Does more Nitro = more speed

[Bruce Clark]

Just curious about running 40 % as opposed to 50 % and 60 %. Has anyone documented the difference between the fuel % they run on their boat. I'm looking for radar tested or gps test results. Also will the difference be only in the smaller engines? Are we looking at 2 mph gain or more. I'm sure the boat hull will make a difference as well.

 

[lohring]

It depends. If the engine, especially the head button, is set up for 40% nitro and you try 60%, there won't be much improvement. If the engine is set up for 60% nitro and you're running 40%, there will be a big improvement when you go to 60%. You also need to consider running more prop with higher nitro since the torque should increase. Big engines run well with lower nitro %.

We tried 80% nitro at the Legg Lake SAWs in an engine set up for 66%. It didn't increase the speed with everything else the same. Jerry Crowther, the source of the fuel, ran a CMB 90 powered mono almost 90 mph with the same fuel.

Lohring Miller.

 

[Terry Keeley]

Mo' nitro always means mo' speed, as long as you burn it and keep it hooked up!

FWIW, I burn 60% in everything from 21's to 90's in heat racing.

SAW 70% and have messed with 80% a little.

 

[dwilfong]

As it has bin stated it depends on the tune of the eng.

It takes load to burn nitro.

Took me some time to figure this out.

So here is where it gets tricky.

More load?

what is it?

Cup?

leading edge pitch?

Blade area?

All of the above!!!!!!!!

Now how heavy is the boat?

How wet is the boat?

How will you run the boat ,heat racing ,fun run, SAW?

It is a very complicated thing and there is no one good answer.

TEST,TEST,TEST and test some more,or use a known set up from a reputable source.

I know this is not a specific answer but it is the truth of it.

 

[Robert Pickard]

Something that was left out the higher the nitro the less adjustment on your third channel

 

[Bruce Clark]

Guess I should have put more information in the post. I was running a 21 outboard OS motor on 50% and on radar I saw 5 mph more when I put 60% in it. Same prop, same boat, same day, and same needle setting.

 

[JimZaremski]

Guess I should have put more information in the post. I was running a 21 outboard OS motor on 50% and on radar I saw 5 mph more when I put 60% in it. Same prop, same boat, same day, and same needle setting.

I can't see how you didn't need to change the needle. Methanol's stoichiometric ratio (where the mixture is neither rich nor lean) is 6.0:1, nitromethane's is 1.7:1. either you were too rich on 50% or lean on 60%.

 

[Tim_Duggan]

Guess I should have put more information in the post. I was running a 21 outboard OS motor on 50% and on radar I saw 5 mph more when I put 60% in it. Same prop, same boat, same day, and same needle setting.

Sounds like you were slightly over propped for your 50% tests then. The OS will pull more prop but be slower than it would be on a prop with less load. In other word it's lugging the prop rather than singing on it. Plus the OS is undercompressed even with 0.004" head clearance, so the extra nitro is helping by adding a little extra torque.
An interesting test would be to optimise the prop and set up for 50% and compare that to a set up optimised for 60%. I ran my OS on both mixes and the prop I used was different for both. The difference was less than 5mph, closer to 2mph, but the lap times were what I was after.

 

[anthony_marquart]

I went from 40 to. 60 and was able to see 7-8 mph on a 21 rigger. I think smaller engines respond to high nitro well. I run 60 in all with a rich needle and short pipes. Don't over think it. Try the high nitro and reset the needle. Revisit pipe length hand your props. I think with some setup changes for the higher nitro you will get more speed. But it's usually not a single change that makes it work

 

[Bruce Clark]

Thanks guys for some tips. Jim you were right about the needle setting. On 50% the plug looked really good. On 60% it started to pull the wire off to the side. It never did quit and it still run more than 6 laps. The motor was OS water cooled with stock exhaust system. I'll do more testing with 60% and see if I can pull more prop.

 

[Jerry Dunlap]

My experience with running 60% rather than 50% in an 21 outboard was a slight increase in speed, but not the ability to pull a bigger prop. This was done a few years back using a K&B Gold Head.

JD

 

[Tim_Duggan]

If it starts pulling the coil on the plug then that is a good sign. Means the muffler is working as a pipe.

 

[shoboat]

Bruce,

I would not put too much propeller on an O.S. 21 Motor.

It will just slow it down. They like to rev hard, try 37mm

To 38mm propellers with reduced cup in the trailing edge.

I would start with an ABC 40 x 53 or a reduced diameter 40 x 52/3.

Buy some O'Donnell Punch fuel, the best you can burn.

Have Fun Testing,

Mark Sholund

 

[Bruce Clark]

Mark, I had Alan Elzer's prop on that you sold him. The fuel I ran was his "BAM Racing Fuel". Its as good as any fuel out there. We tried several props on his boat and mine. The difference became obvious when I change to 60% and gained 5 mph. We tried Prather props, Octura's X series, and 1400 series but settled on the M series prop to be the best. We tried 3 blade as well but didn't take to time to adjust the attitude of the boat to allow for more lift. Looks like I'll have to set it up for 3 blade prop and do more testing.

 

[Robert Pickard]

Try the 60% with the 40x 53 great set up

 

[lohring]

We always removed the head shim on the older OS outboards. The reduced head clearance helped a lot.

Lohring Miller

 

[Kris Flynn]

I have also found that they run hotter when going from 50-60%

Referring to Nova 21 outboard with reduced water cooling volume.

 

[Jeff Schindler]

Usually 60% is slower because it is more dense. A full 8 oz tank will weigh around 1/4 oz more than a full tank of 50%. Try some 30% and you can pull more prop, less weight on the transom.

 

[Bruce Clark]

Jeff are you trying to beat me. LOL I'm just now getting up to speed. I don't think I'll be running 30 % unless my grandaughter is driving it. I do have alot of testing to do before next season.

 

[Jeff Schindler]

It was worth a shot!