deckheight

Link thief... :biggrin: :biggrin:

I don't know... :happy:

Those are both decent pipes... Raise 1.5mm and keep the same basic port shape. Between raising and widening, should work real well for you.

The piston that didn't grenade was running way hot and detonating hard... Bunch of blow-by past both rings, hard dark black cooked oil on the crown. I'll bet there is a spot of cooked oil underneath about the size of a half dollar. Pretty obvious what happened to the other one. If it were me I would start out with the 100 octane this time. That 100 octane is cheap compared to a new top end. Another thing to think about is that you have a way better than average chance that there are pieces of ring down in the cases now...

Not quite that simple when you start raising the exhaust... Gonna need more info. What type power band do you want? What compression (octane fuel)? Rider weight? Tuned exhaust? Carbs? etc. In general, raising the exhaust will also raise and narrow the effective operating rpm range. Without increasing combustion chamber pressures you will lose some on the bottom and gain some on the top... Basically. This is all assuming your not talking about that 521 in your sig that I just noticed???

Yeah, it is worth it. Widening the exhaust will improve your upper mid-range, improve BMEP and slightly raise max rpm. Don't go wider than 42mm and you will be fine.

If the top of the wrist pin hole is apx. 28.25mm down from the top of the piston they are standard pistons. Personally I would go with 21cc domes for 91-92 octane pump.

Don't forget to fix whatever caused the problem in the first place... :biggrin:

You got it right... The OEM CDI already has an advance curve programmed into it. Stock timing w/the stator plate at the factory setting or 0 is apx. 17* advance at idle and 9.5* advance at 9500 rpm. If the stator plated is adjusted to plus 7*, then add 7 to the OEM numbers above = 24*@ idle and 16.5*@ 9500, etc. Forgot to mention in my previous post... EGT sensors are a very good thing when your motor is running near the edge.

I don't run or build alcohol motors... Soooo, from what I have been told, alky needs more ignition advance than gasoline. I do build Gas motors and IMHO the higher octane fuels need earlier ignition advance due to a slower traveling flame front. Again JMHO, with 110 octane fuel you would probably want +/- 16* advance at max rpm. Using OEM ignition components this would be the equivalent of setting the stator plate at approximately 7* advance from the OEM setting. And don't get what I said earlier about "maximum combustion chamber pressures very near TDC" confused with when the spark plug fires. The plug is going to have to initiate combustion well in "advance" of reaching max chamber pressures. When the plug fires just helps determine at what point in crankshaft rotation max pressures occur.

What ignition timing adjustments are doing is controlling combustion chamber pressures. Like has already been said, maximum chamber pressure normally needs to occur at or very near TDC. Too early and the expanding gases from the fuel charge fight the piston on it's way up, thus creating uncontrolled spikes in chamber pressures/heat which promote detonation. In other words, heat energy is lost to surrounding parts instead of exerting downward force on the piston. Max combustion chamber pressures occur too late and the expanding gases are playing catch up for a piston already moving in the opposite direction, thus heat energy is simply released out the exhaust port without exerting downward force on the piston. Almost all internal combustion engines, that I am aware of, and that are available to the general public have been "de-tuned" to some extent from their design efficiency. An appropriate ignition timing advance is just one way to regain some of it. Or exceed it if your not carefull...

Your specific question does not have an answer... However, assuming both cylinders read within 5-10% of each other, your probably good as far as the top end goes.

In general, 18's are too small. If you just gotta have that head assembly get the 18's and have somebody competent open them up or just run higher octane fuel... At best and pretty much no matter what the rest of the overall set-up, 18cc domes and 100 octane fuel puts you spooky close to the edge. IMHO anyway. You could get the 20's and run lower octane fuel of course... Doesn't sound like your leaning that direction though.

LOL! I have not bought diamond tooling since the mid 90's... I don't remember the exact cost back then, but it was considerably more than $16 a peice! Oh well "buy high and sell low" thats my motto, apparently.

Yeah, take em to a movie and buy em dinner :kiss:

I've been riding a J arm bike for the last year or so... Couple things I have noticed: Upper bushings wear faster, much faster. Frame mounts for the upper pivot bolts tend to egg out (had to bush mine recently). And the J arms tend to bend easier in a crash than an A arm. Plus used J arms that are straight seem to be getting scarce. Anyway, I wouldnt pass a deal just because it was a J arm, but it would defenitely be a factor in my decision.

Huh??? I though you said no gas... Plugs dry, manualing primeing the carbs, etc. Now it's a flooding problem??? Might have to hire a Preist, little mumbo jumbo, some holy water...

No problem on the compliment. It really does look good... How so on the cutting part? I hear you about the plated cylinders, given a choice I personally will pass. Tooling cost is a little hard to digest also

My comment about "mapping" was more along the lines of what trex already mentioned regarding the "aggressiveness" of the durations, nothing more. What I was pointing out with the geomentry comment was that in relation to your photo, trex is getting a fairly dramatic increase in time area just with the shape of the roof and corners. In other words trex port geometry will see similar BMEP numbers at a lower rpm.

Not trying to be a smass and I know you said nothing is restricted in the jets or carb body... But you just increased carb signal or vacum by something like 100% by having those rags stuffed in the back of the carbs... Common sense says there is a huge air leak somewhere (maybe intake boot, or crossover tube? Maybe base gasket??) or a carb restriction...???

Yup, I would have to agree with you on that. In my experience it doesn't work that way though, but it could have been something in those specific set-ups I was testing at the time... Maybe the tuned exhaust wasn't in sync with what the bust port was doing, who knows? What I found was that it actually disrupted the flow of gases in the combustion chamber resulting in a less efficient burn on those particular engines. But, like I said, it could have been something else in the set-up contributing to it... At any rate the piston wash will tell you what's going on in there.

Hey 03LB, there's that pesky time area thingy again... Take a good look at the actual geometry of the main exhaust port, especially the top of the port and corner radius's. Kind of recurring themes for you lately eh? No comment on the port mapping, however that is fine looking porting work IMHO. :cool:

Mopar how you bean man?

I don't use compression gauge numbers to estimate fuel octane requirements so I can't comment on that specifically. However, assuming your cylinders have not been decked... And considering the port durations you mentioned... 19cc O-ring type domes would yeild a 100% safe CCR with decent 100 octane fuel IMHO. Truth is, you could go slightly smaller but you will be very near the deto edge around 18.25cc, especially on the right tube! One slip up and your done... I would not recommend it for what your doing. Again JMHO. For polishing exhaust ports I start with the tight wound rosin impregnated 50 grit sprial rolls (sand paper rolls) from C.C. Specialty, then move to the 110 grit, then the 180 grit and finish with maroon colored scotchbrite strips (apx. 2"X 2") mounted in a slotted mandrel. If you have ever polished an exhaust port the "old fashioned" way (compound and buffs) you will never go back... Try a little porting wax or bee's wax on your burrs. It cools things down and lubricates, less chatter and faster cutting plus longer burr life. I am going to plug C.C. Specialty a little here... I have purchased supplies else where over the years because of initial pricing, but I always seem to go back. Their products are more $$$ up front, but they are second to none in quality and longevity and often available nowhere else that I am aware of. I have no affiliation with them other than giving them my hard earned $$$ and don't get any special pricing deals (damn it!). So take that for what it's worth... End of plug.

I usually end up taking the long way around things wether I initially plan it that way or not... But sometimes things just have to be done... Last time I went through all the drama was to verify CDI function, that wasn't it LOL!