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Old 02-03-2011, 10:50 PM
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EGR dilemma

On an 81 Corvette with (now) stock L81 350 which has a basic ecu that runs an electric carb, the distributor timing, and the EGR system.

I'm going to go with a TB efi setup and a "regular" distributor (cuz if I replace the carb the ecu won't function anyway).

I know if controlled properly an EGR can be of some benefit, i.e. detonation reduction and possibly a little better mileage besides emissions (I'm not in an area that smog tests vehicles so that isn't a direct worry)

I'll be replacing the intake manifold with something like a Performer.

Is there any practical way to end up with a functioning EGR that will actually function 1/2 way properly, or am I best off just forgetting it.

I haven't looked but don't believe most of the Performer style intakes have external EGR capability anyway.

I know timing will be a little different, and I'm going to tune the TBI in open loop by using a wide band, and the efi setup will have closed loop control
capability via an 02 sensor.

I'm going to be using a short duration cam that's efi / computer compatible so it doesn't have much overlap - none @ .050 - which I have read can work like an internal EGR by bleeding some exhaust gas thru during overlap.

Never have given this issue any real thought - just curious if anybody's worked this out and would have any suggestions or recommendations.

Thx!



I know i

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Old 02-03-2011, 10:54 PM
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Someone educate me. How can a cam with NO overlap bleed off exhaust gasses into the intake during overlap? HM?
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Old 02-04-2011, 10:11 AM
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I am not an engineer, but this is my opinion. If you are not using EGR to control detonation, it is not much use.
This is why I believe that. I know the reason for EGR is to reduce the peak temperature in the combustion chamber, to reduce the oxides of nitrogen formed. But when you get down to the most basic level, it is the temperature increase in a gas, in a closed chamber, that increases the pressure, that pushes the piston down, that does useful work.
All things being equal, if you are running EGR, the engine is less efficient. To get the power you want at that time you have to use more throttle.
If the engine putting out that same amount of power, is not running EGR, the throttle can be closed slightly. Less throttle, less fuel, better gas mileage.
Because the engine can be ran with less throttle, the engine's peak temperature in the combustion chamber is being controlled by the throttle, and not EGR.
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Old 02-04-2011, 12:54 PM
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Quote:
Originally Posted by macx
I'm going to go with a TB efi setup and a "regular" distributor (cuz if I replace the carb the ecu won't function anyway).
Well, if you use a stock GM style TBI, the ECU controls the distributor as well as the injectors. It also controls the EGR solenoid.
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Old 02-04-2011, 06:20 PM
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First, the cam will have overlap but will be at lifts under .050 which is generally considered the threshold for "effective" valve lift at which there will be effective airflow.

Second, yes I'm aware of all what the EGR is intended to do by lowering the comb chamber temp, significantly to help control detonation, which is why I stated that in my original post.

That is the reason I asked the question if anyone had done anything around retaining EGR functionality in this kind of situation. There are a lot of knowledgeable folks out there and just maybe somebody's studied it or tried it
or even has a way of doing it.

Third, this is not going to be an oem GM TBI, so no ecu at all.
It's a Holley Pro Jection I've had on another vehicle and being I already have it intend to use it on this motor instead of buying something else.
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