dirty_old_chevy

Hi, I was just pondering this thought: can overlap increase octane tolerance at certain rpm ranges? It seems to me that it might. At lower rpm's, you may have exhaust reversion into the intake tract, creating an EGR effect, lowering combustion temperatures, then there would be a certain rpm where the overlap is perfectly tuned for the engine, no reversion should occur, I see no benefit in this rpm range. Then there is the higher rpm range, where the momentum of both the intake and exhaust tracts will draw raw intake charge straight through the combustion chamber into the exhaust, cooling the combustion chamber on the way, in my eyes. It would seem in this rpm range that octane tolerance would be increased also, due to decreased combustion chamber temps. I know there are many other factors that would affect how this all would go down, but would this be true for the most part? Or would the results be negligible?

studderin

iTrader: (28)

yes, VVT dose this.

and the title is not just about raw temp, but also think about the octane of the combusted gases them self, kills the resistant of a clean charge

dirty_old_chevy

So would it be safe to say that a 216/218 on 108+0 cam would have increased octane tolerance over a 216/220 on 110+2 on a 799 headed 6.0l with a stock truck intake, full length 1 3/4 headers, and free flowing single exhaust?

PREDATOR-Z

The cam with the higher dcr will be more sensitive.

Sales@Tick

iTrader: (3)

This x2.

dirty_old_chevy

But they both have the same dcr. Same lobes, same ICL, both IVC are at 36 deg. This is why I was wondering. I have both of these laying around.

dirty_old_chevy

Martin or Pred Z: which one would you use in a 2002 chev 2500 ccsb with 4.10's? Daily driver with occasional towing. Part throttle torque would be a goal, as would running 87 octane. Cruise rpm is about 2000 in o/d and 3000 in 3rd (that's the gear I'll be towing in). Stock 2500rpm 4l80 stall. The rest of the details are in the first and third post.

Sales@Tick

iTrader: (3)

I would run the tighter LSA but install it on a 106.

dirty_old_chevy

Thanks! Umm just curious, are you suggesting the 106 icl to raise the dcr for low end torque, or to bias the overlap more towards the exhaust side of tdc?

Sales@Tick

iTrader: (3)

Actually advancing the cam moves overlap to the intake side of TDC since you're closing the exhaust valve earlier. Also, along with raising the DCR, moving the events 2 degrees advanced will make much more under the curve power along with average power.

dirty_old_chevy

Ok, it looks like I worded that wrong. Thanks for the advice!