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compression

  • Thread starter Thread starter tannera
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T

tannera

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i am going to try to take 1 or 2 shims out of my .25 engine on my savage but can i use 25% nitro fuel when i have i read on a nother site that you can have to much compression. :devious:
 
Refer to the manual of the engine. All engine tolerances are different. Your piston might not have enough clearance at the top of it's stroke and might hit the bottom of the glow plug. Then you have real issues. On a lot of engines you can just switch to 25% and some people will even tell you that you can always switch to 25%. Lots of people on this board have done that without any problems. Sometimes an engine is differnt. My Sirio's came with extra shims and intructions for how many shims for what % nitro.
 
Radio Control Car Action had a How To artical in January 2005 on Power Porting HPI Nitro Star S-25. The said you could safely take out one shim but be careful removing two.
 
stallsmithb said:
Radio Control Car Action had a How To artical in January 2005 on Power Porting HPI Nitro Star S-25. The said you could safely take out one shim but be careful removing two.
Click to expand...
Yup I had mine ported by a member and will be reviewing the mod done. I have only two shims but I am going to see what three is like first and then two after.

Removing more than one seems like you will have problems with the Piston hitting the plug as HB said previously. Be careful as you are advancing your timing and that means you will need to re tune the engine.

I recommend only one shim removed.
 
I can't answer that if it is ok or not. I have yet to run my new s-25 modded. I only run 20% Odonnels. I don't care to go any higher personally. I feel that the engine works hard enough for me. Going higher in Percentage decreases your engine life faster. How fast? Not sure as I don't know how much its driven and cared for.
 
Forgive me for opening up an old thread, but, in my manual for the savage 25 it recommends 20-25% fuel but i have just read here that 25% wears out an engine.
I am currently "breaking in" with 25%
Is this the wrong thing to do?
I don't want to kill my savage
 
From experience, you can take out 2 shims just fine without any clearance issues. If you take out all three it will hit if not getting way too close. I have only run 20%, and that worked fine with only 1 shim.
 
i took one shim out and i put the under head and i think the piston was hiting it so i put it back on and didn't bother doing it. there was 3 shims on it i think i got it wrong and it wasn't hiting it. are try it again and see if i was wrong about it hiting it.
 
Last edited by a moderator:
ac48 .... did you notice a big improvment taking a shim out? ... and did it run even better with 2 out? ....did it tuning it any harder? please lmk
 
Just took 1 shim out and the piston dose miss the under head i got it wrong first time if i take out one more how much more power will i get.
and dose it damage my engine?
 
I tired taking all three out, it hit, so I put on back in. Never ran with 2 in there. I ran the engine for a few tanks with only one and it ran great. It pulled wheelies in my savage and ran very good. I didn't keep it long enough after than to need to tune it, it still held a tune just fine.

If it isn't hitting, your engine should be fine. It may slightly reduce the life of your engine because of the high compression, but only a little if anything.
 
i will take 2 shims out then and once i get the 3 speed it's ging to be flying.
 
I now I was reading your thread earlier, that is very weird. Have you tried putting more shims in yet?
 

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