plane fuel for car

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plane fuel for car - 12/31/2006 4:58:32 AM

Tbone4life

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I'm gonna start using Powermasters fuel.

Can I run powerblend 10% nitro with 18% oil in my truck, (fuel for plane) without hurting performance of TRX 2.5R?

Truck- TRX 2.5R

Plane - O.S. .46 FXi

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RE: plane fuel for car - 12/31/2006 6:30:31 AM

mentorman

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you wont like the 10%. It wont hurt your motor to have extra oil, I used to run powermaster 25/18 and loved it, until the hobby shop stopped carrying it.

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RE: plane fuel for car - 12/31/2006 7:17:54 AM

Tbone4life

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I kinda figured that after reading different threads about nitro, I'm running 20% Traxxas in the Tmaxx and if I go to a lower % its gonna prob be hard to tune. I'd just like to be able to run 1 fuel in both models? I'm still researching and have time (scared to fly the plane yet) thanks for the info.

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RE: plane fuel for car - 12/31/2006 3:29:33 PM

downunder

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I've mentioned this in other threads but my son uses straight 80/20 all castor in his car (Hyper7 with Mach28) and it ran fine out of the box standard. With raised compression it's as fast as the other similar cars using 25% nitro car fuel.

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RE: plane fuel for car - 1/1/2007 12:08:34 AM

asmund

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Plane fuel will make your car take off into the air

No it will be good only a little down on power since car engines is designed to run 20-30% nitro

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RE: plane fuel for car - 1/4/2007 3:04:37 PM

Dil

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how do i raise compression in my 18tm, i knw its obviously by the gaskets, but thoose are soo damm thin i cant understand how it can make a difference,

downunder does your sons car put out a lotta smoke??

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RE: plane fuel for car - 1/5/2007 2:02:57 AM

downunder

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quote:

ORIGINAL: Dil
how do i raise compression in my 18tm

It all depends on the design of the engine but generally speaking taking out shims won't give enough increase to be worthwhile. With my son's Mach 28, taking out the shim would only have changed the compression from 9.4:1 to 9.7 so what we did was to skim the head button in the lathe by .021" to get 12.4:1 which is still a little lower than it could go to (13.5 is about right for zero nitro). Right now we've still got .020" squish clearance so there's plenty of room left to skim more off the head.

As for smoke, it puts out some but not noticeably more than the others. One caution with going to zero nitro though is to use more oil than normal. That's because the needle has to be wound in to get the right mixture setting which also means you can run much longer on the same size tank (he gets 8 1/2 minutes where his mates get 6 minutes). But winding in the needle for the right mixture also means you're reducing the oil flow through the engine so adding oil brings the oil flow back up.

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RE: plane fuel for car - 1/6/2007 2:44:30 PM

Tbone4life

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I measured the squish without the gasket and i'm coming up with .017 on my Tmaxx TRX 2.5R. I'm running Traxxas 20% Nitro, could this be too much nitro? i cant really hear it pinging, but then again I've never tuned a 2 stroke glow engine either. will I hear it detonate?

How do you measure the compression ratio on these small engines? or any engine for that matter?

Thanks, ???

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RE: plane fuel for car - 1/7/2007 5:53:32 AM

downunder

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quote:

ORIGINAL: Tbone4life
How do you measure the compression ratio on these small engines?

Now that's the tricky part

. Back to basics, CR is worked out by taking the swept volume of the engine (its actual volume worked out from the exact bore and stroke) and call it A. Then you add the volume left when the piston is at TDC and call it B. So now you have A+B, but all of this gets squeezed into the "B" part so the formula is (A+B)/B.

The really hard part is measuring the volume of the combustion chamber because it's so small. In your engine it's probably about 0.25cc so a little error makes a big difference. The ideal thing would be a very small syringe with graduations down to at least .05cc but I don't know if there's any that fine. What I use is some clear plastic tubing with a roughly 1/16" inside size and I know exactly what the volume is for a metre of it. I fill it with turps with more than enough to pour into the combustion chamber and measure how much is in it against a ruler. Then I fill the combustion chamber until it's perfectly level with the outside edge of the squish band and measure again to find out what length of turps it took to fill. Knowing how much it holds for a metre I then know exactly how much I've used (within less than .05cc anyway). It's best to work with metric measurements because the numbers are easier to understand.

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RE: plane fuel for car - 1/7/2007 9:17:31 AM

Tbone4life

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"WHEEEW" I used a dial caliper to measure the inside of the sleeve and a VOL calculator I found online
(http://www.online-calculators.co.uk/volumetric/cylindervolume.php) to figure the VOL's.

I measured from top of piston (just closing the exhaust port) to the top of the sleeve (.440"

then subtracted measurement from top of piston @ TDC to top of sleeve (.036"

=.404" entered that number into my online calculator as the height of the cyclinder (stroke) then measured the (bore - .576"

intered that into calculator as radius .288" and came up with a vol for A = .105"

then measurement from top of piston @ TDC to top of sleeve (.036"

entered into online vol calculator as stroke and again same radius .288" makes vol of B = .009"

so then A+B= .114" divided by B (.009"

= 12.6

sound close?

< Message edited by Tbone4life -- 1/7/2007 9:34:57 AM >

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RE: plane fuel for car - 1/7/2007 9:18:52 AM

Tbone4life

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dont know how the winks came about?

< Message edited by Tbone4life -- 1/7/2007 9:19:45 AM >

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RE: plane fuel for car - 1/7/2007 4:29:06 PM

downunder

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The idea was right but you measured the wrong things. But first I should say that there are two different ideas about how to measure compressions. One is called geometric compression which is what I use and measures the full stroke of the piston from BDC to TDC. The other is the so-called actual compression and is measured as you did from when the piston just closes the exhaust port. There are arguments for and against both ways of doing it but for various reasons I stay with the geometric way (which is how all 4 strokes are measured as well).

Your engine is a 2.5cc or .15 cub inch engine so if you'd measured the stroke beginning with the piston as far down as it will go to as far up as it will go then you'd have ended up with very close to A=.15" instead of the A=.105".

The next thing you measured wrong is the volume above the piston. You used the distance from the piston to the top of the liner (.036"

but missed the fact that there's a projection from the cylinder head button down into the liner a certain distance. You mentioned a .017" squish without the shim but I'm not sure if you meant that's the size of the head projection or the gap between the piston and the head when it's fitted. Squish clearance is the gap between the head and the piston (in other words, with zero clearance the piston would just be touching the head.....not good

). For now I'll assume the .017" was the clearance if the head was on the engine so the calculated volume would have been .017x.288 radius in your calculator which would have given around .004 instead of your .009.

Just using those figures (the same as you did) gives A(.15)+B(.004)=.154 divided by B(.004) = 38.5 which would be a rather high compression

so something's wrong.

What's wrong is that you missed out the volume inside the head button itself where the glow plug sits. That's the bit I said was very hard to measure accurately but I'd take a guess it'd be very close to .015" (cub inches of course). Now if you add that squish volume (.004 as above) to .015 then B=.019 so now we can work out the compression with those figures.

A(.15)+B(.019) = .169 divided by B(.019) = 8.9:1 compression which would be very close to what your engine most likely has.

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RE: plane fuel for car - 1/7/2007 5:15:01 PM

Tbone4life

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I knew that it couldnt be right, because of the dome in head where the glow plug is and even the glow plug has a area in it. It was fun trying to come up with the values though, and thanks for the info I have learned alot from this thread.

.017" is the squish band without the shim, it's like .025" with it.

I'll just go ahead and keep running the 20% nitro I been runnin in it ($20 a gallon US).

I think its pretty cool that your sons car is running as good or better with no nitro, than cars with it.

Thanks for the input

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