Sooty spark plugs

[SUPERKYLE]

All,
I am having a problem with a project I'm working on. Here's the specs;
200 CID 4 cyl. 10:1 CR pump gas 250 BHP (60° 29.92 dry air)
240° 248° on 112°C/L
Individual runner EFI (Weber manifold) Accel gen 7 Management system.
The engine has been mapped on the Dynamometer with top quality A/F measuring equipment, mapped in the car with the same equipment. The engine had been run previously with a plenum manifold and Holley 2BBL carburetor.
Now here's the deal, The spark plugs look bad, Like an engine that had been running at 9:1 A/F. I can assure you this one has not. Injector timing has been explored, all the fundamentals.
Do IR engines require different cam timing than plenum manifolded ones? It would appear that the plug color could come from reversion, but the carbureted version did not exhibit this.
Any Weber guys out there care to share their experiences?


Thanks,
Kyle

 

[willeng]

SUPERKYLE:

Some A/F ratio meters show a leaner mixture when the mixture is very rich, i have one now that does this!
It may be that simple?

Believe the plug colour!
Can you post a picture of your manifold etc as fitted?

 

[SMOKEY44211]

Best way I know of to verify the a/f ratio is to measure exhaust gas temps. and exhast gas sample. I don't know what kind of system you're running. Is there any way to change the a/f while its running? How does the power output compare to the carb setup?--------------Phil

 

[ShaunT]

I agree to believe the plug. If this is a drag car, tune for the best time slip. Though it is likely not the case here, something else to consider is Ra's, Rvk's, Rz's, etc of the cylinder wall surface finish. I would look into that if you haven't already, anyway because I am sure you will find some ring seal/durability and oil control improvement.

Good luck.

Shaun TiedeULTRADYNE/LUNATI Austin,TX(stiede@ev1.net)

 

[SUPERKYLE]

Thanks for the reply's
I'll try and answer your questions in order.

Willeng,
Yes, I am familiar with the A/F measuring equipment showing a lean condition when the engine is either too lean or too rich. What happens is that the cylinders have random misfire causing a charge of air and unburnt fuel to pass thru the cylinder and in to the exhaust and the A/F measurement picks it up as dead lean. I am using Horiba A/F measuring equipment.

Smokey/Phil,
I measured EGT's on Dynamometer, all is well there.
The performance is down slightly, approximately 2%
Possibly due to the injector location and the lesser effect of the fuels latent heat of vaporization.
Also perhaps lack of taper in the runners.

Shaun,
I agree that the spark plug doesn't lie.
I also agree that the optimum bore finish can be beneficial.


Thanks again for your thoughts.

Kyle