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PostPosted: Mon Nov 04, 2019 8:22 am 
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Joined: Fri Dec 23, 2011 6:59 am
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Location: Spring Hill, FL.
Looking at sim programs . What are you using and how do you like it?
TIA,MM

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PostPosted: Wed Nov 13, 2019 12:29 pm 
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Joined: Wed Oct 28, 2009 9:24 am
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I've used Engine Analyzer Plus from Performance Trends. It's a pretty good (IMO, without much to compare it to) midrange engine sim at $199.

Like a lot of sims it works best to look at differences between somewhat similar things. I "modeled" my VW 1.6 ITC engine and tweaked the model until it matched the actual power of the engine. I found that it did a pretty good job of predicting the power that my HP engine actually makes.

It is a bit V8/domestic centric but as stated it seemed to work out OK on the VW 1.6.


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PostPosted: Wed Nov 13, 2019 4:55 pm 
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Joined: Sun Nov 08, 2009 12:58 pm
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Location: SJ
I like EngMod4T. It probably has the best 1D gas dynamics package short of the full AVL suite. Cost is $400. It also gives you the most freedom to design the entire package over EAP and Dynomations. That said, because of that, you better be sure what you're putting in is right as there are a lot more opportunities for errors.

Caveats for 1D simulation work:
- At minimum you need an engine dyno to correlate your power curve. Power won't be exact, but will be close, but the shape of the curve should mirror what you have in real life.
- You also will need accurate camshaft data. This means Cam Doctor type resolution. This is really important. Going one step further, Billy Godbold (lead Comp Cams designer) said they use the Spintron data for modeling as it captures deflection and the actual lift curve as rpm's rise.
- Ideally, you should have pressure transducer data (like this: https://www.tfxengine.com/). Going through this right now. Found some errors on my end when we overlayed a sim run over real life measured data and were able to make the corrections. Also, equipment like that will also capture burn rate / duration, which is also fed into the model. The errors go both ways too, I was told of an example where the sim was showing higher values, even though the shape was similar... turns out the pressure transducer wasn't flush with the pipe/port wall, so it was being dampened as it sat up bung / drilled port.
- 1D simulation is not going to capture weird things you do like change the dome design, etc. It's best used as a gas dynamics program looking at duct lengths (intake and exhaust) and diameters, and camshaft profiles.
- You also need flowbench data to help build the CD tables. Remember, 28" H2O is only a pressure ratio of 1.07... a well running engine will seek in excess 100" H2O at peak, but the programs will use that to help figure out the rest of it. You need to have the understanding that the program is not going to capture things you do that can effect flow (valve seat angles, offset the cylinder head, porting stuff, valve sizes (when allowed by the rules ;) etc.). You need to measure this on the flowbench for each change to input into the model and build a new CD table. All the programs will makes guesses if you don't, but GIGO.


It's actually a lot of work just to build a baseline model. You also need to have an understanding of whether the models can accurately capture what is going to happen and be able to discern if there is a modeling error or if what you did is going to do that in real life. That said, they are super powerful tools when you get them dialed in.

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PostPosted: Thu Nov 14, 2019 7:18 am 
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Joined: Fri Dec 23, 2011 6:59 am
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Location: Spring Hill, FL.
Bob, Thanks for taking the time for this post .
The issue that I am having is that the flow bench that I borrow shows little or no change with some of my "Improvements". The guy that owns it says" no change = No power " . But when I make the changes , the engine makes more power . FWIW there are multiple very discrete tidbits within the rules that I utilize.

I was hoping that some program could tell me why.

I suspect that the 28in test and the real world speed are the reason. The way that I read your description , it wont.

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Mike Ogren/Protech Racing, http://www.FWDracingguide.com http://www.ogren-engineering.com/ 352.428-8983 mogren@tampabay.rr.com


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PostPosted: Thu Nov 14, 2019 8:22 am 
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Joined: Sun Nov 08, 2009 12:58 pm
Posts: 461
Location: SJ
Is he just measuring CFM or is he mapping the velocity of the port? Tumble or swirl meters? Checking port stability? Etc.

Collecting data is easy. It’s trying to find the information in that is hard. I think Keith Duckworth said something to that effect by the 1980s. I’ve asked a ton of questions from some very experienced folks. They’re still learning too.

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