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I want to knife edge and cut the turbo shape in my crankshaft also cut away some metal on the outside of the sleeve matching the slots in the block. Mabe trying to induse a swirl effect in the sleeve to try and keep the too much fuel from escaping past the exhaust port. I have done this with my old HPI .25 engine with some very good results. Can anyone give me some tips of do`s and dont`s
Posts: 7 | From: South Africa | Registered: Dec 2007
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that sounds interesting. I modded my old 1004 S7C and changed everything ... but the wrist pin. Now it's well more powerful than my C6-CC. (But I have to admit that I'm educated in these things (UAS)).
BUT: As said, it's faster than the C6-CC on one lap but slower in any distance race ... fuel. Also the drivability is not easy any longer but can be managed by experienced pilots. I knew that before as I did it just for gaining ultimate power, a drag engine if you want. It took me a total of !28h! to do everything on it. Sorry that I can't say things here, because I don't want to make money with it and also that nobody else makes money with it (someone who has the R&D capacities to bring back economy, we are not longer allowed to use our laboratories as some have stolen things ... grrr). I hope you can understand this. But one thing I can tell you for sure: Things were made that officialy nobody else tried yet.
If you want it to use for racing then I would really not change a lot on the sleeve as there are so many different things to keep in mind. Also it takes a lot of R&D to make an engine working well for a main distance. The drivability f.e. is one of the responsible facts for tire wear, economy, constant laps and - very important - the driver's feeling.
Of course you can do the common things like polishing the exhaust port, the inside ports, rounding the crankshaft's turbo cut (not the edges on the side of it!) And you can match the sleeve's windows exactly to the portings. And, as said, a lot things more but this has to be done on your own.
The only thing I can give you on your way is the thing that the exhaust core needs to be kept together and not to be "destroyed".
Good luck.
[ 03. January 2008, 14:47: Message edited by: Stefan ]
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Thanks for the advise Stefan. So in short you suggest not to change the port and crank timing but smooth/polish the edges .
Posts: 7 | From: South Africa | Registered: Dec 2007
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Yes. The reason why I wrote my post detailed was to avoid bad results or even results that are not bad but also not like they finally should be.
[ 03. January 2008, 17:46: Message edited by: Stefan ]
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My 928 is very drivable considering the power it has out of the box..but I did cut on the ports. In return, I noticed that it liked to run a tad bit cooler, yet was more fuel efficient(not by much)...It also liked to start better, even when hot...to this day, this was the very best running mill I have ever owned...I got real close to 15 gallons out of it(probably more) and it has even inhaled dirt...
I'm no engine modder, but here's some pics so that you get the point of what I did...In which was basically following the fuel stains...But my purpose was to try to direct the fuel to the carb side of the combustion chamber(away from the exhaust) to make it more efficient, and to not let unburned fuel out of the exhaust.
Eventually, you can port it just right, to where there are no fuel stains on the outside of the sleeve.
I did nothing to the crank, other than some polishing.
If I would cut the Turbo shape in the 728 crank will that upset the balancing even If I do some counter cutting on the opposite side of the crank?
Posts: 7 | From: South Africa | Registered: Dec 2007
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posted
I would think that it would be OK...But balancing cranks in thse engines are nearly impossible because of the broad RPM range. For instance, you could balance it for maybe 1k to 5k RPMs, but it wouldn't be balanced at 30k-40k...At least from what I know. So as long as you didn't go too extreme, I don't thik balance would be a major problem.
I have a OS speed that has tungsten weights in the crank, but I think it may be more to offset the piston's weight, than actual crank balance.
Does the 728 not have any turbo port? Like I've seen alot of OS engines..
Personally I wouldn't mess with it, as you may upset the engine's timing. If so, then you would have to play with head shims and glow plug temps.
Posts: 67 | From: Covington, La. | Registered: May 2006
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posted
The balancing of the crankshaft is not just for itself but for the crankshaft in combination with the rod, wrist pin and the piston. These things need to be in balance. Once it is done then the rpm doesn't matter. You can try it when just mounting the crankshaft and spin it fast with the fingers. Without the piston and co. you'll notice an imbalance on every crankshaft.
Also here on the RB site the 728 is without any turbo ports.
[ 03. January 2008, 22:20: Message edited by: Stefan ]
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Now it's well more powerful than my C6-CC. (But I have to admit that I'm educated in these things (UAS)).![[Smile]](smile.gif)
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