Topic: High CR 500-550 pistons anybody?

[turboguzzi]

Dear small block SOHC owners, here’s the deal.

The company that supplied me with the pistons I am using in my 500 racer could be interested in doing a custom batch if there’s enough interest. In my racer I used of the shelf pistons from them but had to go through quite a lot of trouble, milling the block, deepening the pockets, etc. to get the high compression and good squish band that I was seeking.

I believe that if there’s enough interest, I could design a bolt on piston that doesn’t require all the above mods and could work with the standard gasket and yet provide high compression, good squish area and be ready to accept hotter cams. The design would be much more modern, slipper skirt style, thinner rings and a good deal less weight through shorter wrist pins, pretty much in the style of the un-obtainable Yoshimura pistons, but with two compression rings rather than one for street use. 

I’ve done already 6 races on the set I’ve got from them, two of them in scorching heat and they stood the test real well, so they certainly know how to make them. In October, after the last race I will pull the motor apart and see how they survived.

So then, a few questions:

1. Interested in such a set?
2. If yes, at what price range?
3. What diameter / c.c.? 56mm to remain stock 498cc.? 58.5mm for 550’s or whoever wants to race in AHMRA F-500? Or maybe 62 mm like in those 608cc kits?

If the response is positive the whole affair is going to take some time, so just trying to see if there’s a market at all to go into this venture.

Thanks

TG

 

[bwaller]

Turbo,

Your timing is impecable, I was just going to contact you about this very issue. I am definitely interested in a set of 58.5mm and for that matter 56 if that's the direction this project takes. Price wise....you tell me, I've put out some feelers on other options without much luck. As you know available interesting pistons are limited.

 My feeble plan is to only make four or five races a year and if it's a 500 or 550 won't matter much in the big scheme of things, I have several of either engines to build from. BUT I'd like to have a vintage middleweight with some grunt also.

One thing I know for sure, my previous roadracing experience proved world champion wasn't in the works, so now it's just to prove to myself I still "have-it" and to have fun getting there. 

Put me on the list.   

Brent

[canttuckmyshirt]

Ball park price? $$ talks...

[turboguzzi]

$$$, I know, it's just that since this requires new tooling, price will be directly dependent on the ammount of sets ordered. I should be able to stay bellow what Dynoman charges  for 458 cc pistons for the CB400 which is 600$ nowadays. Would 500$ be atractive enough?

TG

[isred]

You have my interest, What kind of CR are we talking and are the rings available separately? Also how are the pistons oiled, are there slots under the rings or circular holes? And finally What would the Price's be.

[fastbroshi]

  It would be cool to have a nice bump in CR... I'd still want to run mine on the street though; does 10.0:1-10.5 max sound plausible?  Pair that with megacycle cam, heavy duty cam chain, ported head (yo Reick!).  THAT would be cool. 

[turboguzzi]

Hi guys

The idea would be to go for 1:11. With a proper squish area that shouldn't be a problem, even for the street, still trying to work out with mfg. if there could be a possibility to have different tops, racing, street, etc. In any case, lowering your CR is easier than raising it, just add a base gasket :-)

I am aware that it would be impossible to satisfy all needs, but considering that currently there's nothing bolt-on on the market for the 500-550...

Regarding rings, ideally these should be off the shelf, the kit I got from them uses std. CG 125 rings.

Oiling? series of small holes.

fastbroshi, isred, would like to hear from you, what would be your preferred bore. That's the biggie.

Cheers

TG

[fastbroshi]

  Having trouble finding a metric bore displacement calculator, but no matter, I didn't really have a magic number in mind.  I just wouldn't want to go overboard with the bore/stroke combo.  These motors are considered oversquare, ie bore bigger than stroke, correct?  How much more bore could you add within reason w/o being too heavy?
  Big thanks for the 550 racer pics you posted a while ago.

[turboguzzi]

fastbroshi

Well, the "gentleman express" 550 (dont know where that thread/article is at the moment) used 61mm CB750 pistons for 590 c.c. and there have been 608 c.c. kits around. (62mm I think)

Regardless, I find it hard to believe that there's much chance to make these kits considering the 4 people interested so far, me included :-), maybe if more join in

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 am sending them the design anyway to get a final quote on the investment involved.

Cheers

TG

[QuikSilver]

i might be interested in a 608cc kit here a few months. i just bought an engine to rework and am lookin at a frame today. my 350f project is comin along and once its out of the way my 1971 cbr600RR project will be underway.

what are we lookin at for price?

[j-conn]

i would be interested in a 608cc

[ttr400]

I get the odd request from racers in the UK for 56mm pistons for the CB500 and the CB400F. I would also be interested in the 56mm size for my CB400F race motors.

Kevin

[bistromath]

Sounds like most people are interested in the 62mm. Are there issues with sleeves being too thin when boring to 62? Overheating? Can anyone comment firsthand?

[fastbroshi]

  I'm not road racing, just sticking to the streets, so I'd be happy w/ whatever you came up with.  As long as they're not soup cans you cut in half and scribbled "Yoshimura" on them with a magic marker  .  I just don't want to cut too much into that bonehead margin that Honda built in. 
  The Gentleman's Express article was sent to me by cafe75-550.  In his post they were too friggin small, so I pm'ed him and he emailed them to me.  Pretty cool stuff.
  And $500 sounds reasonable.

[canttuckmyshirt]

Ball park price? $$ talks...

I just re-read my post... Sorry to be so tacky..

$500 doesn't sound bad.

[bwaller]

I'm not sure if a 62mm bore will leave enough 550 sleeve material to be comfortably reliable. It may require boring the cylinders and using maybe 750 sohc or dohc sleeves which would have to be machined as well to fit. Maybe someone here can comment.

I've got 61mm pistons in one and although they are thin it's plenty safe enough.

Turbo, I'm sorry more people haven't jumped on board. The price is definitely in line for "purpose built pistons".

Maybe it's too soon to throw in the cards just yet, it has only been a couple days after all!

[turboguzzi]

If I recall well, the gentleman express project had new sleeves put in.

Have to say that I am more leaning towards producing a light, high Cr piston for classic racing as these are the ones that are hard to find. Either as 58.5mm for 550's or 56mm for 500 (and oversizes too ) 

In a 608 you wouldnt want extra high CR anyway for street use. + if you want a free tip, I heard about XL185 pistons being used for big bores and that's availble of the shelf. with 63mm, it'll give you 630cc! Throw in a 650 crank and you'll get a real 750 eating monster.

TTR, can you give me an idea of how many have asked about such sets?

Thanks

TG

[j-conn]

+ if you want a free tip, I heard about XL185 pistons being used for big bores and that's availble of the shelf. with 63mm, it'll give you 630cc! Throw in a 650 crank and you'll get a real 750 eating monster.

anyone have more info on this?

[turboguzzi]

compression height in the stock 500-550 (wrist pin center to top surf) is 23mm, these xl185 are 25mm so you either machine the edge of the piston or fit a spacer plate between block and crankcase.

These would require new sleeves and opening of the holes in the top crankcase, me thinks..... definetely not bolt on!

That's part of the reason I think that stock 56 or 58.5 sizes (500-550) could be more atractive, just fit and enjoy the ooomph of  higher CR, and whenever you want to throw a hot cam in, you are ready.

Cheers
TG

PS, i'm off to holidays, no PC for the next two weeks....

[Mr Johann Vegas]

I wish I had seen this before I went through the trouble of making pockets in my "Gentleman's Express" pistons.  BTW, I think it might be 500s that need the sleeves, because my 550 bores looked like they had plenty of meat for the 61mm bore.  Best of luck, no matter the outcome of the group deal.

[FunJimmy]

I'd be interested in street performance 550 pistons too. 59 to 61mm would be my preference as that would allow a fresh fit with standard size and readily available cylinders.

Have you considered using a Honda GY6 scooter, performance piston?
They use a 15mm wrist pin and have a couple of different bores available too. Google GY6 performance or visit http://www.ginospr.com/page3.html

FJ

[tank410]

I would be interested in a 608cc kit too.

[hymodyne]

I'm pretty sure you'd have to re-sleeve for a 608 (62mm) piston, which would also mean machine work on the upper portion of the crankcase, where the juggs fit in. A "Kit" now begins to sound like: pistons, rings, wrist pins, new arms and a lightened crank. 

hym

[De La Nooch]

I'd say that I know significantly less about bottom-end engine science than the rest of the posters in this thread. However, I could be interested in a set of stock higher compression pistons for my 550. Guess I would have to do more research though...

[DarkRider]

Would def be interested in such a set in a few months like the others. Though ideally it would be nice to be around 600 cc but im not sure what size of bore that would be.