My car was running pretty decent after bumping the timing back, rebuilding the carb, and swapping jets. Yet it still seemed to be running rich, burning the hell outta my eyes and leaving me smelling like I'd been pumping gas all day after just a short ride. Obviously, something wasn't quite right, and I had a couple of thoughts.
First off, to try and combat some of the fumes, I finally installed a PCV valve. I've seen more people out there running a breather in each valve cover than I have somebody running a PCV valve. Honestly, I think we all assumed the same thing, that the PCV was some sort of emissions equipment that had no place on a street/strip car. Well, come to find out, that's not the purpose of a PCV valve. I knew what a PCV was, it was Positive Crankcase Ventilation valve. I also knew that it operated off of the engine vacuum. What I didn't realize was that running two breathers simply allowed the crankcase pressure to vent, and no matter how good the valve cover baffle, that venting including an oil mist that covered the valve covers, which then ran down to the headers, and added to my engine bay fumes that make cruising somewhat unenjoyable. I went with a PCV valve for a 1970 Chevelle 454, since I figure the pentical of horsepower would be my best bet for my engine.
Next up was why my car was running so damn rich that it burned my eyes. I wasn't exactly sure how a powervalve worked, other than it added fuel during wide open throttle. After checking around online, then taking a vacuum measurement, I had my rich idle condition figured out. My carb was equipped with 6.5 powervalves, and my vacuum was 5 inches, which meant from idle through my powerband my powervalves were dumping fuel in the engine.
A call to Barry Grant's Tech line helped me get in the ballpark regarding which powervalve I needed. They recommended either a 2.5 or 3.5, and stated really it's a trial an error science. After checking my engine vacuum again at idle, this time with the car in drive as suggested by the Tech guy, I rolled the dice and went with the 2.5. My idle vacuum is about 5 inches, and most people seem to suggest dividing your vacuum number in half to determine your powervalve you need. Perhaps this is because there are two powervalves in the carb and the vacuum is divided between them, I'm not sure.
I fired up the engine after swapping in the new powervalves and was rewarded with popping through the carb, which was a sign of a lean condition. After some adjustments, now the engine was backfiring through the exhaust, signaling a lean condition. I need to use the vacuum gauge and an extra set of eyes/hands to get it fine tuned, but it's tons better than before! I took a ride for a bit and was rewarded with a much more pleasant ride. The fumes seemed to be non-existant, acceleration was even better, and throttle response was much more instantaneous! Who says a cam this big of a cam feel "bulky" on the street? This damn thing is a rocket ship with a quick blip of the throttle. Bulky ain't even in my vocabulary.
The car still isn't tuned in perfect, but are they ever? It's tuned in better than it's ever been, and now that I know a thing or two about tuning it, idle and streetability will only get better. Sadly, the car will likely return to my parents' for winter storage in a month or so, but I'll be ready to kick off the cruisin'/car show season as soon as spring is sprung!
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