still some unanswered Questions on 30% Nitro

[godale03]

Hey Guys,

I have been reading past posts on 30% nitro and a couple of weeks ago the guys at my LHS finally talked me into getting a gallon of it. Odonell, 30%. Now I have read so many posts that say, I love, or I hate it, or I don't know. I have an OS RG X on my 1/8 scale bug and according to my guy at my LHS you do not have to shim it. OS's site doesn't even talk about 30% nitro. I don't want to blow my mill up. I am still not that talented with the screw driver yet. What is the real deal with 30%? Is it really as good as they all say? How critical is it to get the needles just right? I have a temp gun, so as long as I monitor my temps and flush with ARO after each day I should be ok? I just read so many conflicting replies that I am really confused as to if I should really be running the Odonell 30%. All the guys at my local track run it in there stuff and they swear by it. I broke the mill in with Trinity 20%. Sorry if the question is redundant I just got so many conflicting posts I got confused. Thanks guys.

Tom

 

[Bouzouki]

30% in a .21 is perfectly fine.

In fact, I consider it normal, 20% is usually for smaller engines.

I dont think you need to shim, use after run oil, yes.

Monitor temps, should be around 210-265F

Since you broke the engine in with another fuel, you will need to re-tune the HSN.

Your not gonna blow it up unless your really clueless

 

[Plaidfish]

w/ the RGs I dropped to 25% and stopped killing conrods...after 2 in a row I was getting worried...if you have a full gallon of 30 then buy a full allon of 20% and mix the 2...make sure you buy the same manufacturer's fuel and the same grade....ie. if the y have a sport mix and a race mix make sure the 2 gallons are the same type just the nitro% will be different......

 

[CorradoPsi]

if you are really concerned add 1 thin copper shim under the head of your engine. the RG is a sport engine and may only be shimmed for 20% which would be why plaid was eating up conrods. the copper shim will take care of it. no need to run a lesser nitro %. add the shim and run the 30%. for me, its all ill run, big blocks, small blocks, it doesn't matter. they all run cool and powerful and i havent had any reduced engine life. my vspec in fact has crazy compression even when hot after 3+ gallons of relentless punishment using 30% low oil fuel.

 

[Plaidfish]

Oh I'm sure that's what was eating the conrods.....I caught the second mill as it was about to esplode on me...it was running funny so I pulled the case cover from the back and saw the lower bushing was spinning on the crank journal....thus ensuring the damn thing got NO oil.....I swapped it out and dropped to 25% pinched the sleeve and I'm on Gallon 3 and it's still got hella compression....yesterday I found out just how off my tuning is....my friend fine tuned it and damn I was rocketing all over the track w/ that thing...now I do have to admit I beveled the crank fuel intake and polished the barrel and fuel/exhaust ports in the case....I didn't do the transfer ports cause they were too hard to hit w/ my tools.......but man that simple mod makes such a difference onthat engine.....anyone know if there's a stronger conrod that fit's the RG??? Corrado????

 

[CorradoPsi]

sorry that i dont know. check the stroke of the RG vs a VZB or RZ, if they are the same, then one of their rods may fit.

 

[FastEddy]

I run O-D 30% in everything. I have never used an additional shim in a .21

Here is what I found.
30% gives me a lot more punch.

It narrows the tuning window. Finding the sweet spot takes more time and or a good ear.

It allows me to run just a bit richer then 20% without sacrificing any power over 20%

Engine temps are cooler because of running richer but if I get on the wrong side of the tuning window it heats up extremely fast.

Just my observations.....

 

[godale03]

I am sorry for the redundant thread, it is just that I have read so much conflicting answers to the question that I was just a little confused. So I think I am convinced that I do not need to shim out the OS. I am understanding that the tuning will be just a bit more teadeous. I also understand that I will have better performance, and a cooler running mill, if my tuning is on the mark.

I do have a couple of other questions that have risin since reading this post however.... Do I need to run a different plug? Right now I am running an OS #8. Also because of 30% has less oil in it, are my after run proceedures any different? Right now I clean the mill real good outside and then about 8-10 drops of ARO, turn the mill over a few times without power, and then leave at BDC. So I am to believe that changing to 30% is a good thing? Thanks guys

Tom

 

[rocknbil]

I agree with almost everything in FastEddy's post. I'd only used 30% expiramentally until the Mayhem, broke it in on it and am still running it, the engine is getting stronger with every run.

The only thing I can't really verify one way or the other is exactly just how much more powerful it is. Doesn't seem to be a **big** difference from what I can tell - but then - never ran 20% in this engine, no benchmark. Next GT engine is going to get both.

As for shimming, I agree, don't need to, and my personal opinion is don't alter the head clearance unless you know exactly why you're doing it and what the effect is. The idea of upping the percentage is to gain power, and if that power gain causes an increase in performance, adding a shim reduces the compression ratio - seems like one works against the other (???)

The one difference I notice w. 30% - that is, besides it's another five bucks a gallon - is the exhaust gasses seem a LOT hotter (measured at the exhaust manfold.)

 

[maxxFX]

Get this somebody at a LHS told me that if you know how to tune it, you dont need 20% I say bullshit I always run 30%!

 

[rocknbil]

Huh?

Well. I'm guessing you mean 30% in the first reference. But there is a bit of truth to that, in some conditions. You have to understand all of the below to see the reasoning.

If you read up on nitromethane, especially it's use in top AA fuel dragsters (and that is NOT the same as our engines - an electrically charged spark plug, etc., many differences) you will come across a passage that states that the reason you see the flame blowing out the exhaust is because there is literally not enough time for the fuel in the chamber to comletely burn. The top AA's run in a near-hydrolock condition and the excess fuel blows out the exhaust and ignites.

Nitromethane in itself is not all that flammable, but it is extremely explosive. Drop a match in a pool of pure nitromethane and it's likely to sputter and go out. Hit the same pool with a hammer and you'll have a crater the size of a car. Nitromenthane burns several times slower than most flammable liquids; in fact, methanol (wood alcohol, our fuel) is WAY higher on the flammability chart than N.M.

The important thing to think about is it burns SLOW.

So in order to make use of this explosive power, you need a catalyst to get it burning. For us, that is methanol, wood alcohol. Alcohol is the actual fuel; nitromethane is an additive. Most hobbyists are under the impression nitro is added for the explosive power, which it is, but that's not the PRIMARY reason.

To get combustion in your engine you need compression and an air fuel mixture in the correct proportion. Now if you could get more AIR into the combustion chamber, you could also squeeze proportionately more FUEL, right? This would give you a bigger burst of engergy.

The chemical makeup of nitromethane contains an exceptional amount of oxygen molecules that when atomized (turned to mist) are freed. So when it gets in your combustion chamber, there are now more molecules of oxygen in that space that would ordinarly be possible under normal atmospheric conditions.

Which allows you to get more fuel in, which makes for a bigger burst of power.

At what point does this oxidation process begin to lose effect, or become overkill? Remember the unburnt fuel of top AA's, and the fact that nitromethane burns many times slower than alcohol. If you keep adding more and more nitro percentage, at some point the engine cycle is going to be too fast to burn it all.

From all of the research I've done (and this is bookwork, theory, weird science and crap ) for an ordinary unmodified engine this drops off at around 25-28%, which means that in an umodified engine, anything more and the unburnt nitromethane wil simply pass through the combustion chamber, unburnt, and out your exhaust.

To make use of nitro percentages over 25-30%, you have to REALLY know engines and alter the compression ratio with shimming. (which I do not. Don't have the budget to expirament. )

This is why you will always hear me say never alter the shim clearance unless you **really** know what you're doing. Most engines do not need a shim adjustment under normal conditions; but if you run over 30% fuel you'll need to do some tweaking to burn it all. If you just throw 40% in an OS out of the box, you're just wasting about 10% of the extra money you paid for the higher percentage.

So, FX, that's where they are coming from. It's probably better said that the difference between 20% and 30% is not worth the difference in cost for most owners.

 

[godale03]

rockinbill,

That is probably the most thorough explination I think I have ever read. I feel smarter by just reading it. Thank you so much for what I am sure took a little while to type, but also research. My hats off to you and thank you again for the great info. Wow...

Tom

 

[rocknbil]

Pshaw . . . lol . . . I cannot take credit, this is just info I've collected over the years from those who know more than I.

 

[badboy2]

i switched to 30% odonnell without putting shims on my engines and they ran cooler ..idk if its good but they dont even reach 200s..like yesterday i was breaking in a picco omega x3 21 and first 2 tanks on idle i was running 170s then 3rd tank on half throttle was 180s after i leaned it