Thread: blocking off egr

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Installed the plate today and ended up with a rough idle. The plate is above the gasket and is sealed up good. Seems to be a rat-a-tat-tat at the plate.

Do I need to readjust the idle mixture? Up the idle RPM? Rough at 650 and smooths out at @800.

To correct myself in the initial post, I do have the PCV at the valve cover to the front of carb. I did'nt know that was an emissions piece.

14 degrees BTDC initial advance with timed vac.advance. The full time vac. and the rear vac. port of the carb are plugged off. Edelbrock 1406. Super unleaded 93.

Originally Posted by DennyW

There are different types. I didn't see where you mentioned on what motor this is, and what are you running for exhaust. Application is needed.

Here are the specs:

Engine Part Number: 12355345
Displacement: 350 Cubic Inches (5.7L)
Horsepower: 300 @ 5000 RPM
Torque: 369 Ft. Lbs. @ 3500 RPM
Maximum Recommended RPM: 5500 RPM
Compression Ratio: 9.1:1
Block: P/N 10105123 Cast Iron with straight four-bolt bearing caps, late model 1-piece rear main seal design.
Bore and Stroke: 4.00” x 3.48”
Crankshaft: P/N 14088527 Nodular cast iron, 1-piece rear main seal design.
Piston Material: P/N 12361371 Cast Aluminum
Connecting Rods: P/N 10108688, 1053 Forged Steel
Cylinder Heads: P/N 10159592 Bare Head, Cast Iron 64cc Chambers [Old P/N 12356026]
Valvetrain: Overhead Valve with Pushrod
Camshaft: Hydraulic Flat Tappet Design
Intake Valve Dia.: P/N 10093027 1.94”
Exhaust Valve Dia.: P/N 14088641 1.50”
Advertised Lift (Int/Ext): .435/460
Rocker Arm / Ratio: P/N 10089648 / 1.50 Ratio
Valve Lash: Zero
Engine Idle Speed: 650 RPM
Spark Plugs: R44TS
Spark Plug Gap: .035
Oil Pressure (Normal): 40 PSI @ 2000 RPM


GM aluminum 4bbl intake
Edelbrock 1406 (600CFM) electric choke
Headman swap/conversion headers
Flowmasters (40 series)
No cats.

THM 350.

Denny,
I used 1/8 plate steel and used the old housing. I dont know if the gaskets have the heat provisions. I do have a 1 inch spacer plate under the carb.

Originally Posted by DennyW

Ok. What I would do is try to reset my mixture and rpm's. Double check timing. If you have a vacuum gauge, that will really assist you in setting the mixtures on the carb. Keep total advance to 36-38 degrees.

ps: I would run the vacuum advance to full time vacuum. That will help all around on heat, and performance for what you have. Set base timing of course, with the vacuum line dis connected and pluged.

So, with the vac. gauge, adjust the mixtures until max vac.? I dont have anything other than the stock pointer on engine for timing. It goes to about 14 degrees. I usually run the highest timing just before detonation.

I have tried in the past to set timing with vac. gauge, but could not eliminate detonation at max vacuum.

Yep, I have had problems in the past with heat at idle. Had to get larger rad and more cfm fan. Maybe the full time advance will help that.
Thanks Denny

This is not a race vehicle by any means. Just trying to free up a little power, and clean up the engine bay. Pluged egr valves just aint pretty. I would like to keep the PCV to help keep the valve covers clean. I tried without once and just one trip down the road I was cleaning oil off the breathers and oil fill hole. Anyhow, Denny I got your point about setting idle mix with a gauge. The procedure is where I need help. Do I adjust the screws to achieve max vacuum? Do I check the vacuum at the manifold or the carb? Do this before or after setting the timing?

Techinspector,
I have no doubt in your experience and knowledge. Just a fun little s10 strickly for the street. Thanks for your suggestion.

What you can do, (I run practically the same setup you have, 355 sbc and an edelbrock 1406) is go to your local parts house and ask for a simple vacuum gauge, nothing fancy nothing too expensive. Should come with a rubber line that fits the small vacuum lines on the very front of the carb.

Get the engine warm and set your timing to what you need it to be (I run 12* BTDC)

The right vacuum port is the one you want to hook it up to since its going to be constant vacuum. The left vacuum port is for your vacuum advance used on the distributor.

Now with the car running and the guage hooked up to the carb, take a flat head screw driver and turn one of the idle screws in front all the way down to where it closes or when the RPM's drop at a noticeable rate, then back the screw out until the vacuum goes all the way up then starts to go down, dial that vacuum in to the max.

Do the same for the other adjusting screw.

And be sure to have a Tach hooked up to the distributor and set your idle to what your motor or camshaft manufacturer tells you to set it to. I have mine set within 650 and 700 rpms since mine is a 268/268, stock lift cam. Nice and choppy.


Now take that hoss out for a drive and see how she responds from a dead start! She should act great now!

Edit: Just combine what I said with Denny, he's got more know-how than I do! I've only got 3 years experience with this whole hotrod/carburator thing :P

Soon after blocking off the egr a rattle/knock noise developed. From the top it sounds like its comming from right under the intake close to the distributor shaft. From underneath it sounds like its radiating all the way down to the oil pan.
This noise is only heard when at idle, in drive or park. Has gotten progressively worse the last couple of days.

The engine doesnt get as warm as it should either, only about 145 cruising,160 running hard, but that may be a separate issue.

So I went hunting for the problem today. Removed the intake to check for obstructions, nothin'. Checked the dizzy gear, nothin'.

Since I am not that familier with how the intake and heads work together I got a question that may sound dumb, but here goes.

Am I seeing a single exhaust port on the intake side of each head?????
These smaller ports have a build up of what I would think would be carbon????

How do these work with the intake?? Could someone explain this? Do I have a problem with this buildup of carbon? Could that be causing the noise?

Mortec.com notes that these heads are 1987-up 64cc chamber 72'center bolt angle cast iron.

5.7LT GM crate-1993.