#1  
Old 08-01-2020, 02:49 PM
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Default Is this normal. Edelbrock Performer

Last fall I decided that my mpg was terrible it dynoed at 217 hp so I decided to pep up the 400.

So I pulled the motor and disassembled it and started over.
A couple weeks ago I was looking for something and I had to move the eddy performer intake that used to be on it. I set it down I saw something I had never seen (old Chevy guy) some of the runners were charred. Some the whole circumference and some halfway.


Is this normal for 2000 miles on a new engine?

Thanks
Greg

  #2  
Old 08-01-2020, 03:01 PM
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The pistons and combustion chambers were charbroiled

Greg


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Old 08-01-2020, 06:45 PM
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No, not normal.

You are either way to lean or your timing was way to advanced. Did they hook up an AFR when you ran your dyno pulls last year?

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Old 08-01-2020, 07:36 PM
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What heads? Looks like gaskets were not aligned, or wrong port size. I just went through this, had too small gaskets for RA4 heads. Mine made a noise back through carb. Yes it had that black too. Now it wants more fuel though !

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Old 08-01-2020, 09:02 PM
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That's reversion from a cam too far advanced and an overly rich mixture. The exhaust gases get sucked back up into the intake tract. In extreme cases it can go all the way up to the plenum and even form a cloud above the carburetor. Oversized headers on a motor operating at low to mid-range rpm can also contribute to reversion as the exhaust gas velocity is too slow for efficient scavenging.

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Old 08-01-2020, 10:39 PM
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Fascinating.

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Old 08-02-2020, 05:35 AM
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Look at how black the Exh crossover is also !

That motor was running very rich, and or or the compression / cylinder pressure was too low at low pistions speeds i.e. Low rpm to pump out the Exh gases.

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Old 08-02-2020, 11:48 AM
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IS this an EGR intake?
Is their a noticeable difference/consistency in runners fed by one side of the carb to the other side?

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Old 08-04-2020, 07:42 PM
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Quote:
Originally Posted by STEELCITYFIREBIRD View Post
IS this an EGR intake?
Is their a noticeable difference/consistency in runners fed by one side of the carb to the other side?

No


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Old 08-04-2020, 08:48 PM
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Exhaust Reflection crosses the Valve Overlap (thatsa Reversion), and carbon tracks the Intake Runner. Fuel probably spitt up out the carb too.

Exhaust "system" needs work with the Collectors to lengthen the reflection point; preferably where the Stock Mufflers are. Or re-jigger the combo to run less Overlap, less cam advance.

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Old 08-05-2020, 08:43 PM
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Poor intake valve seal would also allow exhaust gas back in the runners. Compression test would help tell the tale.

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Old 08-06-2020, 09:38 AM
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My RAIV heads would do that until I switch to smaller better scavenging header tubes and based on E/I flow numbers a "reverse split" cam.

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Old 08-06-2020, 10:27 AM
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Exactly Skip, but your case was low Exh velocity due to unneeded tube size, his issue I firmly believe is lack of cylinder pressure which could be due to a few reasons!

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Old 08-06-2020, 04:02 PM
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And an 85%+ E/I where the exhaust port flowed 90% backwards on the flow bench!

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1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever!
1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand
1965 GTO 4 barrel 3 speed project
2004 GTO Pulse Red stock motor computer tune 13.43@103.4
1964 Impala SS 409/470ci 600 HP stroker project
1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132
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Old Yesterday, 07:43 AM
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Yup that reversion factor a big issue with the iron Round port heads in that they unnecessarily flare out as they approch the flange which is not good nor needed and then some uninformed home porters then make it worse by gasket matching the port exits to there Headers!

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