GS 450 Hybrid race engine

[burning1]

Well, I've been cooking up this project for a while, and I guess it makes sense to start a thread here in the projects section of GSTwins. As a few of you may know, I campaigned a GS500 in 500 twins with the AFM last year. Took 4th place overall in my class, collected a few top novice awards, and a 3rd place trophy. Unfortunately, the GS500 isn't super competitive in that class, especially against the 70+ horsepower SV-500 that sometimes runs there.

However, there is a rules exception in the AFM that permits a 450CC twin to run in the 250 superbike class - the rule exception permits unlimited mods. Toughest competition is a 2 stroke yamaha pulling high 2:04s around T-Hill; that's about 7 seconds better than my best pace. The good news is that a more or less stock GS500 should be powerful enough to consistently podium in the class.

The class it's self is pretty diverse, made up of 2-strokes, 450cc singles, one or two 450 twins, and a lot of production legal Ninja 250s. Broad range of lap times, and excellent competition. Because the GS can be made competitive there, it starts to make sense to put some real money into the bike, rather than running it just for fun.

Goal of the project is to drop 2-3 seconds based on riding skils, and pull down a few more seconds through mods. Thread will document my research, as well as mods.

I already have a bunch of parts, including my crashed out GS race bike.
- 06 GSX-R front end
- Race wheels
- RGV 250 swingarm, wheel, brakes, etc
- Yoshimura Pipe
- GS450 block/Pistons

Planning to add some go-fast parts as well.

[burning1]

Knowing that the GS450 & GS500 share the same crankshaft, stroke, and similar bore was the starting point for this project. I'm in the process of measuring up the various parts to ensure that they can fit together, but I have made the following initial assumptions;

- GS450 block shares the same oil passageways & stud spacing as the GS500.
- GS500 head can bolt to the GS450 block
- Clearances are okay with everything bolted together.

The assumptions seem pretty safe, but need to be confirmed.

GS450 & GS500 are similar, but the GS500 piston isn't simply a scaled up GS450 piston. Even without comparing the two pistons side by side, it's obvious that the GS450 piston has different valve relief. I will compare the two parts with a vernier calliper to see if the relief are due a taller piston crown, or if they are actually deeper, offering more lift. Both would be ideal; since a taller crown will increase compression, and a deeper relief will provide opportunities to machine down the cylinder block, and or install high lift cams. My eventual plan includes a set of Megacycle race cams, which I've read work best on a high compression engine. Crown diameter seems similar between the two pistons, which is a good sign that everything will fit.

If the GS450 piston isn't suitable for use, it's also possible that a 71mm KZ1000 piston will work. It features a high dome, and deep relief for compression, but uses a 17mm wrist pin, rather than the 18 I need to bolt to the GS rods. Ape Performance will machine out the wrist pin hole for $49 per piston. I'll probably buy a stock 70mm KZ piston to confirm that the dimensions are similar to the GS; I'd rather not waste $150/piston until I due diligence.

I have found that the GS450 uses a different style CCT than the GS500. I've confirmed through parts fiche that the GS450 CCT is the same part used on the GS1000.  APE Part number is ST1100, and the gasket is #EC062.

On the bottom end, I'm planning to remove the balance shaft and send the crank to APE for a rebalance/lighten. I'm also considering removing the alternator, and possible the starter for weight and power savings. If I remove the starter, I might have a bolt welded to the counter-shaft sprocket, permitting possible use of an electric ratchet to start the bike on cold mornings.

[burning1]

Suspension work:

I already have a GSX-R 600 front end I've been running at local trackdays. Been very happy there, thanks to the amazing machine work of Bob Brussard.

I also have a R6 shock, that's been running like a champ since it was installed.

At the tail end I've been working on a conversion to a RGV250 swingarm. Bad news is that I started with the double braced swingarm, which uses an atypical wishbone linkage rather than the more common dogbones. The good news is that a GSX-R 600 linkage can probably be made to fit. Will post photos as I complete that project.

It's not a huge priority though; stock rear end is working okay for the time being.

[Big Rich]

You sir, have my attention.

If you haven't already, check around on the GSResources. There is a LOT of info for abusin........I mean "modding" a GS450 engine. Off the top of my head there was a mention of keeping the counter balancer (for ride-ability) and somebody was fitting an 8 valve head to a GS450 (or maybe a GS400?)

[burning1]

Thanks for the heads up. Can't believe I hadn't checked out that website before.

[Big Rich]

Yeah, they have an extensive knowledge of the pre '89 GS's over there. I highly recommend checking it out.

[burning1]

I just measured out the old and new pistons. All measurements were done with a vernier calliper, and are probably only accurate to within half a MM or so. Although there are some clear similarities between the two pistons, there are also some very obvious differences.

To start with, the height of the piston pin to the bottom of the skirt is pretty much identical between the two pistons, and the general construction and casting is very similar.

However, the deck height is quite different - the GS450 piston had about a 0.5 mm lower deck height. Since the two pistons shared the same skirt to pin distance, the measurement for deck height is pretty easy.

Skirt to deck height:
GS500: 56mm
GS450: 55.4mm

The next, and probably most obvious difference is in the size of the crown on both pistons; the GS450 has a much larger dome:

Dome circumference:
GS500: 57mm
GS450: 62mm

Dome height:
GS500: 8.5mm
GS450: 10mm

Valve relief are deeper, and not just due to the increased size of the dome:

Relief depth from deck:
GS500 Exhaust: 2.3mm

GS450 Intake: ~.8mm from deck (1.2mm from crown.)
GS450 Exhaust: 3.22mm

Only big concern is the spacing of the valve relief. Measured from the outside edges of the exhaust relief to the outside edge of the intake relief:

GS500 Estimated at about 59mm
GS450 measured at 57mm (bottom of relief, not top.)

A visual inspections suggests that the valve diameter hasn't increased noticeably on the GS500.

So... Conclusions...

There are some remaining questions about whether the shape of the GS500 combustion chamber will work with the GS450 pistons. Wider, taller dome could potentially cause interference issues with the GS500 head; especially if I deck the cylinders. I am however optimistic, especially based on the wide spacing of the GS500 valves.

Lower deck height means that it's potentially possible to machine down the GS500 cylinder block and/or head for increased compression, and in order to optimize the squish band.

1mm deeper valve reliefs on both intake and exhaust side may help ensure clearance for a race profile cam... I'll have to measure everything out to ensure. According to megacycle, the Race profile add 2.845mm and 2.362mm to intake and exhaust lift respectively, as well as 12-15 degrees of duration. Might be a tall order to find that much clearance without sacrificing compression.

One other good news is that there is plenty of material in the GS450 pistons around the outside edge of the valve relief. If necessary, I could probably machine out the relief a little, if their spacing turns out to be too narrow. If things work out that way, I'll effectively end up adding a little depth to the reliefs as well.

Next stage:

I have a spare GS500 engine that's currently got the bottom end off. I'm thinking I'll start bolting things together to see how everything fits. Plan is to remove the valve springs on one of the cylinders, and actually see how much lift is available on the valves with the GS pistons stock deck height. I'll probably coat the pistons with clay or something to see where the valves end up when they make contact. Will probably also try bolting the engine together without the base and head gaskets to see what happens when the cylinder block is 'decked.'

In the process, I'll fill the combustion chambers with oil, to measure the effective chamber size; should tell me how much I'm raising up the compression. I think a target of 12:1 or so would be good combined with the race cams.

Thoughts?

[Mauricio]

Best of lucks, I am keeping tabs on this thread.

[burning1]

Compression ratio...

According to David J. over on the racers page on the main GSTwins website, It's safe to remove about 1.27mm from the GS500 engine. Since the circumference of the cylinder head combustion chamber isn't quite as big as the circumference  of the piston, we can easily conclude that all the material being removed subtracts space from the combustion chamber at cylinder level... If we assume that there is 1.5mm of combustion chamber in the cylinder/head gasket, and that the rest is in the head, along with the known compression ratio of the GS500 engine and the measurements listed above, we can calculate the following bits of information.

GS450 displacement per cylinder: 224.0cc
GS500 displacement per cylinder: 243.4cc
Total GS500 combustion chamber volume (with piston @ 9:1 compression): 24.98cc

GS500 cylinder combustion chamber space: 6.45cc
GS450 cylinder combustion chamber space (no decking): 8.31cc
GS450 cylinder combustion chamber space (decked so that piston deck is at same height as GS500 piston deck at TDC): 5.94cc

GS500 head combustion chamber space with GS500 piston crown (total, minus cylinder space): 18.53cc

GS500 piston crown volume (ignoring valve relief): 11.16cc
GS450 piston crown volume (ignoring valve relief): 15.61cc

GS500 head combustion chamber space without piston crown (head space + crown volume): 29.69cc
GS500 head combustion chamber space with GS450 piston crown (GS500 head, minus 450 crown): 14.08cc

In conclusion:
GS450 total combustion chamber volume (no decking): 22.39cc
GS450 total combustion chamber volume (cylinder decked so that GS450 piston deck is the same as GS500): 20.02cc

Resulting compression ratio, GS450 cylinders w/ GS500 head: 10:1 (no decking)
Resulting compression ratio, GS450 cylinders w/ GS500 head: 11:1 (decked so pistons are at same deck height as stock GS500)

Potential compression ratio, 1mm decking: 12.1:1
Potential compression ratio, maximum decking* (1.85mm): 14.9:1

* Maximum decking assumes that we can deck the 1.25mm that David J suggests is safe, plus the extra 1mm the GS450 pistons give us. In practice, this is probably not a reasonable assumption, due to issues of valve to piston clearance with GS450 pistons, dome to cylinder head height, spark plug clearance, etc. Beyond that 14.9:1 is probably more compression than I'd want to run on the stock GS500 pistons and bottom end.

All of these numbers are *very* rough of course; they are based on semi-accurate vernier calliper measurements, make quite a few assumptions, and don't take into account the displacement of the valve reliefs. As the resulting compression ratios increase, they are compounded by all inaccuracies. Ultimately, the best way to proceed is through empirical testing. Will be interesting to see how close I got...

[missk8t]

Sounds like it'll be a great thread to keep reading. But don't forget the most important thing.

[burning1]

Will have pictures of the pistons soon, and will continue to post pictures and specifications as I proceed. 

[burning1]

Sounds like it'll be a great thread to keep reading. But don't forget the most important thing.

Comparison of GS500 piston (left) and GS450 piston (right.) Differences in valve relief are obvious.



Side by side:




Pin height:



GS450 piston detail:





GS500 Piston detail:

[burning1]

When I did the initial measurements, I also weighed each piston...

GS500 piston came in at 10.5oz
GS450 piston came in at 9.9oz

Curious what the maximum RPM is for the GS bottom end. I've heard that a spring swap alone is good for an additional 2000RPM or so. With the stock GS power curve, the extra revs would be meaningless... But with a good race cam, they might provide a huge increase in available horsepower, if combined with the right gearing.

[crzydood17]

http://cgi.ebay.com/ebaymotors/1983-Suzuki-GS400E-cylinder-head-/300589603517?pt=Motorcycles_Parts_Accessories&hash=item45fc895abd#ht_760wt_939

get a GS400 head! if they will fit, 4 valve head!

[burning1]

Would love to. They bolt on, but the exhaust ports are pointed directly at the GS500 engine cradle; can't be made to work without extensive modifications. If I'm going to go to the trouble, I'd rather use a GSX-R head.

[burning1]

I'd like to do a shim-under-tappet conversion on the race GS. Doing some research, I found that the GS500 and GS1000 share the same tappet. A little research on the web camshafts website gives me a measurement of 33.5 OD for the GS500/1000 tappets. I'm hoping to find another bike that uses shim-under with the same size tappets, but it might be a long shot. Good news is that one GS1000 kit provides enough tappets to do 2 GS500s.

[Phil B]

Would love to. They bolt on, but the exhaust ports are pointed directly at the GS500 engine cradle; can't be made to work without extensive modifications. If I'm going to go to the trouble, I'd rather use a GSX-R head.

waitwhut? its possible to convert a gs500 to a 4valve-per-cyl jobbie?
Inoramuses like me would very much like to know how this would even be vaguely possible
  (you'd have to get a whole new set of carbs at minimum, presumably?)
and what the likely side effects would be
  (possibly more HP, and correspondingly suck-butt mileage? and probably failing any EPA tests?)

[burning1]

Possible, yes.

A few of the old GSX-R 750 oil-cooled heads use the came cylinder spacing, oil passageways, and bolt patterns as the GS top end. In order to use them though, you have to lop off two of the cylinders, modify the cams, and somehow seal the valve cover. It does require different fuelling, though my guess is that it would run well enough with the stock fueling to get the bike on a dyno for tuning.

Again, the 8 valve GS400 head is probably a no-go in the GS500 frame; the GS400 exhaust ports point directly at the GS500 frame spars. Compare:

http://www.motorcyclespecs.co.za/Gallery%20C/Suzuki%20GS400%2077.jpg
http://www.mcnews.com.au/NewBikeCatalogue/2001/Suzuki/Images/SuzukiGS500_lhf_600p.jpg

Keep in mind that there are also two different versions of the GS400 heads; a common 4 valve model, and a less common 8 valve model.

Either approach would require new pistons, extensive machine work, and would get in the way of finishing this project in time for the 2012 race season. If I stay on a GS for years into the future, I might look into running an oil cooled GSX-R 750 head.

[burning1]

Just re-checked the rulebook, and it looks like AFM permits me to bore the engine 1mm above the class limit of 450cc. Good news, since that would permit use of MTC 72mm KZ1000 pistons; they are available in 2 different compression ratios, and officially support a 1mm overbore on the wrist pin, necessary to run the GS's 18mm pins.

Going this route would bump my overall displacement up to 460.8cc, but the main reason I'm interested is the increase in comp ratio, and the fact that the deeper KZ valve reliefs may be necessary for use with high lift cams.

http://www.mtceng.com/piston/mtc-products/pistons/kawasaki/kz-900-1000

Other benefit is that I wouldn't have to re-sleeve to restore the GS450 blocks to factory tolerances; I could simply bore them out by 1mm if it turns out that there is too much wear on the cylinder.

[burning1]

Looks like some of the early model GSX-R 750 and 1150 bikes came equipped with Mikuni Flatslide pumper carbs, but only in the UK. Would be a great performance mod for the GS. I'll probably import a set and comment on how it works out when I have a chance to fit them.