"Smog Motors" Stealing Back the Stolen Power
12-21-2016, 04:08 PM
#21
Le Mans Master
Reduction of pumping losses as the throttle needs to be opened more and decreasing effective displacement.
The air to fuel ratio is kept constant but you have less room to put air into the cylinder while exhaust gas is being pumped into the cylinder. If 20% of your 5.7L engine displacement is occupied by inert exhaust gases, the effective displacement drops to 4.78 liters. You're now putting 20% less air and 20% less fuel into the engine. -You're getting less power out of it, but I keep hearing statistics like only 50hp is required to push a car down the road at highway cruise speeds anyway.
Exhaust Gas Recirculation is supposed to REDUCE temperatures and knock risk... It's also only recirculated under low loads which should be when you're at the least risk of knocking, too.
Adam
The air to fuel ratio is kept constant but you have less room to put air into the cylinder while exhaust gas is being pumped into the cylinder. If 20% of your 5.7L engine displacement is occupied by inert exhaust gases, the effective displacement drops to 4.78 liters. You're now putting 20% less air and 20% less fuel into the engine. -You're getting less power out of it, but I keep hearing statistics like only 50hp is required to push a car down the road at highway cruise speeds anyway.
Exhaust Gas Recirculation is supposed to REDUCE temperatures and knock risk... It's also only recirculated under low loads which should be when you're at the least risk of knocking, too.
Adam
Nice explanation of the theory but in reality on older engines without computer assist that is not my real personal experience. My 1994 Mustang GT convertible 5.0 with 32,000 miles which is computer controlled (primitive though), the EGR valve operates at any throttle off idle and caused elevated engine temps (nothing like heating cool dense air intake with 500 degree exhaust gas to cause pinging) which in turn elevates the engine temp more and can cause motor damage.
MPG on the mustang has gone UP since I prevented its operation. do not buy the EGR theory and still do not....most engine builders will tell you the same...one function to reduce NO...sorry
At the very least, removing an EGR will have no effect on MPG that is detrimental....
Last edited by jb78L-82; 12-21-2016 at 04:11 PM.
12-21-2016, 04:20 PM
#22
Not exactly. The early vacuum controlled egrs used a thermal vacuum switch. When the coolant temperature raised past set point, it opened the egr to COOL the engine. NOX is formed at high combustion temperatures. The introduction of small amounts of inert exhaust dilutes the oxygen, lowering the combustion temperature.
12-21-2016, 04:33 PM
#23
Le Mans Master
Not exactly. The early vacuum controlled egrs used a thermal vacuum switch. When the coolant temperature raised past set point, it opened the egr to COOL the engine. NOX is formed at high combustion temperatures. The introduction of small amounts of inert exhaust dilutes the oxygen, lowering the combustion temperature.
BTW-I am very well versed in the theory part of the EGR but in my experience the valve does not aid driveability or mileage one bit...NONE!
I am done on this topic which comes up often....I believe what I do and you yours...all good...
12-21-2016, 04:40 PM
#24
No not exactly is correct. On the 94 Mustang GT described above, the EGR operates like I described based 100% on manifold vacuum not ported or controlled by the computer. Anthing off idle to WOT gets diluted by the EGR valve..Again theory versus Reality.
BTW-I am very well versed in the theory part of the EGR but in my experience the valve does not aid driveability or mileage one bit...NONE!
I am done on this topic which comes up often....I believe what I do and you yours...all good...
BTW-I am very well versed in the theory part of the EGR but in my experience the valve does not aid driveability or mileage one bit...NONE!
I am done on this topic which comes up often....I believe what I do and you yours...all good...
I fully believe the Mustang EGR operated that way, as many methods were later used to do this. I did not argue that point.
I agree that EGR does not aid drivability or millage. I did not argue that point.
12-21-2016, 09:13 PM
#25
Maybe I missed it, but on cam timing, timing sets I've seen have dots you match up (unless you are gonna degree the cam but lets not get into that here) to install straight up. In the factory retarded position are the dot's not matching, or the timing set is just machined differently and a replacement timing set (gears and chain) from an older smallblock will effectively advance the cam timing?
And would this advanced cam timing get picked up by the smog sniffer? I've been toying around with using advancing dowels on the stock cam but its a lot of work for an experiment.
And would this advanced cam timing get picked up by the smog sniffer? I've been toying around with using advancing dowels on the stock cam but its a lot of work for an experiment.
12-21-2016, 09:20 PM
#26
Maybe I missed it, but on cam timing, timing sets I've seen have dots you match up (unless you are gonna degree the cam but lets not get into that here) to install straight up. In the factory retarded position are the dot's not matching, or the timing set is just machined differently and a replacement timing set (gears and chain) from an older smallblock will effectively advance the cam timing?
And would this advanced cam timing get picked up by the smog sniffer? I've been toying around with using advancing dowels on the stock cam but its a lot of work for an experiment.
And would this advanced cam timing get picked up by the smog sniffer? I've been toying around with using advancing dowels on the stock cam but its a lot of work for an experiment.
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shok (12-22-2016)
12-21-2016, 10:36 PM
#27
Melting Slicks
The best thing about these smog motors was that they had the bad flat top pistons. Fast forward 30 years and the head technology is all centered around flat top pistons. Add modern heads which will increase CR, a modern Hyd roller cam and free flowing exhaust with duel Cats, Fuel Injection with a ECM to run it and You will end up with more HP and less emissions. Whoops I just built a 1996 LT4 I guess the general already figured that out.
12-22-2016, 07:51 AM
#29
Melting Slicks
I agree, except I still think EGR is worth keeping if you even remotely care about fuel economy.
IMHO, it's like 1970's "variable displacement"- at an idle or cruise RPMs, mostly inert exhaust gas gets recirculated into the cylinder displacing some air and fuel and making the displacement effectively smaller. If I remember correctly it also has a cooling effect. -When you go WOT it stops pulling in exhaust gasses and you've got full power.
I'm probably not going to go put it back on my car but if it were on there and I could easily keep it, I would.
Adam
IMHO, it's like 1970's "variable displacement"- at an idle or cruise RPMs, mostly inert exhaust gas gets recirculated into the cylinder displacing some air and fuel and making the displacement effectively smaller. If I remember correctly it also has a cooling effect. -When you go WOT it stops pulling in exhaust gasses and you've got full power.
I'm probably not going to go put it back on my car but if it were on there and I could easily keep it, I would.
Adam
Last edited by SH-60B; 12-22-2016 at 07:59 AM.
12-22-2016, 10:38 AM
#30
Le Mans Master
Tossing the egr and not retuning for better performance is doing half the job and one can expect half asset results.
the timing chain gear was drilled differently to retard the timing. The 350/350 horse engine used the same cam as the L-82.
tossing the L-82 cam should be the last thing someone should do in modifying that engine, behind tuning,exhaust,better heads.etc. iv seen more than a few engines with that cam run into the 12 sec range it's no slouch. And I will say makes a very drivable package. More 350 hp cams have been sold by speed shops for street perormance over the years than any other cam, bigger numbers don't always mean bigger power. And being able to drive it makes a difference too.
the timing chain gear was drilled differently to retard the timing. The 350/350 horse engine used the same cam as the L-82.
tossing the L-82 cam should be the last thing someone should do in modifying that engine, behind tuning,exhaust,better heads.etc. iv seen more than a few engines with that cam run into the 12 sec range it's no slouch. And I will say makes a very drivable package. More 350 hp cams have been sold by speed shops for street perormance over the years than any other cam, bigger numbers don't always mean bigger power. And being able to drive it makes a difference too.
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NewbVetteGuy (12-22-2016)
12-22-2016, 10:48 AM
#31
So we have one person saying the cam was ground differently to get the retard and another saying the gear itself was drilled differently to get the retard. Any sources that can be cited to definitively answer that question?
This thread could be really useful for the often asked smog motor question that usually gets the boring "rebuild it, it's not worth modifying" answer.
This thread could be really useful for the often asked smog motor question that usually gets the boring "rebuild it, it's not worth modifying" answer.
12-22-2016, 01:24 PM
#32
Instructor
So now were saying that when you replace the intake and carb, to also replace the cam and gears as well? With what a crane 1" or actually go with the original L-82 cam and gears on a smog engine ... Talk about being confused. I use to think I knew 350's 
Last edited by Skybolt; 12-22-2016 at 01:24 PM.
12-22-2016, 03:06 PM
#34
Instructor
12-22-2016, 03:10 PM
#35
Le Mans Master
A tooth is more like 10 degrees,the engine wouldn't run properly. An aftermarket gear straight up gives you about 2 degrees.
12-22-2016, 04:26 PM
#37
Melting Slicks
Thread Starter
Tossing the egr and not retuning for better performance is doing half the job and one can expect half asset results.
the timing chain gear was drilled differently to retard the timing. The 350/350 horse engine used the same cam as the L-82.
tossing the L-82 cam should be the last thing someone should do in modifying that engine, behind tuning,exhaust,better heads.etc. iv seen more than a few engines with that cam run into the 12 sec range it's no slouch. And I will say makes a very drivable package. More 350 hp cams have been sold by speed shops for street perormance over the years than any other cam, bigger numbers don't always mean bigger power. And being able to drive it makes a difference too.
the timing chain gear was drilled differently to retard the timing. The 350/350 horse engine used the same cam as the L-82.
tossing the L-82 cam should be the last thing someone should do in modifying that engine, behind tuning,exhaust,better heads.etc. iv seen more than a few engines with that cam run into the 12 sec range it's no slouch. And I will say makes a very drivable package. More 350 hp cams have been sold by speed shops for street perormance over the years than any other cam, bigger numbers don't always mean bigger power. And being able to drive it makes a difference too.
The L82 cam's duration @ 0.050" is 222. I ordered a custom cam from Mike Jones with my Profiler 195cc heads- a cam that will focus on streetable torque but still get me to an estimated 440hp -and it's intake duration @ 0.050" is only 227 (granted it's a fast-ramp hydraulic roller, but...).
It's the best 1979 had to offer and has others have mentioned produced from the factor 350hp in another motor; it's certainly dated and single profile but it's a good streetable flat tappet cam made of high quality metal- which you often won't get from some modern cam MFGRs...
Adam
12-22-2016, 04:28 PM
#38
Melting Slicks
Thread Starter
So we have one person saying the cam was ground differently to get the retard and another saying the gear itself was drilled differently to get the retard. Any sources that can be cited to definitively answer that question?
This thread could be really useful for the often asked smog motor question that usually gets the boring "rebuild it, it's not worth modifying" answer.
This thread could be really useful for the often asked smog motor question that usually gets the boring "rebuild it, it's not worth modifying" answer.
Adam
Last edited by NewbVetteGuy; 12-22-2016 at 04:29 PM.
12-23-2016, 01:52 AM
#39
Race Director
Not exactly. The early vacuum controlled egrs used a thermal vacuum switch. When the coolant temperature raised past set point, it opened the egr to COOL the engine. NOX is formed at high combustion temperatures. The introduction of small amounts of inert exhaust dilutes the oxygen, lowering the combustion temperature.
My thoughts on the original subject: not a lot of power was ever really stolen in these engines. You're definitely not going to find it playing with EGR and AIR.
The biggest culprits are crappy exhaust systems and lowered static compression ratio. Even then, an L-48 is at best a 250HP engine in its maximum output, and L-82s a bit more.
Modern engines win the game through more efficient cylinder head flows, cams that lift the valves more, increased rotating efficiency, more efficient accessories and drivetrains, better engine management systems, etc.
It's "free" to remove a lot of these systems, but the biggest benefit will be in weight loss and a less cluttered (easier to work on) engine bay.
I've had the 78 in its current form with and without EGR, with and without cats and with and without AIR, I couldn't tell a difference.