Abstract question on displacement, overlap, and fuel smell...
06-06-2007, 04:12 PM
#1
Abstract question on displacement, overlap, and fuel smell... Does displacement (more of) affect the amount of "gas smell" if all other factors (overlap, etc...) are the same???
I have found (in my 346 daily-driver) that a cam with more than 5 degrees overlap @ .050 smells bad enough that I do not want anything to do with it... Would the same amount of overlap smell just as bad with a 427???
Yup... I know, weird question... but I spend a lot of time in my Vette and I hate jumping out of it reeking of unleaded...
I have found (in my 346 daily-driver) that a cam with more than 5 degrees overlap @ .050 smells bad enough that I do not want anything to do with it... Would the same amount of overlap smell just as bad with a 427???
Yup... I know, weird question... but I spend a lot of time in my Vette and I hate jumping out of it reeking of unleaded...
Last edited by SideStep; 06-07-2007 at 06:33 AM.
06-07-2007, 10:17 AM
#3
Launching!
It's not a strange question, IMO. The '67 convert in my sig has 25 degrees overlap at .050 in a 548 CID motor, and even though drivability is very good, it really does reek the whole time I'm driving it, and I reek afterwards.
In general, with everything else being the same - compression, valves, ports, intake, headers - overlap effects decrease with increasing displacement because the combustion chamber is larger, reducing the "communication" between intake and exhaust. But the unburned fuel phenomenon is not something I fully understand - how does the intake mixture go from the high vacuum intake side to the atmospheric pressure exhaust side? Or is it more a matter of poor combustion due to mixing of exhaust gas with the intake mixture? I suspect more the latter.
In any case, I have no definitive answer for your original question, but I'd guess you won't want too much more overlap even with a 427.
In general, with everything else being the same - compression, valves, ports, intake, headers - overlap effects decrease with increasing displacement because the combustion chamber is larger, reducing the "communication" between intake and exhaust. But the unburned fuel phenomenon is not something I fully understand - how does the intake mixture go from the high vacuum intake side to the atmospheric pressure exhaust side? Or is it more a matter of poor combustion due to mixing of exhaust gas with the intake mixture? I suspect more the latter.
In any case, I have no definitive answer for your original question, but I'd guess you won't want too much more overlap even with a 427.
06-07-2007, 04:26 PM
#5
Originally Posted by See5
Lean up the idle, add timing and it helps lots.
I have done those... but there comes a point with overlap that cannot be tuned out... (the smell...) Last edited by SideStep; 06-08-2007 at 05:45 AM.
