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Author Topic: Typical RPM's for Class I & PC Nelson Engines  (Read 1141 times)

Offline bdt-m

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Typical RPM's for Class I & PC Nelson Engines
« on: May 07, 2023, 06:44:31 PM »
Looking for what a high performing engine puts out on the bench with an APC 9x6 prop or whatever prop is best for Class I & PC. I understand the Nelson .40 & .36 engines are the current top choice of the winning entries.

Just trying to see what the target RPM is for each class on 10% Fuel, with the tuned muffler.

« Last Edit: May 08, 2023, 02:42:07 PM by bdt-m »

Offline david smith

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Re: Typical RPM's for Class I & PC Nelson Engines
« Reply #1 on: May 08, 2023, 11:36:29 PM »
I would guess if you can get one to around 18000 on the ground that would probably get you in the mid to upper 90 mph range which would be more than competitive at 99% of contests. Definitely competitive in profile and close in class 1.

Offline bdt-m

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Re: Typical RPM's for Class I & PC Nelson Engines
« Reply #2 on: May 09, 2023, 01:33:38 PM »
I would guess if you can get one to around 18000 on the ground that would probably get you in the mid to upper 90 mph range which would be more than competitive at 99% of contests. Definitely competitive in profile and close in class 1.

Thanks, Dave, for the information....

Just curious as to what RPM's today's .36's & 40's are turning. Since everyone raves about the Nelson's, thought that might be the target to strive to hit.

Offline david smith

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Re: Typical RPM's for Class I & PC Nelson Engines
« Reply #3 on: May 09, 2023, 02:55:55 PM »
This is from Dub Jetts website for specs on the current Q500 engines. There isn't a Nelson for these current classes but the older Q500 Nelsons I would say around the 19000 mark and the converted 36's would be close to the same(these numbers would be with the tuned muffler, probably 1500 to 2000 lower with out muffler). I cant speak to the performance of the combat 36's because I have never had one.

Offline bdt-m

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Re: Typical RPM's for Class I & PC Nelson Engines
« Reply #4 on: May 09, 2023, 05:02:58 PM »
This is from Dub Jetts website for specs on the current Q500 engines. There isn't a Nelson for these current classes but the older Q500 Nelsons I would say around the 19000 mark and the converted 36's would be close to the same(these numbers would be with the tuned muffler, probably 1500 to 2000 lower with out muffler). I cant speak to the performance of the combat 36's because I have never had one.

Thanks Dave for the Info. I hear-read the DJ 40 Q500 engines are not performing as expected. I thought I read a carrier flyer tried one in CI and was not impressed nor pleased with the performance.... any truth to this?

Offline Paul Smith

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Re: Typical RPM's for Class I & PC Nelson Engines
« Reply #5 on: May 11, 2023, 06:41:56 AM »
Looking for what a high performing engine puts out on the bench with an APC 9x6 prop or whatever prop is best for Class I & PC. I understand the Nelson .40 & .36 engines are the current top choice of the winning entries.

Just trying to see what the target RPM is for each class on 10% Fuel, with the tuned muffler.

I've added throttles to combat engines for use in carrier.
Top RPM is not the issue, it's LOW RPM that matters. 
The high RPM is whatever you want it to be as determined by the prop load.
Remember, it's an acceleration timing and less that 20 seconds at top speed, also, no need to stunt.  This takes away some of the issues of combat engines.

I always do bench testing before I commit to a building project. 

« Last Edit: July 13, 2023, 07:54:35 PM by Paul Smith »
Paul Smith

Offline bdt-m

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Re: Typical RPM's for Class I & PC Nelson Engines
« Reply #6 on: May 11, 2023, 11:50:52 AM »
I've added throttles to combat engines for use in carrier.
Top RPM is not the issue, it's LOW RPM that matters. 
The high RPM is whatever you want it to be as determined by the prop load.
Remember, it's an acceleration timing and less that 20 seconds at top speed, also, no need to stunt.  This takes away some of the issues of comabat engines.

I always do bench testing before I commit to a building project.

Static RPM numbers on the bench are just a mark to strive for, as long as the testing is done properly the results will give you an indication of engine 'performance' in the air... yes bench testing is a significant part of the "building project". Just looking for 'bench' mark numbers.

Idle, "LOW RPM" resulting in spot-on throttle response is critical for a good LS hang, without it; you are just not going to be in the top spot(s).

I wonder how some of the other .35-36's & .40's compare to the very top engines...?

Offline Kris Millard

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Re: Typical RPM's for Class I & PC Nelson Engines
« Reply #7 on: July 13, 2023, 08:50:34 AM »
I have two LH .36 Nelsons that turn 19500 with a O.S. 4C carb and stock pipe. I had a much larger Perry carb on that turnd more RPM's but I couldn't get it to draw fuel properly when I slowed down so I went to the smaller O.S. carb at the advice of my mentor. This allowed me to learn the hang without the engine quitting in the transition. Now I'm looking to go back to the bigger Perry. What a party when it comes onto the pipe! I would ask Burt Brokaw what he runs as I have seen him do 100+ pretty consistently with his setup. (I think he runs a Perry, but I'm not positive) I suspect with the bigger carb you can hit 21K at speed.

Offline Motorman

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Re: Typical RPM's for Class I & PC Nelson Engines
« Reply #8 on: July 14, 2023, 01:56:44 PM »
My Fox Combat Special MK4 with Giffy mods hit 21K on the ground with suction insert, 10% nitro and apc 9-5 if that helps. It was a tiny bit slower than the Nelsons in the air.

MM

Offline bdt-m

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Re: Typical RPM's for Class I & PC Nelson Engines
« Reply #9 on: July 15, 2023, 08:27:02 AM »
My Fox Combat Special MK4 with Giffy mods hit 21K on the ground with suction insert, 10% nitro and apc 9-5 if that helps. It was a tiny bit slower than the Nelsons in the air.

MM
I have two LH .36 Nelsons that turn 19500 with a O.S. 4C carb and stock pipe. I had a much larger Perry carb on that turnd more RPM's but I couldn't get it to draw fuel properly when I slowed down so I went to the smaller O.S. carb at the advice of my mentor. This allowed me to learn the hang without the engine quitting in the transition. Now I'm looking to go back to the bigger Perry. What a party when it comes onto the pipe! I would ask Burt Brokaw what he runs as I have seen him do 100+ pretty consistently with his setup. (I think he runs a Perry, but I'm not positive) I suspect with the bigger carb you can hit 21K at speed.

Good information, benchmarks are just that, however useful. Now it's time to decide an engine direction... y1


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