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Obscure SBC Question

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87Z51:

--- Quote ---Originally posted by Reklaw
 The leakage from one side of the air plenum to the other is major, like no restriction at all. ... The air just came straight out the other side, hence my thought that it's the lack of divider in the inlet gasket.  
--- End quote ---


So it leaks from one side to the other , but both sides should have the same fuel content so that doesn't account for the lean cond .
 Edelbrock make a  intake for  Vortec style cylinder heads (RPM Air-Gap #7516) that has the center divider under the carb cut down 1" to enhance top end power.

The plugs? are they white "normal" or white lean?
The black ones; are they normal or black rich?
What does it run like?
If it is leaning out on 4 cyl ( or running rich on the others ) you would expect to notice a drop in performance
What is idle vac reading, is it constant?

Reklaw:
If the Edelbrock has a cut down plenum divider, then this issue of leakage from one side to the other shouldn't be the cause of the "white" plug "black" plug issue, right ?

Which is correct, the "white" or the "black" is a part of the conundrum.
 
The photo below shows the differences. #2 looks a bit lean because it doesn't have a full ring of colour around the base ring. The "black" plugs are dry, it's not oil.

This motor is new, well it's done 400 miles now and it's on its second set of heads (last set were faulty) same readings before and after head change. Makes it hard to comment on how it runs, but it "feels" that it could be a bit better.

Ignition timing is about 15 or so degree initial, it seems to like that better than the usual 8 to 10 degree.

Vacuum at idle is not totally steady, it oscillates between about 12 and 14 inches. Vacuum take off point is the power brake port, which is across both sides of the carb/manifold.

Went over cam timing with a degree wheel/dial indicator when the heads were off last time. All looks good there.

To check vacuum takeoffs (which are on the "lean" side of the manifold), I took it for a run today with the headlight/heater port plugged. Same result with the plug readings.

Don't normall subscribe to Icons, but :p
[/img]

87Z51:
If I saw those plugs without knowing the story I would say the   "black" cyl are runing rich.  If running normally I would expect the insulator to be cleaner.
As you say #2 looks a little clean but # 3+5 look normal while #8 doesn't look alot different from the other side of intake.

Bit out there , but what are the plug lead resistances like?
 If you were losing spark intensity it could account for the incompletel combustion in the chamber

77CVT:
FWIW, porcelain part of the plug should be whitish/grey so to me #2 & #5 look normal to me.  The others look too rich IMO.

Agree on the ignition leads.  I never fit leads with more resistance  than 10k.  Good quality ones should be around the 4-5k resistance.


;42

Reklaw:
Hi guys,
Thanks for the plug lead resistance info - haven't gone down that path before. Leads are Top Gun, their spec says 5K to 6K per metre. Resistances range from 2.8K on shortest lead to 5.7K on longest lead (1060mm) so I think they are all OK.
One thing remains to be done - get it out on the open road, shut the engine down at about 3K revs, coast to the side of the road (hoping I can turn the steering wheel) and check plug readings again, instead of just looking at local driving readings.

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