Increasing EGR flow for better mileage

[tasdrouille]

Tumble and swirl should mix everything together real good.

Christ, the EGR is accounted for from MAF readings.

EGR does in fact slow the combustion rate, so maximum brake torque timing advances with EGR rates. I don't know the details of the sensors in your car, but may I suggest when EGR is activated you also activate a relay adding a very high resistance in line with the IAT sensor. If the ECU thinks it's -40 in there, that might get you ~2 degrees of advance.

[Daox]

Interesting thoughts Christ. The Paseo uses a map sensor and temp sensor for sensing intake air. The map sensor will detect the difference in manifold vacuum, but the temp sensor won't see the hot EGR gas... Is it necessary to compensate for the hot EGR gas? Since I think I will need more ignition advance, I'm thinking that it would be best to bypass the temp sensor. If I'm wrong and get ping, there is a knock sensor to take care of retarding timing.

[Daox]

Thanks for the info Tas. I had a feeling an EGR rich mixture would burn slower. So, I will need a way to advance timing... If the sensor trick doesn't work, I do have a greddy emanage blue laying around I can wire up. I was just hoping it wouldn't come to that. I don't think they deal with P&G well. Although, if this mod works well, I won't be P&Ging anymore (aka, the goal).

[Christ]

I don't think the MAP will actually see a difference in manifold vacuum.

Here's why:

The EGR isn't a forced gas, it's drawn in by vacuum. The ECM will see an increase in vacuum via the MAP sensor, but not understand that some percentage of that void is filled by EGR reflow. The vacuum in the manifold will remain the same regardless of where the flow comes from, but the MAP won't be able to compensate for the EGR flow.

That's why vacuum leaks cause so many problems. The engine vacuum is still the same at the valve's face, but the sensor (or carburetor) doesn't "see" the difference.

If you're already running a HAI, I wouldn't think the percentage of EGR you're going to reflow (less than 20% of total volume, I'd imagine?) is going to really affect temps that much, especially considering how much the gasses have already expanded and cooled by the time you get them back into the engine, so there shouldn't really be a need to compensate for temp, but you will need to adjust timing, like Tas said, to make up for the decrease in flame speed.

How much EGR are you planning to flow? That will help the discussion a little.

[Daox]

As much as I can! I doubt I'll be able to flow as much as the 2010 Prius which has been quoted to run up to 30%. If I had to guess, I'd hope I can get up to 20%.

[Christ]

Going strictly on volume and not mass, and assuming 100% VE, a 20% reduction in intake volume would bring you from a 1.5L to a 1.2L engine. Not bad at all.

Of course, given air temp and actual VE, you'll likely have something closer to a .9 or 1.0 or less at cruise.

[Daox]

Sounds great to me. Throw in a new tranny with lower final drive and I'll be right where I want to be.

[Christ]

Actually, that last number is wholly incorrect, because I didn't account for throttle position during cruise, and for that, I'd have to know the VE and BSFC of the engine in it's new form to determine approximate torque at X rpm blahblahblah.

Still, I'd put cruise displacement somewhere between .6 and 1.0 (Bigger range, is all.)

Depending on things like piston travel and other factors such as exhaust/intake frequency, it could actually be better to stay at a higher RPM after you've reduced your effective displacement so much.

[moonmonkey]

i read in a post about the 3 cyl metro motor ,being damaged by a clogged ? egr valve, im interested in your research ,but am no egr expert, what is the risk of engine damage? if any, i need to get another 150k out of my echo.

[Daox]

I'm not exactly sure what the problem is with the Metro. But, I think it has more to do with uneven amounts of EGR in each cylinder. Metro experts?

That said, EGR isn't the cleanest thing, and I'm sure my system will need to be cleaned out occasionally. Thats something to keep in mind as I route plumbing. Perhaps a U shaped trap like a sink drain has would help? Other ideas guys?

FYI, no progress on this for a little while, I'm on vacation now until the 14th.