87 octane gas...
87 octane gas... I've heard some people claim that 87 octane gas made their LS1 powered car get better ETs because it "burns up" faster and cleaner in the combustion chamber, promoting both better throttle response, power and fuel economy especially if tuned right. I mean how can you tune an LS1 powered car to run 87 octane and run better ETs? Is that even possible with the LS1's stock compression ratio? That doesn't sound right at all because 93 octane suppresses knock because it doesn't burn as fast as the piston moves TDC. Has anyone here ran 87 octane on an LS1 with a "tune" and noticed a difference?
I also heard that if you built a destroked motor with an exceptionally good rod/stroke ratio (1.75 or better) not only would it be able to handle higher rpms because of the less piston sidewall loading on the bore, but it would actually be less prone to knock because the "piston dwells at TDC longer" than a motor that has a low R/S ratio, meaning stroker motors using short rods would be less tolerant of low octane gas. Please explain.
I also heard that if you built a destroked motor with an exceptionally good rod/stroke ratio (1.75 or better) not only would it be able to handle higher rpms because of the less piston sidewall loading on the bore, but it would actually be less prone to knock because the "piston dwells at TDC longer" than a motor that has a low R/S ratio, meaning stroker motors using short rods would be less tolerant of low octane gas. Please explain.
Maybe it would be possible with a cam that will lower the DCR enough to tolerate the 87 octane, but with the stock cam it will ping and detonate. I've never tried it in my LS1 but I've always ran 87 in my Jimmy with the 5.3. My tune has 27 degrees timing at WOT and I rarely saw any knock retard, so it may be possible. The ideal setup for max power is to run the minimum octane rating you can without experiencing detonation.
So how would you be able to calculate the dynamic compression ratio from the static compression ratio with cam timing events?
Seems like if someone wants to lower the octane requirements of a certain motor, they could just swap out the stock cam with something that would have more overlap and duration because it would lower the DCR...
Seems like if someone wants to lower the octane requirements of a certain motor, they could just swap out the stock cam with something that would have more overlap and duration because it would lower the DCR...
I believe there is a DCR calculator somewhere in the stickies, or you can just do a google search and find one. The one I use is from Patrick Kelly and is easy to use.
Theoretically speaking you could choose a cam to run a certain octane. But is all the effort really worth saving a few dollars per fill up? I would say there is more power to be had by upping the compression and running 93.
Theoretically speaking you could choose a cam to run a certain octane. But is all the effort really worth saving a few dollars per fill up? I would say there is more power to be had by upping the compression and running 93.
