modifying a 400f to 494cc... possibile?

[nikosg]

Hey guys,

For my bike, there are no bore kits or anything at all designed for an engine upgrade.

I know with using say, a gsf400 or gsxr400 stock pistons, using those will increase the capacity to 445ish.

However, there is a 59mm JE forged piston kit on ebay (designed for the bandit 400s) that would take my little 400 up to a 494cc sleeping beauty.

Im not sure if this is even possible.... or smart.

But just out of curiosity assuming this COULD be done with new sleeves etc what else would need to be done with a modification such as this?
Valves? cams? Oil cooler?

You dont see many 400s getting this treatment, but after seeing some cool 450 race bikes upped to close to 600 just makes me think what can be done with the smaller 4 cylinder brother.

[Guest]

I don't know anything about your particular bike, but suspect it would be possible. Obviously, cylinder liner thickness is the limiting factor. Maybe someone will know what can be done here. Possibly increased liner size also? Good luck with it. Ray

[GregT]

Hey guys,

For my bike, there are no bore kits or anything at all designed for an engine upgrade.

I know with using say, a gsf400 or gsxr400 stock pistons, using those will increase the capacity to 445ish.

However, there is a 59mm JE forged piston kit on ebay (designed for the bandit 400s) that would take my little 400 up to a 494cc sleeping beauty.

Im not sure if this is even possible.... or smart.

But just out of curiosity assuming this COULD be done with new sleeves etc what else would need to be done with a modification such as this?
Valves? cams? Oil cooler?

You dont see many 400s getting this treatment, but after seeing some cool 450 race bikes upped to close to 600 just makes me think what can be done with the smaller 4 cylinder brother.

Some years back i took an Impulse motor (same as 2nd gen GSXR400) out to 500 cc for a Formula 500 car. Pistons and liners from a CBX550 honda. Quite a bit of machining required but it went very well. no reason it can't be done on the 400F. Given they had a rep for poor oil pressure leading to doing crank bearings - rectified at least in part on later versions i believe - it would be worth trying to fit a bigger oil pump while you're at it. i've just done the wider rotor trick on a CB400F motor - google CB400 oil pump mods to see what that involves. Similar may be possible on your 400 or a pump from a gsxr may go on...

[nikosg]

Thanks guys !

Very nice info there Greg, interesting using the cbx pistons... did they require machining on the top faces?

So could you keep the normal cams and still get a better result? if gsxr400 motors were a bit more common and easy to find id just transplant that into the frame!

ill do some research on the oil pump mods. Seems people have done a bit of experimenting on the CB equivalent - I guess they were a more popular build compared to the gsx counterpart. Hardly any around down here. Dont think any hit the US market at all either.

[GregT]

from memory, the pistons didn't require machining but the block had to be bored out for the CBX sleeves - and spacers made up to go under the top lips of the sleeves as the Honda ones had a thinner top lip. Std cams, ported head big compression and Methanol. think I made a thick alloy base gasket too.
i picked the CBX pistons as the bore size was right and the gudgeon pin size was the same as the Impulse. i remember looking through a lot of manuals at the local library to sort out which pistons to use. probably easier online now....
Don't know if aussie got a lot of the Impulses - GSX400X i think is the designation - they were originally a Jap home market model but sold very well here.

[nikosg]

I dont think we got any impulses actually! not of the 80s era versions. interesting looking bike. I love the 90's impulses (gsx400s)

Sounds like a lot of machining. But that bike would have flown after.

I'd like to keep the stock engine in the bike. I like the idea of a sleeper 400, but guess ill have to do some financial calculations. Sounds heavy!