who uses flat top pistons?

[number5]

I got a 86 68.20mm flat top piston. Whats next? Mill the head? I tried to research on the advantage and only found its better for the rings

[regg187]

I know a little, the motor builders were using yz 250 flat top pistons in the 310's and 330's that they were building,a few years ago. I think they were using the 87 or 97 model piston.

Check with Cleigh I'm sure he knows all you will need!!


I said a little!!;)

[86 Quad R]

Originally posted by regg187
I know a little, the motor builders were using yz 250 flat top pistons in the 310's and 330's that they were building,a few years ago. I think they were using the 87 or 97 model piston.

Check with Cleigh I'm sure he knows all you will need!!


I said a little!!;)

yuppers. ask neil. :cool: there's things that should be addressed with the squish band and dome profile.

[C-LEIGH RACING]

Hummm, 86 model 68.20mm ( 68.25mm ) flat top piston, now thats the first time for one of those, never seen one.
I would say, just guessing, thats one that somebody special cut & made it a flat top.
The 85 to 89 model 250R pistons, all came dome top & the 86 model YZ250 piston did as well.
Wiseco offers a special flat top conversion piston, but best I can remember it is the 87/88/89 model in the 68, & 68.50mm size. Dont have the Wiseco book in front of me to make sure but thats best I can remember.
Normally the piston used for flat top 265 build is a 97 to 01 model CR250R piston.
ESR offers a flat top piston for their 265, I have one of those new. I would need to inspect it real close to be just about sure, but I think its nothing more than a CR piston with the numbers machined off the top. Could though as well be a special order from Wiseco for ESR with the numbers left off, it does come in a white box so that at least is saying special order.

Oh, its said the flat top piston build is better for high rpm drag engines, but, you order a 350PV Pro-x top end with bottom end to midrange porting from CT Racing & it will have a special cut flat top piston inside, :confused: :confused: figure that one out.

Dome top piston builds always better, having the curve just makes everything flow better.

Only thing that will save rings is to smooth out the bore walls, polish out some of the ruffness of the honing process & not make the port windows to wide.
Wide port windows, the rings expand & fall into them more causing more wear in those areas, but, if you want to make more power you got to widen them so its a trade off.
Neil

[number5]

It is a trinity piston. Here is a pic with a pin going through a 68mm pro x.

[number5]

You can see the trinity piston is just about a thousands higher right at the bottom of the dome. The ring location is slightly higher. Found a big bore piston on ebay that is also flat. #270208926030

[C-LEIGH RACING]

Trinity you say, hummm, was it in a white box.
Can you show a pic of the piston by itself, like the intake side & around the wrist pin area.
Any numbers on the top.
From what I can see of the piston, looks like the CR250 one.
Neil

[mineralgrey01gt]

i have the same type of piston i just got off of ebay from Trinity racing, but mine is a 67.45mm

Neil, while your looking up his, here is the #'s off the top of mine:

J83H1
9345
67.45MM

[C-LEIGH RACING]

I just looked number5s up on e bay, I had forgot about trinity having those pistons.

The seller said it was a Trinity superlite flat top & I dont remember them offering a superlite for the 250R, but I'll check my Trinity catolog & see.

The middle number is Trinitys Wiseco customer number.
Neil

[mineralgrey01gt]

yea my piston has wiseco rings in the box with it. Do I need a custom head for this application?

[number5]

Im thinking a head change in what direction milling it? I dont see changing the angle. Now with this set up This is more like a 4 stroke kinda like a hemi head. Maybe just a thin gasket would work. I have a oring cool head now. Im curious to see how much I would loose with that. But it wont be until the end of the year I just rebuilt my whole motor. So the dome benefits on the up stroke better Im guessing forcing exhaust gasses out efficient?

[C-LEIGH RACING]

Originally posted by mineralgrey01gt
yea my piston has wiseco rings in the box with it. Do I need a custom head for this application?

I guess you could call it a custom head.
A flat top piston engine build needs a head dome that is cut flat in the squish area just like the piston top.
Squish clearance needs to be adjusted & set to the proper amount just like it would be for a crown dome top piston.
Neil

[number5]

so your saying like a 4 stroke head its like a nice rounded dome.

[mineralgrey01gt]

thanks a lot neil, would anyone happen to know where I could pick up a head for this type of piston? Ive never seen a flat head like that before

[C-LEIGH RACING]

A flat top dome will have a bowl around the plug just like any other dome but the squish area will be flat, not at an angle.
Neil

[mineralgrey01gt]

thanks for the info. Ill be on the lookout for one

[86 Quad R]

which head are you using mineral?

[mineralgrey01gt]

just the stock one right now. Ive been wanting a cool head for it

[86 Quad R]

if ya gonna run that piston then the best thing to do is to get a cool head and either start with the lowest cc dome or get a blank and have it custom profiled to the setup you want.

[All250R]

Originally posted by mineralgrey01gt
just the stock one right now. Ive been wanting a cool head for it

Your squish velocity and clearance numbers will be very not ideal with that head. Are you sure having a flat top piston is going to pay off for you?

[mineralgrey01gt]

Originally posted by 86 Quad R
if ya gonna run that piston then the best thing to do is to get a cool head and either start with the lowest cc dome or get a blank and have it custom profiled to the setup you want.

i actually want to get a cool head anyways and run an 18cc dome. My brother has all the different cc domes for his so I can adjust them and see what runs the best.

[86 Quad R]

SEE! that's just it. with all the heads out there. whether it be OEM or aftermarket. they all are contoured/profiled to the crowns of the OEM style piston. companies such as CT, FTZ or Trinity's pistons may or may not profile their piston crown different than the norm and therefor profile the chambers on the heads they sell accordingly.

there's alot more going on in profiling a chamber to a pistons crown than you realize. alot of "Race" builders are now profiling a head, not only to a particular chamber but to a particular fuels octane rating and to the final compression ratio to minimize heat at a given rpm and to establish power at a that given rpm. this is dependant on where the engine will spend a great deal of its revs.

this make any sense?

[C-LEIGH RACING]

Yep, it makes sence to me.
Just looking at what you said, if you dont understand it, it dont seam like it means that much but if you study into that, you will see it does alot.
Just that little bit machining on the head & what the end results will produce, is just one of the many million kazillionbillion things it takes all combined together to make a 2 stroke realy run.
Neil

[All250R]

Originally posted by C-LEIGH RACING
Yep, it makes sence to me.
Just looking at what you said, if you dont understand it, it dont seam like it means that much but if you study into that, you will see it does alot.
Just that little bit machining on the head & what the end results will produce, is just one of the many million kazillionbillion things it takes all combined together to make a 2 stroke realy run.
Neil

A lot of people miss that idea. 2strokes are easy to underestimate. When people spend the money to mod it because a racer who many not even understand the product endorsed it, or if the bike is not taken care of, after a while, you start to feel like it just doesn't seem as fun anymore and may be disappointed in the money you spent. This is especially true lately with the marketing climate the way it is.

When 2strokes are setup correctly as a whole system is when the simple motor really pays off in fun and low cost - NOT because it was easy to bolt on some part and go riding. Don't make that mistake or you'll find yourself eyeing your bank account to buy "new" technology because your money didn't take you where you wanted to go.

Neil can correct me if I'm wrong, but flat top pistons are in line with port design that is targeting a high rpm, higher hp engine. Hopefully you are aware that most pistons are not sold that way for a reason and when you buy the specialized one it's supposed to be matched to a certain other set of like-specializations to get the most out of the part.

[mineralgrey01gt]

i think ill sell the flat top piston I have and pick up a 310 top end, or something close to a 310. I would go 330 but dont want to machine the cases

[number5]

I weighed the flat top 68.2mm against a 68mm dome and the flat top is 1.2 oz less.

[Jer250R]

ok, i got impatient of looking for an oem-style piston and bought one of these pistons a couple weeks ago not knowing it was flat top either. i'm just looking for a basic rebuild, but from what i'm reading this piston is pretty much useless unless i get into serious head mods?

anyone want it if thats the case..its 67.45mm

[mineralgrey01gt]

lol your pretty much in the same boat that I am. I just decided to get me a 310 top end

[C-LEIGH RACING]

Originally posted by All250R
A lot of people miss that idea. 2strokes are easy to underestimate. When people spend the money to mod it because a racer who many not even understand the product endorsed it, or if the bike is not taken care of, after a while, you start to feel like it just doesn't seem as fun anymore and may be disappointed in the money you spent. This is especially true lately with the marketing climate the way it is.

When 2strokes are setup correctly as a whole system is when the simple motor really pays off in fun and low cost - NOT because it was easy to bolt on some part and go riding. Don't make that mistake or you'll find yourself eyeing your bank account to buy "new" technology because your money didn't take you where you wanted to go.

Neil can correct me if I'm wrong, but flat top pistons are in line with port design that is targeting a high rpm, higher hp engine. Hopefully you are aware that most pistons are not sold that way for a reason and when you buy the specialized one it's supposed to be matched to a certain other set of like-specializations to get the most out of the part.

You are so correct.

I bet if you lined 10 built 250Rs up side by side, 1 maybe 2 of them would be correctly built with everything matching.
Thats not saying thats bad either, its just that anyone other than a builder of these engines just dont know all the details of what all needs to be done or matched up.

I would have loved to have been a fly on the wall when Curtis Sparks was building & tunning Shane Hitts engines on the dyno.
Its no telling at the amount of pipes he built for each engine & then after a dyno run pulled it off & threw it over in the corner. Those discarded pipes could very well be the pipes that was sold to customers over the years. You know you cant get a new one anymore, hummmm :eek: wonder why ;) .
Ol big daddy aint been around all these years & not learned nothing.
Neil

[j450rking]

damn i have one of those flat top ones:( it's a wiseco. what would hapen if i used it in my stock jug/head?

[C-LEIGH RACING]

Compression would be lower & performance would be poor.
Neil

[j450rking]

then i'll have to get ahold of the guy on ebay that i got it from and see if he'll trade me for a domed one bc i wanna get the most power out of it without going high comp for now at least

[number5]

I think im gonna get a stock head and cut it.