EGR for fuel economy

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travis
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EGR for fuel economy

Post by travis » Tue Jun 12, 2018 10:13 am

Has any of you guys tried using EGR on a mild performance build with a carb to help with fuel economy? I’ve been able to get some really good mileage numbers out of several vehicles that still used the factory carb and EGR setup on a stock or near stock engine, but I’ve never tried it with anything bigger than a 212@.050 cam or on anything with headers. I’m thinking something in 216 to 224@.050 range, headers, dual plane, under 9.5-ish compression, etc. Could you still use a pretty lean primary calibration and a more “normal” secondary calibration and still retain good driveability, good economy, and still have good WOT power?

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Re: EGR for fuel economy

Post by gmc406 » Tue Jun 12, 2018 10:34 am

My EGR is still functional on my 91 EFI 406. Works wonderfully for detionational resistance on a high compression engine. Not 100% sure on fuel mileage, but the the truck will literally get a little better than 20 mpg’s. Built 700R-4 with 3.73’s.

I have a slightly larger cam and more compression than your planned build.

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Re: EGR for fuel economy

Post by travis » Tue Jun 12, 2018 3:09 pm

I forgot to mention the part about helping against detonation. I guess a lot of people don’t use EGR simply because most intake manifolds don’t have it...especially outside of the Performer type dual planes.

How much cam and compression are you running?

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Re: EGR for fuel economy

Post by grandsport51 » Tue Jun 12, 2018 4:10 pm

Ok ,
So disregarding oxides of nitrogen production
You are going to crutch too high a compression ratio
Or poor fuel quality By recirculating exhaust gas.
Although inert it contains quite a bit of
particulates and other detritus etc which is sent unfiltered into your engine.
Sure it might work but additional maintenance costs
Outweigh any benefit in my opinion.
When we first introduced this crap in ‘73
Maintenance was increased tremendously,
I don’t see the point just use E-85
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Re: EGR for fuel economy

Post by bigblockmopar » Tue Jun 12, 2018 4:27 pm

I don't think people don't use EGR because the manifolds lack provision for it, I think it's more because people don't quite understand what it does and on top of it, really don't want to recirculate exhaust gas back into their freshly built engine.

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Re: EGR for fuel economy

Post by In-Tech » Tue Jun 12, 2018 4:33 pm

Keep in mind a camshaft change can "self EGR" as the vacuum increases above idle and even at idle in smaller cam changes. Very noticeable when tuning EFI as well as carb tuning.
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Re: EGR for fuel economy

Post by Brian P » Tue Jun 12, 2018 7:59 pm

The devil is in the details. EGR retrofitted to engines that weren't originally designed for it (see above comment) can kill gas mileage. EGR when combined with other design details could be quite successful back in the day, e.g. the Nissan NAPS-Z engine http://720world.com/forum/topics/some-h ... s-z-engine

EGR slows down combustion ... the NAPS-Z used two spark plugs per cylinder to offset the bad side effects of doing so. That's probably not viable to retrofit. The ignition timing has to be optimised as well - it will want more timing advance under the conditions when EGR is active.

More recently, variable valve timing has been used to achieve an EGR function when running at part load without actually requiring an explicit EGR system. That's not something retrofittable, either.

The average DIYer probably isn't going to have the resources to calibrate and optimise an EGR system in a non-OEM application, and if the engine doesn't have fast-burn combustion chambers and the like, may end up worse off than by not using EGR.

If you're not subject to NOx emission lmiits, just calibrate for "lean cruise" and call it done.
Last edited by Brian P on Tue Jun 12, 2018 8:05 pm, edited 1 time in total.

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Re: EGR for fuel economy

Post by Walter R. Malik » Tue Jun 12, 2018 8:04 pm

With using EGR for fuel economy, it is all about less engine pumping losses.
An engine will have less vacuum when just the correct amount of EGR is allowed to enter the intake mixture; especially at constant speed highway driving.
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Re: EGR for fuel economy

Post by ptuomov » Tue Jun 12, 2018 8:43 pm

In-Tech wrote:
Tue Jun 12, 2018 4:33 pm
Keep in mind a camshaft change can "self EGR" as the vacuum increases above idle and even at idle in smaller cam changes. Very noticeable when tuning EFI as well as carb tuning.
I think that’ll help with pumping losses, but you need exhaust gas cooling to help with knock resistance. My understanding is that in “internal” EGR the heat effect is greater than the inert gas effect. I think.
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Re: EGR for fuel economy

Post by mfdcar51 » Tue Jun 12, 2018 10:00 pm

I always thought of EGR as a way to make a engine "chemically" smaller, inert gas takes the place of oxygen so less fuel is needed

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Re: EGR for fuel economy

Post by Schurkey » Wed Jun 13, 2018 12:17 am

mfdcar51 wrote:
Tue Jun 12, 2018 10:00 pm
I always thought of EGR as a way to make a engine "chemically" smaller, inert gas takes the place of oxygen so less fuel is needed
Possible.

"I" always figured that the EGR made the engine run less efficiently, so that the driver had to add a little extra throttle to maintain the power with EGR functional.

I've seen EGR make a major difference in an engine's ability to avoid detonation. But then, the engine was tuned to promote detonation without the EGR. I've never seen EGR improve fuel economy except when used with the OEM carb and ignition calibration.

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Re: EGR for fuel economy

Post by user-23911 » Wed Jun 13, 2018 1:33 am

It's similar to using water injection because exhaust gas is about half water if you ignore the nitrogen.
It slows the burn and reduces peak temperatures.

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Re: EGR for fuel economy

Post by Truckedup » Wed Jun 13, 2018 6:50 am

joe 90 wrote:
Wed Jun 13, 2018 1:33 am
It's similar to using water injection because exhaust gas is about half water if you ignore the nitrogen.
It slows the burn and reduces peak temperatures.
Chemists say about 71 % nitrogen and 11% water...
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Re: EGR for fuel economy

Post by gmc406 » Wed Jun 13, 2018 3:23 pm

Brian P wrote:
Tue Jun 12, 2018 7:59 pm
The devil is in the details. EGR retrofitted to engines that weren't originally designed for it (see above comment) can kill gas mileage. EGR when combined with other design details could be quite successful back in the day, e.g. the Nissan NAPS-Z engine http://720world.com/forum/topics/some-h ... s-z-engine

EGR slows down combustion ... the NAPS-Z used two spark plugs per cylinder to offset the bad side effects of doing so. That's probably not viable to retrofit. The ignition timing has to be optimised as well - it will want more timing advance under the conditions when EGR is active.

More recently, variable valve timing has been used to achieve an EGR function when running at part load without actually requiring an explicit EGR system. That's not something retrofittable, either.

The average DIYer probably isn't going to have the resources to calibrate and optimise an EGR system in a non-OEM application, and if the engine doesn't have fast-burn combustion chambers and the like, may end up worse off than by not using EGR.

If you're not subject to NOx emission lmiits, just calibrate for "lean cruise" and call it done.
I agree, this makes a lot of sense. I wouldn’t try and retrofit something either. I don’t think it would work as well as it should.

I can’t pinpoint as to what exactly contributes to my economy. Is it the fact it has a good tune with EFI? The EGR? The high compression (12.2:1)? Or is it a combination of all? Who knows.

The EGR was there when my tuner built the engine. It was first put together as a street/strip combo with the emphasis on street. I had to drive 150 miles or so to get to the nearest track. I have no car hauler and e85 isn’t available in my area.

Some people certainly don’t like the fact of regurgitated exhaust gases being fed back into the engine, I can understand that. However, my brother’s 88 Chevy halfton had 450k miles when he sold it. EGR didn’t seem to shorten the life of his engine.

I’m certainly no expert.

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