Topic: Custom 62mm pistons for 750 road racer

[slikwilli420]

I am going to work through getting a set of custom pistons made for my road racer instead of using the DP62 one's other have used. I am in the process of filling the form out right now (Carrillo) and am trying to first, get a sense of what they are asking for and second, see what features would be worthwhile on our bikes.

Here is the custom order form and things I have questions on:

I am also looking through the features found here: http://www.cp-carrillo.com/pt-3507-pistons.html
I want to understand what the "ultimate" road racing piston would have. My stage 4 head and balanced crank assembly (cycle x rods) will support just about anything I can get out of 62mm piston, but I am also sure not all things are necessary.

I am looking at: Accumulator Grooves, Contact Reduction Grooves, Broaches, and Lateral Gas Ports. I will also explore hard anodizing as well as dome coatings. Anything regarding how the dome is finished is where I get lost. I am shooting for that 12:1 range with as flat a dome as possible to get really good burn (per Mike Rieck). I would consider milling additional material off the head to shrink the chamber volume to get a flatter piston with the desired compression, just not sure where to begin.

I would welcome experience from anyone who has some knowledge in this realm, but specifically for the 750/4 in road racing would be ideal. Looking forward to making this happen, likely to be ready for the 2019 season.

[turboguzzi]

riccardo (livefast_dieold) is looking into the same type of pistons for his 750 racer, maybe buying more than one set will save you both some $$$

a proper made to measure piston order should be accompanied by a combustion chamber cast.

ask for a proper squish band to be built, otherwise with 12:1 it will be "detonation day".

go with two compression rings for longevity, even if single ring is more racy....

[slikwilli420]

Carrillo will do 4 pistons, which is one reason I am choosing them over other brands. Mike recommended squish right at .035-.038" (.89-97mm). I agree a chamber cast is going to be key, but waiting to see if and how much should be taken off the head to get a flatter piston with the 12:1 compression I am after. Thanks for the recco on rings as well.

[slikwilli420]

Anyone? Thoughts on taking material off the deck of the head to reduce chamber size, allowing a flatter piston?

[MRieck]

Carrillo will do 4 pistons, which is one reason I am choosing them over other brands. Mike recommended squish right at .035-.038" (.89-97mm). I agree a chamber cast is going to be key, but waiting to see if and how much should be taken off the head to get a flatter piston with the 12:1 compression I am after. Thanks for the recco on rings as well.

I'll just clarify....I have run squish down to .035 in modern 600cc engines. .038 to .040 is what I'd recommend for Matt's engine.

[livefast_dieold]

Here I am!

Well it's very tricky. As far as I have investigated on the topic:

> you can't really take off that much material from the head, the valves are right there already (plus, whattabout distribution chain tension?). I doubt you can reach anywhere close 12:1 without a proper domed piston (just look at how massive is the dp62 piston dome, it's almost 10 mm thick!), but I will more than happy to be wrong :-)

> as for squish, hard to obtain again with a 62mm pistons considering how irregular is the combustion chamber... unless you weld up the chambers (but again the end result would be quite weird, again due to the irregularity of the combustion chamber). Another solution would be to have a mold of the chamber, and to manufacture custom made pistons to follow them precisely. Both solutions aren't going to be cheap and both with questionable/ uncertain results IMHO.

I'm going probably to install lightly modified kawasaki kz650 pistons in my engine, which is a cheap but hopefully effective solution...

[turboguzzi]

back at the time mark from M3 racing had unfinished high crown piston sets to be self machined, maybe try give him a call. he hasnt been around in sohc for a variety of reasons (allow me to skip on this ), but he might have an off the shelf solution.

[cbr954]

Dynoman also does custom pistons with coating and machining options, they also want a mold of your combustion chamber.  Buzz is a good guy to talk too, he will tell it to you straight.