Ok heres a question for ya, Are the aftermarket heads all pretty much the same? I mean is the DUNCAN/Paul Turner "Power Head", and the Pro Design "Cool Head", and the Tudors Racing Head the same? Does one of them perform better than the other?

 

chongo can you recamend a cc dome size for my zilla my powerhead i bought used came with a 64 cc dome.my compression is only 125psi.the jug is drag ported also. it made 55 hp on the dyno befor the trans broke.125 is low the only good thig is the moter would last forever.thanks

 

I don't know for sure if all heads are created =. I am pretty sure that the pro-design and duncan are pretty close. I have never seen a tudors. The domes have grooves/depressions machined into the top side of the dome (where the coolant makes contact with the dome) so you have more surface area in contact with the coolant. As far as one out performing the other, I doubt you would feel a difference or see it on the dyno (all variables being the same). The stock head can be made to work as good as any of the others but in the end you end up spending a decent amount of $ on a head that you can't play with different domes and keep in mind the thinner the head gets from shaving the more likely it is to warp and cause the blown head gasket. The aftermarket heads are pretty thick and are made out of billet aluminum instead of cast. Trinity does alot of work on the stock heads like welding up the coolant passages, o-ring, reshaping the squish area for a smaller dome and or bigger bore (keep in mind that when you get to a certain size bore which I believe is about .080" over the squish band on the stock head is to small in dia.) and even the "turbo" mod. You would save $100.00 but would still have a stock head. They do also offer the Pro-design head for whatever thats worth.

gnjeff, do you know what exhaust duration you are running? or how high the exhaust port was raised? You will notice a big gain if you can get your pressure up from 125. There is alot of discussion on what is too much. Some say that 210/215 is the point of negative return. I am running a 51cc dome and can hit 215. I run VP C-12/Castor927 32:1 with the ignition advanced 3degrees and have had no problem with detonation. Runs great, (just schooled my buddy up on his powervalved 420cc banshee, man was he pissed, he just sank over $5000 in it). I will have to check my notes to get you exh. duration, port height, and squish area.(I am not at home right now) but if you have a "drag ported" cyl. it's probably pretty close to the same. I wouldn't be to worried about it being to high, especially if your only pumping 125 and your rings/head gasket are in good condition.

Quote of the day, "Good head is hard to find"

 

chongo.thanks for the info.im lost on exhaust duration on a 2 stroke. i dont no what you mean. i will ask the guy who ported my jug about the ports.if you run around 200 psi comp wont you run into probs like crankbearing failer, blow the jug off the case.i would like to stay with pump gas. but if i need to racing gas is no problem i have it for my car.i need to get some more pony's out of this bike. its all new.ran for only 15 min and the trans locked up.will diff reeds make it faster im running boison stock replacements now.and how did you figure out how far to turn the stator to get your 3 deg timing im at stock rite now.thanks

 

exhaust duration is how long the exhaust port opens in crank degrees. You need a degree wheel attached to the crank/flywheel to do this. There are other ways (comp. programs and such) but not as accurate and not as easy. So for example we know it takes the crank 360degrees from TDC all the way around to TDC. So if the exhaust port opens when your degree wheel says that the piston is 90degrees past TDC or 0 (while turning the engine over and watching) then it should also close at 90 degrees before TDC. So we now know that the ex. port is closed for 180 degrees or open for 180 degrees which would give you 180 degrees exh. duration. and the same goes with the transfer/ boost, intake ports. I hope I didn't confuse you too bad, it's alot harder to describe than it is to see. I am running about 189 degrees exh. duration. I broke my cyl. and had Trinity weld and gusset the back of it. I did that when it was bone stock. Trinity does a good job at fixing that, they welded it up and it now uses those long barrel nuts like the one that holds down the front right hand side of the cyl. You know the one that looks like a bolt with a hole in the middle of it. So you can imagine those ears on the back of the cyl. are now pretty thick and it will never happen again. It's kind of a flaw with the stock LT. Other that that if you have had the bearing/case bushing mod done then I wouldn't worry about it. Of course you will never get more hp out of an engine and have it last longer but thats kind of trade off. As for how much you decrease the life? Probably not a noticable amount. I have not touched my bottom end or cyl. since I did the bearing mod and fixed the cyl. which was probably 6 yrs. ago. I ride at least two weekends out of the month. Mostly all sand which is harder on the bike than dirt. I race it alot and beat it hard. I run an inframe drag pipe so I really screem the thing and haven't had a problem yet.

You can check timing with a dial back timing light. You can adjust the timing light for say 3 degrees and then move the plate until the marks line up. Or if you don't want to spend the money you can do it the poor mans way. I will probably get some lip for this but there is nothing wrong with it.
Measure your flywheel (accuratly, with dial calipers or a mic.) then find the circumfrence (pie X diameter) and the divide it by 360. The answer is how far each degree is worth. So multiply your answer times 3 and that is how far you have to move the plate behind the flywheel. You may have to take out the three screws that hold down the plate and elongate the holes. They should be already but sometimes not, or not far enough. Remeber to measure that distance where the pickup sits next to the flywheel (I think its in the 4 o'clock position) Your not going to hurt anything if you go too far or not far enough. If it pings you went to far and then back it off. Don't let it ping though, then you will end up in trouble. Don't be afraid to play with it. You will notice your power range changing, more or less top or bottom end. Whatever you like.

You should be able to run pump gas somewhere up to about 175 psi would be my guess and only a guess. It depends alot on other variables like volumetric efficiency, temp, etc. I would run race gas even if it were 140psi. that way I know I have a consistant octane rating. and remember alot of times the way pump gas is measured is different than the way race gas is measured so 91 pump may be less than 91 race gas. I used to mix it ( half VP red 107 to half super) but then I just started buying the C-12 for piece of mind, not to mention the pump gas out here is CA is oxygenated.

I like the new V-force reed cage but make sure you get the one for the LT500. alot of places try to sell you the one for the rm 250 which looks the same but the reeds are different and you won't know until you ride it for a half hour and the reeds explode. Moto Tasanari changed their part # along time ago but some of the vendors haven't updated their catalog still. You can go to their web site and check the right part # yourself. I always like the boysen cages but they don't make one for our bikes. The V-force are alot of money. Whether its worth it or not is up to you, but if I didn't use the V-force I wouldn't use anything else but stock with boysens. I think I have a FMF I would give you for the price of shipping and a Mountain Dew but I wouldn't bother if I were you. I would bite the bullet and get the force.

 

thanks chongo for all the info. they say you learn something new everyday. i should be good for a week now.when my moter and trans gets back i will try to run some test on it to give you more of an idea what i have going..i would like some more performance out of my bike.does v force make a reed cage fo a 87 or do you need to get the one tudors made.i only see 88-90.im going to call duncan to see about another dome for my head. to get the comp up to at least 150. i will be in touch when i get my stuff back thanks.

 

You may have to go with the Tudors Perf. reed cage. I didn't see a listing for the 87 on the Moto Tassanari web site. That doesn't mean they don't make one. I would give them a call, it may be the as easy as putting different reeds on a rm 250 cage. The guys over there are good people and are really willing to help. It's worth the call.
Good luck on your ride, I will look forward to hearing the results.

 

DG: I paid $275 for the head and the dome... I see them on ebay for around $220, but not sure if that includes the dome or not...
What do you think??? make me an offer.

 

go to the duncan racing web site the have them for 250 new. and the directions on how to get the rite cc dome for you bike.my 2 cents worth.