street cams, megacycle cams are the best performance cams in the aftermarket. The .354" lift model us great for these bikes.
The GR650 cams (with GS cam sprockets) are biggest lift of the oem but less duration for more street torque, so less top end.

After any decking or cylinder swapping, DEFINITELY degree the cams and use slotted (or dremeled) Cam sprockets. Set them at 104/106 for best street torque, 110 lobe centers for best top end hp. Dialing this in makes a substantial difference in the engine characteristics... and is MANDATORY after decking or swapping cylinders.

Run the GS500 carbs and intake boots, look to Big Rich's GS450 build thread for jetting on his setup. Or ask Pete. K&N makes a nice lunchbox filter for the GS500 carbs.

What is the i.d. of the 250 exhaust at the head? If the same, it should work!

GS500 forks and caliper + Racetech Gold Valves is a great affordable upgrade (stiffer @ +4mm larger diameter of 37mm and much lighter) that runs the same axle size so you can run the wire wheels you have and have with a gs500 axle and some spacers off of a gs500/gs1000/gs1100e mix& match.
Run a CBR900RR 98-99 rotor drilled out to 8mm mounting bolt holes, jig up in drill press with 6.#(?)mm bit as alignment guide, clamp rotor, swap to 8mm bit diameter of the shoulder on the GS rotor bolts.
run the GS500 forks in an 82-83 GS1100E aluminum triple clamp set (the v-shaped one with more offset than the 80-81 1100E that looks like a rectangular block). Thus will give you great rake and trail for your GS wire wheels.
Run 3/4" to 1" longer rear shocks of good quality, this will quicken the steering to just the right amount with the front end I suggested.

You can also weld twin shock mounts to a gs500 or bandit 400 swingarm and narrow them to get them to fit. I was looking at some motolana sr500 aluminum aftermarket swingarms thinking that they could easily be made to fit the GS400/425/450 twins easier than the budget used steel box tube bandit/gs500 arms that require modding.

The GS500 ignition was a curiosity of mine... could be a great modern budget swap.

A lot of the gs500 is the same below the cylinders, mist of it actually. Due to rearsets configuration, the shift drum is reversed so it would give you a backwards GP shift pattern on a GS with stock setup. The latest version '06 or '07 gs500 came out with revised connecting rods, so if building a big bore 450, DEFINITELY look into ordering those...
I run the 500 master cylinders on a lot of single disc bikes as I HATE rebuilding the old GS masters!!!! What a pain... the gs500 masters are nice and you can get pretty fresh ones for cheap.


Hope all this info helps

[Nessism]

...or pick up an EX500 and be done with it. 50 rear wheel hp and reliable.

Don't take me wrong, I like the GS twins. But it's pretty silly to spend several thousand dollars hotroding one.

[Chuck78]

You can also make a GS527 with a GR650 head (only with 450/500 cam sprox tho), GR650 pistons with the looonnngggg skirts shortened to clear the shorter stroke 450 crank), GS500 cylinders bored to 77mm, & a shaved zero deck block using the gs500 base gasket and a SUBSTANTIALLY SHAVED head deck surface to decrease the massive chamber volume (the big combustion chamber was designed for compression ratios figuring on a huge 70mm stroke crankshaft, the 450 is only 56.6mm stroke - a real high rev friendly high rpm screamer). If you don't do the last substantial head decking step, then your compression ratio will be like 7.6:1. I'm guessing after the 500 base gasket and milling the 500 block to a zero deck piston installed height, you may need to shave 1.3mm+ off of that head. And then run gs500 cams and check valve clearances once you get a decent compression ratio above 9:1. If you need to have the valve reliefs cut deeper on a milling machine with a fly cutter bit, then you'll be lessening the compression ratio again and need to mill it a little more
This is a great setup, however! "GS527 Beast" on youtube.
A couple of racers have done this. Oh, did I mention YOU MUST SLOT THE CAM SPROCKETS AND DEGREE THE CAMS with this setup? Different deck height aways makes that an absolute must... sorry if I sound like I'm preaching to you, not sure how much background you have in this stuff, and putting all this info out there for everyone else who might happen upon it.
A good evening spent measuring the piston dome cc's and chamber cc's and calculating how much to mill from the head to arrive at 9:1 compression with 77mmx56.6mm bore and stroke is critical here. And taking the 77mm bored out gs500 cylinders and clamping the block down with gr650 pistons installed to measure how much you need to mill off the cylinder deck to get a zero deck height. Then visit your favorite machinist!

None of this stuff is outrageously expensive as all the hard parts can be oem used parts as upgrades unless you go Wiseco GPZ1100 or gs1000 1100cc+ pistons.the machine shop work will run the most but it's on my a 2 cylinder so not even that bad. Then you will have an awesome old gs twin racer built on a shoestring budget that looks way more awesome than an ex500...

[Chuck78]

wera90ex (rich graver on the WERA forum) & lizard84(?) On the WERA forum are quite the gs450 tuning experts. Rich has been racing gs450's for a long time (been with wera for 38 years? Racing gs450's since at least 1991 when this 1st pic was taken). His current race bike was one of THE FASTEST in Clubman Expert for the past 15++++ years. The rider is a big part of that as well, he is a total pro...












From CafeRacer.net:

[Chuck78]

$35 1997 GS500 carbs if you're looking. Ask Pete or Big Rich which years are the best to get, as there were many revisions.

http://www.dotheton.com/forum/index.php?topic=71275.0

[pete]

I have the 2001 model carbs on mine, Rich has an earlier set I think? The ones I have are a little different as they have a mid-main jet in addition to the pilot and main jets. It allows for a little more flexibility in that mid range jetting along with the needle... although if you're like me that just means more confusion