A new nitro engine coming soon (some say I am mad for doing this!)

[Ricky Neal]

What sort of head clearance & volume do you guys run for FAI fuel? What plug(s)?

Ten or more years ago the motors we ran (OPS, Picco, CMB) came with fairly low compression, usually around 8:1. They would be OK on 40% nitro but would hardly run on 60%+ unless you leaned the needle down a bunch, I think what was happening was the fuel was lighting too late and most of it was still burning well after TDC. Fuel cars for example fire at up to 65* BTDC: Top Fuel - Wikipedia

The manufacturer's started bumping up the C/R for us and I took it even further running 14:1 on my 45's - 90's and close to 15:1 on my 21's. Motors idle, transition much better and make way more top end power. You may not want to go 15:1 with your new motor but somewhere around 12:1 would be a good compromise for us.

Here's specs from an older CMB RS21 and new Beta.

A thread I did on head buttons a while back: On line head volume calculator.

Thanks Terry, this is very helpful

 

[Marty Davis]

I run low speed needles on all my 21's (an 67's). Wouldn't be without one. Only 21 carbs that I run without, are old flow benched carbs that idle really well.

 

[Steve White]

To expand on Terry's comments.

Another solution for compression ratio would be to package up the engine with a set of head shims and instructions on how to use them. An even better path would be to offer an accessory range of heads with varying compression ratios - that, once they experiment with the shims can order for optimum performance. Then, one could test using the shims and from that data select the optimum head (with best squish clearance) for the particular combination they were running. Offer low, mid and high nitro versions of the engine so the modeler can start in the operating region they want.

That's what those of us do that have machinery and have done for years to attain optimum performance.

I assume you are also targeting the RC car market with this project. Head & shim selection would be a real hit there as well. In addition, heat sink options would be a big plus. I had to battle engine temps with the buggy's which led to inconsistent engine runs. With the boats that's easier to manage.

Just a few thoughts to consider sir. Putting a head selection for compression ratio adjustments and "how to" instructions out there would take away an age old advantage for those of us that have machinery. It would help level the playing field and help the newer guys experience some actual tuning. 6-8 different heads, color coded with a sheet that shows the range of nitromethane each head is optimal for and basic atmospheric relationships - altitude, water, barometer, temperature.

Last night I happened onto an RC car site and read an article on fuel and nitro percentages. Lots a babbling garbage to basically confuse the real relationships - compression ratio optimization -vs- nitro percentage and that the higher nitro % = higher head temperature. Never mentioned the characteristics of the sweet spot and how and why to find it. A bunch of babble about some very simply physics relationships. The article never really stated anything - just a lot of babble.

Put a dyno test run sheet with each engine. Show atmospheric conditions, temperatures, fuel ratios and head used to attain the performance level - so the customer has REAL a baseline. Not some "arbitrary" number of 2.5 BHP @ 28,000 RPM - under what conditions? In the early days of OPS, they at least included an instruction sheet with the engine that stated if you want to run nitromethane, lower the compression ratio be increasing head volume. They also offered a basic methanol tuned pipe and a nitro pipe with increased volume. They didn't say add head shims for nitro, which will of course work just fine - but not yield optimum performance. They said "increase head volume". When you get the head volume right, nitro engines become fire breathing monsters that are also reliable and transition from idle to wide open in a somewhat manageable fashion.

Also add a note, like any crew chief will tell you: The engine that runs best on the dyno, doesn't always run best in the race car or boat or motorcycle. Tuners build "Dyno Queens" every day. Import tuners post ridiculous claims of 600 HP with 1.8 Liters twin turbo. Yea, for 3 seconds on a dyno, not streetable, not even really suited for drag racing. Real crew chiefs use the dyno as a tool to attain optimum performance levels for a given application. Dyno results are translated to fit the application by the crew chief. It's all about the torque curve not peak HP numbers.

In the end, listed HP numbers on an ad won't sell your engines as much as actual real world field performance. Your engine has real HP numbers, while brand X is higher - but at the racetrack, yours goes across the finish line first more consistently and holds together. That's what will sell your engine over the long haul.

"Yes, their engines win the dyno pull competition, but our engines win races".

Get real with your customers.

Great stuff: On line head volume calculator. | Intlwaters.com

 

[Al Hobbs]

I wish you very good luck with your project. I know that it is a big step and expensive.

The hobby needs new engines to create competition among the manufacturers and keep prices as reasonable as possible.

My best advice is to closely read your contract with the manufacturer.

 

[Timbo Whalen]

Hi Allan,

Our project has nothing to do with anyone who was involved in the Averinov engines. Ours is completely fresh and stand-alone.

As for comparing power to the NR or the CMB engines in the same class, we hope to be competitive and even more powerful but from my experience, I have found that outright power figures are a bit misleading, depending on how they are used, some engines can be so peaky and temperamental that its practically impossible to get them to perform to their absolute best. I personally prefer engines that have accessible performance.

Time will tell I guess

Is the design under square, square, or over square (bore to stroke ratio)?.... torque is your friend.

 

[dwilfong]

This is great news!!!!!
That looks like a very nice eng design.
Disk valve is the way to go for sure.
Just from the rendering I can see there is great thought going in to the transfer ports in the case.
Profi is a great eng builder so this should be a winner.
Big volume ports in the case are needed to flow 65% nitro.
I know the tether boats do not run this so smaller ports is in order I presume?
Big case port are a must for HIGH nitro engs.
If the casting is made thick enough to open up this would be a good thing.
Or two different inner case molds one high nitro and one no nitro.
I have a IR .21 boat eng and it is a work of art. But the ports cast in to the removable ceramic coated jug are to small for high nitro.
On a .21 bushed aluminum rods will work just fine as long as replacements are at a good price point for timely replacement with bearing change.
When ????????
I want one!!!!!!!!!

 

[Julio Almazan]

Hi:
From the carburetor layout, I see that you have not thought of making a variant of this engine as outboard motors.
Are you planning to make an O / B variant in the future? ... something that allows us to use the existing 3.5 lower units.
Thank you for your answers.

 

[Timbo Whalen]

This is great news!!!!!
That looks like a very nice eng design.
Disk valve is the way to go for sure.
Just from the rendering I can see there is great thought going in to the transfer ports in the case.
Profi is a great eng builder so this should be a winner.
Big volume ports in the case are needed to flow 65% nitro.
I know the tether boats do not run this so smaller ports is in order I presume?
Big case port are a must for HIGH nitro engs.
If the casting is made thick enough to open up this would be a good thing.
Or two different inner case molds one high nitro and one no nitro.
I have a IR .21 boat eng and it is a work of art. But the ports cast in to the removable ceramic coated jug are to small for high nitro.
On a .21 bushed aluminum rods will work just fine as long as replacements are at a good price point for timely replacement with bearing change.
When ????????
I want one!!!!!!!!!

Remember, these guys are tether racers, minimal nitro- if any, I wouldn't expect 7 or 9 port design. Disc vs. drum is always going to create debate.

 

[dwilfong]

Remember, these guys are tether racers, minimal nitro- if any, I wouldn't expect 7 or 9 port design. Disc vs. drum is always going to create debate.

3 intake and 3 ex is all you need with 65% nitro and BIG case ports to flow all that "FUEL"...........................
K.I.S.S.

 

[Terry Keeley]

 

[LohringMiller]

That's the Profi porting. I'll have an article comparing it to older designs in the next NAMBA Propwash.

Lohring Miller

 

[Buckshot]

I wish you very good luck with your project. I know that it is a big step and expensive.

The hobby needs new engines to create competition among the manufacturers and keep prices as reasonable as possible.

My best advice is to closely read your contract with the manufacturer.

Spoken like a man with experience!

Good luck in your endeavor!

 

[dwilfong]

Some of the Russian eng had a very thick sleeve.
Thy would use this as the inside couture of the port.
This would save on costly specialized molds to do the casting.
Also make it possible to control the port volume depending on fuel used with just a different sleeve.

 

[LohringMiller]

Model engines have seriously lagged behind the designs of larger two strokes. That Profi design came from a collaboration with one of the world's best two stroke designers. Modern porting and transfer shapes combined with a modern tuned pipe lead to that engines domination of world pylon championships. Thay also started with a rear rotary valve, but now run a front rotary valve. The front bearing design allows a large intake with lower friction than rear rotary designs. See below as well as the core patterns Terry posted above.



Lohring Miller

 

[Ricky Neal]

Is the design under square, square, or over square (bore to stroke ratio)?.... torque is your friend.

Hi, We will be testing 2 different bore to stroke ratios but we have pretty much landed on 16.30mm bore, almost identical to the Novarossi's before the DD. It just seems to be what works and we also do not have the R&D budget to re-invent the wheel just yet. If we can make a success of this we will start to look at more radical departures from what has already been proven.

 

[Ricky Neal]

This is great news!!!!!
That looks like a very nice eng design.
Disk valve is the way to go for sure.
Just from the rendering I can see there is great thought going in to the transfer ports in the case.
Profi is a great eng builder so this should be a winner.
Big volume ports in the case are needed to flow 65% nitro.
I know the tether boats do not run this so smaller ports is in order I presume?
Big case port are a must for HIGH nitro engs.
If the casting is made thick enough to open up this would be a good thing.
Or two different inner case molds one high nitro and one no nitro.
I have a IR .21 boat eng and it is a work of art. But the ports cast in to the removable ceramic coated jug are to small for high nitro.
On a .21 bushed aluminum rods will work just fine as long as replacements are at a good price point for timely replacement with bearing change.
When ????????
I want one!!!!!!!!!

Thanks David,

I have really leaned on Profi's experience with this whole project, I thought I was pretty well versed with engines but when you take on something like this from scratch you realise pretty quickly the level of expertise that is needed.

Regarding large ports, This engine is intended to be used for multiple disciplines tethered models using FAI fuel and RC models using high percentages of Nitro, this will be possible with some differences to the head button and piston/liner design and obviously models with a venturi and a carb.

Also, after spending a lot of time discussing things with Profi, they have decided that reducing crankcase volume is critical to how the engine will accelerate through the RPM range and also how well it can maintain peak HP and higher RPM. I have relied on their expertise for this and I hope to hit a good compromise.

I also had to consider the new nitro fuel regulations and limitations in Europe, I would expect that in the near future most competitive running will have a mandate for lower fuel percentages so as to not alienate competition from Europe. with this in mind, it may well bring the differences much closer together.

As for when, If everything goes to plan I would hope to have engines available in the next 6-8months. I will let everyone know when they will start to be available and how they can be purchased.

Before that I will be happy share information and testing as we progress.

 

[Ricky Neal]

Hi:
From the carburetor layout, I see that you have not thought of making a variant of this engine as outboard motors.
Are you planning to make an O / B variant in the future? ... something that allows us to use the existing 3.5 lower units.
Thank you for your answers.
View attachment 287908

Hi,

At the moment O/B is not on the agenda, We have selected the above layout as it seems to fit the widest market but with time and hopefully success we will look to cater for other uses also.

 

[Ricky Neal]

Remember, these guys are tether racers, minimal nitro- if any, I wouldn't expect 7 or 9 port design. Disc vs. drum is always going to create debate.

Actually no nitro at all, 20% castor oil, and the rest is methanol.

Regarding the number of ports, as far as I can ascertain from the testing I have done so far, the number of ports has less impact on outright performance than the overall port area. I would presume that it does have a benefit for controlling the mixture in the cylinder though. As ever it's a balance in the end. With all this in mind, the first piston liner design we will be testing is a 7 port design.

The disk vs drum debate is pretty easy to determine nowadays. Disk seems to always win out. Anecdotally I have run a Soluev .21 engine, with drum valve induction and Zimmerman disk induction and the Zimmerman induction was pretty far ahead.

 

[Ricky Neal]

That's the Profi porting. I'll have an article comparing it to older designs in the next NAMBA Propwash.

Lohring Miller

I am looking forward to that!

 

[Ricky Neal]

Model engines have seriously lagged behind the designs of larger two strokes. That Profi design came from a collaboration with one of the world's best two stroke designers. Modern porting and transfer shapes combined with a modern tuned pipe lead to that engines domination of world pylon championships. Thay also started with a rear rotary valve, but now run a front rotary valve. The front bearing design allows a large intake with lower friction than rear rotary designs. See below as well as the core patterns Terry posted above.

View attachment 287980View attachment 287981View attachment 287982

Lohring Miller

I agree, what Profi and the MB brothers developed with the MB40 really is more advanced than most of what else is available. I am not sure why more did not follow their lead - Maybe how costly it must be to make engines like this?

I particularly like the integrated ball bearing crankshaft, an elegant solution that seems to solve a few problems. Profi use this design on their F2A speed engines also. I also like how they use the spinner backplate to aid in balance.

I look forward to the article in the NAMBA Propwash.