GS 450 engine build

[Guest]

I have a couple of spare GS 450 engines in my shop. I'd like to build up one to a bigger displacement. I'd prefer to do just the barrels and head so I can bolt them onto my running 81 GS450 S. What is the best way to go? Overbore the cylinders, new pistons, valve work, cams, carbs? What can I do from the cases up to get a bigger engine on my existing bottom end?

[pete]

I'm pretty sure the answer to this is a GS500 head on top and it ends up a 527 or something along those lines...

A fella by the name of Mekanix should be along to spill the beans on this one, but I'm keen to see what you do

[Mekanix]

Here we go again


Well, how brave are you ?

http://www.thegsresources.com/_forum/showthread.php?t=172422&page=6

More info:
http://www.thegsresources.com/_forum...d.php?t=170287



After 1980 the gs400(mine), 450 and 500 have the same base engine and only change the cylinder block and head. Before 1980 the block had roller bearings and the head configuration doesn't line up properly with anything after 1980.

If you bore your cylinders from 71mm to 74mm that would make it a 486cc which is what the 500 is.

75mm would make it a 500cc and you would only have 2 mm sidewall left.

You could use a gs500 block and gs500 gaskets.

If you want to mess with deck height, the stock gs450 base gasket is paper and is 0.5mm thick
The gs500 is metal and is half that thickness. So you have some adjustability.
The gs500 head gasket is metal as well.


I'm assuming that you have a 4mm sidewall when the bore is stock at 71mm.


Big bore kits for 750's can be applied to the twins if you can find them.

http://gszone.biz/pistons.html is one example but there are company's like CP, JE, Wiseco,,,, that can make you custom pistons.

The gs4xx piston's have an 18mm wrist pin.

The 1100's have more options for pistons and they might require modification mostly for valve relief depth.


Cometic makes 450 head gaskets in what ever size bore you want starting at $48 for felt type and $57 for copper reusable gasket.

http://cometic.com/powersports.aspx nothing on the website but if you call them they do have stuff available and a 450 gasket in their database.


Oh one more thing , It has been done

http://www.youtube.com/watch?v=tQEVHd1cSyw

Its a 450 with a 500 cylinder block bored to 77mm with GR650 pistons. That makes it a 527. I think the head is from a 500 but i can be sure which year.(89 maybe)


WEB can make you some nice cams.

RapidRay has build a race gs500 and knows what the best cam was for it.

[pete]

Cheers Mekanix, I just don't have the head for that stuff and knew you'd have the goods... and that's the Youtube video I was thinking of too... that thing's a beast!

[olddaddy]

Thanks for the info, sorry to annoy you with another rehash of the topic. I'm not that brave really. I just figured if I ever had to do a rebuild 500cc would be a nice target. If I can get to 486cc simply by boring I'd do that and be happy. The 527 beast is inspirational, but probably beyond my ability and wallet. I do have a GR650 engine sitting idle though........if only I hadn't sold off that GS500 engine last winter! Thanks again!

[Mekanix]

Its alright, I've been copying and editing that post for a while now. Around this time each year there are lots of people wanting to know whats possible.

The easiest thing to do is swap a gs500 top end on it but there is issues with routing the exhaust.

Another option is to buy a gs500 block on E-bay and get some oversize pistons for it. Then just use your 450 head and adjust the height for the new compression ratio.

Your 450 has a 71mm bore and can go another 4 mm bigger max.

75mm is a real 500cc engine with a 10.8:1 comp ratio.

The stock compression ratio is 9.5 I believe.