Topic: High CR 500-550 pistons anybody?

[fastbroshi]

Updates?  Maybe a vote as to what displacement/cr/hp-brags we'd go for?

[turboguzzi]

Hello there

Sorry for not repyling, but was on holidays!

Havent been able to get a clear idea as to what size would be most popular. sounds like there'd be more of a market for around 600cc big bores than stock high CR 500cc,

that being the case, 61mm would allow 550's to be safely overbored while 500's will require new sleeves or a 550 cyl block. In both cases it would result in in 590cc displacement.

funjimmy, looked at thos gy6 pistons while building my racer last year but they seemed a bit spindly. know of anyone using them?

Fastbroshi, from my experience, a piston design with good squish area would be pretty safe even at 10.5:1 CR. Cant brag about HP numbers as there would be quite a lot of other factors involved: carbs, manifolds, cams, exhaust.

TG

 

[fastbroshi]

  That's about the number I had in mind.  Turbo, don't you race a 550?  If I was going to all this trouble to get some high quality pistons, I'd also be thinking about headwork (Mike), cams, (megacycle), and carbs (massage the stock).  Exhaust, well that's just frosting.  But where to get rods?  Who might make a good set?  I've never seen an aftermarket set for the 550's, but 750's abound.
  It seems everything else is readily available but the rods, and if I were taking the above steps I'd want to have a strong set of them.

[turboguzzi]

Hi F-broshi

I race a self tuned / self ported 500 with a megacycle cam and 27mm VM's on custom downdaft manifolds. From all what I read, and judging from my two racing seasons with the engine often hitting 12,000 to 13,000,  I can say that the stock 500's rods are pretty bullet proof. Ditto for the cam chain tensioner, the 750's need help, the 500 are fine.

So esentially the only dedicated component you need for high performance are pistons....

TG

[bwaller]

Has anyone looked at Powroll stuff? They have some pistons with 15mm pins. I haven't asked for dimensions but probably will. I never thought much of their stuff back in the day, but there isn't much else....

Turbo how many sets would it take to make this a go? I need either 56 or 58.5 and if the choice is for big bore I'll keep looking elsewhere.

[fastbroshi]

Hi F-broshi

I race a self tuned / self ported 500 with a megacycle cam and 27mm VM's on custom downdaft manifolds. From all what I read, and judging from my two racing seasons with the engine often hitting 12,000 to 13,000,  I can say that the stock 500's rods are pretty bullet proof. Ditto for the cam chain tensioner, the 750's need help, the 500 are fine.

So esentially the only dedicated component you need for high performance are pistons....

TG

  Really?  I guess there is a difference between a modded 70-90 horse 750 and a modded 55-70 horse 550.  Not as much stress on them, given similar metallurgy.  And I thought the chain tensioner was a weak spot.  Maybe just because 30 years of neglect will make anything break down.  Heck, I just had to replace mine becuase the adjuster nut seized up.  I don't think I'm alone here. But I guess it's a different scenario when a close eye is kept on adjustment.
  What kind of power is your 500 making?  And what displacement are you working with? Lastly, what brand is VM, is that just your abbreviation or the name of the carb?

[turboguzzi]

Bwaller, esentailly I was looking to make race 56mm pistons too, just cant see much of a market for them now. working on the CAD 3D desgin now, let's see what the mfg. says about tooling costs.

Fastbroshi, I am running 500cc as I race in the 500 class. read more here

http://forums.sohc4.net/index.php?topic=36477

TG

[fastbroshi]

  VERY cool.  I'd definitely be down for some 605 pistons.  What style were you thinking of?  Hyperteuctic, forged, etc.  I don't even know if forged would be overkill, but as long as there's bozos out there making 60 horses it's a good idea.

[fastbroshi]

TurboG, 

   I was just rereading the posts, and saw you said:

I know that most performance oriented SOHC'ers are into 750's, so not that surprised. I still believe that if the kits will be available at the right price, then people will go for them, so maybe I should just take the plunge.

  I couldn't agree more.  I think the reason there's so much 750 stuff right now is the market got started back in the 70's, so it's had plenty of time to grow.  And rather than have to manufacture different kits and take into account differences (if few) between the 500's and 550's, the 750 was focused on instead.

  Just by looking at these forums and the number of members w/ 550's, I think it would definitely build momentum after starting.  Why wasn't more racing done on these bikes?  Was it just a class or rules limitations thing?  Got me drooling all over again.

[schofell84]

I can't say I have the funds for them right now, but it sounds like an item that would be very feasible for a rebuild this winter. Oh, and re-sleeving isn't as cost effective of an option either, I'd like to see some stock bore pistons. If you were going to make a re-sleeve kit, I'd work a stroker crank into the deal.

[turboguzzi]

Hi shoefell

Agree with you only partially. I think that there's a big differnece in cost between resleeving and a stroker crank, more to the point, cant think of many people that would go the stroker way with a 500-550 when you can always adopt a complete 650 bottom end that is already "stroked".

Mind you, I am just into it for fun (and maybe make a buck or two to help my racing effort), having those pistons made is one thing, no sweat really other than the investment in tooling. a stroker 500-550 crank would be on another, wouldnt know where to start even. maybe Big Jay would pick this idea up?

In any case, more than everything,  I would be interested in knowing what bore would you be interested in.

Fastbroshi, I believe that most of the go-fast stuff is for 750's for the simple reason that when you want pure performance, bigger is always better. the smaller sohc's appeal(ed) to a different kind of rider, then as now. The things were raced, mostly in production classes but were always overshadowed by the big CR750's (see the sticky above mine).


Even now, in vintage racing, not many choose them as in most classes you are up against the two stroke RD's that are way easier to make fast.

 
Thanks

TG

[TwoTired]

A stroker crank is going to push the pistons up higher than the cylinder block deck. You'll need shorter rods, or pistons with wrist pin in different location, or cylinder block spacer and longer studs to restore piston to deck relationship.  Would be nice to get that for free, huh?

Cheers,

[fastbroshi]

Bump.  Please keep this stickied.

[Shenanigans]

I am very interested in the 605. Especially if the stock sleeves could be used.

[SteveD CB500F]

Turbo. Have you finished with this yet?

Can I "unsticky" it?

Steve

[fastbroshi]

  TG, I see that there's really no consensus as to what bore we'd like, so I'd like to propose a poll, however I'm not familiar w/ what measurements would be the most logical, I've heard 61, 59, etc.  Or maybe someone else could hack that up. 
  Also, who'se up for a set if they were $500? Please respond for a final count.

1. Fastbroshi

[JZEROE]

I would potentially be interested in the biggest pistons you could get without re-sleeving a 550. What kind of increase in performace would this net? I imagine that it would help with the low-end, ya? But has anyone put 61mm pistons in a 550, and does that potentially imaginary person have anything to say about the power increase?

So here's where I am, you know, in case ya'll care: Rebuilding this winter and just want to eliminate the flat spot and get a little more low end so I can lose the smaller front sprocket. As is, the highway is a little bit nerve-wracking, what with the tach hovering around 8K at 80mph.

Can anyone here give me their opinion about whether this would be a good option for someone who doesn't need a speed machine, but wants a little more oomph without sacrificing reliability?

Thanks,
J

[bwaller]

Ilink=topic=38006.msg410609#msg410609 date=1219970453]
I would potentially be interested in the biggest pistons you could get without re-sleeving a 550. What kind of increase in performace would this net? I imagine that it would help with the low-end, ya? But has anyone put 61mm pistons in a 550, and does that potentially imaginary person have anything to say about the power increase?

So here's where I am, you know, in case ya'll care: Rebuilding this winter and just want to eliminate the flat spot and get a little more low end so I can lose the smaller front sprocket. As is, the highway is a little bit nerve-wracking, what with the tach hovering around 8K at 80mph.

Can anyone here give me their opinion about whether this would be a good option for someone who doesn't need a speed machine, but wants a little more oomph without sacrificing reliability?

Thanks,
J
[/quote]

I've got 61's in a street 550 with just a mild Web cam, 10.1:1 CR and it does really wake them up. Removed forty pounds off it too and that helped as well. 61mm is as large as you can safely bore a 550 liner.

I don't think TG got the response he was hoping for. I need a set of 58.5mm high comp pistons but I don't expect anyone to get too excited about making one set! 

[JZEROE]

Well I'd probably be interested in a set of 61s. What's the diameter of the stock, piston, out of curiosity, and is there clearance to shave down the head to raise compression that way?

[turboguzzi]

Been a bit busy (race preparation) but here are my final thoughts:

High CR 12:1, stock + oversizes for 500 or 550, racing use - low interest (even if those are the ones i need!)

bumped CR, 10.5:1, 61mm (fit stock 550 liners, 500 will need new sleeves) - high interest.

I will proceed to fwd the mfg. the drawings and see the investment required, if it's low enough, maybe there's a chance to do both options, will keep you updated.

Thanks for all your responses

Cheers
TG

(Steve, you can unstick, just leave it on the forum so I can update if need)

[j-conn]

u can put one more in teh 61 camp.
any updates btw

[turboguzzi]

Well, last update is that I've been quoted 3000$ for tooling but then price per piston would be quite good if not downright cheap.

Cant see myself going into that right now, so unless that company manages to find a way to build the piston based on some exisitng tooling, then it's a no go....

Sorry

TG

[j-conn]

my profile pic is how i feel about that...
 

[fastbroshi]

Modded 750 tooling maybe?

[moham]

I just came across this thread and sad to see its a no-go. Incidentally, I just received some 60mm pistons (from an 85 ninja) that I'm going to try and fit into a 74 550. They came from Soos and he cut some valve pockets for me. Now comes the hard part, getting the sleeves bored and seeing if I can get it all to work. They already have some valve relief for the four valves it had so I am interested to see what all the numbers work up to be.