Hi to all boaters. This is mostly intended for Scott or Marc but any bodies input is appreciated. We have been boating for about 3 years now, and in our quest for more power we have decided to build a dyno. Manufacturing of the mechanical components is not a problem for us as we have an engineering business. we just need some input from others who have been down the road as what is the best way to go? For starters, what is the better route, either inertia or brake? In other words, the most accurate and repetitive system to use? What are the pros and cons of either system? If anyone has built a dyno, it would be appreciated if they can advise what would be the best software available for these small engines. Any designs or ideas for the mechanics would help a great deal, as well as the most essential sensors required for example, weather stations,temperature, gas analyzer etc. Also, what is the most accurate tuned pipe software that anyone has come across? We would like to share as much info with the people out there. We are from South Africa and in the last 3 years we have taken the sport to new levels and many people here are constantly asking us for assistance to promote the sport! Many thanks. Misty. South Africa.

Misty,
First off welcome to MGB

I am NOT qualified to give much dyno information due to not having one or ever building one ... That said

IMO a break type dyno is the best way to duplicate a somewhat close to actual load having the heat dynamics of the engine/pipe/spark plug be more real world stabilized.

Inertia types while very useful can only give you flash readings of data per rpm point as data is collected. At no point in a few second pull will engine be stabilized enough to give a solid reading on whats happening at any specific rpm point. Because the mass of the inertia dyno flywheel is so great it in a sense dampens the fine detail of hick ups in power where as a break dyno would show the discrepancy in greater detail allowing you too load engine at that point allowing tune changes to be made and view differences at that specific rpm.


This just my opinion ....

Hi Scott.

Thanks for the quick response. I have been following MGB for quite some time, actually its been a good information tool! I agree with your opinion regarding the dynos 100%. Only problem is that there is not much resources for small engine dynos here in SA. Went to go see a group of dyno specialists today and unfortunately I was dissapointed once again not to have any luck? Would you possible not know who I could contact in the States who could assist us? I have been through google but there are many to choose from???

On another note, Oil content? I have been running 16:1 for quite sometime now? i've read on other posts more oil = more power and better compression seal but heres whats odd to me. Im using motul 800 2T, and at that ratio it seems like too much oil because Ive noticed carbon build up and i just cant get the plugs to burn that tan brown colour now matter how rich or lean i go with the needle settings? Last Sunday, decided to blend a 30:1 ratio, off to the dam, and seemed to get alot less carbon with a cleaner, crisper, sounding engine as well as that tan brown color on the spark plug. People tell me 13:1 is even better? Motul bottle says 50;1 for racing and 66;1 for general use, so Im puzzeled? Do u think Oil ratio And the amount of watercooling go hand in hand here?

Though id post a photo of a Fully modded Cy26 that we actually broke through the casting in thin errors that we repaired with steel putty. Runs great at 6000ft above sea level with a max speed record of 92km/h in a monohull. Take note of the water jacket that is bolted with the same bolts hat hold the jug down. Cant tell u how many times I have dunk it and it just keeps goin...

Here are a few sites for dynos and information:

www.land-and-sea.com/

www.trik-dyno.com/

www.tdkmotorsports.com/dyno.htm

I have a dyno that I built myself a few years back. It is an inertia dyno that utilizes a modified Eagletree Data Logger (some mods done to it by Eagletree for the application) and software that I did myself with assistance from Mike Hoffmeister (used to be with M&D engines). I also picked up a lot of info from the TDK Motorsports website above. Personally I prefer the inertia dynos because of the way we ramp up the engine rather than choke it with a load. I feel it more realistically represents real-life conditions, but that is just my own personal opinion...and we all know what they say about opinions!!! I use my dyno for personal use only..to compare engine mods and sometimes to compare different manufacturers' engines. It has been compared with the factory results Zenoah gets on stock engines, as well as with a few other dynos from engine builders...I must say it's pretty reliable and accurate, even though I don't have the weather station on it (manual entry of parameters in software). To do back to back comparisons though, the weather station isn't really that important for me. The Eagletree system logs 10 samples per second for a pretty good sampling rate. Another good data logger to get if building your own dyno is the Performance Trends Datamite. It's not too expensive and has many available options and sensors. On mine I use Exhaust temp EGT, Head temp, ambient temp, and RPM sensor.

As for your oil and carbon buildup question...I've noticed that with some brands of oils, even synthetics... I tried Klotz with Castor: terrible, Amzoil Dominator: not too bad, Castrol Syntec: not too bad, Honda HP2: very good, and now will be trying Cool Power Blue this year... I've heard that this oil leaves no buildup at all, even in the pipe. The HP2 never left buildup in the engine, but it did accumulate in the pipe. So far though it's been the best synthetic I've used. As for the conventional oils, well the few I've tried all left major carbon buildup at the mixture I use, which is 16:1.

All our small engine development has been on an inertial dyno. Though it has limitations as Scott points out, it has huge advantages. The most important is that you can get 50 complete power graphs in an afternoon. We also have Stuska dynos for larger engines, and they are much more time consuming. We built our dyno because we wanted to duplicate the conditions of a SAW run, which it does. I still believe the information we get is very applicable to heat racing as well. An article describing the dyno's construction can be found in Model Engine Builder, issue 15. A copy can be purchased at www.modelenginebuilder.com/subscribe1.htm I can send you a spreadsheet we used in the flywheel design. It gives stresses and estimated run up time for different engines with different size flywheels.

We have run the dyno with a variety of gasoline engines from 2 to 12 hp and had no problems. We melted pistons on several nitro engines, however. I recommend a smaller flywheel for that testing. We used a Performance Trends data logger. It's been bulletproof, unlike the Eagle Tree that we run in all our on water tests. The price reflects the difference. It comes with excellent dyno software. However the instructions take time to master. See performancetrends.com/dtm-dyno.htm We only use the dyno rpm sensor as the ignition sensor is unreliable at high rpm. We also manually input weather data. Exhaust gas temperature would also be valuable, but we seldom use it.

Articles on our testing are available on this site:

www.modelgasboats.com/Magazine..._Record_Engine/
www.modelgasboats.com/Magazine...icles/Gasoline/
www.modelgasboats.com/Magazine...es/Tuned_Pipes/
www.modelgasboats.com/Magazine...Pipes_-_Part_2/

Lohring Miller

I have some "preformance Trends" inertia dyno software, and data collection hardware ("pick up and the "Black box 2" fromperformance trends.
performancetrends.com/

I once used this same set up with a direct drive inertia dyno for these small engines, and it worked pretty good, considering I was not controling EGT, head temp at all, and air quality not very well (just punched in the numbers once a day). I got a average of 2.78hp on a stock G260 with no exhaust at all, and 2.8hp is what Zen claimed. The varience was pretty big, like + or- .2hp for the max power, but I am sure that is because I was not able to control all the factors I need to to get quite repeatable graqphs.

I will sell the performance trends stuff for 1/2 of retail, and sketch the design for you with the formulas to get the flywheel inertia right for the power of our engines. The flywheel I used was small in diameter (adout 6.00" in diameter), but also about 6" long, instead of a large diameter and thin flywheel to get the correct inertia. The small diameter flywheel will have much less chance of coming apart under 20,000 RPM.

I went all out to build a water brake dyno after I bought the performance trends stuff. I never finished my own inertia dyno, and I still need to finish the water brake in a pic here.

Shoot me a call during normal business hours if your interested---or anybody else.

Doug Johns @ Earth Surfer Products (ESP)
(616) 458-8103 (EST)

Pretty much finished now. (This pic has a new 4:1 reduction ratio, not the 2:1 in the above pic--which fryed the clutch)

It has the EGT (too far from the piston face now)
It has the head temp (to record at proper running temp after determined)
It has the consistant weather station--so all the air in the world is the same.
It has two RPM sensors (one engine, one water brake at 4:1 reduction), so it can be
set up to tell me if the clutch is slipping.
It has a nice lexan gaurd, so the belt does not hit me in the face if it breaks.

I have something new to play with this weekend (and for years to come). It is like Christmas at 5 years old, when I got a nitro COX chopper (trike motorcycle chopper) for my first two stroke introduction. I am excited.

Got a few runs under my belt with a stock CY26cc air cooled engine with a Baja pipe on it. I have to add some weight to the adjustable clutch, so I can measure below 10,000RPM without slipping the clutch, but the rest of the curve repeatability seems pretty darn good---for a amature operator especialy. With my last two runs recorded at 150 deg engine temp (I have testing to do to find optimum recording temp yet), all most all the points above clutch slippage, matched the other graph with in + or - .02 to .05hp (2 to 5 one hundredths of a HP). One point was out .1hp. I have a lot of learning to do yet---but those repeating numbers made me say----"AHOOOWWWW--I feel gooood".

Yes folks, you may be looking at the best dyno in the gas rc engine industry---but I know the operator has a long way to go at the moment.

Hi Martin Lohring. We have finally decided to go ahead and manufacture an inertia dyno machine for our engine and pipe testing. Quite a while back in a previous post you said that you would send me a spreadsheet for the roller weight design for various engines and run up times. It would be greatly appreciated if you could send me that info to This e-mail address is being protected from spambots. You need JavaScript enabled to view it for the attention of Misty. another question? What grade material would you advise for the roller at those rpms? En19T or En24T or would En9 be sufficient?

Many thanks

Misty

South Africa

For the flywheel, I think just a mild steel should do, if the geometry of the flywheel is not a large diameter. The inertia dyno I used years back (from a boater who made it in his machine shop) had a flywheel mass that kept the rotation acceleration slow enough to collect data for a engine of about 7hp (you pick the HP in the formula, to figure out the inertia you need for the flywheel to control it. You can make a "stackable flywheeel" also, so you can adjust the inertia, and report it to your software). I do not have measurements for the flywheel I used (direct drive--no speed reduction belt/gear mechanism), but it was about 6" in diameter x 6" in length. The length is long and the diameter is small, because a large diameter skinney flywheel may just come apart at 20,000 RPM. I would bolt on a nice tight, heavy duty gaurd around the flyweel, in case it comes apart or comes off the shaft totally (like a broken shaft--not very possible IMO, but just in case)

Shoot me a call Misty. I have some "performance trendz" software and data collection hardware that will work very well with a direct drive intertia dyno, and I can share with you the design of the dyno I used also. It can fit in the front seat of your car---so you can even easily take it to the races---to see if that Zen piston port cylinder is really making over 7hp---with accurate flywheel inertia calculations and construction.

The inertia dyno is as accurate as your flywheel calculations, pretty much. The simple physics and construction of the flywheel can make the dyno accurate and repeatable. You can use a weather station, or hand input the air quality before each run with a cheaper hand held devise. My weather station cost $500.00 (ouch), and you can use a EGT gauge in the header section of the pipe to assist with jetting. I love my water brake dyno, but I don't think it is 10 times better than the cost of a inertia dyno. The inertia dyno I used---seemed to give me very good numbers also.

Congratulations with "endurance offshore championship" using one of my reed case engine builds. I bet no other reed case engines were there either. That is the way I like it. One engine--one championship. We have won races, but not a Chamionship over here so far. Thanks for helping ESP win their first boat Championship. I could not have done it without you and some effort on your part.

Doug @ ESP
(616) 458-8103 (EST Zone)