Chevy Impala SS Forum banner
41 - 49 of 49 Posts

· Registered
Joined
·
2,950 Posts
... I think if the GM engineers felt a "common" EGR part would suffice for both platforms, B&F, then that part would have been used.
Like any manufacturer they would not spend $.02 on anything if it was needed to reduce CAFE #'s amongst their car platforms.
I suspect it was emission function was the primary reason the 2 are different.
B bodys were the comfort/cruise platform and F bodys more a performance model with different exhaust systems.
With that said, IDK part # for the Vette EGR ... but suspect it is also different for the LT1 years.
Don't think it was CAFE, think it was EPA in this case, mandating that there be different EGR Valves for what the EPA considers sufficiently different applications.
That said, I basically agree here.

That the EPA may occasionally mandate that there must be two (or even 3?) different EGR Valves, does not necessarily indicate or imply that the OE B-car LT1 4L60E EGR Valve is BETTER for those keeping the restrictive OE muffs and tailpipes than the F-car LT1 T56 EGR Valve.

More research would be helpful ...
 

· Premium Member
Joined
·
5,314 Posts
Guys do some reading on N and P egr valves.
Any change in the exhaust pressure will affect the operation.
Plus , of course , exhaust pressure will affect the amount of flow in relation to opening.
The factory valves were tailored to flow the amount they needed to reduce NOx to their target and still run acceptably on each platform.
Too much egr , cars don't run great.

Egr affect performance?
Cruise around in a situation where Egr is on for a while. Floor of intake gets hot enough to burn oil on the bottom and vapor on the inside.
Now go wot , what is that hot floor doing for you? .
Egr and mileage, how come endurance race cars and every street car doesn't have egr , just for the mileage gain.
Egr allows more timing , or do you need more timing because of the egr just to get back to square one?
Goes against everything people say, but the best highway milage my lt1 wagon got was no egr and 3.73.
Could get into lock up fourth and stay there.
Zeroed adder table , ran as much light throttle timing it liked.
"Your mileage may vary"
 

· Registered
Joined
·
6,532 Posts
CAFE (Corporate Average Fuel Economy) and EPA are DIRECTLY related. EPA levels standards on what manufacturers must state in their MPG per car model. If collectively the car line, GM for example, the MPG's are low than they don't meet CAFE regulations and thus get their nuts wacked basically it is costing GM $

EGR valves, both P&N, for idle, part throttle exhaust gas "recirculation" in yet another attempt of reducing emissions. MPG is a secondary concern.

The F body 6 speed had, compared to a B body, a freer flowing exhaust for performance benefit. With that said it also had 4 CATS IIRC as it had to meet 50 state emission standards. States like CA with heavy standards are a primary tail wagging dog in that math

Again GM had to do the dance and provide EGR's that either P or N had to do what they needed to do for EPA, CAFE standards and goals

My $.02 is running a stock pipe size exhaust in a B body use a B Body EGR. If 2 1/2", or larger, pipe then yes move to the F body. Neither in those applications has a negative effect on HP or performance assuming all components, including emissions, are working properly

Now has the aftermarket "bundled" their EGR version for any LT1 vehicle purely to reduce manufacturing cost, maybe.....
 

· Premium Member
Joined
·
5,314 Posts
We HAD a weird adaptation of the Calf inspection .
Same im240 , same specs , but only a cursory visual.
Specs , every year inched down based on averages and voodoo.
Government stations run by a US firm .
If the swipe with the mirror saw a Cat or Cats somewhere under the car, no check engine , no leaks no smoke and you passed the treadmill , you were good to go.
Never opened the hood.
I would drop in the egr cal for the test.
Forgot once , still passed although with elevated NOx.
 

· Registered
Joined
·
6,532 Posts
Here in CA Gerry I get the full smog colonic. Visual, plug-in and treadmill/tailpipe. I have walked a fine line since owning the SS since new. Needless to say my 383/T56, header, etc car gets attention when I take it in. I get no breaks but it has always passed. More credit to Ed Wright, RIP.

I also was asked about my "new" CATS on my last test as the guy did the mirror look....he asked if I had the "registration cards" for them...I did. Exploding walled $500 each CARB/OBD2 Cats. MagnaFlo

Car always had 2 IM monitors "not ready". in 2018 the aholes in Sac City reduced it to only allowing 1...they were always CAT heat and EGR. Always had CATS and EGR. Well Ed got me around that dance but yeah here in CA it is brutal. Very rare finding the $300 use donor car shop these days so have to keep all emission stuff on and working properly
 

· Registered
Joined
·
2,950 Posts
EGR affect performance?
Cruise around in a situation where EGR is on for a while.
Floor of intake gets hot enough to burn oil on the bottom and vapor on the inside.
Now go WOT. What is that hot floor doing for you?
EGR and MpG, how come endurance race cars and every street car doesn't have egr, just for the MpG gain.
EGR allows more timing? Or do you need more timing because of the EGR just to get back to square one?
Which leads me to, how does an otherwise properly operating EGR affect, not just 'enthusiastic' performance, but otherwise boringly normal operations?
Chilled EGR became a thing for a reason, but I don't know what that is.
(On all my tunes going forward, should I suggest to clients that their LT1s would last longer if I disable the EGR?)
Goes against everything people say, but the best highway MpG my LT1 wagon got was no EGR and 3.73.
Could get into lock up fourth and stay there.
Zeroed adder table, ran as much light throttle timing it liked.
"Your mileage may vary"
Who the hell are these people?
Only reasons why I did not have the same experience with 3.73 are
a. I used to drive it like I'd stolen it
b. I used to highway cruise @ 75-90MpH whenever I wasn't goosing the gas
But if I let anyone else drive my car, it could get highway MpG in the low 20s with 3.73.

Still think Lean Cruise would do EGR's job better, especially once the AFR approaches 16:1
 

· Registered
Joined
·
2,950 Posts
My $.02 is, running a stock pipe size exhaust in a B body use a B Body EGR.
If 2 1/2", or larger, pipe then yes move to the F body.
Neither in those applications has a negative effect on HP or performance assuming all components, including emissions, are working properly.
My question, which may not be worth $.02:
Is using the F-car LT1 T56 EGR Valve on a B-car LT1 with OE muffs & tailpipes in any way to be avoided?
 

· Registered
Joined
·
360 Posts
Discussion Starter · #48 · (Edited)
My question, which may not be worth $.02:
Is using the F-car LT1 T56 EGR Valve on a B-car LT1 with OE muffs & tailpipes in any way to be avoided?
That was half of my initial question too. I've never heard anybody say "do not use" over all these years, but I also haven't heard a good recipe to help someone make a decision to switch to the F-Body one or not. Generally speaking, it's been a blanket statement... something like "if your EGR fails, replace it with a F-Body one for an upgrade".

To summarize what I've read so far here, you should definitely switch to the F-Body EGR if 2 or more of these mods:
  • Upgraded exhaust system (2.5")
  • Upgraded mufflers or straight pipes
  • Upgraded high-flow cats
  • Run a manual transmission

If you want to reduce intake heat, oil coking, allow for some extra low RPM timing, you can take the legal risks:
  • Block off the EGR, leaving it in place for visual, and tune it out.
  • Delete the EGR system entirely and tune it out.
(when this thread ends, I will post that recipe as the last reply once we establish if one is helpful)

On stock setups, there's still some questions as to the actual benefit of the F-Body upgrade.

There's been lots of good explanations in this reply, so thanks guys! Keep it coming.

I have read about N type EGR valves, which is the kind our B-Body uses (as per FSM). I think what we are all missing (and may never know!!!) is the actual specification difference between both EGR valves. Port and pintle sizes, vacuum activation thresholds, exhaust backpressure thresholds, and so on. Therefore some of this still feels anecdotal at best unless/until we can get more science behind it. Wouldn't it be hilarious if they were identical and the only difference is a PN for EPA records.
 

· Registered
Joined
·
6,532 Posts
Well some of the myth may be more the Spinal Tap philosophy which is if its bigger or on a faster model it must be good for all theory (read the F Body EGR goes to 11)

My $.02 is the differences have more to do to different exhaust back pressure between the F & B body platform with the F body exhaust having less backpressure. But my only qualification beyond having a 2 1/2" header exhaust system is I stayed in a Holiday Inn Express last night so YMMV

I can say on "my" SS the F body EGR has not caused any negative results "I" or the smog test police have noticed in the last 20+ years...again YMMV
 
41 - 49 of 49 Posts
Top