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-   -   The Truth about engines (http://www.helifreak.com/showthread.php?t=374788)

Toxic Al 01-15-2012 06:54 PM

The Truth about engines
Hi Guys, I had to write this thread because there is misleading info that is being put out there on another forum. Due to the rules of that forum, dispute of advertising claims are not allowed without reprimand so I will address it here:

There are different philosophies about building and engines:
  • torque vs. hp
  • high rev verses low rev
  • over square vs under square
  • etc.
My business is building motors and as a builder try to give the public the best product I can possibly deliver. I have built a couple of thousand engines since I started my business and know how to build engines consistently and appropriately for their intended purpose.

One of the questions I'm often asked is will running an engine at high RPMs cause it to wear engine out quicker than one turning lower RPMs?

The answer is it depends on the set up, tuning, oil and qty, break in, warm up and maintainance.

One of the misconceptions is that a stroker motor does not have to turn high RPMs because of it's "massive" torque at lower rpms and because of that it will last longer.

The truth is while a stroke extended engine will have a stronger torque curve than a non-stroked engine it's piston speed will in fact be higher at the same given rpm as a shorter stroked motor.

So what is piston speed and how does it effect the engine?

Piston speed is the measure (usually measured in feet per minute) a piston travels at a given rpm which is determined by stroke and rpm.

Example 1: motor with a stroke of 28mm
at a rpm of 13,500 the piston speed will be 2480.31fpm

Example 2: motor with a stroke of 30mm
at a rpm of 12,800, the piston speed will bve 2519.68fpm

As you can see that on the motor with the longer stroke, even though it is turning slower the piston has traveled 39 fpm farther than the motor with a shorter stroke.

The reason the piston speed is higher for the stroker engine at a lower rpm is because as the piston travels from TDC to BDC it has to move farther and faster than the smaller stroke engine does.Think of it like a running track where they stagger the starting position of the runners because the guy on the inside(short stroke) has to run less then the guy on the outside(longer stroke) to get to the finish line

Now obviously the exact RPM that each motor is turning will determine the measurement in each example but it is not automatically true that the piston speed of the motor with the longer stroke is slower than that of a motor with a shorter stroke. As with most things, it depends!

Will the pistion moving faster and farther wear more than the one thats moving only slightly slower? The truth is both engines will be fine and deliver consistent power for many, many gallons of fuel if built right and with the proper care. Any references to the rebuild time on normal stroke motors being much shorter than that of longer stroke motors is ridiculous.

Most longer stroked motors are not intended to rev for other reasons that I could spend a lot of time explaining (but there is a lot to cover so I will address that in a later post) but balance is not usually one of them.

I am NOT saying stroker motors are not effective,

I am saying for the model helicopter application after hours of testing for 3D flying, high RPM operation using the proper gear ratios has been most the most effective combination for me.

For those of you who don't like high revving motors and don't have any need to turn high head speeds, that is fine a longer stroked engine might fit your application but my engines are versatile and through "proper porting changes" the power range can be moved up or down in the RPM range depending on your needs.

I have a dynamometer that I use to help make the power curves more usable but the reality is I can't determine the final configuation until it is installed in a helicopter or boat , that is when we can really see what it does in the real world.

I don't publish results because they can confuse people and not tell what is really happening.

I would never tell someone that one of these motors can make 8hp in good conscious because in the format we run these engines it is "IMPOSSIBLE"!

Those numbers are generated by using specialty tuned pipes and are provided largely for marketing purposes.

I have seen first hand what my competitors motors are capable of and none of them (including the ones I modify) will produce close to 8hp in the configurations used for model helicopters.

When you buy engines look at the reputation of the builder, the length of time they have been in business, and talk to the guys flying their motors and find out what type of flying they do with them and what their experiences are.

No hype, just truth!!

Peace, Al

desertstalker 01-15-2012 07:38 PM

You may wish to edit some of the formatting and wording on that. It comes across as a bit of a rant, which will not help your case much. Its also a bit difficult to read.

I do however agree with what you say. The best a lower RPM on a long-stroke engine is going to give you is slightly longer crankshaft bearing life and I dont recall seeing people reporting them dying. Power claims are mostly meaningless, without a dyno standard (suited to the load being used) it is impossible to make a comparison based on numbers.

Toxic Al 01-15-2012 10:38 PM

I am sorry if it is coming off that way, I am not good with the written word. I will answer any questions and explain anything that has to do with engines,mods and so forth. Tell me what needs to worded differently and i will work on it. I am just trying make people understand things are not always what they seem or what told to believe. Peace, Al

Toxic Al 01-15-2012 11:18 PM

tell me if it is any easier to make out. thanks.

Peace, Al

desertstalker 01-15-2012 11:46 PM


Originally Posted by Toxic Al (Post 3560079)
tell me if it is any easier to make out. thanks.

Peace, Al

Much, paragraphs make a huge difference :thumbup:

ddavison 01-23-2012 09:03 PM

Good post AL, never thought about piston speed/distance/rpm. Dave

Toxic Al 01-23-2012 09:29 PM

Thanks Dave, there are many aspects of these motors and what is looked at when modifications are performed.I am going to start explaining some of these topics soon so pilots might have more of an understanding about engine sizes ,mods and how they affect our applications. Peace, Al

Rototerrier 01-25-2012 06:24 PM

Learn something new every day. Great read and thanks for your contributions.

PeterW 01-27-2012 12:42 PM

I understand nothing :quotes
I hope I made ​​a good choice when I have a TRM VX 231RS and a RadikalG30 on the way home?

Toxic Al 01-27-2012 03:27 PM

Hi Peter, what don't you understand? The motor you have will work great in the rad30. If there is anything I can better explain let me know. Peace, Al:)

PeterW 01-28-2012 07:17 PM


Originally Posted by Toxic Al (Post 3595393)
Hi Peter, what don't you understand? The motor you have will work great in the rad30. If there is anything I can better explain let me know. Peace, Al:)

I'm afraid I will regret that I did not wait for TRM 26cc would come back in stock?
I have locked myself in, more cc are better​​.................... looked at other brands.

Has good experience of Esprit Model so when the choice was 23cc so hope I will not regret it, afraid that it will feel tired?

Toxic Al 01-28-2012 08:29 PM

Bigger is not always better, the 231rs is a very good engine and has very good power. the 26cc is a good engine as well but with better torque at lower rpms. if the motor is run the correct way the 231 runs great. Peace, Al

Doug Darby 01-29-2012 07:49 AM

In the past 3 months I swapped my 26 for a TRMVX231 and I find it to be stronger in my 700G as it is making power at a higher RPM and holds my requested RPM better.

You will be very pleased with your TRM 231.

Ranger71d 01-29-2012 08:24 AM

Thanks Al. Good info and I lok forward to future posts explaining engines and the many factors that affect their performance in helis.

Tine 01-29-2012 02:32 PM

I have TRM231RS in G30, gear ratio 1:6,9. It is very powerful and smooth, you could do tic-tocs, piroflips,...without a problem. I was impressed.

Toxic Al 01-30-2012 07:53 AM

Thanks Guys, I will be adding more topics soon that have to do with engines,mods and myths. Peace, Al:peace

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