R/C Tech Forums

Go Back   R/C Tech Forums > General Forums > Nitro On-Road

Thread Tools Search this Thread
Old 06-15-2003, 09:16 AM   #16
Tech Elite
popsracer's Avatar
Join Date: Oct 2002
Location: "Hot, Sunny Southern California"
Posts: 3,120
Default I run the XP12

Originally posted by rodneybarrett
OB42TC3: With the extra shim in how much is your clearance now? .6 mm ?

Also, I run the XP12 as well but I only use 20% nitro. Do you think the original shim is enough for it or should I put another in.

This is a good topic. Let's keep it going. I can learn a lot of good stuff here.
Take the thin shim out and just run the thick one. The engine will run better not hotter, and you can run 30% without having to add another shim. I should add that I ALWAYS run MC59 plugs and never have problem burning them out.
popsracer is offline   Reply With Quote
Old 06-15-2003, 09:22 AM   #17
Tech Elite
popsracer's Avatar
Join Date: Oct 2002
Location: "Hot, Sunny Southern California"
Posts: 3,120
Default Shim and Nitro content debate


I also have an STS MT12 in my Kids Reflex and ran that last night at our big permanent track here on 30%.
The original head clearance was .027, I have reduced it to .012 (Total) to some performance out of this engine. Runs better, but still slow to what I'm used to.
popsracer is offline   Reply With Quote
Old 06-15-2003, 10:09 AM   #18
Tech Addict
Join Date: Aug 2001
Location: Richmond, Va
Posts: 679


There's really no right or wrong answer for this debate. Two indentical engines will run different at different altitudes, humidity, ambient temp, fuel type (manufacturer, not nitro %), etc. EVERYTHING is relative to engine performance.

This is from personal experience. I have a few .12 engines, all run O'Donnell 30%, and all run Novarossi plugs (either 6 or 7). One of my stock MT12s runs beautifully with stock shims (.3mm I think). My other 2 stock MT 12s needed an extra .1mm shim to run at a safe temp & still have good performance. Two of my Richey MT12s needed a .1mm shim, while another need a .3 shim. My 3 port Sirio did not need extra shims, but the 5 port Sirio needed a .1mm shim. All these engines run in the same climate, same fuel, same plugs, and there is that much difference in them. And we won't even talk about my .21 engines!!!

Also, remember when the engine gets really worn, you may need to take out some shims to get performance back up to a respectable level. Obviously, this isn't a solution to "renew" a worn out engine, but it can help get a little more life out of it.

Basically, what I'm saying is run the engine, if you don't like the performance, try adding a shim. You will not hurt the engine by adding shims (but you can definetly hurt by taking out too many). If you don't think it helped, take it back out. EXPERIMENT!!!!!!
tekrsq is offline   Reply With Quote
Old 06-15-2003, 02:05 PM   #19
Tech Apprentice
Join Date: Dec 2002
Posts: 74

The problem with running 30% nitro in a small block engine is it changes the timing of the engine, This causes the fuel to ignite to quickly, The other problem is it can cause detonation (the fuel explodes rather then burns). By adding a shim you are addressing the symptom (timing) but are not addressing the problem (detonation). Many in the hobby have bent connecting rods running high nitro. A general rule of thumb is the higher the nitro the cooler the glow plug, so if you are running a high nirto fuel you should be running a cold plug and it does not require taking the engine apart. If this does not work (engine still over heats), then try adding shims. There is no such thing as pre-detonation, what is refered to as pre-detonation is actually pre-ignition, where the fuel ignites to early in the cycle.
nitro dipstick is offline   Reply With Quote
Old 06-30-2003, 09:08 AM   #20
Tech Adept
chachi's Avatar
Join Date: Mar 2003
Location: vancouver, bc
Posts: 149
Default Update

Thanks for all the information. Apparently there is no correct answer...

I contacted Serpent USA about the issue (like Accord), since I am running a Novamega SX12 3P MS RT with 25%. They claim not to use any shims when running 25 or 30%. I have been running an extra shim since I got the engine, and the performance was great. Last week, I took out the extra shim and retuned my engine. The increase in power was very noticeable. I was worried that I might ruin the engine, but I have not been having any problems with detonation or burnt glowplugs. For now, I am going to keep running without the extra shim. BTW, the climate here is moderate humidity and temps around 20-25 degrees C.

On a similar note, someone here is running 40% in an RB .15 with no shims, and the engine screams. The power almost seems uncontrollable. Seems a little dodgey to me.
chachi is offline   Reply With Quote
Old 06-30-2003, 09:36 AM   #21
Tech Champion
TimPotter's Avatar
Join Date: Sep 2001
Location: Boynton Beach Fl > Randoph NJ
Posts: 7,481
Trader Rating: 14 (100%+)
Send a message via AIM to TimPotter

I have a SX12 that I have run nothing but 25% in it. Never shimmed, runs and idles like a champ. No additional shims-lots of power. BTW run 25% in my unshimmed OS12 TR too.
Clean Title & Escrow|p3|TRF|Tamiya|SerpentAmerica|FSEARA|Team Butter|RC 3|Munno |RCTECH #29|EAMotorsports|BMI|Novak|SpeedPassion|RadioPost
TimPotter is offline   Reply With Quote

Similar Threads
Thread Thread Starter Forum Replies Last Post
Nitro, oil content slipgate Nitro Off-Road 8 09-09-2008 11:29 AM
30% NITRO DEBATE GSPOT Nitro On-Road 28 06-03-2008 08:21 PM
Higher nitro content = lower engine temps but.... Team Duratrax Electric Off-Road 9 08-15-2005 07:41 PM
My Great TC EP vs Nitro Debate scoobydo Electric On-Road 56 02-28-2005 07:44 PM
Changing Nitro content Brett.w Onroad Nitro Engine Zone 5 02-11-2005 02:28 PM

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off

All times are GMT -7. It is currently 06:50 PM.

Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net

SEO by vBSEO 3.5.0