Compression rate, Engine simulations.

[Revolve_Engine]

Hello!
Was wondering if anyone have experience with a simulation software called Engine Analyser Pro from PerformanceTrends? Ive been doing a lot of simulations but it seems like the software is not accurate when calculating knock index (detonation) at high compression ratios such as 11:1 ++ on 4 cylinder 600cc engines.

This has made me have to lower the compression to about 10.8:1 to eliminate detonation (in the software) but in my mind this is way too low. Even modelling a stock gsxr600 shows detonation at 12.5:1...

The camprofiles and intake / exhaust tuning seems to be quite accurate though aswell as power figures.

What CR are you guys running on your 4cyl engines?

Im currently switching over to GT Power, but it is a bit more extensive, and I havent gotten very far yet http://fsae.com/groupee_common/emoticons/icon_smile.gif

We are running a 06 gsxr for our first year.

Thanks,
Andreas - Engine tuning

[Revolve_Engine]

Hello!
Was wondering if anyone have experience with a simulation software called Engine Analyser Pro from PerformanceTrends? Ive been doing a lot of simulations but it seems like the software is not accurate when calculating knock index (detonation) at high compression ratios such as 11:1 ++ on 4 cylinder 600cc engines.

This has made me have to lower the compression to about 10.8:1 to eliminate detonation (in the software) but in my mind this is way too low. Even modelling a stock gsxr600 shows detonation at 12.5:1...

The camprofiles and intake / exhaust tuning seems to be quite accurate though aswell as power figures.

What CR are you guys running on your 4cyl engines?

Im currently switching over to GT Power, but it is a bit more extensive, and I havent gotten very far yet http://fsae.com/groupee_common/emoticons/icon_smile.gif

We are running a 06 gsxr for our first year.

Thanks,
Andreas - Engine tuning

[Mbirt]

I've no experience with EAP, but do you have a restrictor in the model? You'll find posts on here from 4-cyl teams stating that they've run 40-70 degrees of advance at WOT. Using some common sense, I would turn off the knock prediction in EAP if you can.

If I were you, I would move on to the industry-standard software right away. Start with tutorials and you'll surprise yourself with how little time it takes to get results which make sense. With that said, I still leave knock prediction off in GT-Power.

[Revolve_Engine]

The restrictor is modeled on my fsae file, but duo to these knock issues I tried modeling a stock gsxr without the restrictor and still it shows detonation. I cannot turn the knock prediction off, but the simulation completes, and show all calculations in tables or graphs.

If Im not able to predict knock and CR, how can I know if my engine will run? I know restricted superbikes have been as high as 16,5:1 !

How do you proceed here?

Thank you for your answer Mbirt http://fsae.com/groupee_common/emoticons/icon_smile.gif

Andreas

[Revolve_Engine]

I have investigated further and it seems like the knock prediction is very hard to model as it depends on a lot of variables - like hotspots, wall temperature, geometry, start temperature, combustion rate etc etc etc. For this knock prediction to be accurate it would need calibration from live testing.

This means that the knock index / prediction is out of the question. But as previosly asked, how do I then proceed with experimenting with CR?

Many thanks,
Andreas - Revolve, Engine Tuning.

[Mbirt]

Because your intake design, among many other things, influences your engine's IMEP, I think you should complete at least one season of development and calibration with the stock pistons first. You don't want to buy 14.5:1 c/r pistons first and then get crazy knock at the 7000 rpm peak torque speed you've tuned your intake, exhaust, and low-overlap, early IVO cams for. The pistons should be chosen after you've found that you're safely knock-free.

My experiment with CR would be the following:
-Create a GT-Power model which correlates to the restricted, stock compression dyno engine setup.
-Price out off-the-shelf high-compression pistons for the motor.
-Model the various "upgrade" pistons by simply changing the compression ratio parameter in GT-Power.
-Compare the gains in power to the stock curve and perform a cost:benefit analysis. Are they really worth it considering the purchase price and the risk associated with tearing down and reassembling a perfectly fine, affordable 4-cylinder bike engine?

I'm sure GFR did the analysis for their CRF450X and the design of a high-compression piston and the use of E85 is a capstone project for at least one Oregon State student right now. Don't let that sway you one way or the other, but just FYI.

[Rex Chan]

I'm not quite sure I understand your question about what CR we run.

You seem to be treating it as a variable that you can adjust, whereas most teams (I think) leave the CR of the engine stock (12:1 for a CBR600RR). We do have an engine that has a higher CR (13-14:1), but this was due to the head being machined down after damage to the head.

We're a N/A team, but I'm pretty sure the restrictor means you can only get max 100kPa in your manifold/cylinders.

I suppose what I'm saying is that you should start off by leaving the CR at stock. You do not need to modify the internals of your engine for performance reasons to be competitive at FSAE comps, as many/most teams have problems even finishing enduro, with a significant majority haveing engine reliability problems.

[Revolve_Engine]

Thank you guys. Its not easy starting up a new team, having no earlier teams to learn from http://fsae.com/groupee_common/emoticons/icon_smile.gif

The engine is already in pieces. Theres no problem in assembling a new engine.

Simulations show that VE is greatly affected by changing CR, but it does not show anything about how engine response is affected. This is why I asked about what CR you run.

If GT Power cannot model knock prediction without calibration I will have to do this in the dyno in January for next years simulations. We are currently looking into the 13:1 Wiseco pistons as they show a good power increase. We get them very cheap from our sponsors.

Luckily theres some good feedback on the cam profile and intake / exhaust tuning simulation in EAP from other builders, saying they are accurate.

I have been in contact with some very experienced race engine builders for superbikes and they always say upping the CR is the way to go on restricted bikes..

What VEs are you guys getting on your engines?

Best regards,
Andreas

[EC]

Just an FYI, I have seen many Wiseco pistions melt down and be very sensitive to A/F ratio and knock. Make sure you have very good tolerances on everything and also play it to the safe side on the detonation points if you plan to stick with the Wiseco pistons. For different types of fuel you can go with different CR, typically 91 pump gas is safe to 12:1; 100 race fuel is good to 13.5:1, and E-85 is safe to 18:1. From a reliability stand point of all racing stock or Mahle pistons seem to have a better history.

[Mbirt]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by EC:
typically 91 pump gas is safe to 12:1; 100 race fuel is good to 13.5:1, and E-85 is safe to 18:1. </div></BLOCKQUOTE>Completely unsubstantiated. If I were a design judge, there would be no way I could let this slip by. The stock compression ratios for the regular unleaded-friendly CRF250R and Yamaha YZF-R6 are 13.2:1 and 13.1:1 respectively. Blindly choosing an 18:1 static compression ratio with no due diligence because you've heard the fuel can handle it is even more foolish yet.

[RANeff]

After working with our drivetrain department for ~3 years, I can tell you that focusing on CR is the wrong way to tune an engine for FSAE. But that is besides the point.

If you are getting problems with your model, either your inputs are wonky or something else isnt right: either way you cant trust its output. If we were designing a wing package, and CFD was telling us we had 1500lbf of -lift at 30mph with 3 lbf of drag, would you trust it? Back when I ran Virtual 4-stroke, there were many variables/inputs that would change my outputs, so Id start there...