3.3 fuel change

[mayrider]

I'm switching my jato from 20% traxxas fuel to byrons 30% my question is can i change my headgasket to the thinner one to increase compression or should i stick with the original one?

 

[Extreme RC Mods]

You need to measure the squish before the question can be answered. .008 should be ok.

 

[mayrider]

explain the squish please I've never heard that term

 

[Extreme RC Mods]

It's the clearance between the head button and the piston ATDC.

 

[2revo1maxx]

When increasing nitro it's common to add a shim, but with a 3.3 you should be able to run 33% nitro in the stock configuration without any detonation.

 

[Greywolf74]

you'll probably want to switch from a hot to a medium plug when the weather gets warm again too but yeah you should be able to use the stock shim just fine.

 

[Racer 1966]

You need to measure the squish

Isn't it usually called compression ratio?

 

[2revo1maxx]

Typically, if it's cold outside you may want to try a medium plug, then switch to a hot plug in warmer weather.

 

[Extreme RC Mods]

Isn't it usually called compression ratio?

No, it's called the squish band and you want to make sure there is enough clearance so the piston doesn't smack the head button after you remove a shim. The compression ratio will change slightly but with most RTR engines I have ever check, both geometric and trapped compression ratio's are well below what they can be so IMO as long as there is enough "squish clearance" you should be fine to increase the compression ratio

If your worried about over compressing run it up to temp and then run it hard for a few minutes. Pull the head button and check for detonation, if there is any then either use a better fuel or put the shim back in.

The glow plug determines the ignition timing of the engine, it has nothing to do with it being warm or cold outside, IE, you don't run a hot plug because it's cold and a cold plug because it's hot. You run a hot plug for lower nitro and a cooler plug for higher nitro. If your experiencing detonation you can go to a cooler plug and it will retard the timing so the piston can get higher in the stroke before ignition, OR you can decrease the compression by adding a head shim. A hotter plug will advance the timing and a cooler plug will retard the timing.

There is way more to it then most people know and most manufacturers will tell you just to add a shim because they don't know the quality of fuel your running or the type of plug. A high end fuel will resist detonation much better then lower quality fuel but how do they explain this to the average newb? simple, add a shim if you add more nitro

 

[Greywolf74]

I knew about using cooler plugs with higher nitro% but for some reason I thought it was because the higher nitro % made the engine run hotter therefore I figured ambient temps played a role also. I'm still learning and its really easy to pick up bad info off of the internet. thanks for the lesson there.

What grade fuel is O'donnells considered? top shelf or middle of the road? I usually use O'donnells 20% and I've been running hot plugs in my smaller engines and either medium/hot or medium plugs in my bigger engines. Does that sound right or is that wrong? Only thing I've up to know is bash thats why I've been using 20%. Now next year I'm thinking about doing some rookie racing so I might use 30% fuel for that.

 

[Extreme RC Mods]

Higher nitro will make the engine run cooler, adding more nitro is like adding more oxygen so you need to richen the mixture because you can now burn more fuel. More fuel will make the engine temps come down as most of the cooling come from the fuel, not the cooling head. I have never run O'donnells fuel but I would have to guess that it's good due to the number of people having good results from it.

One other thing to consider is a higher nitro fuel (30%) will start better, tune more easy and run cooler then 20%. For the couple extra dollars it costs, there are many benefits you will gain from running the 30% over 20%.

Oil content is another factor, 8% is all you really need so for every extra 1% of oil you run, you take away 1% of the actual power making formula that makes these engines go. IE, 16% oil content fuel has 8% less alcohol/nitro content then the mentioned 8% oil content fuel, that can be quite a noticeable gain.

 

[mayrider]

good info extreme thanks thats exactly what i was looking for.

 

[Greywolf74]

OK, I'm having to unlearn everything I thought I knew about fuel and glow plugs. I was told by my LHS that 30% nitro fuel was harder on your engine than 20% thats why I've been running 20%.

So everyone agrees with what Extreme RC Mods is saying? I mean I'm inclinded to believe you since you are a vendor, please dont take it the wrong way, but it seems like I've been fed alot of conflicting info in this area and I just want to make sure I'm getting the facts correctly this time so I dont have to re-relearn this If this is indeed the case I'm going back to using 30% like I did when I first started!!! grrrrrrrrr lol

 

[Extreme RC Mods]

Don't take my word because I'm a vendor, just have a look at the stuff I build and run. One of my modified picco .28's won the National Championship for monster truck racing in all of Australia. 1st and 3rd at the No Limit World Finals for big block pulling. The first land based tuned pipe to have both great bottom and top end and a baja 5B with a CY 26cc modified engine and pipe that pulls wheelies Down Hill LOL. I go by purenitro on other forums for those who care to look, I've never been called out on any advise I give because if I don't know for sure, I'm not going to claim to

 

[Greywolf74]

I'm sure I probably just didnt learn it right the first time around. Like I said no offense is intended I just want to make sure I learn it right I am still fairly new to this. Only been at it for about 1.5 years and not all of that was active.

 

[REVO-5309]

so does 30% nitro wear your motor more? iv been running 20% as i heard it makes the motor last longer. over here the temps range from 25-35 degrees in summer and winter so its generally warm. and my motor seems to run well at 135 degrees which is a bit on the warm side from what iv been told. will 30% nitro reduce temps and not reduce life of motor if i tune it right and give me more power?
25-35C -> 77-95F
135C -> 275F

and is there more i can read about with shimming the head etc as I'm keen to learn a bit more about that.

 

[2revo1maxx]

With 30% nitro you still have to richen the needle, regardless of the temps. More nitro means more o2, so more fuel is needed. I know Robin better than he thinks lol, and his knowledge is 2nd to none IMO.

If you're burning up engines on 30% it's because the hsn is too lean.

 

[mayrider]

so to measure the squish do you remove the head and measure from top of the jug to the top of the piston at TDC then subtract the head depth with calipers or depth gage?

so does 30% nitro wear your motor more

I assume that like 1:1 cars any time you increase horsepower you increase wear or risk of wear.

 

[Extreme RC Mods]

so does 30% nitro wear your motor more? iv been running 20% as i heard it makes the motor last longer. over here the temps range from 25-35 degrees in summer and winter so its generally warm. and my motor seems to run well at 135 degrees which is a bit on the warm side from what iv been told. will 30% nitro reduce temps and not reduce life of motor if i tune it right and give me more power?
25-35C -> 77-95F
135C -> 275F

and is there more i can read about with shimming the head etc as I'm keen to learn a bit more about that.

With 30% nitro you still have to richen the needle, regardless of the temps. More nitro means more o2, so more fuel is needed. I know Robin better than he thinks lol, and his knowledge is 2nd to none IMO.

If you're burning up engines on 30% it's because the hsn is too lean.

This pretty much answers the last question and, thanks, whoever you are

so to measure the squish do you remove the head and measure from top of the jug to the top of the piston at TDC then subtract the head depth with calipers or depth gage?



I assume that like 1:1 cars any time you increase horsepower you increase wear or risk of wear.

But that's just it, adding 10% nitro isn't like a 200HP shot of NOS lol. The gains aren't huge except for the added lubrication as that's the only thing protecting the parts at 600 rpSec. At that speed I would want all the lube I can get with no loss in performance, it's a win win.

It's best to just measure with the head on, the overall reading will be more accurate with the shims compressed.

 

[2revo1maxx]

You can't get enough compression to hurt anything in a nitro rc engine.....it's detonation, lean fuel mixtures, and the piston hitting the head that you have to watch for.