Reenabling the egr

[80' 427]

If you read my new build thread you know I bought a low mileage blue hair bullet. Everything on the engine is in great shape but someone broke the thermostatic valve for the egr so it is plugged off. Knowing the egr not only helps prevent detonation by filling the cylinder with inert gases as well as reducing pumping losses I am thinking of repairing it. Does anyone have specific real world input? If you are a mouth breather that heard from your uncle Rick (from Gatlinburg) that "u shulda tore out that junk rite a way case it dun steals 30 hp", kindly see your way out of this thread. Thanks

 

[Justin V]

(from Gatlinburg)

Haha

 

[diesel4me]

Find the engine code,determine what it is,and if its original or a transplant,and then you can order a new thermal vacuum switch to activate the EGR--I assume your talking about the one in the thermostat housing ?.....be prepared to spend quite a bit,those switches aren't cheap any more,some are hard to find too...but "most" of them are similar,so you can use one off some other applications..

 

[black dawg]

It has been a long time since I messed with that stuff, but it seems like the valves I was using would open above 150 degrees, allowing ported vac to egr valve.

It was always impressive the mpg that could be added with using egr and lots of timing.

 

[80' 427]

Napa has the part for $20. Turns on at 100 deg

 

[dyeager535]

If you look at the back and forth from the non-mouth breathers, I never saw consenus achieved on whether or not it hurts or helps. That I'm aware of, dyno tests with/without don't exist.

It helps reduce NOx, and probably greatly so, as far as I can tell that is the only reason to run it. I had/have EGR on my setup (and spent a fair dollar to get it up and running) and since it was easy to control, the on/off difference in regards to economy was authoritative IMO. It didn't hurt, nor help my mileage. With EGR off fueling and timing are not changed to compensate for it, so it's as if the engine was designed without it being a thought...unlike carbed setups where part throttle EGR was anticipated with rods that went lean to compensate, which is then an unfair comparison if you just yank it and do nothing to the tune.

If there was some way to keep the EGR from mixing with the air/fuel charge, then I would think more benefit would be possible. The inert gas isn't just helping displace volume, it's also diluting the air available to support combustion, which means it's less efficient. I'd say the net gain is zero (less fuel used, less efficient burn) if discounting the emissions aspect, which alone would have been enough to drive all manufacturers to use it as necessary. Just like ported vacuum advance, it didn't appear because it made more power or better economy. It was due to emissions requirements.

Having lived it, outside of being forced to by emissions regulations, I'd never run EGR unless it was already there and operating correctly, or purely as a science experiment. I'd much prefer to get the induction system tuned properly, and use a catalytic converter to tame whatever is left, that it can (which is also personal preference to eliminate most rich exhaust smell).

 

[80' 427]

My fundamentals of internal combustion engines book shows improvement in BSFC with a egr but a 1974 egr system may be quite a bit different than a lab test. Idk, I should use it as a "Ebke learning test" doing a-b-a testing.

 

[82355]

Dyno it.

Martin

 

[campfire]

My fundamentals of internal combustion engines book shows improvement in BSFC with a egr but a 1974 egr system may be quite a bit different than a lab test. Idk, I should use it as a "Ebke learning test" doing a-b-a testing.

What book do you have? I'm curious as to the theory here, I have not heard that before.

Dyno it.

Martin

This.

 

[80' 427]

This book
https://www.amazon.com/gp/aw/d/1259002071/ref=tmm_pap_title_0?ie=UTF8&qid=&sr=

Chassis dyno are hard to get to read BSFC on a carb because you need a flow meter in your fuel line. Even then you could only do steady state because it doesn't have away to figure for the fall in fuel bowl volume. I have thought about buying one but thus far I have had better places to spend my money.

 

[dyeager535]

Tell me if this thought process is wrong: on an injected setup, you should be able to look at the injector numbers with EGR on/off over the same road surface, and answer the question, no?

Obviously the variables you can't control will influence the numbers, but if it's any significant change with EGR on/off, I'd think it would be something you could measure. Should be a lot easier to get those numbers than dyno.

 

[campfire]

This book
https://www.amazon.com/gp/aw/d/1259002071/ref=tmm_pap_title_0?ie=UTF8&qid=&sr=

Chassis dyno are hard to get to read BSFC on a carb because you need a flow meter in your fuel line. Even then you could only do steady state because it doesn't have away to figure for the fall in fuel bowl volume. I have thought about buying one but thus far I have had better places to spend my money.

Cool. I have that book, and I have read it. I just don't remember the EGR-helps-BSFC part.

 

[Blue85]

It's been a long time, but it seems like I remember an adjustment screw on the factory thermostatic switches.

 

[campfire]

For what little it is worth, I have put about 40,000 miles on my beater Saturn. About half of those were with EGR, and about half of those are with the EGR unplugged to see how what difference it makes. I can detect no systemic change in fuel mileage, it still seems to be a function of driving habits only.

Not a laboratory test, but I'm confident that the difference isn't huge.

Deleting EGR on my c-code 6.2 did appear to make a small difference, but I think that engine was starved for air with the c-code manifold. It seems to generate less smoke with the open manifold vs the way it ran in factory configuration, and mileage mildly improved. Still not a real test, but it's all the info I have so far.

Am curious to see what results you wind up with.

 

[80' 427]

You can figure BSFC with efi but I am not sure how relatable it is to a 42 year old carb engine.

 

[80' 427]

Tell me if this thought process is wrong: on an injected setup, you should be able to look at the injector numbers with EGR on/off over the same road surface, and answer the question, no?

Obviously the variables you can't control will influence the numbers, but if it's any significant change with EGR on/off, I'd think it would be something you could measure. Should be a lot easier to get those numbers than dyno.

The bigger deal I have about BSFC I'd if you knew actual number for specific engine builds you could gear it for specific rpms at highway speed. My Malibu plan is to use a tall gear and overdrive to hardly turn any rpm at 65-70 hoping big block grunt will let if loaf along getting better mpgs, but that is only an idea and expensive to do 3 gear sets to nail it down. I plan on using a q jet on the 496 so it is hard to get injector pulse numbers for it.

 

[black dawg]

My only experience adding egr to an older engine was on an early 70s 460 that I put into an f250. The thing had a pretty serious detonation problem even with mild timing. With it jetted and timed for no detonation, mpg was 10 ish and had poor power. After adding egr and optimizing timing and fuel again was able to pull 14 mpg consistently on the highway.....gas station to gas station. These mpg figures were at 60mph and same 400ish miles of highway.

oh, and it would not ping after adding egr.

 

[dyeager535]

The bigger deal I have about BSFC I'd if you knew actual number for specific engine builds you could gear it for specific rpms at highway speed. My Malibu plan is to use a tall gear and overdrive to hardly turn any rpm at 65-70 hoping big block grunt will let if loaf along getting better mpgs, but that is only an idea and expensive to do 3 gear sets to nail it down. I plan on using a q jet on the 496 so it is hard to get injector pulse numbers for it.

I don't know all the intricacies that go with modern motors, but I know that on my car, that does not have cylinder deactivation, MPG is best at right around 2000RPM's, but that is at rolling speeds over about 30MPH. It would be interesting to know if there are any calculators that are capable of estimating where MPG would be best with a specific engine.

I'd be looking to see what RPM's the lightest GVW 1/2 tons were running up until model year 2000 with the 5.7L, at around 60MPH. I'd suggest the 7.4L, but part of the problem there is going to be gearing in the heavier vehicles they were installed in. With the 1/2 tons, the highest gearing offered would be more towards economy, not power. IIRC, generally it seemed the trucks were in the 15-1700RPM range at cruise, in the light duty apps.

Looks like the old 305/3.08 trucks could have been around 1400RPM at 60MPH (31" tires, 700R4), but the difference in economy between that and a 350 at the same RPM's, or even higher, don't seem to be measurable, or marginal at best.

I'm done trying to get good MPG out of trucks or old school cars with large motors. I'll never get anywhere near the 40MPG that my new car gets, and the only way to increase economy enough to be worth screwing with, seems to be by going diesel. The amount of expense necessary to TRY and get good MPG, and still not achieving it (depending what your goal is) with a gas engine, can't be recouped in MPG gains, unless you drive multiple tens of thousands of miles.

Not saying don't try, but if there was a magic bullet, GM would have used it...I don't think there is enough gain to be had to trade performance for economy. Obviously an OD trans is a no brainer, going with 2.73 gears to equal what you can run with 3.42 and OD, hurts felt power.

 

[80' 427]

The only advantage i have is I can lean it out more than emissions allow. Of course I don't expect 40 mpg, more like 20s. I wouldn't drive a little fuel sipper if I had it.

 

[dyeager535]

The only advantage i have is I can lean it out more than emissions allow. Of course I don't expect 40 mpg, more like 20s. I wouldn't drive a little fuel sipper if I had it.

What does it get now? I'd think 24-25 feasible with a basic 350 in a car with moderate gearing.

The point about the econobox is expectation management. If you understand the problems you face with an older/larger vehicle is weight, aerodynamics and displacement, things that are impossible to change, then you understand the limitations.

Running lean seems to be worth about a 15% increase, but that is possible, safely, only with being able to keep the engine from running lean constantly. GM had designed that into the early injection setups (lean cruise), but had to disable it due to the EPA finding out they were "cheating".

In 40 years GM has achieved about 25% increase in economy on the trucks. I'm not sure if the modern ones are running cylinder deactivation to get there.