Gs500 cams in my gs450

[Guest]

Hi. Just got back to work on my 82 GS450 after a long hiatus. Got my 1st house in march and have been busy ever since. So pulled the engine out last weekend. Going to strip the bike and do it right finally.
So while the engine is out, I'm considering putting in gs500 cams and possibly port the head. My question is what all is involved? Is it even a worthwhile upgrade?. I've already punched the 450 out to a 500 using the 500 jugs/pistons and adjusted the valves. Was pleased with the results. Are the cams a drop in affair?

[Shaun6691]

The particular set of GS500 cams I'm looking at are from a 2005

[John Park]

The early 500 cams have a gear for the tach drive while the later ones don't. I'm not sure of the switch date, but I'm guessing 1998??

You may end up with a lot of endplay in a 450 head. This can lead to cam walk noise and require some endplay washers and machining of the cam thrust faces to get within a hopefully quiet spec. The endplay increases as the head expands, so a close fit cold is no problem.

I have 87 450 cams in an '81 head and they are pretty loose; an '83 head I have has a very close fit.

Later cams were designed to have thrust washers and some had a wavy spring washer pack to deal with cam walk so a 2005 cam will require an electric tach and some possible creativity to fit. I'd look for an early pair and hope they're reasonably snug. Shim washers are available from Suzuki in .5 and 1mm [as I recall??] and wavy spring.

You can look up the variations and shims and such at cmsnl.com

Without the carbs and exhaust to match, I wouldn't expect any great performance gain, but maybe enough extra lift and duration to help feed the bigger hole at high revs.

[John Park]

Regarding porting, I don't think there's much to gain there as the ports are already pretty huge. Breathing is limited by the basic design and Suzuki's next move was to a four valve head. By 1980 the hemi was fully sorted and trying to improve on what's there is difficult. You can gain a bit up top at the loss of a lot down low which is only useful on the track, especially on a twin which is kinda marginal below 6K to begin with.

I have a head on the bench now and was just about to have a good look for any potential gains, but the last time I looked I didn't see anything. Skimming a mm off the head might give something around 10:1 compression, but the octane sensitivity would go up and you'd probably have to retard the ignition. Putting that mm back would be challenging if it didn't work out. You'd want to check the valve interference with the pistons with putty before doing it.

[pete]

I did a thread when I put 2001 camshafts and carbs onto my '82 450E but for some reason Chrome is preventing me copying the link in here... do an advanced search on titles including "GS500 Camshaft" created by me and you'll find it straight away.

The thread got Photophucket'd so the pic's are no longer there, but I can tell you that while the difference isn't huge, it is most definitely noticeable.

The 500 carbs let it breathe a lot easier due to the much larger intake size, and the camshafts make the power a bit more useable in the mid range. I feel like there's a touch less up above 8K RPM but you can get there quicker. I changed the carbs first then the camshafts a while later.

Once thing with the camshafts is the GS500 ones have a shim on them to prevent the cam walk, so you may need to buy different sized shims to make them fit. The shims that were on mine were one size too large so I had to go down a size.

Also, make sure you get the intake boots from the 500, there's enough of a difference that the 450 boots will cause you grief.

Keeping in mind the rest of my 450 is still stock displacement, I currently have 20 pilots, needle lifted to the middle position, 65 mid main jets, and 127.5 main jets. She's definitely running rich which I haven't spent any time on yet, but my plan is to drop back to the stock 62.5 mid main jet as a next step.

Oh, I found some velocity stacks to fit which are huge (99mm bell mouth diameter ) and they just touch the fuel tap on the left. I got some filter material from RamAir in the UK so they're filtered also.

Good luck and keep us up to date!

[GregT]

I have a head on the bench now and was just about to have a good look for any potential gains, but the last time I looked I didn't see anything. Skimming a mm off the head might give something around 10:1 compression, but the octane sensitivity would go up and you'd probably have to retard the ignition. Putting that mm back would be challenging if it didn't work out. You'd want to check the valve interference with the pistons with putty before doing it.

Firstly - 500 pistons under a 450 head are close on the exhaust valve side. I've posted pics of a 500 piston cut to match the 450 and I'd recommend doing that if you plan on either machining the head or putting in bigger cams.
Secondly - if you've got the 450 head with the dam across the inlet ports just in from the carb rubbers, don't remove it...If anything, look at filling the bottom of the port. The dams are there to cause a bit of turbulence and effectively reduce the area of the port. They're actually too big.
Filling the port runner lower side and getting a better short side radius will gain power everywhere.

[John Park]

Firstly - 500 pistons under a 450 head are close on the exhaust valve side. I've posted pics of a 500 piston cut to match the 450 and I'd recommend doing that if you plan on either machining the head or putting in bigger cams.
Secondly - if you've got the 450 head with the dam across the inlet ports just in from the carb rubbers, don't remove it...If anything, look at filling the bottom of the port. The dams are there to cause a bit of turbulence and effectively reduce the area of the port. They're actually too big.
Filling the port runner lower side and getting a better short side radius will gain power everywhere.

Thanks for this info. I agree; the port is overly large when you take the butterfly and shaft area into account. I think they just continued the carb mouth diameter because it was easy; the GSX400s have a reduction in the boot base as I recall.

I always assumed the dam with the slot was there to prevent raw gas puddles dribbling down too rapidly into the chamber. Otherwise, the little slot makes no sense.

What do you recommend building up the port with? I have access to welding, but the possibility of distortion worries me. Epoxy based fillers worry me long term on the street, and the temperature is a bit of a crapshoot.

Establishing good velocity at medium rpm and then getting the flow around the corner at high rpm is the problem; too big ports with awkward corners can end up doing neither.

[GregT]

Thanks for this info. I agree; the port is overly large when you take the butterfly and shaft area into account. I think they just continued the carb mouth diameter because it was easy; the GSX400s have a reduction in the boot base as I recall.

I always assumed the dam with the slot was there to prevent raw gas puddles dribbling down too rapidly into the chamber. Otherwise, the little slot makes no sense.

What do you recommend building up the port with? I have access to welding, but the possibility of distortion worries me. Epoxy based fillers worry me long term on the street, and the temperature is a bit of a crapshoot.

Establishing good velocity at medium rpm and then getting the flow around the corner at high rpm is the problem; too big ports with awkward corners can end up doing neither.

Ray has quoted somewhere in his posts the epoxy filler he uses. I have my own favourites but what is available here is mainly British origin. At least it is possible to insert through the underside of the head, screws to give the filler something to bond to.

[Shaun6691]

Forgot I had posted this! Sounds like its not worth my time then. I'm pretty happy with the mods done to the engine anyway.