GS600EFI Build

[WolfTechnics]

I wish to start a new thread chronicling my GS450E build, in which I’ll be using a beefed-up GS400 bottom end with a GR650 head to create a 600 cc two-valve engine. I attempted something similar in the past, as documented in a thread I started in 2014. However, I no longer have access to that username, and the old thread is full of dead photos and links, so I want to start over. This time with less naivety, more in-depth research and more realistic goals.

So what are those goals, you ask?

A 608 cc, 11:1-compression two-valve GS twin based on the GS400X bottom end, with GR650 barrels and head, custom pistons and rods. I plan to achieve this by doing the following:

- Boring out the upper crankcase to accept massive jugs (hehe...).
- Moving the cylinder studs to accept the GS500E/GR650-style cylinder block.
- Machining out the original 28 mm crankpins and replacing them with 29 mm GS1000 crankpins. We can use this opportunity to increase the stroke from 60 mm to 60.5 mm. I may skip this step if custom rods prove necessary anyway.
- Using a GR650 cylinder block, which can be bored out to 80 mm.
- Ordering custom CP-Carrillo pistons designed to match the bore and GR650 combustion chamber.
- Using stock GR650 cams at first.
- Building a custom exhaust.
- Installing a full EFI system to control and monitor the engine.

There are many—and I mean many—things to consider when building an engine like this properly. My main goal is reliability, so I won’t be chasing the absolute maximum possible horsepower. That can wait until I eventually get around to building a four-valve GS twin engine. I hope to achieve more than 60 horsepower at the rear wheel, which would be a very nice result. I have spent a lot of time thinking about this build over the past few years, and I believe this is the best route to take.

A little backstory

The GS450E that this engine will eventually go into was my very first motorcycle, bought for the grand total of €100! I never plan on getting rid of it, but I do want to turn it into something fun: a strengthened frame, lightweight wheels, a beefy USD front fork and a radical engine.

My previous attempt at building this engine, many years ago, ended when the balancing company lost my rotating assembly, including the CP-Carrillo pistons and rods. The company went bankrupt, and I never spoke to or saw the owner again. That was a lot of money down the drain, and the project has been collecting dust ever since.

I have always wanted to complete this build, but I used to work on too many projects at the same time and ended up finishing none of them. I have now done away with the other projects and am focusing solely on GS twins as a hobby. I am currently building two GS500Es to OEM+ specification, and that project takes priority over this one. On top of that, I have a baby on the way, so progress on the GS450E probably won’t be particularly fast.

So why start a thread already?

I intend to use this first post as a repository for all sorts of information I have gathered. I want to chronicle what I learn along the way and make it easier for someone else to attempt a similar build in the future.

 

[WolfTechnics]

Useful Data

This section will be used to update data as I find new information. Please feel free to correct anything you deem incorrect; the goal is to have all relevant information for GS twin modifications in one place.

If one wanted to build a fun engine for considerably less money, the stock 28 mm crankpins could be machined out of the GS400 crank and replaced with pressed-in 29 mm GS1000 crankpins. This would allow the use of GS1000 connecting rods, which are geometrically the same as the GS400X connecting rods but use an 18 mm wrist pin.

The larger wrist pin would allow the use of GS500 pistons and the GS500 head, resulting in 516 cc: essentially a stroked GS500E. Deck height and compression ratio would still have to be sorted out.

Connecting Rods​

Engine Type	Big-end Bearing	Big-end Width	Big-end Outside Ø	Big-end Weight	Piston Pin Ø	Small-end Width	Small-end Weight	Total Weight	C-C Length	Rod-Stroke Ratio
GS400X	28x38x19.8				16				114.9	1.915
GS450E	Ø34 plain shells				18
GS500E	Ø34 plain shells				18		50.5
GR650					18
GS1000	29x39x20				18				114.9

I find the comparison between the GS500E and GR650 heads interesting. The cam-chain tunnel on the GR650 is much bigger. The head gasket lines up, but not nicely. At the front and back, in line with the tunnel, there is very little overlap between the GR650 head and the GS500 gasket. It will work, but be aware of this.

The GR650 intake channel is actually smaller than the GS500E intake, which surprised me. The smaller intake channel but much larger intake valves on the GR650 head probably have to do with the focus on swirl in the GR650 head. It would be interesting to see whether any gains can be made by increasing the intake size on the GR650 head, but this will be for later.

• The valve covers are interchangeable between the GR650 and GS500E.
• The chain guides are interchangeable between the GS500E and GR650, but I do not know whether the GR650 variant is longer. This is still unknown to me.
• Camshafts, buckets, shims, springs and valve keepers are all interchangeable between the GS450, GS500 and GR650.

Cylinder Heads​

Engine Type	Exh Ports	Int Ports	Chain Tunnel	Spark Plug Angle	Int Valve Angle	Exh Valve Angle	Camshaft Interchangeable with GS500
GS400X
GS450E							Yes
GS500E	31.0	35.0	11.5x139				Yes
GR650	34.8	32.8	21.5x155				Yes

Valvetrain Component Weight​

Engine Type	Intake Valve	Exhaust Valve	Shim	Bucket	Valve Cotters	Spring Retainer	Inner Spring	Outer Spring	Spring Seat
GS400X
GS450E
GS500E	25.51	20.20		13.52	0.6	5.93	8.36	18.07	5.55
GR650
GS1000

Camshafts​

Engine Type	Intake Lift	Exhaust Lift	Intake Duration	Exhaust Duration	Overlap
GS400X			280	280	74
GS450E	8.5	8.0
GS500E	8.5	8.0	277	267
GR650	9.25	9.25	268@1mm	268@1mm

Pistons​

Engine Type	Weight	Diameter	Compression Height	Overall Height	Crown Height	Skirt Length	Ring Set Weight	Circlip Weight	Pin Boss Inside Width
GS400X		64.5	24.25	63.50	11.8	51.1			24.25
GS450E
GS500E*	217	74.5	26.2	64.58	8.52	56.06	6.72	0.18	24.00
GR650	274	76.36	26.93	64.00	5.03	58.97	6.82		23.00
GS1000

* = First oversize

Wrist Pins​

Engine Type	Diameter	Length	Weight	Inner Diameter	Wall Thickness
GS400X	16	53.5	20.98	10.85	2.575
GS450E
GS500E	18	55.5	21.04	12.90	2.55
GR650	18
GS1000	18

Please feel free to post information that should be added here; I will add it to the tables.

 

[WolfTechnics]

Parts Selection

With parts selection I mean to say how do you know what combination of parts to pick to build a proper motor, and oh boy! do I think about this a lot, there are so many factors to consider that it becomes difficult to keep track of. So writing it down here actually becomes rather therapeutic.

First I feel like I should address my choice for the bottom-end, why the GS400X? and why not the stock GS450E or even the GS500E bottom end? Here's a list of personal reason why I choose the GS400E bottom-end:

• It has kick-starter, I will look cooler
• It has MASSIVE roller bearings for the crankshaft, and balancer shaft.

The GS500E engine, and in extension the GS450E engine as well, is not particularly known for accepting an increase in power very readily; cracked crankshafts, worn out big-end bearing and worn out balancer shaft bearings are all part of the game when you increase power even slightly. Sure, there are stories of bored out GS500's with a cut-off GXRS-750 head, only using the inner two combustion chambers, but they had to replace the crankshaft every race season.

Now, if you have deep pockets, sure, you could make the GS500 engine work with a billet crankshaft, but with money you can do anything, that's no fun isn't it? and you still would not have the most important quintessential ingredient to a cool bike, the kick-starter! No we have arrived at the heart of all of this shenanigan, the crankshaft. The GS400X crankshaft uses the same bearing layout as the GS1000 (except for the con-rods, but more on that later), and the GS1000 is a well known name in the racing and drag strip community. For instance the Yoshimura GS1000 AMA Superbike achieved 133HP @ 10.000 RPM, that's 33.9HP per cylinder. Just simply (and it never is "simply") converting that to the GS400X twin means the little beast would be good for 68.8HP when considering only the crankshaft. But it gets better, by a lot. The R.C. Engineering / Terry Vance & Byron Hines GS1000 Pro Stock was bored up to 1176cc and made 175HP @ 11.000 RPM, that's a whopping 44.4HP per cylinder using a stock welded crank and stock GS1000 con-rods. That puts the maximum HP that the GS400X crank can take at 88.8HP, maybe even more considering this crank only has to deal with the dynamics of 2 pistons instead of 4.

Anyway, achieving these kind of power figures is a far-away dream without throwing serious money at it, but the point is clear, the GS400X roller bearing crankshaft is a much better foundation to build on than the GS500E plain bearing crankshaft. You'd also get the added benefit of a 60mm stroke instead of the 56.6mm of the later models.

Are there any downsides? well yes, and big ones at that, here's a list:

• The GS500E/GR650 cylinders don't just fit on the GS400X bottom end, you'll need to bore out the casing to accept bigger jugs. 6/8 cylinder studs need to be moved, and then you have the dowel pins to figure out.
• Internal oil passageways will not line up between GS400X bottom end and later type cylinder blocks, a solution will have to be figured out.
• The GS400X balancer shaft is only meant to balance out the secondary dynamics of the tiny stock pistons. Put bigger and heavier pistons in this engine and you will run into balancing issues, I will talk about this more later.
• The power the stock GS400X crankcase can handle is an unknown. I hope to change this, by either it not being relevant (ie., it's plenty strong), or ending up with a cracked crankcase and cracked hopes and dreams.
• The attachment points to the frame are different, welding is required, unless you want to run a GS400 frame. In fact, the complete bottom end is different and shares little parts with the GS500 type engine.
• The small end on the con-rods is only 16mm in diameter, this is plenty strong for good power but it severely limits piston choice.

The 16mm wrist pin situation can be resolved by using the GS1000 con-rods, which are geometrically the same as the GS400X's (see the con-rod table), but again -as with everything- this is not easy. The challenge here is that the GS1000 uses 29x39x20 bearings for the big-end, whereas the GS400X uses weird 28X38x20 bearings. I have acquired an GS1000 crankshaft to compare parts, and this is an area I am actively researching, but I believe the solution is a modification to the GS400x crank counterweights. You'd have to remove completely the integral 28mm crank pin from the inner counterweights and re-drill to 29mm, this will allow you to run the stock GS1000 con-rods, benefiting from a slightly larger crank pin and the 18mm wrist pin diameter. Don't forget to have the crank welded once put together.

That's it for an explanation on the bottom-end so far, more soon!

 

[alke46]

And at last, we have found that guy with too much time on his hands.

 

[Rich82GS750TZ]

Yep. I think you’re going to get a whole lot of following along here. Maybe not a lot of contribution. But it appears you know what you’re doing and why. I don’t get it, but I don’t have to. Following out of sadistic curiosity.