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Hello all i just got a 3.3 revo engine that had been rebuilt. I noticed the head was turned wrong so i removed it to turn and noticed there was no cooper shim between cooling head and block. I run the Traxxas 20% nitro. Someone told me no not unless i go above 33%. But i wanted to make sure thanks for the time.

Snook Man

rcbence

No you don't. Just run 5-10% nitro MAX. Most any engine will seal just fine. This is how misinformation is spread. People who talk without any kind of testing.

Maj_Overdrive

My Feedback: (11)

Most engines will seal? Will the TRX 3.3 seal? Have you tested what nitro contents the TRX 3.3 can run without a head shim or head shims of varying thicknesses? Which makes the most power? What heat range plug works best with what nitro % and head shim to prevent detonation? If so why not share so the OP and everyone can benefit? Is it a secret? Your post seems like a blanket generalization with no factual or substantial information given for the engine being discussed. Snook gives a nicely detailed post relevant to and helping the OP as much as possible. But of course you criticize Snook for not testing and spreading misinformation while basically telling the OP to buy more fuel in a different nitro content instead of the much cheaper head shims that will allow the engine to run as it was designed by people who definitely know more about their engine than you do.

1QwkSport2.5r

Note post number 1 & 2 is from 2012...

rcbence

OK you have a point. I brought up a dead threas as well.

Yes they will seal. I'm running it right now and have ran plane engines without the shim. Yes it's best to run whatever is recommended because its been designed that way. Plenty of clearance without shim. More than .008 which I've ran half that on a tt pro without any problems...
But .008 is a good safe minimum. 10% nitro is getting up there with no shim and hot plug. It won't detonate.... But I believe the slight power gained isn't worth the extra heat. 5% is probably a safer bet. No pitting whatsoever running 10% and no shim though. The thinner .2 shim by traxxas works great with 10% and hot plug. I'd feel safer. Hard to detonate on low nitro. Methanol can take lots of compression.

If someone wanted to save a bit money on fuel and wants the most out of it..
Run the thinner trx shim with 20% nitro. Power will be same or right up there with 30% and stock shim. Won't detonate. Medium plug.

I said most because well nothing is 100%. The gasket isn't a seal in this case. It's just a shim. I will probably go back to the thinner shim myself. Ive ran plenty of fuel through it with no pitting.

I ran my Revo on 2.5% nitro with no shim just to see how far down I can go. It ran fine.....although the idle wasn't the best. 5% was noticeably better.

Maj_Overdrive

My Feedback: (11)

Damn, I'm usually pretty good at catching that, probably would've said something either way.

Much better, thank you for the informative post.

1QwkSport2.5r

The stock 3.3 will run fine on 25% nitro and hot plug with the stock shim installed. I've ran no nitro with stock head shim and it ran fine as well albeit with a much more sensitive needle. 30% nitro and peak needle setting will likely collapse the glow plug element. I only use hot plugs and high nitro all the time without too many issues. The key to using hot plugs and high nitro is having the mixture rich enough, and it helps to have the right pipe on it to take the most advantage of the fuel. An engine will almost always make more power using higher nitro and lower compression than an engine with higher compression and little to no nitro. Those FAI speed engines will turn some crazy rpm without nitromethane.

jkdv8

My Feedback: (1)

I was gonna say the shims are only used to raise/lower compression with changing levels of nitro. Doesn't have anything to do with acting like a gasket. People who don't run any nitro in their mix remove the shims.