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Old 05-27-2010, 05:50 AM   #1
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Default Volumetric Efficiency VE

So, I am playing with the Hydra program while I count the days until I return from Afgan. Trying to find the other 40hp I am told I could make. While looking at my maps I see that my VE map has a high number of 94. 94WTF? How can this be? (Click on my link to see my set up) I figure that 10psi would push the VE higher than that.

Can anyone explain how this could be.

Here are some numbers to work with. Stock engine, no mechanical problems, 10psi, AFR under boost 12.7, the Hydra uses the VE map for auto-tuning and I have burned a lot of fuel letting it do its thing, still only 94VE.

I did search.

I will reply when I can there is a war going on, except for fridays and sundays, or whan ever you have a pay problem.
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Old 05-27-2010, 06:51 AM   #2
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Try adding fuel so that your motor doesn't run dangerously lean and you might see that VE number go up. Also remember that our motors breathe through coffee straws and you aren't going to see 100% VE. 94% VE at 10psi sounds about right to me.

Seriously, 12.7:1? Who told you that was OK?
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Old 05-27-2010, 08:06 AM   #3
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Add more fuel.
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Old 05-27-2010, 09:53 AM   #4
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omfg...12.7 in boost? You need to call FM and tell them what you've done.
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Old 05-27-2010, 11:05 AM   #5
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I'm not sure how the hydra implements VE, but remember also that the numbers in that table are not actually the REAL VE of the motor. In fact they are simply a relative scale compared to some arbitrary point of performance of your motor.

For all we know, your map could be tuned so that 100% (relative) VE is 300kPa psi and 8500 RPM. Or it could be 3000 rpm and 100kPa. Or wherever...

All the map says is "use X% of the fuel required at some fixed MAP and RPM".
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Old 05-28-2010, 08:56 AM   #6
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Yea, I know I have some tuning to do. The AR target map was lean too. (Honestly I didn’t think it was too lean. I thought 12.1 or so was good) I plan to address it when I get back. I never heard any knock and my data log didn't show it was pulling timing. No excessive heat either. It pulls well but it isn’t making the power Jeremy said it should. I am guessing 240-250.

Once I feel comfortable with the tune (and my tuning abilities) I will bump the pressure to 12 and run at that until I get some other areas of the car sorted out. I am planning a rebuild 6 to 8 months after I get back. This will give me a learning curve for tuning and once inside I can look at the combustion chamber and see if I fail at tuning.

Hustler thanks for the word of encouragement, lol.

Y8, yes I noticed that there is a huge hole that Hydra dug in the map at cruse. At first I didn’t realize that it is only logging what it sees. Partial throttle opening = low VE numbers. It was climbing to 94 at peak torque but falling off above 6800 RPM. My fuel map drops off there too so I will fatten that area up. It makes since now. Boost was falling off too in that range.

I have been using the VE map for tuning but would it be better to use the fuel map? The Hydra will (cant remember the term) write to either map. Tune on VE and write to fuel or tune on fuel and write to VE. Maybe it would work better tuning on the fuel map.
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Old 05-29-2010, 01:19 AM   #7
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So, going off of memory doesn’t work to well. I didn’t look at the whole log before I posted. Looking further I see that I added fuel between each pull. Still, above 7000 is it running lean. Below that and it was at 11.1 to 11.7. I see where the problem is and plan to fix the high rpm lean when I get back. Tuning alone without a dyno is time consuming but I have learned a lot.

I noticed on my data log that as I tuned and added fuel the boost took longer spool. When it was leaner it reached its target boost earlier. It is reaching 11.5 AFR at 2-3 psi.
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Old 05-29-2010, 04:47 AM   #8
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Funny you mention the AFR. I spoke to an rally team the other day. They use 2l turbo charged VAG engines putting out around 600bhp tuned by a rally specialist. Their engines run up to 30 psi and they run between 12.3-12.6 A/F ratio. Anything above or below and something is wrong.

So.. I know Sav's first engined knocked terribly when leaner than 11.x and other issues. But we have a few members running 12 in boost no issues and 12.5 still is the optimal A/F ratio for power.

Kinda curious why some of us run so overly rich - I'm part of that group actually.
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Old 05-29-2010, 07:33 AM   #9
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Quote:
Originally Posted by Spookyfish View Post
Funny you mention the AFR. I spoke to an rally team the other day. They use 2l turbo charged VAG engines putting out around 600bhp tuned by a rally specialist. Their engines run up to 30 psi and they run between 12.3-12.6 A/F ratio. Anything above or below and something is wrong.

So.. I know Sav's first engined knocked terribly when leaner than 11.x and other issues. But we have a few members running 12 in boost no issues and 12.5 still is the optimal A/F ratio for power.

Kinda curious why some of us run so overly rich - I'm part of that group actually.
Safety. Seriously though, aren't those rally engines rebuilt after every race as well as tuned before every race?

Simply guessing on this one.
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Old 05-29-2010, 09:52 AM   #10
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I have several maps saved while tuning. One map from some time ago was saved as "best power yet" When I looked at it it was leaner than a newer map that I run now. This new map feels down on power and less responsive but is richer. That older map really hit hard, almost felt like a big NA engine.
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Old 05-29-2010, 09:54 AM   #11
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Quote:
Originally Posted by DOHCPanther View Post
I have several maps saved while tuning. One map from some time ago was saved as "best power yet" When I looked at it it was leaner than a newer map that I run now. This new map feels down on power and less responsive but is richer. That older map really hit hard, almost felt like a big NA engine.
What AFRs are we talking about?
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Old 05-29-2010, 09:59 AM   #12
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Quote:
Originally Posted by Fireindc View Post
Safety. Seriously though, aren't those rally engines rebuilt after every race as well as tuned before every race?
Simply guessing on this one.
No, but at 3 bar (40psi) they do replace every weekend.
I doubt that is related to their AFR.
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Old 05-29-2010, 03:49 PM   #13
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Quote:
Originally Posted by Spookyfish View Post
Funny you mention the AFR. I spoke to a rally team the other day. They use 2l turbo charged VAG engines putting out around 600bhp tuned by a rally specialist. Their engines run up to 30 psi and they run between 12.3-12.6 A/F ratio. Anything above or below and something is wrong.
Are these the new direct-injection engines, or old port-injection engines? DI lets you tune with massively greater resistance to knock. And those engines are without a doubt engineered so every detail is working in harmony with all the others, with no expense spared.

MT.net (I'm here, too) is pretty much caveman in comparison to a modern race engine development program, and the Miata engine itself is really archaic in a lot of ways, even compared to contemporary stuff from competitors, such as the Honda B-series. K-series motors that have been around for 8 or 9 years now are a quantum leap past Bs.
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Old 05-29-2010, 04:42 PM   #14
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Quote:
Originally Posted by Spookyfish;
curious why some of us run so overly rich - I'm part of that group actually.
Because washing down the cylinders is a lot slower process then too much knock. Going too far in either direction is never good. Like everything else, adding timing and fuel is a balancing act to get it right.
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Old 05-29-2010, 05:15 PM   #15
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I am reading this and it sounds like some of those guys know what they're talking about.

http://www.sr20-forum.com/tuning/160...welcome-4.html
and this:
http://195.159.109.134/vemsuk/forum/...opic,97.0.html

Last edited by Laur3ns; 05-29-2010 at 06:16 PM.
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Old 05-29-2010, 06:24 PM   #16
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sounds likes he good at copying and pasting from innovate motorsport's website.
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Old 05-30-2010, 04:50 AM   #17
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The point being that if 12.4-12.6 is what we should aim for optimally, but we want safety, then 12.0 is already alot of extra fuel.
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Old 05-30-2010, 06:28 AM   #18
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Quote:
Originally Posted by Spookyfish View Post
and 12.5 still is the optimal A/F ratio for power.
No it's not. Ben had results from forever and a half ago of his car picking up power going from 12.0 to 11.6:1 AFRs. I replicated the same results 9 months ago, at boost levels as low as 6psi. Going from 12.0:1 to 11.6:1 netted something like 5whp - not an insignificant gain. Our motors like lots and lots of fuel, and clearly the 2 liter VAG motors don't.

Hustler has UOA that says his limiting factor is fuel contamination, though, so we definitely run more fuel than we should - the motors just make power with boatloads of fuel. I want to try a standoff injector setup someday and see if that makes a difference - I have a theory that moving the injector back in the intake runner will allow us to run a little leaner and still stay safe and make power (and not wash the walls down).
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Old 05-30-2010, 07:03 AM   #19
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Quote:
Originally Posted by Savington View Post
Hustler has UOA that says his limiting factor is fuel contamination, though, so we definitely run more fuel than we should - the motors just make power with boatloads of fuel.
Maybe US fuel is different that BP Ultimate 98 that we run. The RingMazda (complete stock 120kmiles 94 1.8 engine) with an old T25 was making 220whp at AFRs around 12.

I am going to see next week what changes with I go from 11.2 in boost to 11.9-12.

This is my spark map:
Attached Images
File Type: png afrtable-rich.PNG (10.7 KB, 34 views)
File Type: png afrtable-medium.PNG (11.9 KB, 26 views)
File Type: png afrtable-optimal.PNG (11.1 KB, 29 views)
File Type: png sparktable-current.PNG (20.9 KB, 35 views)
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Old 05-30-2010, 07:26 AM   #20
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Quote:
Originally Posted by Spookyfish View Post
Maybe US fuel is different that BP Ultimate 98 that we run. The RingMazda (complete stock 120kmiles 94 1.8 engine) with an old T25 was making 220whp at AFRs around 12.

I am going to see next week what changes with I go from 11.2 in boost to 11.9-12.

This is my spark map:
BP98 is the equivalent of like 94-95 octane in the US. Most of us can't get better than 91, the lucky ones get 93.
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