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Author Topic: High Nitro  (Read 1006 times)

Offline Motorman

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High Nitro
« on: December 15, 2020, 08:29:54 AM »
Don't know much about carrier but I remember they used lots of nitro at one time. What % of nitro was typically used and how did you calculate compression ratio?


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Offline david smith

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Re: High Nitro
« Reply #1 on: December 15, 2020, 08:18:44 PM »
I usually ran 60 or 65%. No more than 70 and add shims until it doesn't blow glow plugs or knock.  I think 45 to 50 is a better range. Much past that the performance vs headache ratio goes up too much to be worth it.  With current tech and rules the best bang for the buck is running a tuned muffler like a Jett or a Nelson.  I think some of the Thunder Tigers were a 1000 to 1500 rpm gain just by bolting on a Nelson muffler. 

Sorry I don't know any actual number on compression ratio, maybe reach out to Burt Brokaw or Eric Conley. They are pretty knowledgeable on the current Nelson related stuff specific to carrier. Better yet call Henry or Mike Langois(current producer of Nelson engines). Mike used to mess with high nitro/high performance stuff.

Offline Bill Calkins

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Re: High Nitro
« Reply #2 on: December 16, 2020, 02:16:45 PM »
70% Nitro, 20% oil 10% Propylene Oxide. If you can't get Prope, try 65% Nitro, 20% Oil and 15% Methanol.
Oil is 100% synthetic, NO Caster Caster turns into clogging balls. For more info, IM me.

Offline Paul Smith

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Re: High Nitro
« Reply #3 on: December 24, 2020, 01:56:36 PM »
how did you calculate compression ratio?

Like many other thing the principle is simple, but getting the numbers is not so easy.

Swept volume is the part of the displacement with all the ports shut. (SV)
Combustion chamber is the volume with the piston at TDC. (CC)

So compression ratio would be (SV + CC) / (CC)

Measuring the combustion chamber volume of a tiny engine would be quite a chore unless it's a cone or a simple hemisphere.  Maybe filling it with a liquid would suffice.

On that note:  If a muffler prevents the exhaust from fully exiting the engine, the gas will be somewhat compressed to begin with, thus increasing the effective compression ratio.  This might HELP and undercompressed engine or KILL an engine that was overcompressed to begin with.




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Offline Motorman

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Re: High Nitro
« Reply #4 on: December 24, 2020, 09:12:40 PM »
Compression ratio in today's modern era is full swept volume plus head space divided by head space. Japan was trying to figure on exhaust closing but abandoned it way back in the 60's because there were too many variables between different engines.

I guess I should have asked the question better. What was your compression ratio? I don't think anyone ever measured it. Guess I'll have to go through the cut and try method once again.


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Offline Bill Calkins

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Re: High Nitro
« Reply #5 on: December 25, 2020, 06:09:40 AM »
I just kept adding head shims until I stopped blowing plugs. Some motors like the old Super Tigre .35 blew a plug a flight.

Offline Motorman

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Re: High Nitro
« Reply #6 on: December 25, 2020, 11:55:24 AM »
How many shims did you end up with on your Tigre 35?


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Offline gordon tarbell

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Re: High Nitro
« Reply #7 on: December 26, 2020, 11:30:54 AM »
Would motoring the engines through with compression gauge in place of glow plug be a repeatable measure of where you are as far as cyl pressure/compression ratio limits when running heavier loads of nitro. When getting close to/ into  detonation I found success with the use of Toluene when percentages of nitro of 60% and higher are used. In some cases replacing the methanol with straight toluene as the co-solvent.
Gordon Tarbell AMA 15019

Offline Motorman

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Re: High Nitro
« Reply #8 on: December 26, 2020, 09:52:32 PM »
I have a burette graduated in 100ths of a ML for measuring head volume. The head I made is definitely too big for 10% nitro so maybe I'm in the ball park.


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Offline C.T. Schaefer

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Re: High Nitro
« Reply #9 on: December 27, 2020, 04:48:03 AM »
What motor are you talking about?

Offline Motorman

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Re: High Nitro
« Reply #10 on: January 20, 2021, 10:58:49 AM »
SuperTigre 35. Just wondering if anyone had worked out a formula for the compression ratio.


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Offline Robert Whitley

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Re: High Nitro
« Reply #11 on: January 20, 2021, 09:17:31 PM »
Which model of Super Tigre 35?

Offline Motorman

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Re: High Nitro
« Reply #12 on: January 21, 2021, 07:44:20 AM »
G21 35 Mk2 with Perry ports.
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Offline Robert Whitley

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Re: High Nitro
« Reply #13 on: January 21, 2021, 09:14:45 AM »
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