Can factory 650 pistons handle boost?

[ashdricky]

I am curious to know if the factory GS650 pistons are capable of handling light boost? I am thinking of fitting an AMR500, which displaces 500cc per revolution. The head has not been milled for increased compression or anything like that, effectively still a factory 650.

 

[rapidray]

They will for a LITTLE while. First time it detonates will kill the ring lands! Ray.

 

[Big T]

There's a reason the factory turbo has lower compression and different pistons

If you want a turbo, there's one for sale in NC on Ebay

 

[ashdricky]

They will for a LITTLE while. First time it detonates will kill the ring lands! Ray.

Thanks, Ray, So realistically I will need to get new pistons, and when I do that I should probably do an overbore, and lower compression, are the factory conrods strong enough to handle light boost?

I would like to use an AMR500 supercharger, ideally fairly low boost ~8 psi. A turbo wouldn't look good on this bike.

 

[Big T]

I would think you'd need to find some forged pistons with a lower CR

Good luck with that for a 650

It would be cheaper to buy a faster bike

 

[ArttuH]

Well, I don't have any experience about 650 pistons, but I guess they might handle moderate boost IF you can keep the mixture correct and avoid detonation. Usually it's detonation that kills parts on boosted engines and stock cast pistons don't handle it well. Forged pistons are a bit more forgiving.

So if this is a low budget experiment I would try stock pistons first. But if you want everything right at first time then it's better to get some forged pistons.

 

[ashdricky]

I would think you'd need to find some forged pistons with a lower CR

Good luck with that for a 650

It would be cheaper to buy a faster bike

I planned on ordering custom pistons, with slight overbore and lower CR. Yes there are many cheaper alternatives, bit this is what I want.
Supercharging would be for next year, I as I can afford only the blower at this point. and I am still working on a clutch.

Well, I don't have any experience about 650 pistons, but I guess they might handle moderate boost IF you can keep the mixture correct and avoid detonation. Usually it's detonation that kills parts on boosted engines and stock cast pistons don't handle it well. Forged pistons are a bit more forgiving.

So if this is a low budget experiment I would try stock pistons first. But if you want everything right at first time then it's better to get some forged pistons.

I considered adding toluene or xylene to my fuel, to increase octane ratings. at this point I am simply mapping out my next step.

 

[SqDancerLynn1]

Just buy a 750 or 1000 Cheaper money wise, More reliable

 

[ArttuH]

It would be cheaper to buy a faster bike

Just buy a 750 or 1000 Cheaper money wise, More reliable

Considering this forum section is called "Performance/Tuning/Mods" I have hard time to understand this kind comments I guess most of people understand it's easier and more cost effective to buy a fast bike than try to build one from old piece of junk. But for some people the catch is building something by themselves not buying it.

 

[ArttuH]

I considered adding toluene or xylene to my fuel, to increase octane ratings. at this point I am simply mapping out my next step.

Just get AFR and ignition timing right and maybe drop compression to 8.5-9:1. Should be fine for 8 psi and pump fuel.

 

[ashdricky]

Just get AFR and ignition timing right and maybe drop compression to 8.5-9:1. Should be fine for 8 psi and pump fuel.

Considering this forum section is called "Performance/Tuning/Mods" I have hard time to understand this kind comments I guess most of people understand it's easier and more cost effective to buy a fast bike than try to build one from old piece of junk. But for some people the catch is building something by themselves not buying it.

Yes as I said before, I don't want a larger bike, I want my bike, and I have already spent alot to get it to where it is, my sig is a brief description of where we are at now with it.

I can control the ignition curves by reprogramming the Dynatek, with forced induction would I want to retard timing, rather than advance it right?

 

[rapidray]

Yes, you would retard the timing. No more than 30 degrees full advance with what you are talking about. Ray.

 

[ashdricky]

Yes, you would retard the timing. No more than 30 degrees full advance with what you are talking about. Ray.

I am still learning the software, and have a very general understanding of advance curves. So that is no more than 30 degrees before TDC? Im using a dynatek 2000 if that helps. Is there ever a scenario where one would retard the ignition to after TDC?

 

[ashdricky]

My idea was to use an Aisin AMR500 roots supercharger, and a draw through carb, am I correct in thinking that the compressor will help with atomization of the fuel? and further more which carb would be the one to use?

Note: the AMR500 displaces 500CC per revolution, will this be ok for 674CC? I know the pulleys can be changed

 

[Nessism]

Have you seen Blower's supercharged GS thread? http://www.thegsresources.com/_forum/showthread.php?t=94468
Reading though this thread will give you some insight as to what's involved with building a bike such as you are proposing. Blower is both knowledgeable and a master machinist and fabricator. No doubt he has a good deal of disposable income as well. Hope you are all these things as well as you embark on a project like this.

 

[GregT]

My idea was to use an Aisin AMR500 roots supercharger, and a draw through carb, am I correct in thinking that the compressor will help with atomization of the fuel? and further more which carb would be the one to use?

Note: the AMR500 displaces 500CC per revolution, will this be ok for 674CC? I know the pulleys can be changed

The answers are yes, and no....Yes, that blower wil work. Yes, it will atomise the fuel quite well...but, the distribution becomes quite critical particularly on an aircooled motor. Wrong manifold shape and you can have probs with one or more cylinders running lean. Do your research (read the books) on what you need.
Also, on pump gas on the street, you will be surprised at just how hot the blower and manifold get. This itself can cause some weird problems as "hot blower" symptoms include not restarting and possible manifold/blower backfires....Don't forget to include an explosion valve on the inlet manifold - and preferably where it won't torch your leg....

 

[Pete's GS]

The suggestion to get a bigger bike was a good one. It sounds like you want to make a grenade.

 

[ArttuH]

My idea was to use an Aisin AMR500 roots supercharger, and a draw through carb, am I correct in thinking that the compressor will help with atomization of the fuel? and further more which carb would be the one to use?

Note: the AMR500 displaces 500CC per revolution, will this be ok for 674CC? I know the pulleys can be changed

Charger sizing sounds pretty good. 1:1 drive ratio will result about 7psi boost, in theory. And maximum speed for the charger seems to be 16000 rpm so there is some headroom to rise the boost if needed.

I'm not sure about atomization. The compressor may help atomization to some degree but on the other hand there will be lots of surface area where the fuel can condensate. Draw through systems in general are quite notorious for uneven fuel distribution between the cylinders due to fuel separation and condensing.

Depending on charger placement I would seriously consider using the stock carbs (or something similar) in blow through configuration. Or even blow through EFI but that's a project on it's own.

 

[ashdricky]

Charger sizing sounds pretty good. 1:1 drive ratio will result about 7psi boost, in theory. And maximum speed for the charger seems to be 16000 rpm so there is some headroom to rise the boost if needed.

I'm not sure about atomization. The compressor may help atomization to some degree but on the other hand there will be lots of surface area where the fuel can condensate. Draw through systems in general are quite notorious for uneven fuel distribution between the cylinders due to fuel separation and condensing.

Depending on charger placement I would seriously consider using the stock carbs (or something similar) in blow through configuration. Or even blow through EFI but that's a project on it's own.

I am currently finishing a slipper clutch conversion, for this bike, and am only collecting information the next phase, I am considering EFI and may have to go that way, I am having trouble finding space to mount the supercharger and still have room for the intake and injectors.