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.

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?

Add more fuel.

omfg...12.7 in boost? You need to call FM and tell them what you've done.

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".

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.

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.

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.

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?

No, but at 3 bar (40psi) they do replace every weekend.
I doubt that is related to their AFR.

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.

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.

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

sounds likes he good at copying and pasting from innovate motorsport's website.

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.

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).

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.

It should be just fine to run that lean at lower boost levels if your car is tuned. I don't get richer than 12.0 until after 10#. I've even ran as lean as 12.2 at over 20# on several occasions just to see if it made more power (it did). Tune the car on the dyno and it will let you know where it's happiest. With my tune, the extra fuel is there because I wanted a little safety buffer.

Point begin in those threads that 11.x isnt going to help you stay out of detonation range when your timing is on the edge and intake temps sky rocket.

What I'm trying to account for is minor cylinder to cylinder variations that exist in every car. If your timing is on the edge and your intake temps sky rocket you have other issues.

I remember that thread...

End of the day it depends on many factors... Rules only apply to well sorted motors.

Spookyfish, my AFR was at 12.7 at the upper RPm limit and richer at peak torque 12.0. That is on 93 octane and water wetter in the FM radiator at Savannah temps. 80's-90's As I richened it up it didnt have the crisp response it had when it was leaner.

Savington, you said you richened yours up and found power. I am wondering if you added it to the whole map, the peak torque, or the top of the rpm range? Mine still felt like it wasn't as responsive when it got richer.

Y8, hook me up man, no reply? I know you have benn working with the Hydra a while now.

The reason for retuning now is that the old map went to 30 psi. I remaped it to 21 psi for a finer tune. Also the old AFR map was very basic. 14.5 off boost quickly sloping to 11.5 by 8psi. The map didnt have any change for deceleration, idle, or rpm. I am shooting for a slightly lean highway cruse 14.7 to 17.0 on decel. The map is sloped to slowly richen to 11.5 at 21 psi and lean about .5 from 4000 to 7400. It is rich at idle 13.8 to help smoth the big injectors and A/C idle problems.

Also my timing map was not very smooth either. I may be shooting my self in the foot with this but it is a learning experience and an attempt to make the map as fine as possible. I did make some det cans to use when I get back.

it's "y8s" and I didn't see the direct question to me but let me try to guess...

I haven't used VE / fuel dual maps on the Hydra. Mine was only a 2.1 version. But if I was going to, I would start by setting the VE map to 100% everywhere and getting a rough tune on the inj pw map.

Here is why:

most engine management has a fixed resolution for fuel pulse. lets say it's .01 ms. At idle on a 550cc injector, your fuel pulse is around 1.50 ms. .01/1.50 = .0067 or .67% of the fuel delivered.

at max boost at high rpm, you might need 15.00 ms. .01/15.00 = .00067 or .067% of the fuel delivered.

In short, you gain effective resolution at the place you dont really need it.


... enter VE.


VE (Volumetric Efficiency) traditionally is the amount of air sucked into a motor compared to its displacement. At a given load and RPM, you can predict the fuel needed by knowing how much air the motor ingests. (this is what AFR is, right? Air / fuel ratio).

For tuning, the theory is similar only a little backwards. You know the fuel (you type it into your pulsewidth map) and then measure the airflow (MAP and RPM) and have to create a synthetic VE value to correct any error.

If by some miracle your fuel pulsewidth map was ABSOLUTELY ERRORLESS AND PERFECT, then the VE table would be the actual VE of the BP motor. But we know your map is imperfect as any tuned map is (except maybe Mazda factory maps)...

So you get close in the fuel pulse map and just make it nice and smooth. You could just do a planar map increasing pulsewidth from 0kpa to 300kpa and flat from 0rpm to 8000rpm and let the VE map do the rest. That's how Electromotive (Tec3) and (I think) Adaptronic do it... assume fuel delivery is linear and increases directly with MAP (not RPM) and correct with VE.

y8s Thanks for the reply. I have been a little tied up getting helicopters back in the air. I had to print your reply to digest it. It is a little deeper than I expected but I think I understand what you are telling me.

Because FM sent a pretty good map I am working off of it. I will concentrate on the fuel map and then let it build the VE map from it. Before I let it auto tune the VE map and let it build the fuel map but because I didnt have a dyno to load the car at a certain rpm the auto tune could not see the cell long enough to tune.

sorry to threadjack here, but you more experienced tuning guys do lend the knowledge here. After reading that some of you say 12's are too lean for full boost it raised an eyebrow for me, I was on a rich basemap sinking to 10.5's in full boost. Pulled some fuel made some changes, seeing about 12.3-12.5 full boost with no knock at all, this is on a very conservative spark map. To my question though, what exactly do you guys feel like is a good/safe AFR for idle, light load/cruise, decel?

14.7:1

idle, light load, decel, and WOT all have very different requirements.

idle needs reasonable power and stability but also efficiency so you're not wasting gas sitting still. 14.7 is obvious but not always stable (maximum N/A power is what, 13.5AFR?). Since you have limited airflow and RPM, you can only generate more power by either advancing spark or changing fuel. I personally try to idle around 14.3 as a reasonable compromise. If your car idles well at 14.7, do it.

light load/cruise is all about efficiency and emissions. too rich and you waste fuel and pump out hydrocarbons. too lean and you raise EGT and pump out NOx. 14.7 is the best AFR for emissions, but you can go as lean as the car will reliably run. Reasonable range is probably 14.7-15.4. Some guys here have run up to 16:1 and possibly higher without issue.

decel: shut off the injectors.

the track guys tend to like a slightly rich biased tune in boost since they like the margin of safety over absolute optimum power. I tend to agree once you start getting to serious boost levels.

Remember you can't always hear detonation. It's worth 5%-7% more fuel in boost to reduce the chance of the silent killer. 11-11.5 AFR once you're above 5 psi.

There is an article written by Klaus from Innovative Motorsports that goes over this.

http://www.innovatemotorsports.com/resources/rich.php

In the end, when you're talking about taking an engine to 2-3x the stock power level and detonation being the biggest enemy, running richer is just a simple way to keep an engine safer.

Good input, I appreciate it. I'm currently running 13.8-14.3 at idle, 13's in the light cruise/load, and it just shuts fuel out all together in decel full lean. I got rid of my chinacharger last week and have a garrett on the way so I'm curious to see how the change in size of compressor and turbine plays out on my already slightly adjusted AFRs

^Troof. This approach also helps keep exhaust gas temperatures in check, which is no bad thing.