SlowMoe

The idea is not to raise the port, but to make the port open all at once. look at the sketch the center of the cutout is even with the piston crown. This will not cause the port to open earlier just make the port open more abruptly once it cracks open. I have been told that 1mm is safe to shave off the piston crown if doing so to increase port duration. I have gone as deep as 3mm with no ill effects, however the cuts were at the transfers so they were not as long. In my experience as an API 510 inspector and by knowledge of the ASME pressure vessel codes, in a situation where the strength of a component in a pressure application is in question due to low thickness, the thickness along the critical plane may be averaged along a line in that plane. In other words if a pressure vessel, lets say a propane bottle for instance were subjected to a pressure of say 1000 psi it would take (hypothedically) .100" of thickness for that vessel not to rupture. Now you can have local areas within that vessel that are below .100" as long as the average thickness along theaxial plane (a straight line drawn from head to head) no longer than 1/2 the vessel diameter is .100" or more. I know that this is a different application but im my mind if milling .040" in a general area is safe, and 3mm in a (fairly) localized area is safe then it would be safe to cut the piston crown as shown in my diagram to 2mm or so deep at the extremeties, as long as you don't leave any stress risers (sharp corners). Again, this is my theory but I feel as though the piston would have more than enough strength after cutting it as I described...

Also the cases are ported, and I forgot to add dual pingel valve $60

All prices are firm and include shipping: Milled and rechambered head for race gas/ Avgas. Bought this a couple weeks ago from Kevin Herr $100 Drag ported cylinders WITH 64.5mm pistons rings wrist pins/ bearings and new circlips. Very nice cylinders ready to rock $475 34mm Keihin PJ's come with billet intakes, K&N pods, brand new throttle cable, extra jets $275 Boyesen pro series reeds brand new never used $80 Vitos Fat Bastard pipes Chrome, one pipe has a very minor ding which is visible and another very minor ding that is not visible once installed. The chrome is in great shape and the silencers are still tight. Overall in very good condition. These are rumored to be the pipe to beat on the serval cylinder; pull like a shearer up top but have a broader powerband. $425 Complete bottom end. The cases have been port matched, the crank has been trued and welded and the specs re-checked by sleeper 06, never ran since inspected, cut transmission (one step down from dunable), shift star mod, billet inmotionpowersports clutch basket, brand new never used heavy duty clutch pack with drag springs (said to hold up to 90 hp) I will include the stock/ medium duty springs as well, timing plate modded for +4, billet impeller, flywheel, kicker, covers, new clutch cover gasket, new base gasket for ported cylinders, and everything associated with the bottom end. Bolt on your cylinders and go. $1000 11 paddle SLS haulers there is a 2" puncture behind one of the paddles, so they are tubed. The tubes have held up fine with a 521 cheetah engine. The ones in my sig $200 Rolling J-arm frame. This includes everything minus the engine, pipes, carbs, gas tank. Includes works dual rate fronts, marvin shaw competition rear, +8 swingarm, ITP holeshot rear tires. $650 PLUS shipping or local pickup in north east texas. Will part out frame if it doesn't sell. I will post up pics later. Everything minus the pipes/ cylinders are a couple of hours away (I am working out of town this week) so pics/ shipping will be available on friday. I can make the drive sooner if you want a large item. Pics to come, thanks for looking!

Aight I just recently got these cylinders. They are supposed to have been ported by a guy named "Coonie". The port work looks a little different but the quality of the work is really good. They are drag ported and I measured 26.5 mm from deck to top of exhaust and 42mm from deck to mains, secondaries 44mm from deck to boost. They are set up especially for gas; I am guessing the timing in near 198/128 but not sure. Any help would be appreciated. Thanks!

This is what I have in mind. Thoughts?

Hehe

Ok, what I am trying t get at here is the theory I have been kicking around in my head; here's what you do.. 1. Transfer the profile of your NON-flat port roof to a sheet of paper. 2. Transfer the profile to your piston in a way that the center is even with the piston crown. 3. Pie cut your piston, following the profile, going aproximately 2mm deep at the extremeties. Seems to me like this would be worthwhile especially in a drag engine but I am just a little concernad with weakening of the piston and causing my powerband to narrow. Oh, BTW cam on the other forum in the thread about the welded transfers I commented on your post about the c compared to the [ transfers . It involves epoxy....

What do you think? lol

I like this thread

I'm not mad buddy. I like you. But, aside from it being extremely confusing, I have a problem with this statement; when we first became acquainted (back when we got along) I would ask technical quiesions on here and you would send me PM's with tips, and ask me not to share the information you gave me, like it was some kind of big secret. And I actually respected that and never shared anything you asked me not to. But now you come out and say I am wrongly accusing people of doing the same exact thing that you do, probably on a regular basis. Bad memory? And what's with this "we" stuff? Are you the official BansheeHQ spokesperson/ guardian or something? You must think that everyone is stupid and will just blindly follow the recommendations of someone on this website without getting second opinions. To be honest, I have made my share of bad decisions in the past, and I have paid for them, but you know what? I learned from every one of them. You think the top builders out there got where they are by staying inside the limits of what was taught to them? No they got where they are by pushing the boundaries and learning from their mistakes. No guts no glory right. Do I believe others should modify their engine based on speculation on my part? No. But if it IS speculation, I will do my best to let that be known. Since you have never done it, how can you know all this? It appears that there may be a little speculation involved...? Strange I thought it was only Slo who did that. And .002% hidden power? Really? I would be willing to bet my paycheck against yours that there is much more than .002% to gain from going from an oval port to a port with a 12mm radius on the corners and a flat roof. Offer stands.

You're probably talking about 10 hp or so more with the cub, depending on who did your port work.

So you're either stupid or just plain arrogant Just saying BTW how's Seminoe been lately? The last time I was in that area i believe it was flooded badly.

and so because but Sorry Mike, i couldn't help myself

Well I will tell you one thing this forum never changes. One helpful person out of every four is about par for this course. I am about to stop posting technical questions on here because there are apparently much better sites out there for that type of thing. To be honest I really didn't expect my question to be answered on here, I was just hoping perhaps everyone could maybe learn something here, as I planned on sharing information I gained from other sites with the members on here, but once again my gut instinct proves right and even though this IS a fairly basic question whose answer is likely known to 90% of the builders people out there, everyone acts like it should be super hush hush. I am willing to bet money that half of the builders out there would be happy to divulge this type of information, because as said earlier it probably is common knowledge amongst the pros out there, and to not divulge this type of information in fear of losing their compedetive edge would be something only a person, in my opinion, not intelligent enough to be doing this sort of thing in the first place would consider.

I've read the 2 stroke books enough to know that a flat exhaust port roof vs an arched one for a fixed port duration will, theoredically give you: A. Higher peak hp due to increase in blowdown area B. Higher peak hp due to a stronger pulse wave C. A narrower powerband due to the strong but relatively short duration pulse D. Shorter ring life due to the abrupt return to the ring lands My question is, from real world testing/ experience, has anyone noticed a MEASURABLE increase in hp from the flat roof and Is there a perceivable narrowing of the powerband? In theory and most certainly in real life both of these would hold true but to what extent is the question. Any feedback is appreciated Slow

Haven't seen too much of either of these guys. I saw Jones live in Denver when he broke Brandon Vera's face, and a couple of tv bouts he looks like a young phenom for sure. The way he dominated Ryan Bader was really impressive considering Bader is usually very dominate. Ever since I saw Rua's fight against Mark Coleman I never really liked him much; Coleman was looking so old and decrepid and looked like he needed an oxygen mask yet Rua couldn't put him away. Looked good against Chuck and Machida though... I don't see it going all the way

1. FIRST find out why you have 20lbs difference/ fix. Then 2. Mod your timing plate to +4 degrees------------------------------------------------------------------>Free 3. Shave 1mm off your piston crown adjacent to the exhaust (we can help)---------------->Free 4. Reduce your tire pressure to 2psi------------------------------------------------------------------------>Free 5. Clean up that nasty porting ONLY if you know what you're doing (we can help)-------->Free 6. Pull the airbox lid off and rejet----------------------------------------------------------------------------> Free(ish) I guarantee once you do this you will destroy that raptor.

This will be on a drag engine w/ vitos pipes, 160lb rider, approx.180 lb. compression, sea level