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engine mods

Old 02-21-2004, 12:46 AM
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magyarbacsi
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Default engine mods

After reading all the info on engine mods I find a lot of contradictions, yet the builders claim better performance. For example, to increse the crank case pressure thus speeding up the rate of fuel mixture exchange, stuffing the case is what is suggested. That is the most agreed on method. Another builder grinds parts of the crank to create a "turbo" effect, but the result is less case volume. Hence defeating the theory of case stuffing. There are several cranks out there, e.g. ADA, SIKK, that have the voids filled with some resin/plastik like material that acts as a full circle crank. There was some credit to performance accredited to the full circle rc231 crank. Yet one of my 260 motors came stock with what I believe is an LE crank. Any professional builders/racers have an input. I welcome you reply.
Old 02-21-2004, 12:59 AM
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Mr Cajun Gator
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Default RE: engine mods

stuffing the crank case: with less room for expansion as the piston is on the down stroke, the more fuel/air mix is forced in the cylinder.
turboing the crank; again forces more volume in the crank case, making less room for expansion.
The idea behind doing mods is getting more fuel/air mix in and out of the cylinder faster. This could have been explained in more detail, but I hope this little basic stuff helps.
Old 02-21-2004, 01:08 AM
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BajaBob-delete
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Default RE: engine mods

Its not really contradictory,its actually two schools of thought on case volume.Both have their good points.
Old 02-21-2004, 04:28 AM
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Default RE: engine mods

IMHO grinding on the crank is foolish. The idea of turboing is to use the crank as a scoop so to say to force mixture up the transfers but grinding the crank sets the static balance off. The best mods to date are raising compression, larger carb, tuned pipe, trasnsfer largening, intake largening, exhaust largening, intake timing, exhaust timing, tranfer timing, ignition timing, lightening of the piston, flowing of all ports, piston flowing, transfer flowing, lightening of flywheel, etc, etc.There are so many mods that could be done and most are trial and error. Harmonically a single cylinder cannot completely be balanced but a compromise between static and harmonic has to be achieved. Depending on your use, the mods would be up to you.[8D]
Old 02-21-2004, 02:17 PM
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BajaBob-delete
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Default RE: engine mods

When the piston is modified,the crank gets turboed it balances again.Two stroke mods, like four stroke mods are not a matter of trial and error, the effects of changes to port timing are well known to informed engine builders,picking the rpm range you want the engine to operate in and then modifying to that set of parameters is how its done.
Old 02-22-2004, 08:49 AM
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Default RE: engine mods

the term "turbo'ed" refers to the streamlining of the crank throws so it doesnt plow through the fuel air mix. its typically good for a 1000 rpm increase.next off is the port enlargement ya gotta get the air in there and removing all the restrictions humps and bumps is crucial. now we have the flow of the gasses when they actually enter the combustion chamber, many scientific papers have been written covering this subject which is the stratification of the fuel air charge and each builder either addresses this or not.
here in the near future a crank will be available for the zenoahs that is a full circle and will accept the resin filler piece to stuff it even more then " turbo ing" the crank will be a thing of the past. all of the engine guys have arrived at their combination of mods by testing, testing and more testing. some are more willing to share their secrets than others so keep askin and we'll try to answer your questions.
Old 02-27-2004, 09:48 AM
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magyarbacsi
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Default RE: engine mods

Thank you for all the responses re engine mods. I have been following the mod posts for months and even dug up some old posts where pistons are drilled to enhance the transfer flows. That practice I see has now stopped. I'm familiar with the principals but was not sure what was the simplest and functional. I used to rebuild regular engines, Porche, Vetts,Volvos.. as a hobby and some out of need, but small 2 cycles are new to me. I have several of the Hp23 and Superior and Zen. motors, the big bore kits and different cranks,i.e. stuffer, full circle, 1mm stroker and in the process of modifying. Was looking for info which way to go. I dont get radical as I do this as stress relief, and dont race either. All of your inputs have helped. Thanks again. My fastes, so far, boat is a 20# 60 " cat with a mild mod 260, at 44.7 mph on gps.
Old 02-27-2004, 09:53 AM
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magyarbacsi
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Default RE: engine mods

that should of been "principles," not the principals.
Old 02-27-2004, 01:52 PM
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Default RE: engine mods

windowing of the pistons has not stopped, at least with my set of modifications.
Old 02-27-2004, 03:40 PM
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Default RE: engine mods

Larry,
I think I read one of your posts somewhere that you are now windowing the piston into the transfers only to the exhaust side now with a 3/16" hole.
Why have you stopped venting into the 4 transfers?
With the turboed crank, are you profiling both leading & trailing edges?
Sorry for all of the questions. I just like to roll my own & any input is appreciated.
Paul.
Old 02-27-2004, 04:20 PM
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Default RE: engine mods

i window the exhaust side transfer of the piston only. because of the way the transfer tops are formed to direct flow for scavenging. both leading and trailing edge is knife edged and where the rod journal is also ground down/or radiused to the rod journal. typically, tests done on the crank compared to a stock crank is about 1000 rpm gain with the work performed.
the largest single part gain in hp will be the full circle crank from superior engines that will be made for the pum style flywheel. then add the stuffin kit to the crank which is a resin insert then a giant leap in performance will be seen.
Old 02-28-2004, 10:56 AM
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magyarbacsi
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Default RE: engine mods

I hve purchase and installed a full circle crank with the resin filler, but in an HE23HP motor and also put the Sikk bb 27cc jug on it. Have not hads the opportunity to run in a boat. I wan to replace the stock 260 crank, which I think is an LE ? crank( not sure if that is what its called) with one of the after market like ADA or Sikk full circle stuffers. Will these cranks fit the Zenoahs with out any mods to the flywheel, and is the timing different. In an earlier post by Mid West, there was mention of having to make an insert in the fly wheel to change the off set. Too much work for just sport boating unless one likes to tinker with machines.
Old 02-28-2004, 11:08 AM
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magyarbacsi
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Default RE: engine mods

Regarding the piston mod. There are 2 transfer ports, one front , clutch side, and one 180 opposite, fly wheel side. Then each port is divided into intake side and exhaust side. Do you drill a hole in the piston in front and back? I looked at the piston you have posted it appered that the two holes were on the same side? Does this mod inhibit the idle or low end and only benefits top end?
Old 02-28-2004, 10:03 PM
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Default RE: engine mods

i should really update that picture. two holes get drilled one on each side in the exhaust side transfer port area only. the superior crank will fit the zenoah rc230 only. but they are comin out with a crank that will fit the PUM style engine it will have a longer ignition side shaft for the pum style flywheel. rt now its a ton of tinkering to get the hybrid thing going but well worth it if you are racin. so be patient and good things will come[sm=sunsmiley.gif]
Old 02-28-2004, 11:07 PM
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Default RE: engine mods

I was reading in the April edition of R/C Boat modeler on page 51, Thunder Pro INC is planning to release a line of cranks and hp pistons made by Racing Performance Motors (RPM). The crank is a full circle stroker and the piston is a 21g billet piece. The parts would be for the 22.5cc and 25.6cc Zenoah, J&G and QD engines.Looks promising but who the heck are they?
Old 03-01-2004, 08:18 AM
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Default RE: engine mods

Thunder pro has been around for ever "Rich" is the owner and they are in New Jersey. if ya cant find a part he usually has it. Superior like i explained is coming out with the same stuff in a stock 1mm and 2mm stroker and at about 1/2 the price of the RPM pieces. the full circle cranks have been around for a while but at $200 (ouch) you dont ever see any body runnin them. This will be the biggest in performance single mod you can do to your engine.

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