Suzuki GS400 to GS450

[Guest]

Hi,im wondering if its possible to swap the cylinders and cylinder head of my GS400 with Gs450 parts?
My GS is from the 1979 with contact points,if i swap the head and cylinders with 450 will i need to change the ignition to electronic?

I need more power from my bike and i dont want to swap bike( for the moment my license allow me to ride bikes to 35kW,and i love my bike) and finding here parts of the 450 engine its easier than finding the whole engine and i will pass cheaper,maybe just swapping the cylinders(and pistons) will be enough to gain displacement but the camshafts are different for the german market (GS400 20kW) so i will not gain the full power of the GS450 if i just bore my cylinders....

[Rensdw]

The GS400 has 16mm wrist pins, the GS450 18mm, plus the GS400 has a bigger stroke (60mm vs 57.6mm), so you would need to swap the crankshaft but the GS400 has roller bearings the GS450 has plain bearings.
Nothing is impossible but this would require extensive modifications and I would not recommend this as a "simple upgrade"
Instead, If I were you I would look for a cheap GS450 or GS500E engine en put that in your frame, you may need to change some of the engine mounts I don't know.

If you do decide to do this the hard way (more satisfaction )
You could keep the GS400 crankshaft and the 60mm stroke and search for some 16mm wrist pin pistons with the right bore, valve clearance, and compression ratio.
The piston deck to cylinder deck height is managed by thicker or thinner gaskets/plates, you can play with the CR too.
You should swap the barrels of a 450 into the 400 instead of trying to make the cylinder fit, that is a pain in the ass, trust me; I know
Doing it this way you most likely have to modify the crankcase a little bit for it to accept the bigger sleeves, but that is not a big deal.

Edit: Fuuuuuuuuu**! I just thought of the stud spacing, if you want to mount the GS450 top end you should check my topic about my GS400x built, there you see what it takes to mount the GS450 cylinders.
Only the part about the stud spacing is relevant because I am not using a gs450 top end, and I am not sure about the oil passages lining up.

My topic is in the racing section (gs400/500/650 hybrid)

[Andy24]

thanks,,i will consider this as an option

[John Park]

If you look at top speed figures, there isn't a whole lot more functional power in a 450 anyway. The German market cams are shorter duration; I don't have the figures for the two valve 400 but the four valve had a cam timing of 36 before and 64 after intake and 58 before and 42 after exhaust. The German numbers were 22, 50 and 28, 41. Swapping for US cams would make a major difference especially at high revs. The main jets would probably be different.

Swapping a whole 450 engine could be problematic at the air box and carbs as the intake boot spacing appears different. You'd need the 450 carbs and then use pod filters, which presents another challenge. The front motor mount plate is also different. GS500 engines would not work because of the exhaust ports being aimed at the frame down tubes.

You can get two 400 cams for maybe $30 each or less. I recall the main jets were 117.5 [?] . Good opportunity to adjust the valves and maybe do the intake boot o-rings anyway.

They all seem to max out at about 150kph or 95 mph. How fast they accelerate has a lot to do with how much you weigh. A well tuned 400 can be faster than a poorly tuned 450. Top speed is dependent upon the wind resistance which rises as the square of speed. If it takes 15hp to make a bike go 60 mph it will take 60hp to go 120 mph. 40 hp works out to about 95 mph, so you're going to need almost another hp for every mph increase in speed. Aerodynamics will be the easiest method to increase top speed and also reduce drag for better economy and less engine heat and wear. With lower bars and a small windscreen I used to cruise all day at 125kph on the 400 without feeling guilty.