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izitbrokeyet?

Well-Known Member
Joined
Apr 5, 2003
Messages
1,908
Has anyone in here ever calculated Brake Mean Effective Pressure for a Typical Modified .21 sized motor (Bmep)?

Norm, Marty, Rod, (Brian?)?
 
izitbrokeyet? said:
Has anyone in here ever calculated Brake Mean Effective Pressure for a Typical Modified .21 sized motor (Bmep)?
Norm, Marty, Rod, (Brian?)?

74265[/snapback]

Yes, we used BMEP as our standard. We also did compare another propriatary indicator that Brian came up with which measured launchability. Since we have so much reliance on the ability to launch props, it is critical to have HP in the area where that is based.

I guess the next question will be: "What is the highest BMEP that you saw?"

low 13's. :) , ACTUALLY, we saw 14 with poor launchability, but with great launchability, 13's. The larger the engine the lower the BMEP. The best 67's or 90's rarely saw 10.

Marty Davis
 
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I sat down one night and organized this MASSIVE file of the stuff they were doing. (screen captures) I found a lot of patterns in the data that were very impressive. A lot of 13s A couple at 13.60. Some well into the 3 HP range. Of course I think they tested every 21 engine known to man. LOL
 
Kurt Tedford said:
Our 25.7 cc engine is between 7 and 8 bmep.
check this out for an explanation of bmep.

BMEP Explanation

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Kurt- Very interesting link, was good reading except for this part-

" This material is for personal use only. Republication and redissemination, including posting to newsgroups, is expressly prohibited without the prior written consent of TSR Software."

Sure hope these guys are cool with the link at least............

:unsure: :unsure: :unsure: :unsure: :unsure: :unsure: :unsure: :unsure:
 
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I did read the webpage, before I included a link to it. I was respectful of their statement and did not copy their web page, I only provided a link to others in this community to go too and read for their personal benefit. I guess I will go crawl back under the rock I came from.
 
Kurt Tedford said:
I did read the webpage, before I included a link to it.  I was respectful of their statement and did not copy their web page, I only provided a link to others in this community to go too and read for their personal benefit.  I guess I will go crawl back under the rock I came from.
74528[/snapback]

Lighten up dude! Nothing directed at you, just said hope they are cool with it. ;)
 
I can't see why wouldn't they be cool with it. The page is an advertisement for their software that they are trying to sell commercially. They have just got some exposure.

So is BMEP a suitable method of comparing engines? And does the results mentioned mean that 21 engines are particularly efficient in comparison to larger engines?

VERY interesting thread really. B)
 
TimD said:
I can't see why wouldn't they be cool with it. The page is an advertisement for their software that they are trying to sell commercially. They have just got some exposure.
So is BMEP a suitable method of comparing engines? And does the results mentioned mean that 21 engines are particularly efficient in comparison to larger engines?

VERY interesting thread really. B)

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Very interesting thought. It could be the smaller bore. Or it could be that they can be made more efficient.
 
Norm,

I don't suppose there would be any test results for a smaller capacity engine than a 21 in your data?

The other possible difference could be the operating rpm range is higher on the smaller engines.....

I did some backward calculations on the figures you listed - either they are making very high rpm's around 40K or they were making some decent ponies at lower rpm.... closer to 4hp than 3.

How were the HP figures established? Inertia Dyno?

Tim.
 
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Heya Norm.....thanks for the Info!

you guys have always been very helpful with the data you pulled. No doubt you went through a lot of trouble (fun) to get it and it's appreciated.

can you verify that you guys were using PSI as units for your Bmep calcs. It appears I have a bust in one of my formulae
banghead.gif


I wanted to rule out unit math as the source of the bust.

Thanks again :)

turkey.gif
Happy Thanksgiving
turkey.gif
 
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TimD said:
Norm,I don't suppose there would be any test results for a smaller capacity engine than a 21 in your data?

The other possible difference could be the operating rpm range is higher on the smaller engines.....

I did some backward calculations on the figures you listed - either they are making very high rpm's around 40K or they were making some decent ponies at lower rpm.... closer to 4hp than 3.

How were the HP figures established? Inertia Dyno?

Tim.

74547[/snapback]

They were running those numbers at around 29K on some pulls. Some a little higher. Yes they built an inertial dyno. I know Brian Calihan, Marty, Ackerman, Norris Sparks , Joe Kramer and Tom Grannis all had a role in building this thing I believe, I hope I did not leave anyone out. It is quite the neat little machine.

They did A LOT of experimentation in the test cell to come up with all that horsepower. Some of the stuff did not work. Other stuff was an eye opener. It seems they looked at every component in the engine. Included exstensive fuel tests.
 
izitbrokeyet? said:
Heya Norm.....thanks for the Info!
you guys have always been very helpful with the data you pulled.    No doubt you went through a lot of trouble (fun) to get it and it's appreciated.

can you verify that you guys were using PSI as units for your Bmep calcs.    It appears I have a bust in one of my formulae 
banghead.gif


I wanted to rule out unit math as the source of the bust.

Thanks again  :)

turkey.gif
  Happy Thanksgiving 
turkey.gif


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That would be all Marty, Brian and Ackerman. I have not a clue. They did all the testing. I am just the lucky guy to have all the data and the machine to test new stuff on.

All I know is that the thing works really good and is very accurite. LOL

And yes they did A LOT of pulls on the thing. I have found nothing on smaller engines. As I am sure you can imagine, most of the pulls are on 21 engines.
 
The BMEP numbers mentioned so far are in Bar. One Bar is about one atmosphere pressure. To change them to psi multiply by 14.5. If you use the formula in the title of this post be sure to use consistant units.

Lohring Miller
 
Lohring thanks :)

backchecking a few motors was an order of magnitude off
banghead.gif


I double-checked everything and figured it must be a units issue :)
 
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Norm Doerr said:
izitbrokeyet? said:
Heya Norm.....thanks for the Info!
you guys have always been very helpful with the data you pulled.    No doubt you went through a lot of trouble (fun) to get it and it's appreciated.

can you verify that you guys were using PSI as units for your Bmep calcs.    It appears I have a bust in one of my formulae 
banghead.gif


I wanted to rule out unit math as the source of the bust.

Thanks again  :)

turkey.gif
   Happy Thanksgiving 
turkey.gif


74591[/snapback]

That would be all Marty, Brian and Ackerman. I have not a clue. They did all the testing. I am just the lucky guy to have all the data and the machine to test new stuff on.

All I know is that the thing works really good and is very accurite. LOL

And yes they did A LOT of pulls on the thing. I have found nothing on smaller engines. As I am sure you can imagine, most of the pulls are on 21 engines.

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I would suggest that you contact Brian Callahan for specifics of calculations. He will no doubt privide you with the calculations that we used as well as the normalization factors we used for temp and humidity. He probably will also provide you with the calculations for our "n" calculation which was the measure of launchability that we had in every dyno pull. All the mathmatics are fairly straighforward and I am sure that he would be happy to share those with you. Please contact me via e-mail and I will supply his new e-mail address to you.

By the way, he is now Doctor Callahan (finished up his thesis and defense this month). He has accepted a position with a company in Anderson, SC.

Marty Davis

[email protected]
 
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Hi Marty,

So break it down for a country boy, who's formula is pie are round cornbread are square :lol:

Which 21 engine was the best overall from these tests?

Gene :D
 
Slideblues said:
Hi Marty,So break it down for a country boy, who's formula is pie are round cornbread are square  :lol:

Which 21 engine was the best overall from these tests?

Gene  :D

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Gene:

You don't know how difficult a question that is for me......

I have never been able to spell the word "STOCCK" !!

Seriously, I can give you a few tidbits that may or may not help you.

The Nova Rossi is a GREAT engine, but the variation in liner/piston fit is critical. You can go through 10 engines and get one out of that 10 that really run well. It is mostly a result of the best liner/piston fit. There is a lot of potential in that engine if you get a good liner/piston fit.

I had really good luck with the MAC 21 in it's early stages. The engine responds to a lot of things and will run as well as ANY 21 engine that I have ever run. A study of time/areas of the ports will direct you to some changes that will make the engine even better. I have a different preference in carbs and the way that they work for racing, so I made that switch right off the bat. I like a carb that has a low speed needle. The MAC does have a propensity to detonate if you pump up the CR and run high nitro fuel.

The OS is a cool little engine, but it does not have much low end. The workmanship is superb and the fit is such that you can put one part into any of 10 engines and it fits perfectly. Takes a ton of CR to make this engine run well.

The CMB is an engine that will run very well, but doesn't keep a good liner/piston fit for very long. It also responds to higher CR.

Dave Richardson (of RPM Rod Fame) wrote a response a couple days ago that hit the mark. He indicated that tuning and modifying engines is not the area to concentrate on. Boat setup, driving skills, preparation, attention to detail in your model, are FAR more important than engine tuning I AGREE TOTALLY. Only after you can use all your engine's performance efficiently, should you be looking at engine tuning.

Marty
 
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