Real-world AFRs at WOT...

Enthalpy · Post by **Enthalpy** » Sat Jan 21, 2006 8:21 pm

saqmaster wrote:You want to keep the EGT between about 750C and 850C.. that is without a cat.. with a cat you need to keep it in the 750C region.. mapping a car with a cat is a very complex task..

Can I ask where you get this information? I'm not being aggressive at all, I simply want to learn.

saqmaster · Post by **saqmaster** » Sun Jan 22, 2006 12:51 am

Enthalpy wrote:
saqmaster wrote:You want to keep the EGT between about 750C and 850C.. that is without a cat.. with a cat you need to keep it in the 750C region.. mapping a car with a cat is a very complex task..
Can I ask where you get this information? I'm not being aggressive at all, I simply want to learn.

I get my information from engineers at Ford, several of my friends work on the dyno cells at the european r&d facility near me.. And a close friend was the chief engine & electronics engineer on the Ford WRC team for 10 years

I do electronics work in association with http://www.grovegarage.com

Enthalpy · Post by **Enthalpy** » Sun Jan 22, 2006 4:38 pm

I was hoping for a publication you could show me. It's a fascinating discussion regardless!

Why would the Ford WRC lead engineer be concerned at all with cats? He must have done factory cals before the race team?

Please correct me if I'm off here, I haven't tuned with cats in the car. Here's how I see it:

OEMs have to make cars with catalysts that will last 100,000 miles in every car. Yikes! We don't have that restraint. Most modified engines won't last that long anyway.

EGT so much as a few feet away from the head can be almost 100 * colder, surprisingly enough. If the cat is far enough away, then it's much easier, right?

Even if your cat is close, calibrating the engine for colder EGTs really isn't that complicated. 750 *C out of an NA engine that isn't knock-limited isn't difficult. Go richer if the MBT EGT is too hot. Then, re-establish MBT timing and realize you didn't lose much power (if any) and enjoy the colder temps. The fuel usage will likely be higher, but you can avoid that by keeping your foot out of it.

Does this sound like good advice? I have a hard time just leaving it at "it's difficult". Nothing is too difficult if someone else can do it.

woh · Post by **woh** » Sun Jan 22, 2006 4:58 pm

saqmaster wrote:
No, peak power will occur in the region of 12.5:1 - 13.0:1. Your exhaust gas temperature will be dangerously high running stoichiometric mixtures at WOT, you may even lose an exhaust valve or two.

At what level of trottle opening (kPA) would you consider it 'save' to tune for stoichiometric mixture?

Here in Colorado WOT is 82kPa. So tuning for Stoichiometric seems 'save' except when max power at WOT (83kPa) is expected.

PSIG · Post by **PSIG** » Sun Jan 22, 2006 8:53 pm

Enthalpy wrote:. . . Cooled EGR is being used as an ON-BOOST knock supressor, allowing much leaner mixtures without engine output sacrifice. The main goal here is fuel savings.
. . .
My implimentation makes plenty of flow available if I cool it and recirc it before the turbo. My valve doesn't have to be monsterous at all.

Okay, I understand all that - in splite of 'on-boost fuel savings' being a near oxymoron for the average MSer.

However, in my case that is entirely true. While towing up a long grade with my twin-turbo 5.7 Suburban I had to ease the pressure to prevent the onset of det as it gets hotter from working hard. Det suppression is a factor for me, but so is economy in boost; a situation very few others (except aircraft and boats) need to address.

I have already examined the typical economy suggestions you made and just wanted to visit the application of EGR recirc you mentioned having great success with in case I might make use of it in this app. How are you tapping the exhaust gas? How do you cool it and how much? Is it regulated or fixed flow? In effect - what do I need to replicate your system to lean my AFR?

GOT BOOST?

David

Enthalpy · Post by **Enthalpy** » Sun Jan 22, 2006 9:38 pm

Actually, I use my own controller, not the megasquirt. I have a buddy that's getting his master's in control systems. I have a 3D map that outputs a PWM signal. I then use a home-grown PWM to linear stepper motor to convert to EGR position.

I'm not done with it yet. There are definitely kinks to work out. It's not cooled yet either.

Boosting up a hill with a gasoline turbo motor is extremely hard on the turbo itself. Detonation is only one concern here. Downshifting to your max power RPM and staying out of boost would probably give you savings here.

saqmaster · Post by **saqmaster** » Sun Jan 22, 2006 11:58 pm

I was hoping for a publication you could show me. It's a fascinating discussion regardless!

Unfortunately most of the literature on the internet is either a) incorrect, b) a matter of opinion or c) badly repeated and out of context. My source of knowledge is people in the industry (manufacturers, works teams) and books such as the Bosch Automotive Handbook (priceless, I highly recommend it).

Why would the Ford WRC lead engineer be concerned at all with cats? He must have done factory cals before the race team?

Because he's also been involved in several road car projects and engine designs.

EGT so much as a few feet away from the head can be almost 100 * colder, surprisingly enough. If the cat is far enough away, then it's much easier, right?

Sorry, I wasn't clear. 750C is the temperature at the cat. OEM's map each load site until one of two things occurs: 1) Peak torque or 2) cat temp = 750C. If (1) occurs above 750C cat temp, then fuel is added until cat temp = 750C. This is why most production cars run so very rich (even as low as 11:1) at WOT, and another reason why cats are a smoke screen and a waste of time.

Does this sound like good advice? I have a hard time just leaving it at "it's difficult". Nothing is too difficult if someone else can do it.

It depends on what you're trying to achieve. It is difficult to tune an engine on the street or on a rolling road (chassis dyno) to maintain a 750C cat temperature. You need an engine dyno that can hold the engine at a load site.

saqmaster · Post by **saqmaster** » Mon Jan 23, 2006 12:00 am

woh wrote:
saqmaster wrote:
No, peak power will occur in the region of 12.5:1 - 13.0:1. Your exhaust gas temperature will be dangerously high running stoichiometric mixtures at WOT, you may even lose an exhaust valve or two.
At what level of trottle opening (kPA) would you consider it 'save' to tune for stoichiometric mixture?

Here in Colorado WOT is 82kPa. So tuning for Stoichiometric seems 'save' except when max power at WOT (83kPa) is expected.

It depends on so many factors. People always want blanket statements to cover things, it's simply not black and white!

One safe way would be to view it as percentages. Configure the bottom 80% of your table at stoich, the 90% area as say 13.8:1 and then the 100% (WOT) line at your given target AFR.. You can't go much wrong with that.. Of course that is assuming your given engine, package, fuel, environment, etc etc will let your car idle/cruise at stoich mixtures at certain load sites..

woh · Post by **woh** » Mon Jan 23, 2006 7:52 am

Thanks, that is what I was looking for to clarify my understanding.

Enthalpy · Post by **Enthalpy** » Mon Jan 23, 2006 4:35 pm

saqmaster wrote:Unfortunately most of the literature on the internet is either a) incorrect, b) a matter of opinion or c) badly repeated and out of context. My source of knowledge is people in the industry (manufacturers, works teams) and books such as the Bosch Automotive Handbook (priceless, I highly recommend it).

Good reply, thanks. In response to this specific statement, you are absolutely right! That's why the only publications I really use are SAE papers and the like. These are technical, peer-reviewed, Ph.D.-compiled papers that are scientific enough to take the guessing and flat out misinformation out of the equation.