Engine simulation

[arosaneto]

Hello All,

Anybody here using DynoSim for Lotus TC engine simulation? Would you share the configuration file?
I'd like to have a std engine model and play with the CAM configurations.

Thanks!

[rgh0]

Hi
I use dynosim and a have number of models of both a standard sprint engines and various race versions that I have calibrated versus real dyno tests. Happy to share the files.

What version of dynosim are you using as the files are not totally compatable between the various program versions over the years.

cheers
Rohan

[arosaneto]

Hello Rohan,

I am running Dynosim5 (v5.02), just got the software. Thanks for sharing your files!

Regards

Ari

[rgh0]

I used dynosim up to version 4.1, it used a .sdy file extension. I then changed to dynomation 5 which is from the same company and uses a .dym file extension but can also read the .sdy files for dynosim. Dynomation has the dynosim model plus a more advanced wave action model and more detailed modeling of the inlet and exhaust system. It can run either of the models or a combination hybrid model.

What is the extension of version 5 dynosim file ?

cheers
Rohan

[arosaneto]

The file extension on DynoSim5 is .dyn, maybe Dynomation can also save in DynoSim5 format?

Regards

[ill_will]

There are a couple of interesting newer threads that mention engine simulation on here, but this looks like the most relevant thread re: specific simulation package details.

I've been looking around at current options from Motion Software and it looks like Dynomation-5 is NLA, and Dynomation-6 is very pricey (500USD shipped.) DynoSim6 is about 150USD and DynoSim5 is a more affordable 70USD.

Looking at the spec sheets it looks like DynoSim5 includes the same basic filling/emptying model used by the more expensive packages, but omits the "wave dynamics", however I vaguely remember a comment in another post that the former gave better sensitivity correlation to dyno data.

Now that we are a few years down the line, does anyone have experience of DynoSim6 vs DynoSim5 at all?

Some of the shared data appears to show that Dynomation-5 captures cam/timing/port changes well (thanks Rohan), so I'm basically wondering if DynoSim5 runs the same model under the hood and is likely to do the same, or if it is dumbed-down in some way?

Thanks,

Will

[rgh0]

I have not used Dynosim 5 or 6 but I suspect they are the simplified versions of Dynomation 5 and 6. For most modelling purposes Dynosim 4 was pretty adequate and Dynomation 5 did not really improve the model results a huge amount versus dyno testing though it did give more flexibility in testing various parameters. Whether getting Dynomation versus either version of Dynosim is worthwhile is hard to say.

cheers
Rohan

[ill_will]

Thanks Rohan. I took the plunge and went for DynoSim 5 - has been enjoyable playing around with a few setups so far.

Interesting to see how it suggests some mods will benefit everywhere (iirc bigger bore exhausts, bigger diameter pistons) whereas others you get 'rotation' of the torque curve and lose some on one side of the point of rotation whilst gaining on the other.

One thing I struggled to find was flow bench data for a standard Sprint head. I did some port area-based scaling of some data I found for a McCoy head (a thread on here showing a comparison of three different flowed heads: McCoy, Duclos, Boggs.) Is anyone aware of any measurements of a reasonably stock head?

My assumption is an SAS head will be similar to the McCoy head, but this is just a guess. I have the following specs for the former ('full race' spec):

- Inlet port 1.3" diameter, 1.625" valve, top of runner 1.77" assumed (DCOE 45)
- Exhaust port 1.25" diameter, 1.4" valve

The inlet port size looks a bit tight (?)

It seems the casting has unmachined port sizes approx 1.14" in and 1.25" ex.

[ill_will]

To anyone using DynoSim (5), I spotted something unexpected relating to cam profiles in the package and wondered if I'm missing a trick.

An example is shown in the screengrab below. Here, I’ve entered some details of a cam using the manufacturer’s datasheet. In this case, 0.42” (10.66mm) lift, 280deg duration, and timed it according to their spec. I don't have the 0.050" lift figure for the cam.

Looking at the lift trace in 'CamManager', it can be seen that the lift at TDC is approximately 1.5mm. This is a figure given by the manufacturer (in this case 2.23mm) so is the only datapoint I have relating to the ramp rates and area under the curve.

If I increase the ramp rate to 7 this goes up to approx. 2mm; if I decrease ramp rate to 1 it goes down to approximately 1mm. However, even on the highest ramp rate (and these cams are just about usable in a street car, so not too crazy) the lift at TDC comes in more than 10% below the manufacturer’s spec. I've seen have seen this issue for a few cam specs, from different manufacturers, so don't think the data is incorrect.

Am I doing something wrong, or missing something, or is the graphic incorrect?

With 2.23mm lift in 32 deg I guessed that maybe the duration at 0.050" might be around 240deg (corresponding to ramp rate of about 2.6): after entering this piece of information the lift at TDC in the graph is around 1.2mm, so around half of spec.

[nmauduit]

Thank you for this concrete exemple feedback: I'm quite interested in camshaft optimization, and would wonder whether cam timing could be changed in your settings, or rather would only be set as per the screenshot...
Also, whether the simulated profile be arbitrary (ramps 1 to 7) or related to actual profile measurements may play a role... (what about the Newmann phase 5 profile?)
My personnal goal would be to consider asymetric cam profiles (I would opt to an acceleration ramp being faster than decceleration ramp), in order to optimize spring pressure for a non symetric load (opening and closing)... I'm not sure how to get such a cam been ground though, or how much this would typically cost.

[Andy8421]

This is a very interesting area, that to be honest, I know very little about.

In answer to the above question, there are firms that will grind a custom non-symmetric profile using a CNC grinder:

https://lmengines.com/pages/custom-cam-design

Reading the information provided, it would seem that modern cars may need asymmetric profiles, as the usual cam follower 'finger' arrangement changes the ratio of cam lift to valve movement depending on whether the lobe is acting close to the finger pivot or further away as it rotates and wipes along the finger. The maths involved are beyond me, but it does look fascinating. At first glance, higher acceleration on valve opening could be achieved simply by having a symmetrical cam profile, but using finger actuators - perhaps this is an intentional part of the design.

Not a practical way of asymmetric valve acceleration / deceleration in the Elan, the buckets are always 1:1 with the lobe, but interesting none the less.

[nmauduit]

Not a practical way of asymmetric valve acceleration / deceleration in the Elan, the buckets are always 1:1 with the lobe, but interesting none the less.

thank you for your lead! I will sure check them up for a quote...

as for the trick you mention with buckets, I suppose one could get by with non rotating buckets with a non flat top, but since my goal is to maintain reliability while in search of the last HP (rather than max power at all cost even if for one single race), I did not feel that road worth pursuing.

[ill_will]

I got a response from Larry at Motion Software - he has been very responsive.

He confirmed that with the (older) version I have, DynoSim5, the cam model is not set up to output lift at TDC such that it relates to the cam supplier spec. In version 6 there is apparently a more detailed model which allows better alignment, and these figures can be put in directly.

Back in version 5, the manual states that the most accurate way to align the simulation with the real cams is to enter both the seat to seat duration, and the 0.050" duration, and then presumably some shape functions are used to map these values to a lift profile during the cam's revolution. (nmauduit: When you are entering the information this way, the ramp rate is calculated rather than entered.) Version 5 doesn't let you use asymmetric profiles, but iirc version 6 might (?)

I've also been looking at the Newman profiles, and some Tony Ingram profiles too - both have some promising options around the 280 deg seat to seat / 245deg at 0.050" @ 0.42" - 0.44" lift mark (for a 1700cc road engine.) Newman also mention that they do some small volume prototyping work so may be able to do a custom grind for you, but no idea how much a pair would cost.

[rgh0]

One of the many subtle issues with cams and engine modelling is ensuring everyone ( the cam maker, the modelling program and the cam tester, if you get them measured ) are quoting numbers and doing caclulations based on the the same set of assumptions.

i.e.
What is the assumed valve clearance ? as this has a significant affect on quoted "seat to seat" duration.

At 50 thou "checking height" is this cam lobe lift or actual valve lift after allowing for valve clearance?

What is the basis of the lift measurements and quoted degree numbers ?- Is it based on a flat tappet lifter or on a point measured on the cam lobe radius. With a flat tappet follower the contact point moves across the tappet follower and is most of the time not on the cam lobe radius contact line which affects the actual lift versus cam degrees as the geometry changes versus a point follower ( like a roller followers) that is always aligned with and in contact with the lobe at the radius. Many cam profiles from grinders are used in multiple types of engines with different types of follower arrangements


Often hard the get this data

cheers
Rohan